Proceedings Volume 7386

Photonics North 2009

Réal Vallée
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Proceedings Volume 7386

Photonics North 2009

Réal Vallée
View the digital version of this volume at SPIE Digital Libarary.

Volume Details

Date Published: 5 August 2009
Contents: 10 Sessions, 117 Papers, 0 Presentations
Conference: Photonics North 2009 2009
Volume Number: 7386

Table of Contents

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Table of Contents

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  • Front Matter: Volume 7386
  • Biophotonics
  • Fiber Lasers and Devices
  • New Optical Materials and Nanophotonics
  • Next-Gen Networks
  • Optical Sensors and Detectors
  • Optoelectronics, Integrated Devices, and Networks
  • Photonics Design and Simulation
  • Plasmon-Assisted Sensing Mechanisms
  • Ultrashort Lasers and Applications
Front Matter: Volume 7386
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Front Matter: Volume 7386
This PDF file contains the front matter associated with SPIE Proceedings Volume 7386, including the Title Page, Copyright information, Table of Contents, and the Conference Committee listing.
Biophotonics
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Light scattering characterization of single biological cells in a microfluidic cytometer
Xuantao Su, Sean E. Kirkwood, Hilal Gul, et al.
The characterization of single biological cells in a microfluidic flow by using a 2D light scattering microfluidic cytometric technique is described. Laser light is coupled into a microfluidic cytometer via an optical fiber to illuminate a single scatterer in a fluidic flow. The 2D light scattering patterns are obtained by using a charge-coupled device (CCD) detector. The system is tested by using standard polystyrene beads of 4 μm and 9.6 μm in diameter, and the bead experimental results agree well with 1D Mie theory simulation results. Experiments on yeast cells are performed using the microfluidic cytometer. Cell results are studied by finite-difference time-domain (FDTD) method, which can simulate light scattering from non-homogeneous cells. For example, a complex biological cell model with inner mitochondrial distribution is studied by FDTD in this paper. Considering the yeast cell size variations, the yeast cell 2D scatter patterns agree well with the FDTD 2D simulation patterns. The system is capable of obtaining 2D side scatter patterns from a single biological cell which may contain rich information on the biological cell inner structures. The integration of light scattering, microfluidics and fiber optics described here may ultimately allow the development of a lab-on-chip cytometer for label-free detection of diseases at a single cell level.
Integrated biophotonic uTAS for flow cytometry and particle detection
Arvind Chandrasekaran, Muthukumaran Packirisamy
Recent advancements in the integration of photonic technologies with microfluidics for Micro-Total Analysis Systems (μTAS) have paved way for the realization of a lot of potential applications in the field of biosensing and biomedical detections. Some of the prominent features of these integrated μTAS are improved performance, high sensitivity and signal-to-noise ratio, reduced consumption of samples and reagents, and portability, among others. In this work, a hybrid integrated biophotonic μTAS on silicon-polymer platform is presented. Herein, the optical fibers are directly integrated with the Silicon microfluidic chip and an Echelle grating based Spectrometer-on-Chip on Silica-on-Silicon (SOS) is integrated with the opto-microfluidic assembly. Flow actuation within the system is enabled by a mechanical Piezodriven Valveless Micropump (PVM). Finite Element Analysis (FEA) has been carried out in order to study the behavior of the fluid flow within the microfluidic channels due to the piezo actuation, and the geometry of the bio-detection chamber within the microfluidic system has been optimized accordingly in order to obtain no-stagnation flow conditions. The opto-microfluidic performance and the piezo-actuated valveless micropump were characterized in separate experiments. The integrated μTAS was tested for flow cytometry and particle detection using laser induced fluorescence. The experimental results show that the system is suitable for high throughput biodetections.
Swept-source full-field optical coherence microscopy
Full-Field Optical Coherence Microscopy (FF-OCM) is a microscopic imaging device based on interferometry. It can produce cross-sectional images of bio-tissue or cell samples at a resolution in the order of a micron. Because it can extract an en-face image directly from the sample, it does not need 2D scanning mechanism, which greatly increases the imaging speed compared to fibre-based OCT systems. However, a controlled translation stage is still required in the reference arm of the interferometer to perform the depth scan. Swept-Source OCT (SS-OCT) technology is the second generation of the OCT systems, which not only removes the mechanical scanning, but also increases the signal / noise ratio of the extracted OCT images. In this paper, we describe the design and implementation of a swept-wavelength source based FF-OCM with 60X magnification; 8 um depth resolution; 4 μm depth resolution; 20 mm working distance and 15 frames / second imaging speed.
Single-molecule fluorescence study of the inhibition of the oncogenic functionality of STAT3
Baoxu Liu, Daniel Badali, Steven Fletcher, et al.
Signal-Transducer-and-Activator-of-Transcription 3 (STAT3) protein plays an important role in the onset of cancers such as leukemia and lymphoma. In this study, we aim to test the effectiveness of a novel peptide drug designed to tether STAT3 to the phospholipid bilayer of the cell membrane and thus inhibit unwanted transcription. As a first step, STAT3 proteins were successfully labelled with tetramethylrhodamine (TMR), a fluorescent dye with suitable photostability for single molecule studies. The effectiveness of labelling was determined using fluorescence correlation spectroscopy in a custom built confocal microscope, from which diffusion times and hydrodynamic radii of individual proteins were determined. A newly developed fluorescein derivative label (F-NAc) has been designed to be incorporated into the structure of the peptide drug so that peptide-STAT3 interactions can be examined. This dye is spectrally characterized and is found to be well suited for its application to this project, as well as other single-molecule studies. The membrane localization via high-affinity cholesterol-bound small-molecule binding agents can be demonstrated by encapsulating TMR-labeled STAT3 and inhibitors within a vesicle model cell system. To this end, unilaminar lipid vesicles were examined for size and encapsulation ability. Preliminary results of the efficiency and stability of the STAT3 anchoring in lipid membranes obtained via quantitative confocal imaging and single-molecule spectroscopy using a custom-built multiparameter fluorescence microscope are reported here.
High resolution imaging with TM01 laser beams
Using the vectorial diffraction theory established by Richards and Wolf, we demonstrate that the resolution of a two-photon microscope can be improved with a radially polarized TM01 laser beam and an interface between dielectrics, instead of the linearly polarized Gaussian beam already used in laser scanning microscopy. To verify the theoretical results, we developed a mode converter producing radially polarized beams and we have integrated it in a commercial two-photon microscope.
Optical modeling of a line-scan optical coherence tomography system for high-speed three-dimensional endoscopic imaging
Mohammad Kamal, Narayanswamy Sivakumar, Muthukumaran Packirisamy
The optical and analytical modeling of a line-scan optical coherence tomography (LS-OCT) system for high-speed three-dimensional (3D) endoscopic imaging is reported. To avoid complex lens system and image distortion error, an off-axis cylindrical mirror is used for focusing the line illumination on the sample surface and a micro mirror scanner is integrated with the proposed configuration for transverse scanning. The beams are swept on the cylindrical mirror by the micro mirror rotation and finally focused on the sample surface for transverse scanning. A 2mm by 3.2mm en-face scanning is configured with a 2mm focused line and ±3° scanning mirror rotation. The proposed configuration also has the capability of dynamic focusing by the movement of the cylindrical mirror without changing the transverse resolution. The cylindrical mirror enhances the image quality by reducing the aberration. The system is capable of real-time 3D imaging with 5μm and 10 μm axial and transverse resolutions, respectively.
Calcified lesion modeling for excimer laser ablation
Holly A. Scott, Andrew Archuleta, Robert Splinter
Objective: Develop a representative calcium target model to evaluate penetration of calcified plaque lesions during atherectomy procedures using 308 nm Excimer laser ablation. Materials and Methods: An in-vitro model representing human calcified plaque was analyzed using Plaster-of-Paris and cement based composite materials as well as a fibrinogen model. The materials were tested for mechanical consistency. The most likely candidate(s) resulting from initial mechanical and chemical screening was submitted for ablation testing. The penetration rate of specific multi-fiber catheter designs and a single fiber probe was obtained and compared to that in human cadaver calcified plaque. The effects of lasing parameters and catheter tip design on penetration speed in a representative calcified model were verified against the results in human cadaver specimens. Results: In Plaster of Paris, the best penetration was obtained using the single fiber tip configuration operating at 100 Fluence, 120 Hz. Calcified human lesions are twice as hard, twice as elastic as and much more complex than Plaster of Paris. Penetration of human calcified specimens was highly inconsistent and varied significantly from specimen to specimen and within individual specimens. Conclusions: Although Plaster of Paris demonstrated predictable increases in penetration with higher energy density and repetition rate, it can not be considered a totally representative laser ablation model for calcified lesions. This is in part due to the more heterogeneous nature and higher density composition of cadaver intravascular human calcified occlusions. Further testing will require a more representative model of human calcified lesions.
Antigen detection at atomolar concentration using optical tweezers
Mathieu Laliberté, François Bordeleau, Normand Marceau, et al.
Methods that avoid intermediate amplification steps to detect protein markers of pathological disturbances would be of wide interest in the clinical environment. This is particularly the case in cancer diagnosis, where protein fragments are released into the blood by the emerging cancer cells. These fragments generate an antigen-antibody reaction, and the concentration of the antigen is known to modulate this interaction. Here we report on the development of a novel optical tweezers-based procedure to measure minute amount of antigen in a biological fluid. The force was applied on a 3μm polystyrene bead coated with Bovine Serum Albumin (BSA) attached on a 1.5 μm diameter borosilicate rod tip coated with anti-BSA antibody. First, we verified that the binding strength was dependent on the protein concentration on the bead. We then assessed the sensitivity range by finding the minimal BSA concentration in solution that can still interfere with the bead-rod linkage. On the whole, the results demonstrated that proteinous antigen present in a biological fluid could possibly be detectable at atomolar concentration through the use of an optical tweezers.
Surface-enhanced Raman scattering detection of amino acids and peptides in a microfluidic device
A. Kandakkathara, I. Utkin, R. Fedosejevs
Here we report the results of investigations of Surface Enhanced Raman Scattering (SERS) from amino acids and peptides. In order to obtain optimum signals a standard microfluidic chip has been modified with the help of laser micromachining technique to increase scattering light collection efficiency. We have studied the SERS signals from the following amino acids: tryptophan (Trp), phenylalanine (Phe) and glycine (Gly) and peptides Trp-Trp and Gly-Gly-Gly. The optimum conditions for observing the spectrum from these amino acids and peptides have determined. In our studies the highest enhancement observed is from the amino acid Trp. Large signal enhancements were observed and the lowest detectable concentration of Trp was estimated to 4·10 -9 M.
Characterization of microfluidic systems with Doppler optical coherence tomography
L. Carrion, E. Hamel, A. Leblanc-Hotte, et al.
Doppler Optical Coherence Tomography (DOCT) is a biomedical imaging technique that allows simultaneous structural imaging and flow monitoring inside biological tissues and materials with spatial resolution in the micrometer scale. It has recently been applied to the characterization of microfluidic systems. Structural and flow imaging of novel microfluidics platforms for cytotoxicologic applications were obtained with a real-time, Near Infrared Spectral Domain DOCT system. Characteristics such as flow homogeneity in the chamber, which is one of the most important parameters for cell culture, are investigated. OCT and DOCT images were used to monitor flow inside a specific platform that is based on microchannel division for a better flow homogeneity. In particular, the evolution of flow profile at the transition between the microchannel structure and the chamber is studied.
Development of an optomicrofluidic flow cytometer for the sorting of stem cells from blood samples
In this paper, we report the preliminary development of a fiber coupled microfluidic flow cytometer with its potential application of sorting the very small embryonic like (VSEL) stem cells out of a mixture of platelets and VSEL stem cells. The identification of a VSEL stem cell from a platelet is based on the large difference of their abilities to scatter light. A simple cytometer prototype was built by cutting the fluidic and other channels into a polymer sheet and bonding it with epoxy between two standard glass slides. Standard photolithography was used to expose an observation window over the upper coated glass to reduce background scattered light. Liquid sample containing micro-particles (such as cells) is injected into the microfluidic channel. Light from a 532-nm CW diode laser is coupled into the optical fiber that delivers the light to the detection region in the channel to interrogate the flowing-by micro-particles. The scattering light from the interrogated micro-particle is collected by a photodiode placed over the observation window. The device sorts the micro-particle into the sort or waste outlet depending on the level of the photodiode signal. We used fluorescent latex beads to test the detection and sorting functionalities of the device. It was found that the system could only detect about half of the beads but could sort almost all the beads it detected.
Two-dimensional cell tracking by FPGA-optical correlation method
Iraís Solís, M. Torres-Cisneros, J. G. Aviña-Cervantes, et al.
Our work uses 1080 images sequence obtained from "in vitro" samples taken every 4 min from a microscope under phase contrast technique. These images are in JPEG format and are 500×700 pixels size with a compression rate of 3:1. We developed an algorithm and characterize it over several image operations against the tracking effectiveness and its robustness respect mitosis and cell shape change. Image equalization, dilation and erosion were the image processing procedures founded to provide best tracking results. Equalization procedure, for example, required a time delay of 5 sec for a size target of 60×90 pixels and 9 sec for size target of 89×100 pixels. This algorithm was implemented into a FPGA which controlled our optical correlator in order to performance all Fourier operations by optical method. Our results showed that the use of the optical correlator can reduce the time consuming in the image process until for 90% which able us to track cells in vascular structure.
Microchip-based flow cytometry for effective detection and count
Canjun Mu, Zhiyi Zhang, Min Lin, et al.
High-throughput detection and identification of foodborne pathogens are in increasing demand for rapid bacteria detections in food safety and quality monitoring. As an effective method, microchip-based flow cytometry (microcytometery) has a potential to be less expensive and high throughout, and requires less bulky instrumentation than conventional methods. In this work, a low-cost and robust microcytometer with a simple optical setup was developed for demonstrating the high-throughput identification of foodborne bacterial pathogens that integrate sample flow focusing and detection into one testing procedure. High performance identification capability was achieved through simultaneously detecting the fluorescence and scatter light emitted from micro-fabricated channel, after designing and optimizing the laser shaping optical system and the micro-channel structure to improve the excitation light intensity as well as the detection sensitivity. In our configuration, the simple testing configuration with the collection angle of 42° in the orthogonal plane to micro chip presents the best SNR for both signals through simulation and systematic measurements. As a result, the maximum throughput of 83particles/s for the fluorescence-labelled bead with diameter of 1.013μm was obtained as well as the high detection efficiency (above 99%) and the correlation percentage (above 99.5%). Apart from the high detection sensitivity and identification power, this microcytometer also has the advantages of simple optical structure, compactness and ease in building.
Cell recognition by image processing and nonlinear cross correlation
E. Pérez-Careta, M. Torres-Cisneros, J. J. Sánchez-Mondragón, et al.
This work implements a novel hybrid method for detection and tracking of biological cells of "in vitro" samples (Goobic,1 2005). The method is able to detect and track cells based on image processing, nonlinear filters and normalized cross correlation (ncc) and it is tested on a full sequence of 1080 images of cell cultures. In addition of the cell speed, Cell tracking differentiate itself from tracking other kinds of tracking because cells show: mitosis, apthosis, overlapping and migration (Liao,2 1995). Image processing provides an excellent tool to improve cell recognition and background elimination, set as a priori task on this work and conveniently implemented by a Fourier analysis. The normal cross correlation was developed in the Fourier space to reduce time processing. The problem of the target detection was formulated as a nonlinear joint detection/estimation problem on the position parameters. A bank of spatially and temporally localized nonlinear filters is used to estimate the a posteriori likelihood of the existence of the target in a given space-time resolution cell. The shapes of the targets are random and according to the sequence, the targets change of shape almost every frame. However, the cross correlation result is based on the target shape matching, not in the position; and the system is invariant to rotation. Nonlinear filter makes a robust cell tracking method by producing a sharper correlation peak and reducing the false positives in the correlation. These false positives may also be reduced by using image preprocessing. Fourier and nonlinear filtering implementation showed the best results for the proposed cell tracking method presenting the best time consumption and the best cell localization.
A novel method for multiple lifetime recovery in time-domain optical imaging
S. Fortier, G. Ma, M. Jean-Jacques
A new multiple lifetime fitting algorithm is presented which deconvolves a time-domain system Instrument Response Function (IRF) from a measured Fluorescence Time Point Spread Function (FTPSF) prior to lifetime fitting. Deconvolution is followed by filtering, using a special case of the optimal Wiener filter, where the signal-to-noise ratio (SNR) in the spectral domain is evaluated empirically, and thus tuned with respect to each specific FTPSF-IRF combination at hand. Comparisons between the proposed deconvolution scheme and the classical Iterative Convolution (IC) scheme over a set of simulated and experimental data reveal that the proposed scheme typically exhibits order-of-magnitude performance gains (accuracy and efficiency combined) over the IC scheme in realistic conditions.
Spatial localization of discrete fluorescent inclusions with early photons: an analysis on the stability with respect to variations of optical properties
Geoffroy Bodi, Yves Bérubé-Lauzière
We recently developed a time-domain technique for localizing in 3D discrete fluorescent inclusions embedded in a scattering medium. It exploits early photon arrival times (EPATs), that is the time of flight of early arriving photons at a detector determined via numerical constant fraction discrimination. Our localization technique requires the knowledge of the speed of propagation of diffuse light pulses in the turbid medium to convert measured propagation times to distances. We have developed an experimental method for measuring the speed of propagation of such pulses. We have shown that time differences between a reference detector position and other positions around the medium allow finding the position of the inclusion. Our technique allows localizing inclusions to millimeter precision in a thick 5 cm diameter turbid medium. Herein, we analyze the stability of EPAT differences introduced above and propagation speeds with respect to changes in the medium's optical properties for optical properties typical of biological tissues. As we target small animal imaging, we concentrate on optical properties of mouse organs and tissues. Our objective is to determine bounds to be expected on the precision that can be achieved when media properties can vary and determine the limits of validity of our localization technique. Our results show that EPAT differences and propagation speeds obtained by our approach can vary; these values depend on the medium. We study 5 kinds of mouse organs and tissues. Propagations speeds are between 2.97 × 107ms-1 and 5.52 × 107ms-1. Thus, it becomes important to evaluate the discrepancy between true geometrical distance differences and distances as obtained by our approach using a constant propagation speed and the measurement of EPAT differences. It is such discrepancies that ultimately determine the localization accuracy of our algorithm because if distance differences based on EPATs are far from true distances, our algorithm although it has a certain tolerance will have to consider that. The distance error and so the localization accuracy of our algorithm is between 2.5mm and 8.6mm.
A single-photon fluorescence and multi-photon spectroscopic study of atherosclerotic lesions
Michael S. D. Smith, Alex C. T. Ko, Andrew Ridsdale, et al.
In this study we compare the single-photon autofluorescence and multi-photon emission spectra obtained from the luminal surface of healthy segments of artery with segments where there are early atherosclerotic lesions. Arterial tissue was harvested from atherosclerosis-prone WHHL-MI rabbits (Watanabe heritable hyperlipidemic rabbit-myocardial infarction), an animal model which mimics spontaneous myocardial infarction in humans. Single photon fluorescence emission spectra of samples were acquired using a simple spectrofluorometer set-up with 400 nm excitation. Samples were also investigated using a home built multi-photon microscope based on a Ti:sapphire femto-second oscillator. The excitation wavelength was set at 800 nm with a ~100 femto-second pulse width. Epi-multi-photon spectroscopic signals were collected through a fibre-optics coupled spectrometer. While the single-photon fluorescence spectra of atherosclerotic lesions show minimal spectroscopic difference from those of healthy arterial tissue, the multi-photon spectra collected from atherosclerotic lesions show marked changes in the relative intensity of two-photon excited fluorescence (TPEF) and second-harmonic generation (SHG) signals when compared with those from healthy arterial tissue. The observed sharp increase of the relative SHG signal intensity in a plaque is in agreement with the known pathology of early lesions which have increased collagen content.
Development of methods to study the conformational dynamics of quantum dot-oligonucleotide conjugates by single molecule spectroscopy
W. Russ Algar, Maxim B. Prigozhin, Baoxu Liu, et al.
The optical properties and significant surface area of CdSe/ZnS QDs make such nanoparticles an interesting platform for the preparation of nucleic acid biosensors based on fluorescence resonance energy transfer (FRET). Interactions between QDs and oligonucleotides affect biosensor performance and are not fully understood. Ensemble data obtained via FRET experiments indicated that, on average, 4-5 added oligonucleotides saturated the surface of green emitting QDs. An increase in the number of oligonucleotides per QD appeared to cause the oligonucleotides to transition from collapsed to upright conformations. Since bulk averaging hides details of such processes, methods must be developed and materials identified for studying QD-oligonucleotide conjugates at the single molecule level. Single QDs have been immobilized and fluorescence intensity trajectories measured. High count rates and good photostability were achieved using carboxyl polymer-coated QDs. Modeling of FRET efficiency based on the dimensions of QDs and oligonucleotides indicated that transitions between collapsed and upright conformations can be accurately measured based on changes in QD fluorescence lifetime. The ultimate goal of this work is to elucidate QD-oligonucleotide dynamics for better design and optimization of nucleic acid biosensors based on QDs.
Fiber Lasers and Devices
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Output power and threshold gain of apodized DFB fiber laser
Effects of apodization on distributed feedback fiber laser (DFB FL) output power and threshold gain are theoretically investigated by employing the transfer matrix method. Three distinct types of profile are investigated: the gaussian, flat or nonapodize, and sigmoid profile. The gaussian and sigmoid profiles are the two extreme cases examined; the former has a strong profile around a centrally located phase shift, while the latter is with a weaker profile. Findings indicate that the tradeoff between output power and higher order mode threshold performance are resulting from the interplay between these profile shapes. The comprehensive results presented in this paper should assist the development of high performance DFB FLs.
Radiation-balanced Tm3+-doped fiber amplifier
We present a theoretical scheme for a Tm3+-doped radiation-balanced (athermal) continuous-wave fiber amplifier. This mode of operation allows amplification without detrimental heating of the fiber with optical pumping. Athermal amplification is realized by laser cooling in which waste heat is disposed of in the form of spontaneous fluorescence by balancing the radiated and absorbed power. The athermal fiber amplification can be realized using a specially designed distributed pumping scheme.
Analytic theory of self-similar mode-locking with rapidly varying mean-zero dispersion
Self-similarity is a ubiquitous concept in the physical sciences used to explain a wide range of spatial- or temporalstructures observed in a broad range of applications and natural phenomena. Indeed, they have been predicted or observed in the context of Raman scattering, spatial soliton fractals, propagation in the normal dispersion regime with strong nonlinearity, optical amplifiers, and mode-locked lasers. These self-similar structures are typically long-time transients formed by the interplay, often nonlinear, of the underlying dominant physical effects in the system. A theoretical model shows that in the context of the universal Ginzburg-Landau equation with rapidly-varying, mean-zero dispersion, stable and attracting self-similar pulses are formed with parabolic profiles: the zero-dispersion similariton. The zero-dispersion similariton is the final solution state of the system, not a long-time, intermediate asymptotic behavior. An averaging analysis shows the self-similarity to be governed by a nonlinear diffusion equation with a rapidly-varying, mean-zero diffusion coefficient. Indeed, the leadingorder behavior is shown to be governed by the porous media (nonlinear diffusion) equation whose solution is the well-known Barenblatt similarity solution which has a parabolic, self-similar profile. The alternating sign of the diffusion coefficient, which is driven by the dispersion fluctuations, is critical to supporting the zero-dispersion similariton which is, to leading-order, of the Barenblatt form. This is the first analytic model proposing a mechanism for generating physically realizable temporal parabolic pulses in the Ginzburg-Landau model. Although the results are of restricted analytic validity, the findings are suggestive of the underlying physical mechanism responsible for parabolic (self-similar) pulse formation in lightwave transmission and observed in mode-locked laser cavities.
Spectral filtering highly chirped pulses in all-normal dispersion fiber lasers
We present a theoretical description of the generation of ultra-short, high-energy pulses in an all-normal dispersion laser cavity with spectral filtering. A reduced variational model based upon the Haus master mode-locking equations with quintic saturation is shown to characterize the experimentally observed dynamics. Critical in driving the intra-cavity dynamics is the nontrivial phase profiles generated and their periodic modification from the spectral filter. The theory gives a simple geometrical description of the intra-cavity dynamics and possible operation modes of the laser cavity. Further, it provides a simple and efficient method for optimizing the laser cavity performance.
Code generator using distributed phase shifts applied on a chirped fibre Bragg grating in a semiconductor fibre ring laser
Alexandre D. Simard, Sophie LaRochelle
As data traffic increases on telecommunication networks, optical communication systems must adapt to deal with this increasing bursty traffic. Packet switched networks are considered a good solution to provide efficient bandwidth management. We recently proposed the use of spectra amplitude codes (SAC) to implement all-optical label processing for packet switching and routing. The implementation of this approach requires agile photonic components including filters and lasers. In this paper, we propose a reconfigurable source able to generate the routing codes, which are composed of two wavelengths on a 25 GHz grid. Our solution is to use a cascade of two chirped fibre Bragg gratings (CFBG) in a semiconductor fibre ring laser. The wavelength selection process comes from distributed phase shifts applied on the CFBG that is used in transmission. Those phase shifts are obtained via local thermal perturbations created by resistive chrome lines deposited on a glass plate. The filter resonances are influenced by four parameters: the chrome line positions, the temperature profile along the fibre, the neighbouring heater state (ON/OFF) and the grating itself. Through numerical modeling, these parameters are optimized to design the appropriate chrome line pattern. With this device, we demonstrate successful generation of reconfigurable SAC codes.
Optimization of signal gain and core composition for low photodegradation in Yb-doped fiber amplifiers
Pierre Laperle, Louis Desbiens, Huimin Zheng, et al.
Photodarkening and photobleaching processes affect the level of photodegradation of Yb-doped fibers. Characterization and modeling of each process is crucial to understand how to optimize the operating conditions of fiber amplifiers and lasers to obtain acceptable output power degradation. We show that photobleaching is a key factor in the modeling and simulation of a 10-ns pulsed Yb-doped LMA fiber amplifier. Each parameter of the model was separately determined from induced excess loss measurements under selective pump and wavelength excitations. The model was used to simulate accurately the measured fiber amplifier degradation. Optimized fiber length and gain were calculated to improve the output power stability over time and increase the fiber lifetime. Furthermore, eight fibers have been fabricated with various Yb, Al, and P content using the MCVD process to optimize the core composition. The level of photodarkening in each fiber was evaluated by measuring separately rate coefficient and excess loss. It was found that all fibers followed a similar inversion-dependent rate while the maximum excess loss was dependent on the ratios [Al]/[Yb] and [P]/[Yb]. The proposed model allows for rapid evaluation and optimization of fiber parameters and operation conditions to assist Yb-doped laser system design in achieving the desired performance with low photodegradation.
140-uJ, narrow-linewidth, robustly single-transverse mode nanosecond infrared fiber laser platform with fine pulse tailoring capability
Pascal Deladurantaye, Mathieu Drolet, Louis Desbiens, et al.
The work presented in this paper had two main objectives. The first objective was to develop a very stable nanosecond infrared pulsed fiber laser oscillator platform offering a straightforward and accurate control over the pulse characteristics in the time domain. The second objective was to deliver what we call "high quality photons", which means delivering pulses with high energy and excellent beam quality and narrow spectral linewidth, all at the same time and with very good stability. Oscillators with such attributes find applications in material processing fields, for example in memory repair, photovoltaic cell processing or micro-milling, to name just a few. In order to achieve the first objective, an embedded digital platform using high-speed electronics was developed. Using this platform and a computer, pulse shapes have been programmed straightforwardly in the non-volatile memory of the instrument, with an amplitude resolution of 10 bits and a time resolution of 2.5 ns. Optical pulses having tailored temporal profiles, with rise times around 1 ns and pulse energy stability levels better than ± 3% at 3σ, have been generated at high repetition rates (> 100 kHz) at a wavelength of 1064 nm. Achieving the second objective required amplifying the low power master oscillator signal (10-100 mW) to output power levels in the range of 1 to 50 W. A multi-clad, polarization maintaining, Yb-doped large mode area fiber was specially designed to allow for the amplification of high peak power optical pulses, while keeping control over the nonlinear effects and preserving an excellent beam quality. Optical pulses with tailored shapes and pulse energy levels in excess of 140 μJ have been produced for pulse durations in the range of 10 to 80 ns, with 86% of the power emitted in a 0.5-nm bandwidth. The linearly polarized beam M2 parameter was smaller than 1.1, with both the astigmatism and the asymmetry below 15%. The pulse energy stability was better than ± 3% at 3σ. We conclude with a discussion about some of the applications of the developed platform.
Micro-milling process improvement using an agile pulse-shaping fiber laser
David Gay, Alain Cournoyer, Pascal Deladurantaye, et al.
We demonstrate the usefulness of INO's pulse-shaping fiber laser platform to rapidly develop complex laser micromachining processes. The versatility of such laser sources allows for straightforward control of the emitting energy envelop on the nanosecond timescale to create multi-amplitude level pulses and/or multi-pulse regimes. The pulses are amplified in an amplifier chain in a MOPA configuration that delivers output energy per pulse up to 60 μJ at 1064 nm at a repetition rate of 200 kHz with excellent beam quality (M2 < 1.1) and narrow line widths suitable for efficient frequency conversion. Also, their pulse-on-demand and pulse-to-pulse shape selection capability at high repetition rates makes those agile laser sources suitable for the implementation of high-throughput complex laser processing. Micro-milling experiments were carried out on two metals, aluminum and stainless steel, having very different thermal properties. For aluminum, our results show that the material removal efficiency depends strongly on the pulse shape, especially near the ablation threshold, and can be maximized to develop efficient laser micro-milling processes. But, the material removal efficiency is not always correlated with a good surface quality. However, the roughness of the milled surface can be improved by removing a few layers of material using another type of pulse shape. The agility of INO's fiber laser enables the implementation of a fast laser process including two steps employing different pulse characteristics for maximizing the material removal rate and obtaining a good surface quality at the same time. A comparison of material removal efficiency with stainless steel, well known to be difficult to mill on the micron scale, is also presented.
Linewidth of high-power fiber lasers
In this work, we examine how the linewidth of high-power Yb-doped fiber lasers changes as a function of laser power. Four-wave mixing between the various longitudinal modes of the laser cavity tends to broaden the laser linewidth, while Bragg reflectors have a narrow bandwidth that limits the extent of this broadening. An analytical model taking into account these effects predicts that the laser linewidth scales as the square root of laser power, in agreement with numerical simulations [1]. This model has been previously validated with a low-power Er-doped fiber laser [1] and with Raman fiber lasers [2]. In this paper, we compare the measurements taken with Yb-doped fiber lasers at power levels ranging from a few watts to hundreds of watts with the model. The broadening of high-power fiber lasers deviate from the model. Experimental data show that the linewidth broadens as a power function (between 0.5 to 1) of the laser power. A simple modification of the model is proposed which fits all the experimental data.
Compact laser system with a ~1-mJ, 1-ns output at a multi-kHz repetition rate
A. Knigavko, A. V. Kir'yanov, S. M. Klimentov, et al.
We demonstrate and optimize, for a mJ/ns release, the operation of a compact laser system designed in the form of a hybrid Q-switched Nd3+:YAG/Cr4+:YAG microchip laser seeding an Yb-doped specialty (GTWave-based) fiber amplifier. A gain factor as high as ~25 dB is achieved for nanosecond single-mode pulses at a 1-10-kHz repetition rate as the result of optimization
Influence of different laser operation regimes on the specific energy required for rock removal in oil and gas well drilling applications
Florian Albert, Alexander Grimm, Michael Schmidt, et al.
Although many practical hurdles remain to be addressed in the future, laser oil and gas well drilling has potential advantages over the conventional rotary drilling approach, such as a smaller footprint of the drilling rig, higher rates of penetration, reduction of downtime due to dull bits, reduction of waste caused by drilling mud, creation of a natural casing while drilling, and ability to drill in hard rock formations. One of the most promising applications is downhole laser perforation for well completion as an alternative to explosive technologies currently in use. In order to establish both the technical and economic feasibility of using lasers in oil and gas drilling operations, one can measure the laser energy required to remove a unit volume of rock. The resulting specific energy is a measure of the efficiency of the laser drilling process and depends on the rock type and the laser operation regime that determines the laser-rock interaction mechanism. In the present feasibility study, we compare the results of laser drilling tests conducted in two types of reservoir rocks, namely limestone and sandstone, at different laser wavelengths and for different laser operation regimes (continuous wave and pulsed regimes, different repetition rates and duty cycles) in terms of specific energy. We also discuss preliminary results on the influence of the temporal shape of the laser pulses in the nanosecond regime on the rock removal process as obtained with INO pulse-shaping fiber laser platform, with the objective to take advantage of the flexibility and the agility of such a laser source for drilling operations in different rock types.
Recent advances in mid-IR optical fibres for chemical and biological sensing in the 2-15um spectral range
Animesh Jha, Xin Jiang, Joris Lousteau, et al.
The invited paper explains the transmission properties of a range of near-, mid-, and far-IR optical fibres for their applications in chemical and biological sensing. Methods for the fabrication of single and multiple-core mid-IR fibres are discussed in view of controlling the thermal and viscosity properties for fibre drawing. In particular, the need for removing impurity bands in the 5000 to 1000 cm-1 range is explained. The importance of engineering multi-core fibres is also discussed for simultaneous measurements of Raman, IR and surface plasmon enhanced modes together with say, temperature using a mid-IR transmitting tellurite fibre e.g. in a chemical process. The paper explains the principles and advantages of evanescent wave coupling of light at the resonant frequency bands for chemical sensing using a fibre evanescent wave spectroscopic sensor having a GeTeSe chalcogenide fibre. Using fibre based techniques, measurements for Cr6+ ions in solution and As3+ and As5+ in solids have been characterized at visible and mid-IR regions, respectively. In this paper we also explain the importance of using mid-IR fibres for engineering novel laser and broadband sources for chemical sensing.
A novel technique for electronic phasing of high power fiber amplifier arrays
We report high power phase locked fiber amplifier array using the Self-Synchronous Locking of Optical Coherence by Single-detector Electronic-frequency Tagging technique. We report the first experimental results for a five element amplifier array with a total locked power of more than 725-W. We will report on experimental measurements of the phase fluctuations versus time when the control loop is closed. The rms phase error was measured to be λ/60. Recent results will be reported. To the best of the authors' knowledge this is the highest fiber laser power to be coherently combined.
New Optical Materials and Nanophotonics
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System for variable stripe length optical gain measurements in structures containing silicon nanocrystals
D. Koshel, D. Barba, F. Martin, et al.
The variable stripe length (VSL) is a convenient method for the measurement of optical gain. However, several inherent experimental constraints such as pump beam non-uniformity, diffraction from the movable cache and sample edges, and gain saturation challenge its proper implementation. A modified VSL configuration, which addresses these constraints, has been developed and implemented for gain measurements in SiO2 structures containing silicon nanocrystals. A microprocessor based acquisition of several control parameters provides reliable and reproducible optical gain measurements.
Electro-optical properties of silicon nanocrystals
Alexandre Lacombe, Félix Beaudoin, François Martin, et al.
In the last decade, the luminescent properties of silicon nanocrystals (Si-nc) have been increasingly studied, since Si-nc are considered as good candidates for optical interconnects between ever-smaller integrated circuits (ICs) components, and for the monolithic integration of all-silicon photonic and electronic devices. For these applications, an efficient coupling between optical and electrical signals within Si-nc structures is required. In this article, the interaction between simultaneous optical and electrical stimulation of Si-nc is examined. To this end, the photoluminescence (PL) spectra of Si-nc obtained by ion implantation in a thin (40 to 60 nm) oxide layer of metal-oxide-semiconductor (MOS) devices has been recorded as a function of variable applied voltage biases at room temperature. Two remarkable features have been observed: an optical memory effect, due to asymmetric PL intensity modulation with respect to biasing polarity, and an efficient optical switching of an electric current in reverse bias operation. These results are explained in terms of the competing effects of the storage and the photogeneration of charge carriers in Si-nc and oxide defects, as indicated by the correlation between the PL intensity and the current flowing through the MOS devices. Moreover, the use of positively- and negatively- doped substrates in the MOS structures distinctly shows the different effects of electron injection over hole injection in Si-nc and their surrounding SiO2 matrix. These novel optoelectrical features of Si-nc are expected to add more functionality to future all-silicon photonic and electronic ICs.
Light interference effects: a tool for the modulation of the Si-nc luminescence spectrum and the determination of the emitting center depth distribution
C. Dahmoune, D. Barba, F. Martin, et al.
Recently, it has been shown that the photoluminescence (PL) spectrum emitted by silicon nanocrystals (Si-nc) can be modulated by means of light interference effects, when the Si-nc are produced by the implantation of Si ions in a SiO2 film grown on Si substrate (SiO2/Si). Optical interference must be considered for both the pump laser and the light emitted by the Silicon nanocrystals. In this study, strong variations of the PL spectrum intensity are observed as a function of the SiO2 thickness so that a PL intensity up to three times greater than the one recorded from Si-nc embedded in fused silica has been observed. A Fresnel equation solver [1, 2] has been developed and used to model the emission spectrum of Si-nc in these structures. This model determines the normalized depth profile of emitting centers using the measured luminescence spectra of a series of samples covering a range of SiO2 thicknesses, providing a powerful tool for the study of the Si-nc luminescence mechanism by comparing the shape of the emitter depth profile to those of Si-nc and implanted Si+ depth distributions.
Nonlinear optical characterization of ionics liquids
C. E. Valencia Loredo, K. A. Barrera-Rivera, M. Trejo-Durán, et al.
In this work, we show results about the nonlinear optical characterization for four ionic liquids (ILs), namely 1-buthyl-3- methylimidazolium tetrafluoroborate ([BMIM][BF4]), 1-ethyl-3-methylimidazolium Bis((trifluoromethyl)sulfonyl)imide ([EMIM][TF2N]), 1-ethyl-3-methylimidazolium trifluoroacetate ([EMIM][CF3COO]),1-buthyl-3-methylimidazolium trifluoroacetate ([BMIM][CF3COO]), using z-scan technique.
Self-diffraction properties in nanotubes (CNTs)
E. E. Gracia-Espino, D. Hernández-Cruz, M. Terrones, et al.
Nonlinear effects are consequence of interaction of height intensities of energy with the matter. Self-diffraction is nonlinear effect and rings are produced. We analyzed the increase of rings due to changes in intensity of CW Ar laser that modify the nonlinear refractive index. The Carbon Nanotubes (CNTs) were dispersed on different solvents: a) water, b) ethanol, c) isoprophanol, and d) acetone. The concentrations were 10ml:1mg in all samples. The dependence between power and concentration of CNTs is shown.
On the characterization of a random monolayer of particles from coherent optical reflectance
F. Alarcón-Oseguera, M. Peña-Gomar, A. García-Valenzuela, et al.
We present the viability of obtaining the particle size and surface coverage in a monolayer of polystyrene particles adsorbed on a glass surface from optical coherent reflectance data around the critical angle in an internal reflection configuration. We have found that fitting a CSM to optical reflectivity curves in an internal reflection configuration around the critical angle with a dilute random monolayer of particles adsorbed on the surface can in fact provide the particle's radius and surface coverage once the particles are sufficiently large.
Effect of depth etching on Bragg reflectors realized by focused ion beam in Ti:LiNbO3 waveguide
K. Ghoumid, R. Ferriere, B.-E. Benkelfat, et al.
In this paper we have studied effect of depth etching on the Bragg gratings (BGs) realized by Focused Ions Beam. This technique has the advantage to induce a direct waveguide structuring without intermediate media, comparing to traditional methods. A reflectivity of 96% within a window centred at 1550 nm is obtained. The effect of the depth etching on the transmittance and the bandwidth at half maximum is demonstrated.
Microtapers and nonlinear couplers based on hybrid chalcogenide/polysulfone structures
Chams Baker, Martin Rochette
Hybrid chalcogenide/polysulfone structures are proposed for the implementation of microtapers and nonlinear couplers. In addition to high mechanical robustness, hybrid microtapers provide design advantages that enable the implementation of nonlinear couplers with low switching threshold powers.
Solitons propagation in a tandem arrangement of nonlinear materials
J. J. Sánchez-Mondragón, A. Alejo-Molina, M. Torres-Cisneros, et al.
Spatial and temporal solitons are at the core of many physical, geological, biological, transmission and information processing and other problems. However, in most cases we have focused on their steady behavior, and therefore on homogeneous media and their single soliton eigenvalues spectrum. This has been done even in the case of an all optical simultaneous loss and amplification, where we have assumed stability of those eigenvalues. However, the transient behavior has received little attention, often disregarded under a generic pulse reshaping or experimentally diafragmed as often occurs in large amplifiers. But such transient behavior can be frozen in a periodic nonhomogenous media, tandems, where such behavior corresponds to the soliton convergence in each tandem media, producing a regular but not steady behavior. We discuss the resonant pulse propagation in a two level atom media tandem, described by a real convergence and a Kerr intensity dependent nonlinearity, described by a complex convergence.
Production of Ti3+ :Al2O3 nanoparticles by pulsed laser deposition
Stéphan Paquet, Michel Piché
Ti3+:Al2O3 (Titanium doped sapphire or Ti:sapphire) nanoparticles were produced by the means of pulsed laser deposition (PLD) of bulk Ti:sapphire in background gas with the substrate at ambient temperature. The effect of background gas pressure and composition is studied, having a major impact on the shape, size and aggregation level of the particles. The nanoparticles were characterized by scanning and transmission electron microscopy (SEM and TEM). Preliminary results for the PLD of Cr3+:Al2O3 (ruby) nanoparticles are also presented.
Nonlinear pulse propagation in a square waveguide filled with a conducting nanoparticles composite
Waveguides coupling have been widely studied; however, nanowaveguides of high refraction index contrast open the opportunity of studying the nonlinear dynamics of coupled waveguides, in particular those filled with metallic nanaoparticles composites. Those composites show a Quantum Mechanical Kerr Nonlinearity and a classical field amplitude nonlinearity that are compared by using a iterative WKB to introduce the field nonlinearity and based in the ensuing M matrix. The produced nonlinear supermodes show a confinement of the pulse in the waveguides and a breaking of the coupling at small and large core waveguides.
Layered cylinders in a 2D square lattice
D. L. Romero-Antequera, A. Alejo-Molina, J. J. Sánchez-Mondragón
We present the characterization of a photonic crystal slab with a square lattice, whose basis elements are layered cylinders. The cylinders are conceived as glass cores and subsequent layers of two alternating media with different refractive indices, the thickness of each layer is a quarter of a tuning wavelength within the media. The band structure in the dispersion relation is computed by means of numerical simulation and compared to the band structure of a square lattice with plain cylinders, with the same size, and refractive index equal to the average index of the layered ones. We have found that the band structure shrinks to lower frequencies as the number of full periods of layers increases, although keeping the average refractive index and filling factor. This shrink occurs even when the index contrast is kept constant.
Nonlinear pulse propagation in an optical fiber doped with conducting nanoparticles
J. Sánchez-Mondragón, M. Torres-Cisneros, C. Velásquez-Ordoñez, et al.
Metallic nanoparticles, of a few nanometers radii, show nonlinearities that are the object of experimental and theoretical studies, in particular in the framework of composites. A quantum mechanical analysis of such structures predict a Kerr type nonlinearity, however quite a recent publication on a classical approach has shown that a classical metallic nanoparticles composite shows a nonlinearity proportional to the electric field amplitude, not to the intensity as is in the Kerr case. The capability of filling up the core of a piece fiber with such composites open the possibility of preparing long enough pieces of fiber with such a composite as well as the straightforward drawing of a fiber doped with nanoparticles. In this work we carry on the numerical simulation on such class of fibers, with the specific aim of looking at the corresponding soliton propagation in an optical fiber with a core doped metal nanoparticles.
Er-doped Si nanoclusters waveguides longitudinally pumped by broad area lasers for optical amplification
We present an extensive study of an Er doped Silicon Rich Silicon Oxide (SRSO) based material used for the realization of optical waveguide amplifiers in which Si-nanoclusters (Si-ncls) are formed by thermal annealing. In particular we focus our attention on the confined carrier absorption (CCA) mechanism within the Si-ncls and on the fraction of Er ions coupled to them. Experimental data are used for accurate modeling of Si-ncls sensitized EDWAs (Erbium Doped Waveguide Amplifiers) longitudinally pumped by visible broad area lasers. Although the material requires further optimization to be effectively deployed, accurate numerical simulations of Si-ncls sensitized EDWAs, based on this material and longitudinally pumped by visible broad area lasers at 660 nm, point out significant benefits provided by the nanoclusters sensitization. Our model, based on the Finite Element Method, performs the modal analysis of the guiding structure, and then allows to study the propagation of pump and signal electric fields along the waveguide amplifier; the rate equations for the coupled Er/Si-ncls system account for their coupling ratio. Numerical results, based on measured material parameters, point out that resonant pumping at 660 nm provides significant benefits in terms of gain enhancement, with respect to standard EDWAs, even at low Er/Si-ncls coupling ratio. This feature suggests that a careful design can lead to the realization of compact integrated amplifiers and lasers, compatible with CMOS technology.
Next-Gen Networks
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Experimental demonstration of a centralized light source OCDMA-PON based on polarization multiplexing
A novel centralized light source OCDMA PON without wavelength filters is proposed and experimentally demonstrated. The OCDMA coded signals and the unmodulated clock pulses are polarization-multiplexed and simultaneously transmitted in the downlink. Then the received clock pulses at the ONU side are used as the source for the uplink transmission. The experiment results based on a two-user 2.5 Gb/s OCDMA system show that excellent performance can be achieved after a 20-km transmission.
An analytical method for performance evaluation of a DQPSK channel in presence of OOK signal
Vahid Tavassoli, Thomas E. Darcie
The impact of cross-phase modulation in a multichannel hybrid on-off-keyed (OOK) and differential quadrature phase shift keyed (DQPSK) system is evaluated analytically. Results confirmed by simulation provide a simple method for determining induced RMS phase error.
Optical Sensors and Detectors
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Single eye and camera with depth perception
Bart Farell, Dawit Negussey, James Flattery, et al.
It is possible that each light sensor pixel in the eye has the capability of measuring the distance to the part of the object in focus at the pixel. One can also construct an electronic camera where each pixel can measure the distance to the portion of the object in focus at the pixel. That is, these devices have depth perception
Velocity measurements comparison of water and pentane travelling in capillary optical fibers coated respectively with a xerogel and a poly(dimethylsiloxane) absorbing layer
Serge Caron, Claude Paré, Antoine Proulx, et al.
An analysis of the optical signal transmitted by a polarimetric sensor developed for the measurement of velocities of fluids in a capillary optical fiber is presented. It allows one to determine whether a fluid is moving in the vapor or the liquid phase.
Brillouin spectrum narrowing in high extinction ratio nanosecond pulse from phase locked DFB lasers
Yun Li, Xiaoyi Bao, Jeffrey Snoddy, et al.
The Brillouin spectrum narrowing phenomenon for nanosecond pulses in Brillouin Optical Time Domain Analysis (BOTDA) sensor system is demonstrated with high extinction ratio (ER > 24 dB) nanosecond pulse over short fibre length (10 m). The line width of the Brillouin spectrum is ~52 MHz for 10 ns pulse by feedback phase locking of the pump and probe waves from: 1) DFB lasers (2 MHz bandwidth) and 2) fibre lasers (5 kHz bandwidth) at the Brillouin frequency. It is found that the coherent length (inverse of the Brillouin line width in the fibre) of the Brillouin scattering process is not determined by the laser bandwidth, rather by the enhanced phonon field generated from phase locked pump and probe lasers for nanosecond pulses. For the same bandwidth of the pump and probe lasers, the line width of the Brillouin spectrum with high extinction ratio nanosecond pulses under the phase locking of the pump and probe waves is much narrower than that from the frequency locking of the pump and probe waves at the Brillouin frequency.
Digital TAcy: proof of concept
Annie Bubel, Jean-François Sylvain, François Martin
Anthocyanins are water soluble pigments in plants that are recognized for their antioxidant property. These pigments are found in high concentration in cranberries, which give their characteristic dark red color. The Total Anthocyanin concentration (TAcy) measurement process requires precious time, consumes chemical products and needs to be continuously repeated during the harvesting period. The idea of the digital TAcy system is to explore the possibility of estimating the TAcy based on analysing the color of the fruits. A calibrated color image capture set-up was developed and characterized, allowing calibrated color data capture from hundreds of samples over two harvesting years (fall of 2007 and 2008). The acquisition system was designed in such a way to avoid specular reflections and provide good resolution images with an extended range of color values representative of the different stages of fruit ripeness. The chemical TAcy value being known for every sample, a mathematical model was developed to predict the TAcy based on color information. This model, which also takes into account bruised and rotten fruits, shows a RMS error of less than 6% over the TAcy interest range [0-50].
Open path spectroscopy of methane using a battery operated vertical cavity surface-emitting laser system
Matthew Dzikowski, Aleksandr Klyashitsky, Wolfgang Jaeger, et al.
Tunable diode laser spectroscopy (TDLS) is a well-established method for trace gas detection. TDLS systems usually employ edge-emitting diodes with a distributed feedback configuration. Recently long wavelength vertical cavity surface emitting lasers (VCSEL) have emerged as an alternative source for spectroscopic applications. The relatively low cost, low power requirements and large tuning range of VCSELs make them particularly attractive for portable gas detection systems. In this paper we describe a battery-operated VCSEL spectroscopy system operating near 1650 nm for methane detection. Wavelength modulation spectroscopy (WMS) is commonly used in TDLS systems to improve sensitivity. WMS in these systems is usually implemented with a hardware based lock-in amplifier. We report on the construction of a new system with software WMS and compare its operation with a conventional system. The VCSEL TDLS system is used to probe the 2v3 band of methane over an open path. The relative contributions of optical and electrical noise to the system signal to noise ratio and minimum gas detection level is presented. Finally, challenges and future design considerations in VCSEL spectroscopy are discussed.
Temporal phase shifting method using acoustic-optic modulated stroboscopic interferometer (AOMSI) for characterization of microstructures
Davoud Mohammadalizadeh, Muthukumaran Packirisamy, Narayanswamy Sivakumar
Temporal phase shifting method, which is commonly used for characterization of the microstructures, requiring phaseshifter has inherent errors due to non-linearity. To overcome this, an Acoustic-Optic Modulated Stroboscopic Interferometer (AOMSI) was developed using the principle of Stroboscopic Interferometer. The technique utilizes the advantage of stroboscopy to create phase shifted images without requiring any component for phase shifting. Using Carré algorithm and developed AOMSI the curvature of microstructures due to residual stress was extracted. Experiments were performed on a silicon wafer to demonstrate the feasibility of the presented technique. Further, experiments were performed on a designed micro cantilever to extract surface-height information using the proposed method. To verify the accuracy of the presented method, the same micro cantilever was characterized using a WYKO surface profiler and the comparison was found to be in good agreement.
Study of laser guided measurement robot
Jianfei Ouyang, Lin Duan, Yong Tian, et al.
A Laser Guiding Measuring Robot (LGMR) based on the new technology of Laser-Guiding, SMR-Tracking has been developed. LGMR can be guided by measuring laser beam to do 3D laser tracking measurement automatically. LGMR consists of a measuring robot and a laser tracker system (LTS). The measuring robot is employed to carry SMR to track the measuring laser beam from LTS. LTS is used to measure 3D position of SMR and then complete the measurement. The CAD model of a measured object can be used to control the measuring laser beam from LTS to point to the measured position. The measuring robot then tarcks the guiding laser beam and drives SMR to the measured position. This paper presents the working principle and system framework of LGMR. The details of the robot design, implement and experiment are also provided. The experiments prove that the proposed LGMR can measure a complicated object automatically by using the CAD model of the measured objects. The developed LGMR makes it possible for LTS to do 3D tracking measurement automatically by using the CAD model of a measured object to guide the measuring robot.
Simple fiber optic refractive index sensor based on evanescent higher order modes
Jiahua Chen, Wojtek J. Bock, Predrag Mikulic
This paper presents an optical fiber refractive index sensor based on the evanescent higher order modes. Its structure and principle are quite simple. The sensor is composed of two segments of optical fibers that are spliced together. An ordinary multimode fiber with a core diameter of 50 μm is used to input the light. The functions of a second multimode fiber with a core diameter of 200 μm are twofold. In the region of the splice, a section of the cladding a few centimetre long is removed by an electrical discharge. This part works as a sensing element, and the rest of the fiber is used to output the light. Once the light travels though the input fiber and crosses the splice to enter the second fiber, numerous modes both guided and leaky are generated due to the abrupt increase of the core diameter. The evanescent light fields of these guided modes are sensitive to changes in the refractive index of the material surrounding the fiber cladding. The evanescent field change directly causes a change in the output light intensity. The developed sensor is compact in size, simple to fabricate, promising in performance, and has a high potential for practical applications.
Silicon-on-insulator photoconductors for noncontact ultrasound vibration measurement using laser speckle
Jonathan Bessette, Elsa Garmire
The motion of a vibrating specular surface can be measured by monitoring the change in speckle pattern of a reflected laser beam. Smaller speckles allow for a more sensitive measurement, but provide a weaker signal when monitored with a correspondingly sized photodiode. The signal of a photoconductor, on the other hand, scales with the ratio of its dimensions, and so can be resized without loss of signal. Here we present a prototype detector made from micron-scale, isolated mesas of intrinsic silicon, fabricated lithographically from a commercial silicon-on-insulator wafer. The prototype has a frequency response extending into the megahertz regime, making it suitable for ultrasound testing applications. Only a single laser beam, with no separate interferometer or optical reference, is required for displacement measurement with laser speckle monitoring, so such a system provides a robust and simple alternative to other optical detection methods. Initial tests have captured ultrasound Lamb wave vibrations and standing waves induced by optical excitation in thin copper and aluminum strips.
Optical properties of gold particles with near micron size: localized and propagating surface plasmons
Ludovic S. Live, Jean-Francois Masson
This proceeding summarizes the optical properties of plasmonic structures from nanoscale to macroscale. Of particular interest, Au triangles and hole arrays of near micron size exhibit concomitantly surface plasmon resonance (SPR) and localized surface plasmon resonance (LSPR) optical properties in the Vis-NIR region, resulting in excellent optical properties for biosensing. In transmission spectroscopy, 15 nm nanoparticles absorbs at λ = 525 nm, nanotriangles of > 200 nm edge length absorbs at λ > 600 nm while nanohole arrays exhibit a more complex spectrum including absorption and enhanced optical transmission (EOT) features. Nanohole arrays are also sensitive to refractive index (RI) change and it can be optimized by tailoring the hole diameter and the periodicity. Au triangles ranging from nano (200 nm) to micron size (1.5 μm) are active in LSPR with an absorption peak that redshifts with the increasing aspect ratio of the structure. In total internal reflection (TIR) experiment, Au triangles with an edge length of 500 nm or greater present an absorption peak at λ = 800 nm. Also, triangles of 700, 950 and 1800 nm have a maximum transmission around λ= 650 nm that is highly sensitive to refraction index (RI) variations. This absorption peak is attributed to propagating SPR, similarly to the optical phenomenon occurring on a smooth Au film as used in the Kretschmann configuration of SPR. Lastly, nanohole and microhole arrays spectra, measured in TIR, are a composite of both triangles (LSPR) and thin film spectra (SPR).
Temperature and strain characterization of Bragg gratings impressed with femtosecond laser radiation in suspended-silica-core fibers
Fiber Bragg Gratings (FBG's) are widely used in various fields, including optical fiber sensors. In this work, the temperature and strain response of C-band FBG's in pure silica four-leaf clover shaped suspended-core fibers was analyzed. These FBGs were fabricated by femtosecond laser exposure, which enabled the refractive index modulation of the pure-silica-core of the fibers. We compared the Bragg wavelength variation with strain and temperature for two different suspended-core fibers (256b2 and 256b5). The 256b2 fiber has a core diameter of 4,9 μm and a hollow hole inside the core with 1,4 μm; the 256b5 fiber has a solid silica core with a 7,2 μm diameter. For strain and temperature characterization, the sensing head was attached to a translation stage with a resolution of 1 μ;m and was placed in a tubular oven, which permits a temperature reading to be set with an error smaller than 0,1 °C. Both have shown the same sensitivity to strain (1,2 pm/με) but different sensitivity to temperature variation (8,4 pm/°C and 10 pm/°C respectively). The relative difference between the thermal coefficients of the two selected Bragg signatures is 16%. The results obtained indicate that these gratings can be used in optical fiber sensing, for example in the context of the important problem of simultaneous strain and temperature measurement.
Nondestructive testing by digital shearography using a Savart plate
F. Michel, P. Blain, E. Auger, et al.
Shearography is a growing optical technique in the field of non-destructive testing (NDT)[1],[2]. Hololab developed an out of plane, in line and almost common path interferometer based on polarization states separation using a coated prism for digital phase-shifting shearography[3]. This setup is efficient but does not allow varying the shearing direction that is an important parameter for defects detection[1]and quantification[2]. To overcome this disadvantage, the coated prism is substituted by a Savart plate device that allows scanning several shearing directions by rotating the device around the light propagation axis. The behaviour of the Savart plate as a shearing device is experimentally analyzed to optimize its integration within the interferometer. Recorded phasemaps in NDT for different shearing directions are presented.
Waveguide evanescent field fluorescence microscopy: waveguide mode scattering by non-uniform grating and defects in the wave guiding film
Abdollah Hassanzadeh, Kenneth Kar Ho Wong
Waveguide evanescent field fluorescence microscopy is an evanescent field based microscopy to visualize cell-substrate contact regions and solid thin films. Despite some advantages of this method compared to other evanescent field based microscopes, non-uniform illumination source and background are reported to be the problems for producing nonuniform images. We noticed similar non-uniformities in our primary results with ultra- thin solid film and cell-substrate contact regions. We used various microscopy methods to demonstrate induced inhomogenities in the waveguide evanescent field fluorescence microscopy images by secondary patterns in the gratings, and defects in waveguides surface. We discuss their effects on the waveguide microscopy background, ultra-thin solid films, and cell-substrate contact region images. Defect-free waveguides with uniform gratings fabricated and used to image phase separated lipids monolayer LB films and cell-substrate contact regions.
Spherical prototype to determine the irradiance patterns produced by divergent sources
In this work, the development of a spherical irradiance meter is presented. The illumination intensity measurements are made by means of a photo-detector assembled on a mechanical setup. The received power by the detector is useful to obtain the irradiance profile of the lighting source under test, considering a discrete set of points. This detector is located at the edge of the mobile arm of the mechanical system, which makes a sweep considering two movements directed by the azimuthal and zenithal angles, generating analogous paths to the terrestrial meridians, covering a semi-sphere of 27 cm of radius. The concentric trajectories consider lighting source under test at their center. The radiation pattern of each lighting source is generated using the irradiance data and the detector positions. The mechanical structure has a horizontal mobile base, which allows a 360° rotation. At the same time, one of its extremes serves as base of the mobile arm, which allows the vertical movements and provides the sensor support. The movements are controlled by step motors determining the data collection points. They also define the horizontal and vertical resolution. The obtained data is visualized by means of a display.
Rectangular prototype to determine the irradiance pattern produced by directive sources
In order to determine the irradiance profile of a directive source on a plane XY, we present an arrangement of geometry similar to conventional scanners. It is formed by two vertical bases of a mobile rail. On this rail, a photodetector is located, making it able to move from right to left, covering a mesh of 14x15 detection points. The XY movements of the setup are determined by servo motors, which determine the resolution, but considering the interest of researchers in this area, and the feasibility to use a table XY for the scanning, we implement its use as a part of this meter. The detector is located at the corner of the mobile section. The height of the light source under test is located at the central part of the described area. The utilization of only one photo-detector was decided with the purpose of a higher homogeneity of the irradiance measurements. The detector must have high stability and low noise. The resolution XY is determined by the movements on the axes of a length determined by the DSPIC programming. The use of this device instead of commercial hardware for data acquisition contributes to the low costs of the prototype. It was realized all the necessary tests for the generation of reliable information, establishing the time needed to achieve the stability of the system, as well as the levels of noise due to the presence of the detector and of the electronic elements. This prototype has a very simple geometry and relatively low cost. It constitutes a good option to determine the irradiance profile of directive sources.
One-dimensional photonic crystal with a conducting nanoparticles composite
J. Escobedo-Alatorre, J. Sánchez-Mondragón, C. Vazquez-Ordoñez, et al.
A nonlinear stack is one of the handier photonic crystals where new schemes and methodologies can be tested. Nonlinear Stacks have shown the presence of switching, chirping and bistability, but in practice it is hard to find nonlinear material with the adequate physical and mechanical properties. Metallic Nanoparticles are well known to have strong nonlinearities and their composites show the desired nonlinear properties. The nonlinearities are Kerr when described Quantum Mechanically and field amplitude, when described classically. In this report we describe the band gap of such classical composite stack.
Spherical 3D photonic crystal with conducting nanoshell and particle core
We discuss a structured 3D Dielectric Photonic Crystal with both a metallic core and a metallic shell. We discuss the role of each one, the stack, the core as well as the cavity formed between the core and the shell. The low frequency metallic core features becomes much more significant as it gets smaller and get diluted by the cavity.
Optoelectronic mixing in NbN superconducting nanowire single photon detectors
Zhizhong Yan, A. Hamed Majedi
In this paper, we present our experimental results on the electrically pumped optoelectronic mixing effect exhibited in a niobium nitride (NbN) superconducting nanowire. The experimental setup in order to test the mixer has been reported in detail. This superconductive nanowire optoelectronic mixer demonstrates photodetection and mixing in an integrated manner. We have explored both effects under a great variety of external conditions, such as temperature and bias current, in order to seek potential ways toward quantum optoelectronic detection and mixing by such nanowire device.
Optoelectronics, Integrated Devices, and Networks
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Breakdown voltage investigation of fusion SiO2 optical coupler switch using Pockel effect model
. Saktioto, Nor Faridah Hanim Mat Junit, Sze Phing Ho, et al.
This paper describes a new model for the breakdown voltage of SiO2 fiber coupler using the Pockel effect and empirical equation. The model is evaluated by using the coupling coefficient and the changes in the refractive index. We found that the breakdown voltage is in the order of 102 volt correspond to coupling coefficient by the order of mm-1. Increasing the value of coupling coefficient between the electrodes leads to a reduction in the breakdown voltage.
Correlation study between contamination and signal degradation in single-mode APC connectors
Steve Lytle, Matt Brown, Tatiana Berdinskikh, et al.
This paper summarizes the correlation study between contamination and scratches on singlemode APC connectors and signal degradation; leading to an Acceptance Criteria Matrix. The study is a continuation of International Electronics Manufacturing Initiative (iNEMI) research on development of cleanliness specification for singlemode angled physical contact (SM-APC) connectors. Twenty-five APC SC connectors on one-meter patch cords were used for this study. The Design of the Experiment (DoE) was a multi-step process that involved: (1) inspecting, cleaning and inspecting connectors being tested (devices under test, or DUTs) and launch connectors; (2) making multiple matings and dematings of each DUT, in a pristine state, with a reference connector, and recording Return Loss (RL) data after each cycle; (3) manually applying dust to the cleaned end-faces of the DUTs; then (4) mating contaminated DUTs with clean reference connectors at least five times, taking RL measurements after each mating and saving fiber end-face images for both connectors. It was shown that connectors with the contamination at the core (9um diameter) demonstrated a dramatic decrease in average RL of 14.2 dB. In comparison, the samples with contamination on the cladding and clear core demonstrated a negligible change in RL of 0.15 dB. For highly contaminated samples in the cladding layer, we found the changes of RL to be about 5-6 dB. Further investigation established that particle migration during successive matings also occurs on the ferrule within the contact zone (approximately <250 μm in diameter). Polishing scratches had no impact on RL of APC connectors. Based on the experimental data described in this paper, an inspection criteria matrix is proposed for SM-APC connectors including the zone definitions and number of allowable defects (contamination and scratches) for each zone. The recommendations on pass/fail criteria have been provided to the IEC (International Electrotechnical Committee). It is expected IEC-61300-3-25, which contains these criteria, will publish in 2009.
Error rate performance of pulse position modulation schemes for indoor wireless optical communication
Nazmy Azzam, Moustafa H. Aly, A. K. AboulSeoud
Error rate performance of pulse position modulation (PPM) schemes for indoor wireless optical communication (WOC) applications is investigated. These schemes include traditional PPM and multiple PPM (MPPM). Study is unique in presenting and evaluating symbol error behaviour under wide range of design parameters such symbol length (L), number of chips per symbol (n), number of chips forms optical pulse (w). Effect of signal to noise ratio levels and operating bitrates on symbol error performance is also discussed. A comparison between studying modulation schemes is done. Relation with IrDA and IEEE 802.11 indoor WOC standardization is also investigated. Results indicate that PPM achieve great symbol error performance at reasonable signal to noise ratio and high bitrates with large symbol length.
Tunable optical buffer using a fiber Bragg grating array and a widely tunable wavelength converter
A. K. AboulSeoud, Moustafa H. Aly, Heba A. Fayed
This paper demonstrates a tunable optical buffer with widely variable time delays using an array of fiber Bragg gratings (FBGs) filter and tunable wavelength converters (WCs). The flexibility of the proposed system gives an exact required delay and, consequently, better output port utilization. This system is designed to be compatible with 10 to 40 Gbps RZ communication systems.
Stability analysis of the mode-locking dynamics in a laser cavity with a passive polarizer
A low-dimensional model is constructed via a variational formulation which characterizes the mode-locking dynamics in a laser cavity with a passive polarizer. The theoretical model accounts explicitly for the effects of the passive polarizer with a Jones matrix. In combination with the nonlinear interaction of the orthogonally polarized electromagnetic fields, the evolution of the mode-locked state reduces to the nonlinear interaction of the amplitude, width and phase chirp. This model allows for an explicit analytic prediction of the steady-state mode-locked state (fixed point) and its corresponding stability. The stability analysis requires a center manifold reduction which reveals that the solution decays to the mode-locked state on a timescale dependent on the gain bandwidth and the net cavity gain. Quantitative and qualitative agreement is achieved between the full governing model and the low-dimensional model, thus providing for an excellent design tool for characterizing and optimizing mode-locking performance.
Optical intensity dynamics in a five-emitter semiconductor array laser
The intensity dynamics of a five-emitter laser array subject to a linearly decreasing injection current are examined numerically. We have matched the results of the numerical model to an experimental AlGaAs quantum-dot array laser and have achieved the same robust oscillatory power output with a nearly π phase shift between emitters that was observed in experiments. Due to the linearly decreasing injection current, the output power of the waveguide decreases as a function of waveguide number. For injection currents ranging from 380 to 500 mA, the oscillatory behavior persists with only a slight change in phase difference. However, the fundamental frequency of oscillation increases with injection current, and higher harmonics as well as some fine structures are produced.
High speed semiconductor optical amplifiers and their performance in pseudo-random bit-stream generation
Semiconductor optical amplifiers are important for wide range of applications including optical networks, optical tomography and optical logic systems. For many of these applications particularly for optical networks and optical logic high speed performance of the SOA is important. The speed of operation of SOA is limited by the gain and phase recovery times in the SOA. We have demonstrated higher speed operation (i) for SOAs with a carrier reservoir layer, (ii) for SOAs with a multi-quantum well modulation doped active region, and, (iii) for SOAs with a quantum dot (QD) active region. The multi-quantum well SOA has been integrated with InGaAsP/InP based waveguides to build Mach- Zehnder interferometers (MZI). XOR optical logic has been demonstrated at 80 Gb/s using these SOA-MZI structures. XOR operation has been analyzed by solving the rate equation of the SOA, for SOAs with both regular and QD active region. Mach-Zehnder interferometers fabricated using SOA with quantum dot active region (QD-SOA) can be used for XOR operation at 250 Gb/s. Pseudo random bit stream (PRBS) generation using both regular and QD-SOA have been studied and their performance modeled. The model shows QD-SOA based devices can be used to produce PRBS generators that operate near 250 Gb/s.
Tunable silica-on-silicon planar lightwave circuits for signal processing applications
Claire L. Callender, Patrick Dumais, Sarkis Jacob, et al.
The development of silica planar lightwave circuits (PLCs) employing multiple phase-shifting elements to achieve optical signal processing is presented. Thermo-optic switching in Mach Zehnder interferometer (MZI) structures has been demonstrated with typical switching powers of 250-300 mW. 6-loop lattice-form MZI devices designed with specific filter responses have been fabricated, packaged, and tested. 10 GHz to 40 GHz pulse repetition rate multiplication has been achieved, and the tunability of the 6 phase control elements allows the generation of arbitrary 4-bit binary code patterns. Further improvements in complexity, power consumption, loss, and polarization sensitivity in these devices are discussed.
Automatic multirate all-optical routed network based on optical code division multiplexing solution
H. Brahmi, M. Menif, D. Erasme
This paper proposes a distinct packed-switched architecture for all-optical mesh networks. It is a transparent multi-level and multi-rate solution employing all optical flip-flop and optical code gate. It relies on duplicating and filtering packets using Optical Code Division Multiplexing technology.
Measurement of SOA alpha factor using AM-induced FM laser operation in a fiber ring cavity
Simon Lambert Girard, Ana Carrasco Sanz, Hongxin Chen, et al.
We present a new method for measuring the semiconductor optical amplifier (SOA) linewidth enhancement factor, employing a configuration wherein the SOA is placed within a loss modulated fiber ring cavity operated in the FM laser regime. This allows an easy phase-index measurement in lasing operation at small modulation frequencies. A comparison with the conventional FM/AM technique enables independent measurement of the two underlying phase modulation mechanisms: thermal effects from the current modulation and gain-to-refractive index coupling.
Direct acousto-optical spectrum analysis of ultra-high-frequency radio signals based on the collinear wave heterodyning in a medium with dispersive acoustic losses
Alexandre S. Shcherbakov, Abraham Luna Castellanos, Daniel Sanchez Lucero
This work is devoted to the problem of improving the frequency resolution inherent in a parallel acousto-optical spectrum analysis via involving an additional nonlinear phenomenon into the data processing. In so doing, we examine possible application of the wave heterodyning to the real-time scale acousto-optical analysis of the frequency spectrum belonging to various ultra-high-frequency radio-wave signals. The nonlinear process of wave heterodyning is realized through providing a co-directional collinear mixing of the longitudinal acoustic waves of finite amplitudes. This process, which is beforehand studied theoretically, allows us either to improve the frequency resolution of spectrum analysis at a given frequency range or to increase by a few times the current frequencies of radio-wave signals under processing. The theoretical findings are used in our experimental studies aimed at creating a new type of acoustooptical cell, which is able to improve the resolution inherent in acousto-optical spectrum analyzer operating over ultra-high- frequency radio-wave signals. In particular, the possibility of upgrading the frequency resolution through the acoustic wave heterodyning is experimentally demonstrated using the cell made of lead molybdate crystal. The obtained results demonstrate practical efficiency of the novel approach presented.
Suppressed carrier techniques for multi-octave high dynamic range microwave photonic links
Charles Middleton, Richard DeSalvo
Optical transmission of microwave signals offers many advantages such as increased bandwidth, immunity to electromagnetic interference, reduction of size and weight, and minimal loss over long distances. But microwave photonic links often lack the sufficiently high dynamic range and large instantaneous bandwidth required in many applications. Optical carrier suppression has been used to increase link dynamic range, but second harmonic distortion terms limit the operational bandwidth to sub-octave applications. We present a method to apply carrier suppression to microwave photonic links while maintaining multi-octave operation. Our technique uses double sideband suppressed carrier modulation together with coherent heterodyne balanced detection to increase dynamic range, eliminate bandwidth-limiting second-order distortion terms, and reduce link noise figure. This approach provides efficient amplification of the modulated signal while limiting the effect of shot noise from the source laser and reducing common-mode noise terms such as source laser RIN and amplifier-related beat noise.
Characterization of the beam shaper and Fourier transform system in a prototype of the acousto-optical spectrometer for the Mexican Large Millimeter Telescope
Alexandre S. Shcherbakov, Daniel Sanchez Lucero, Abraham Luna Castellanos, et al.
Two optically matched by each other subsystems related to an advanced prototype of acousto-optical spectrometer for radio-astronomy are analyzed in frames of this work. The main peculiarity of the spectrometer's prototype is exploiting a large-aperture tellurium dioxide cell in the regime of anomalous light scattering by acoustic waves, so that just this circumstance determines the majority of technical requirements to both the subsystems under consideration and their potential performances. This is why the initial section is devoted to describing basic properties inherent in the chosen regime of acousto-optical interaction. Then, within characterizing a multi-prism beam shaper, we restrict ourselves here by the case of linear state of the incident light beam polarization. Broadly speaking, such a restriction does not provide the highest performance data of spectrometer, in particular, the most efficient anomalous light scattering in tellurium dioxide crystal, but similar restriction is exactly in a line with the to-day's level of our progress. The characterization of Fourier transform subsystem is directed, of course, to achieving the resolution corresponding as much as possible to theoretically desirable value, namely, to a pair of the CCD-pixels for each individual resolvable spot. The obtained theoretical and preliminary experimental results are presented and discussed.
Closed-loop control of magnetic fluid deformable mirrors
Azhar Iqbal, Zhizheng Wu, Foued Ben Amara
Adaptive optics (AO) systems make use of active optical elements, namely wavefront correctors (WFC), to improve the resolution of imaging systems by compensating for complex optical aberrations. Recently, magnetic fluid deformable mirrors (MFDM) were proposed as a promising new type of WFCs. These mirrors are developed by coating the free surface of a magnetic fluid with a thin reflective film of nano-particles. The reflective surface of the mirrors can be deformed using a locally applied magnetic field and thus serves as a WFC. MFDMs have been found particularly suitable for ophthalmic imaging systems where they can be used to compensate for the complex aberrations in the eye that blur the images of the internal parts of the eye. However, their practical implementation in clinical devices is hampered by the lack of effective methods to control the shape of their deformable surface. This paper presents a control algorithm that facilitated the first-ever use of a MFDM in a closed-loop AO system. The algorithm utilizes the influence function technique to decouple the multi-input multi-output system and features a proportional-integral controller structure. Experimental results showing the performance of the closed-loop system comprising the presented controller and a 19-channel prototype MFDM are presented.
Investigating pluggable transceivers' laser linewidth, chirp, and stimulated Brillouin scattering effects on data transmission in different kinds of optical fibers
Ahmad Atieh, Serge Terekov, Rathy Shankar, et al.
Pluggable transceivers; either small form factor (SFP) that operates up to 2.5Gbps or XFPs that operates at 9.95Gbps, transmitter's laser characteristics are investigated experimentally. The laser linewidth and chirp in addition to stimulated Brillouin scattering (SBS) threshold for different transceivers are measured over many kinds of optical fiber. The measured transceiver's parameters are correlated and used to explain different system performance penalties encountered during data transmission over different kinds of optical fiber. This knowledge is valuable to system engineers as it is not available and not provided by transceivers' vendors. System performance penalties for different kind of fibers with positive and negative accumulative dispersion are measured experimentally at OC-192 and OC-48 modulated signals for different XFPs and SFPs, respectively.
Design of experiment optimization of erbium-doped fiber to single mode fiber splices
Optimizing splicing of Erbium Doped Fiber (EDF) to Single Mode Fiber (SMF) is a critical requirement to maximize the efficiency of Erbium Doped Fiber Amplifiers (EDFAs). This paper describes the key parameters which affect the splice loss of EDF-SMF splices as well as the optimization process used to achieve 50% splice loss improvement. Before performing the optimization process, the measurement system was validated with an evaluation including: laser stability, detector linearity and Gage R&R (Repeatability & Reproducibility). The optimization of EDF and SMF splicing was performed using a design of experiment with 2k factorial design and using MiniTab software for data analysis. A commercially available fusion splicer was used. There were 53 parameters available for setting, They were selected and divided into two groups. The first group included the parameters which might affect the splice loss and the second group included the parameters which might affect the estimated splice loss. The optimization process for the first group of parameters was performed until the target loss was met. The Arc1 Power and Arc1 Time were identified as the most critical parameters for loss. Then the optimization process for the second group of parameters was performed until the slope of the graph of estimated splice loss to actual splice loss was nearly one. This method reduced the average actual splice loss from factory setting of EDF-SMF splicing (0.18 dB) to 0.10 dB and SMF-EDF splicing to 0.09dB. The difference between estimated loss and actual loss was less than 0.05dB for either direction (measurements in the EDFSMF and SMF-EDF direction). The proposed design of experiment can be used as a reference process to perform the optimization of EDF to SMF splicing when Erbium Doped Fiber is changed to the other fiber types.
Photonics Design and Simulation
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Modeling of a multicharged ion beam line using SIMION
Multicharged ion beams (MCI) are promising tools to probe or modify the surface of materials with applications in microelectronics and nanotechnology. Ion beam lines are parts of the MCI systems connecting the ion source with the processing chamber and they perform the function of extracting, accelerating, decelerating, focusing and scanning the ion beam on the surface of the target. In our work we present results of modeling of an MCI beam line using the SIMION code to simulate the flight of ions, with the purpose of optimizing the yield of the line and avoiding spurious effects due to interaction of the ions with the metallic elements of the line, such as heating, outgassing and excessive Xray emission. We show that a two stage ion extractor could significantly reduce ion beam losses.
Mathematical approximations for the amplitude of the fundamental mode field (LP01) of a dispersion shifted fiber at six wavelengths
Louis Lamarche
Hydro-Quebec optical network includes more than 5,000 km of optical ground wires [1] (OPGW) using dispersion shifted fibers (SMF-DSTM) [2]-[3]. This paper provides a model of the index profile for a typical reference fiber and the mathematical approximations of the amplitude of the LP01 mode at six important wavelengths (1.31, 1.41, 1.45, 1.48, 1.55, 1.625 μm). The fiber model has a triangular core and a quadratic ring shape. The weakly guided mode is obtained using the variational principle [4] implemented using an algorithm based on a Laguerre-Gauss-Bessel approximation of the field [5]. We modeled the wavelength dependence of the index of refraction of germanium doped silica using an experimental formula [6]. A comprehensive algorithm was developed to compute the normalized damping factor W and the normalized propagation constant U in the variational algorithm. The mode field diameter, group velocity and chromatic dispersion were also computed at the above wavelengths.
Optimization of triangular lattice defect in dynamic photonic crystal structures for optical storage and processing
Mostafa Shalaby, A. K. AboulSeoud, Moustafa H. Aly, et al.
A triangular lattice GaAs photonic crystal structure was proposed in a previous work [1] for optical storage in a dynamic modulation process. This work presents a defect optimization of this tunable coupled resonator array. Preserving translational invariance and adiabaticity, this structure exhibits an optical analogue to electromagnetic induced transparency. This triangular lattice structure shows an advantage over the previously proposed square one [2, 3] in compressing higher bandwidth pulses. The main problem of this structure is the introduction of higher group-velocity dispersion. In the present work, the structure is redesigned so as to change the operating range of frequency for the propagating pulse. In this way, the group-velocity dispersion is eliminated to values close to that of the square lattice structure. The final design, therefore, combines both higher compressible bandwidth and lower group-velocity dispersion in addition to a fabrication advantage.
Waveguide arrays and spectral filtering for multi-frequency mode-locked pulse sources
Current optical fiber-communication networks increasingly rely on wavelength-division multiplexing (WDM) technologies in conjunction with optical time-division multiplexing (OTDM) of individual WDM channels. The combination of high-repetition-rate data streams with a large number of WDM channels has pushed transmission rates to nearly 1 TB/s, creating a demand for all-optical transmission sources that can generate pico-second modelocked pulses at various wavelengths. Through nonlinear mode-coupling in a wave-guide array and a periodically applied multi-notch frequency filter, robust multi-frequency mode-locking can be achieved in a laser cavity in both the normal and anomalous dispersion regimes. We develop a theoretical description of this multiplewavelength mode-locking, and characterize the mode-locked solutions and their stability for an arbitrary number of frequency channels. The theoretical investigations demonstrate that the stability of the mode-locked pulse solutions of multiple frequency channels depends on the degree of inhomogenity in gain saturation. Specifically, only a small amount of inhomogeneous gain-broadening is needed for multi-frequency operation in the laser. In this presentation, the conditions on the system parameters necessary for generating stable mode-locking is explored for arbitrary number of frequency channels. The model suggests a promising source for multi-frequency photonic applications.
Numerical simulations of the spatial-temporal dynamics and mode-locking in a waveguide array laser cavity
Colin McGrath, J. Nathan Kutz
We theoretically demonstrate X-waves as global attractors that enable mode-locking of a laser cavity operating in the normal dispersion regime. This result is based upon a fully comprehensive physical model of the laser cavity, where the nonlinear discrete diffraction dynamics of a waveguide array mediates the spontaneous periodic generation of spatio-temporal X-waves.
Acousto-optical interaction in strongly dispersive isotropic media
Characterizing the Bragg normal light scattering by the traveling acoustic waves in isotropic medium in with essential optical dispersion is performed for the first time. It is shown that the scattering process under consideration includes the main properties peculiar to the anomalous light scattering in optically uniaxial anisotropic media. In particular, an optimized non-collinear light scattering and collinear interaction become to be unexpectedly possible in just isotropic media. These opportunities can be exploited in acousto-optical devices to improve their performance data.
Characterization of the time-frequency parameters inherent in the radiation of semiconductor heterolasers using interferometric technique
Alexandre S. Shcherbakov, Pedro Moreno Zarate, Joaquin Campos Acosta, et al.
The specific approach to characterizing the train-average parameters of low-power picosecond optical pulses with the frequency chirp, arranged in high-repetition-frequency trains, in both time and frequency domains is elaborated for the important case when semiconductor heterolasers operate in the active mode-locking regime. This approach involves the joint Wigner time-frequency distributions, which can be created for those pulses due to exploitation of a novel interferometric technique under discussion. Practically, the InGaAsP/InP-heterolasers generating at the wavelength 1320 nm were used during the experiments carried out and an opportunity of reconstructing the corresponding joint Wigner time-frequency distributions was successfully demonstrated.
Optimization design of the diffraction grating profiles based on genetic algorithm
Shuwei Fan, Qinghua Zhou
In this paper the rigorous coupled wave analysis (RCWA) was used to analyze the grating diffraction efficiency properties. First, the RCWA must to be improved to avoid instability when the grating period and grating groove depth are relatively large especially for TM mode incident wave. Then the global optimization method-genetic algorithm was used to optimize the grating profile to achieve high diffraction efficiency. Based on the improved RCWA the grating optimal design software(GODS) was developed with the aid of the genetic algorithms (GA). The optimized structure parameters of several typical grating profiles in arbitrary incident angle were given by GODS within short time once the optimal control parameters were selected.
Design and simulation of ultralong Raman laser links for optical signal transmission
Ultra-long Raman fiber lasers (URFL) have shown great potential in applications including supercontinuum generation, multiwavelength signal processing and quasi-lossless transmission. In this manuscript we focus our attention on the latter, briefly reviewing some of the available tools for the study and numerical optimization of ultra-long laser cavity transmission links reliant upon standard single-mode optical fiber. A typical URFL makes efficient second-order distributed Raman amplification possible from single-wavelength pumps, through the generation of a Stokes wave that is trapped in the transmission link itself by fibre grating reflectors. By adjusting the pump power injected into the active link, it is possible to precisely compensate for attenuation locally all across the transmission length, achieving close-toideal gain distribution and virtual transparency in the fiber. The efficiency with which signal excursion (and ASE noise generation) can be minimised depends on factors such as link length, pump depletion, gratings reflectivity and pumping symmetry. As we will show, numerical simulation can be used to find the optimal cavity design parametres that maximize transmission performance in a variety of circumstances.
Dual-wavelength distributed feedback laser for the generation of terahertz radiation
The use of terahertz radiation bears great potential for various applications. We propose a method for obtaining terahertz radiation based on frequency difference generation from two-longitudinal-mode emission of monolithic distributed feedback lasers with modulated gratings. The frequency separation of the two dominating longitudinal modes of the proposed device structure can cover a wide range and several structural and operation point parameters can be used for coarse- and fine-tuning. Moreover, the nearly perfect overlapping of the dominant modes' optical field transverse distributions is enabling high-efficiency terahertz generation. The paper presents design formulas, simulation results and discusses the influences of the fabrication inaccuracies on the target frequency separation.
Silicon photonic WDM devices: simulation, design, and implementation
Passive wavelength division (de)multiplexer (WDM) devices are required as basic building blocks for WDM-based on-chip optical interconnects. In this application, many copies of the devices will be placed throughout a single die, requiring that the device occupy as small a footprint as possible. Furthermore, it is critical that the demultiplexing characteristics be very uniform from device to device, therefore the device must be tolerant to small fabrication variations. There are various wavelength demultiplexer designs that lend themselves to on-chip integration with CMOS integrated circuits and that could potentially reach the above specifications. In this presentation we will show the layout and simulation of demultiplexer designs based on cascaded Mach-Zehnder wavelength splitters and on Echelle gratings and compare these to measurement results of realized devices. The results on the Mach-Zehnder devices show that this type of device is relatively sensitive to process variations. A fit of a device model to the measured curves shows that the device variations result primarily from random phase errors in the optical delay lines, which are probably due to small width variations in the waveguides. This problem should be strongly reduced in devices based on Echelle gratings, because in this case the light does not propagate through channel waveguides in the part of the device that shapes the optical response. This assumption is confirmed by the measurement results, which show good demultiplexer response and excellent reproducibility between devices.
Supercontinuum generation from intense partially coherent laser beams in optical fibers
P. Corredera, S. Martín-López, M. González-Herráez
This paper analyses the advantageous features of supercontinuum (SC) generated from continuous-wave (CW) excitation. It has been shown that both the generation mechanisms and the temporal and spectral properties of supercontinuum produced with CW pump lasers are different from those of generated by means of pulsed excitation, in particular the remarkable smoothness of CW-SC spectra. We show that these unique spectral features stem from the fission of the partially coherent CW input beam into a train of subpicosecond pulses induced by the modulation instability (MI). These subpicosecond pulses lead to the formation of optical solitons with inherently random parameters, which self-frequency shift differently depending on their characteristics. The resulting supercontinuum spectrum is hence the average of many different soliton spectra, which have suffered different frequency shifts. Different experimental setups used in our lab are presented and the dependence of the SC generation on the coherence of the fiber laser and the fiber dispersion profile are shown.
Gain spectrum of silica erbium-doped CROW amplifier
S. Nodehi, A. R. Bahrampour
An Erbium-doped silica CROW can be employed as a band pass and band stop amplifier in telecommunication systems. Also it can be proposed as wide band amplifier as well as narrow band amplifier. We investigate theoretically and simulate structure of Erbium-doped CROW (EDC) with different parameters to realize its performance and possible applications as an amplifier. In this paper we try to consider effect of different parameters on gain spectrum of systems.
Experimental and theoretical characterization of multimode fiber Bragg grating external cavity lasers
Qing-Yang Xu, Jian-Wei Mu, Chang-Qing Xu, et al.
In this paper both statistic and dynamic behaviors of the multimode fiber Bragg grating external cavity lasers (MMFBG_ECL) have been studied experimentally, and simulated numerically by time domain traveling wave (TDTW) rate equations. Experimentally, multiple wavelength selection has been realized by offsetting the coupling between the laser diode (LD) and the MMFBG. Small signal modulation responses at these wavelengths have been measured and over 8 GHz modulation bandwidths have been demonstrated at several wavelengths. Numerically, the TDTW model has been employed to simulate the multiple wavelength lasing selection and L-I curves. Comparison between single mode fiber Bragg grating external cavity lasers (SMFBG-ECL) and MMFBG-ECL have been addressed. In addition, steady experiments and numerical simulated are made to verify our numerical model.
The optical forces of vortex arrays in two-dimensional photonic crystals and slabs
Jeffrey Wheeldon, Henry Schriemer
Applications of optical forces for particle trapping and manipulation would be greatly enhanced if the simultaneous generation of multiple trap sites could be realized "on-chip". We demonstrate that this may be possible through the exploitation of vortex arrays in hexagonal photonic crystals for a band 1 mode at the K point. Flux vortices whose existences are symmetry-required may be located using phasor geometry in the vanishing contrast limit. Direct solution of Maxwell's equations using the Finite Element Method (FEM), for high-dielectric-contrast 2D and 2D-slab geometries, validates the symmetry approach. Optical forces on particles much smaller than the wavelength of light have been calculated using the Lorentz force model, yielding optical gradient and radiation pressure terms. Interestingly, the complementary hexagonal symmetries appear to express optical force distributions of fundamentally different character. The high-index "pillar" geometry has trap sites at Wyckoff A positions for TE modes, while the low-index "hole" geometry has trap sites at Wyckoff B positions for TM modes. Only in the latter case do the trap sites co-locate with the flux vortices that may exert net rotational forces on finite particles. In the former case, the vorticity at a trap site is zero and the net optical force must be purely irrotational.
Design of silicon and polymer photonic waveguide structures for sensing applications
Rainer Hainberger, Roman Bruck, Paul Muellner, et al.
The design of optimized V-groove waveguides for evanescent surface sensing as well as for the exploitation of nonlinear optical effects in low index materials is presented. Morever, the leakage behaviour of horizontal ribtype slot waveguides is discussed, which has been calculated employing MaxWave, a novel simulation package of electromagnetic mode solvers for the computation of the optical field in integrated optical waveguide devices. An integrated all-polymer Mach-Zehnder interferometer based biosensing concept is presented. We show that efficient coupling of light into thin low index contrast single mode waveguides via surface gratings becomes feasible by applying a high index coating on the grating. We provide an experimental verification of this effect as well as homogeneous sensing results.
Modeling scattering and diffraction elements in a SPICE like optoelectronic framework
Pavan Gunupudi, Tom Smy, Jackson Klein, et al.
This paper presents efficient modeling of optical interference devices such as optical connectors and cross-couplers in a SPICE1 like optoelectronic simulation framework. This framework is based on formulating modified nodal analysis equations that integrate electrical and optical elements in a single engine simulator. A significant difference in optical modeling with respect to standard electrical spice simulation is the need to model optical interference. Efficient modeling, within this framework, of devices based on interference effects is described in detail. Several examples using this framework are presented. These examples include optical links, cross-couplers, Machzehnders, optical connectors and other optical components.
Sliced fiber Bragg grating used as a laser diode external cavity
Pin Long, Justin Carignan
A new type of fiber Bragg grating is proposed, which is called sliced fiber Bragg grating. Unlike the regular fiber Bragg grating which is a fiber based working device, the new sliced fiber Bragg grating can be used as a free space component. For example, a sliced fiber Bragg grating can be used as a laser diode external cavity. A multimode fiber Bragg grating written on a 100um core size is cut into small segments of 1 to 2mm. Each end surface of the fiber Bragg grating segment is polished and then coated with an anti-reflection coating. The fiber Bragg grating segment, or sliced fiber Bragg grating, is used to manufacture an external cavity laser diode. The sliced FBG external cavity laser diode bandwidth is reduced from 0.19nm to 0.06nm.
Theory of mode-locking using phase-sensitive amplification for saturable absorption
Simon Hachey, Christopher R. Jones, J. Nathan Kutz
An averaged evolution equation is presented and its dynamics studied for a mode-locked laser where the intensitydiscrimination (saturable absorption) in the cavity is provided by phase-senstitive amplification. The phasesensitive amplifier acts as a phase-filter for selecting the specific intensity dependent phase-rotation of the modelocked pulse that locks the phase to the amplifier pump phase. The resulting averaged equation is a Swift- Hohenberg type model which is a fourth-order diffusion equation with cubic-quintic nonlinearities. Additionally, the governing evolution has a new linear growth term which couples to the nonlocal cavity energy. This parameter is a standard bifurcation parameter in Swift-Hohenberg models and is controlled by the cavity saturable gain. Such a modification to the governing evolution is the first of its kind to be considered theoretically in the context of the Swift-Hohenberg equation, and its significant impact on the mode-locked pulse dynamics and multi-pulsing behavior is explored.
Plasmon-Assisted Sensing Mechanisms
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Selective functionalization of gold arms of a surface plasmon polariton Mach-Zehnder interferometer for biosensing
In long range surface plasmon polariton (LRSPP) sensing, in a Mach-Zehnder interferometer (MZI) configuration, gold arms have to respond differently to the analyte as to form layers with different refractive indices. This can be achieved if the arms are coated with different thiol-based self-assembled monolayers (SAMs), one of which should block adsorption and the other should specifically adsorb the analyte of interest. Since the MZI arms' width and the distance between them are in the micron range, such a chemical differentiation is a challenging task which nevertheless could be achieved with two techniques (1) Microspotting trough droplet confinement and manipulation using a solvophilic guide and (2) Toposelective electrochemical desorption of SAMs where the arms are subjected to different potentials. We found the latter approach the most promising because of its scalability to the wafer level. During the electrochemical desorption the potentials of both arms have to be independently controlled with a multi-channel potentiostat. Subsequent deposition of another SAM on the freed MZI arm is accomplished with minimal thiol exchange. The resulting MZI was analyzed and imaged by time-of-flight secondary ion mass spectrometry (ToF- SIMS) and with phase shift atomic force microscopy which confirms the desired MZI structure in which only one arm has specific affinity to one protein while the other would block any interaction.
Synthesis and optical properties of anisotropic gold nanoparticles
Stefan Stoenescu, Simona Badilescu, Muthukumaran Packirisamy, et al.
Gold nanoparticles (GNPs) have been synthesized by a seed-mediated growth method. Hexadecyltrimethylammonium bromide (CTAB) was used as a surfactant for both the seed formation and the anisotropic crystals growth. Anisotropic GNPs of various sizes, shapes and aspect ratios were obtained by using different amounts of silver ions, temperatures and durations of growth as parameters of the process. The SEM images and the Localized Surface Plasmon Resonance (LSPR) bands in the UV-Vis of the anisotropic GNPs have been studied. Preliminary sensing experiments have been carried out as well. This work has proved again the high sensitivity of the synthesis with respect to the conditions of reaction.
Ultrashort Lasers and Applications
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Optimizing waveguide array mode-locking for high-power fiber lasers
Brandon G. Bale, J. Nathan Kutz, Bjorn Sandstede
A comprehensive theoretical treatment is given of the mode-locking dynamics produced by the intensity discrimination (saturable absorption) generated by the nonlinear mode-coupling in a waveguide array. Emphasis is placed on the mode-locking stability as a function of the critical physical parameters in the laser cavity. The theoretical characterization of the laser cavity's stability and dynamics allows for a comprehensive optimization of the laser cavity parameters towards achieving high peak-power, high-energy pulses in both the anomalous and normal dispersion regimes.
Tightly focused, ultrafast TM01 laser pulses
Nowadays, the generation of laser pulses focused to a spot size comparable to the wavelength and whose duration is only a few optical cycles of the electric field is achievable. Moreover, TM01 laser pulses are of considerable interest, among other things, because of their remarkable focusing properties. In order to describe theoretically the spatiotemporal behaviour of such nonparaxial, ultrashort TM01 pulses, one needs expressions of their electromagnetic fields. To obtain these expressions, Maxwell's equations must be solved rigorously. The method of the Hertz potential, the complex-source/sink model, and the use of a Poisson-like spectrum are exploited to solve the vectorial wave equation. Closed-form expressions for the electric and the magnetic fields of an isodiffracting TM01 pulse are presented and they can be used to study the behaviour of tightly focused, ultrafast TM pulses.
Fiber Bragg grating inscription with DUV femtosecond exposure and two beam interference
Martin Becker, Joachim Bergmann, Sven Brückner, et al.
Fiber Bragg gratings (FBGs) are today fundamental components in fiber optics. They can be used as sensors, in signal processing, e.g. telecom applications, as wavelength stabilizers in fiber lasers or in dispersion compensators. However, there are applications where the demand for fiber Bragg gratings is not compatible with standard photosensitivity techniques like germanium doping or hydrogen loading. Examples are their use as laser-mirrors in spliceless all fiber fiber-laser solutions or the fiber Bragg grating inscription in suspended core all silica fibers for evanescent field sensing. Fiber Bragg grating inscription with femtosecond-laser exposure is a challenging new method to realize grating structures for waveguides made of materials which do not provide UV-photosensitivity. Especially fs-IR-inscription has been demonstrated for Bragg grating inscription in a variety of material systems such as boron-silica glass, sapphire and pure silica glass. The feasibility of the phase mask FBG inscription technique with DUV femtosecond lasers was also shown, which allows grating inscription even in pure silica microstructured fibers. The phase mask inscription method requires that the fiber will be placed directly behind the phase mask. While the laser beam should be focused onto the fiber to support nonlinear material interaction, this inscription method also leads to phase mask degradations, presumably due to non-bridging oxygen holes (NBOH). Our solution to avoid the mask degradation is to increase the space between fiber and phase mask by using a Talbot-interferometer. Another advantage is the wavelength versatility of this inscription setup. Due to the short temporal coherence length of the femtosecond pulses, the angular alignment variability of the interferometer mirrors is limited and restrictions concerning the wavelength versatility of the interferometer arise. Grating arrays in pure silica suspended core fibers are demonstrated as an example for the versatility of the inscription arrangement.
Initial stage of the active mode-locking in semiconductor heterolasers
Alexandre S. Shcherbakov, Alexey Yu. Kosarsky, Joaquin Campos Acosta, et al.
We make an attempt to develop a novel approach to describing the initial stage of the active mode-locking in semiconductor laser structures based on analyzing the properties of dispersion relations in terms of stability for small initial perturbations. Nonlinear process of shaping optical pulses is interpreted as manifesting instability of diffusion type. For the purposes of experimental investigations, the auto-manual opto-electronic measuring system detecting average time parameters inherent in ultra-short optical pulse trains has been designed. This system is able to register auto-correlation functions of the second order exploiting the interferometric technique as well as to identify a pulsed character of the incoming light radiation. Experimental confirmations of appearing the diffusive instability within the active mode-locking process in semiconductor laser structures operating in the near infrared range are presented.
Generation of optical beams with angular momentum
In this paper we describe the fabrication of reflective spiral phase plates with a deposition system. This plate was used to transform Gaussian beams into Laguerre-Gauss beams with angular momentum. These beams are characterized by a helical wave front and zero intensity at center. By focusing a femtosecond Laguerre-Gauss beam with an axicon, we have produced surface modifications in a BK7 glass sample.
Spectral and temporal effects of coaxial apertures on ultra-short pulses
Gabrielle Thériault, Réal Tremblay, Nathalie McCarthy
Ultra-short pulsed laser beams are frequently used in optical systems containing many limiting apertures. Unfortunately, the spectral and temporal effects in the near field of a sequence of circular apertures on ultra-short pulses are little known. We have investigated these effects, and our numerical simulations predict results that could have significant consequences in certain optical systems.
Laser micromachining of transparent glass using ultrafast Bessel beams
Véronique Zambon, Nathalie McCarthy, Michel Piché
We fabricated optical waveguides in fused silica by focusing femtosecond laser pulses with an axicon. With this technique, we also produced microholes by using chemical etching. The axicon, which is a conical lens, generates an optical beam with a transverse intensity profile that follows a zero-order Bessel function. Bessel beams produced by axicon focusing have a narrow focal line of a few micron width which is invariant along a long distance (>1 cm). By focusing femtosecond pulses with an axicon into fused silica, we induced permanent modifications over the extented focal line of the axicon without scanning axially the glass sample. The waveguides so fabricated exhibit low losses and no detectable birefringence due their excellent circular symmetry. By translating the glass sample during the inscription process, we have fabricated planar waveguides. Microfluidic channels were obtained by soaking the exposed samples into a HF solution.
All-fiber, high power, rugged ultrashort-pulse laser source at 1550 nm
Vincent Roy, Louis Desbiens, Yves Taillon
We present here the architecture of an all-fiber, high-power FCPA source emitting at 1550 nm. This system generates sub-300 fs pulses at a repetition rate of 22 MHz and with an average output power of 1.5 W after pulse compression. The power amplifier consists of a polarization-maintaining Er:Yb doped LMA fiber which results in a beam quality factor M2 < 1.2. The seed laser pulses are stretched to 240 ps using dispersion-shifted fiber before being amplified and compressed using a bulk compressor based on a diffraction grating pair. The output power of the source is not limited by the onset of detrimental nonlinear effects such as self-phase modulation or stimulated Raman scattering since the accumulated nonlinear phase-shift in the power amplifier is well below π rad. Maximum output power is rather limited by the available pump power; a likely five-fold increase, given actual state-of-the-art technology, would thus yield a laser source that may serve as a substitute for widespread solid-state lasers in various fields such as laser machining, biophotonics and nonlinear optics.
High power Nd:YAG ceramic lasers: passive Q-switching and frequency doubling
Ruijun Lan, Robert Fedosejevs, Hong Liu, et al.
A high power passive Q-switched laser and a continuous-wave (CW) green laser both with a neodymium-doped yttrium aluminum garnet (Nd:YAG) ceramic as the laser material have been demonstrated. Two Cr4+:YAG crystals with 73.9% and 79.6% initial transmission at 1064 nm have been used as saturable absorbers. In Q-switched regime the laser generated up to 209 μJ, 4.5 ns pulses, which corresponds to a peak power of 46.8 kW. In CW regime at 1064 nm the laser generated 11.3 W of output power at a pump power of 21.6 W, corresponding to an optical-optical conversion efficiency of 52.3%. By using a type-II cut KTP crystal, the CW frequency-doubled operation of Nd:YAG ceramic was achieved. The maximum output power of 1.86 W at 532 nm has been obtained. The one-dimensional intensity distribution of the green beam cross-section was observed to be Gaussian. When the output power was 1 W, the M2 factor was measured to be 1.7.
Two-photon absorption and emission in doped fibers
We present new results on the dynamics of laser amplifiers based on two-photon stimulated transitions. We have developed a mathematical model predicting stronger gain and faster saturation than what is observed in a conventional one-photon amplifier. We also demonstrate that two-photon stimulated emission can lead to pulse narrowing with compression factors over 5.
Spectral and temporal control of an actively mode-locked fiber laser
Jean Filion, Michel Olivier, Bryan Burgoyne, et al.
We report theoretical and experimental investigations on the spectral and temporal control of a mode-locked fiber laser using a chirped fiber Bragg grating and a loss modulator in either a undirectionnal ring cavity or a standing-wave cavity. The fiber laser generates picosecond pulses with a rapid tuning over a large bandwidth. Tuning is achieved by controlling the frequency of the applied modulation waveform. The adjustement of pulse duration between 40 - 500 ps and the rapid tuning from 1513 nm to 1588 nm are described.
Characterization of the laser beam distortion due to the thermal load on high average power femtosecond laser systems
S. Fourmaux, C. Serbanescu, L. Lecherbourg, et al.
We report observation of laser beam distortion due to the thermal load associated with high energy (110 mJ) and high average power (11 Watts) femtosecond laser system with vacuum compressor. To improve laser-based light source brightness, it is crucial to develop laser systems with higher energy and higher average power. Managing the high thermal loading on vacuum optical components and demonstration of brightness stability are key issues in the implementation of this approach. We characterize such thermally induced distortions using beam wavefront measurements and propose compensation methods to attain long term stability.
Parametric investigation of laser wakefield acceleration versus F-number of focusing optics
N. Vafaei-Najafabadi, A. Ali, J. A. Chakera, et al.
Laser wakefield acceleration is a growing area of research with the promise of generating high energy, low divergence, and short duration electron bunches from tabletop scale accelerators. To date, electron beams with maximum energy of 1 GeV with 2.5% energy spread have been generated using a 3cm plasma channel[1]. However in order to advance the maximum energy of electron beams beyond this limit, better understanding of the physics and effect of different parameters on the interaction are essential. In this paper we report on our parametric studies of wakefield electron acceleration using the 10TW chirped pulse amplified laser system at the Advanced Laser Light Source (ALLS), Montreal. Laser pulses with energies of ~210 mJ at 33fs were focused using a short (f/6) and a long focal length (f/12) off axis parabola onto 2mm supersonic helium and nitrogen gas jets at different pressures. Nitrogen with electron densities of up to 2×1020 cm-3 and helium densities up to 5×1019 were used. Beams with energies of tens of MeV were observed using the short focal length parabola and beams with energies of several MeV were observed using the long focal length parabola. We also found that electron beams are more easily generated with higher levels of prepulse, consistent with previous reports of prepulse generated guiding channels in the plasma[5].
Micromachining of thin glass plates with a femtosecond laser
D. Hélie, R. Vallée
We present a novel method for cutting thin borosilicate glass slides, as well as other results pertaining to laser welding related to an existing technique. Based on the concept of stealth dicing for semiconductor wafers, we have demonstrated that by giving our samples an initial stress and by creating optically induced defects inside the glass, it is possible to efficiently cut a thin glass substrate. The edges are sharp along the whole length of the cut and exempt from debris deposition and deformations. We have also perfected a femtosecond laser welding technique to join borosilicate glass samples with very distinct welded regions.