Flexible microfluidic devices made of poly(dimethylsiloxane) (PDMS) were manufactured by soft lithography, and tested in detection of ionic species using optical absorption spectroscopy and electrical measurements. PDMS was chosen due to its flexibility and ease of surface modification by exposure to plasma and UV treatment, its transparency in UV-Vis regions of the light spectrum, and biocompatibility. The dual-detection mechanism allows the user more freedom in choosing the detection tool, and a functional device was successfully tested. Optical lithography was employed for manufacturing templates, which were subsequently used for imprinting liquid PDMS by thermal curing. Gold electrodes having various widths and distances among them were patterned with optical lithography on the top part which sealed the microchannels, and the devices were employed for detection of ionic species in aqueous salt solutions as well as micro-electrolysis cells. Due to the transparency of PDMS in UV-Vis the microfluidics were also used as photoreactors, and the in-situ formed charged species were monitored by applying a voltage between electrodes. Upon addition of a colorimetric pH sensor, acid was detected with absorption spectroscopy.

Quantum dots (QDs) have been widely adopted as integrated components of bioassays and biosensors. In particular, solid phase nucleic acid hybridization assays have been demonstrated to have several advantages and permit the detection of up to four DNA targets simultaneously using fluorescence resonance energy transfer (FRET). This work explores the potential for miniaturization of a solid-phase nucleic acid hybridization assay using QDs and FRET on a microfluidics platform. A method was developed for the immobilization of Streptavidin coated QDs and the preparation of QD-probe oligonucleotide conjugates within microfluidic channels using electrokinetic delivery. Proof-of-concept was demonstrated for the selective detection of target DNA using FRET-sensitized emission from a Cy3 acceptor paired with a green emitting QD donor. The microfluidic platform offered the advantages of smaller sample volumes, nearly undetectable non-specific adsorption, and hybridization within minutes. This work is an important first step toward the development of biochips that enable the multiplexed detection of nucleic acid targets.

Integration of microfluidics with the integrated optical waveguides enables the realization of devices capable of performing the biodetection and analysis on small scale using fluorescence biolabels such as Quantum Dot (QD). Polydimethylsiloxane (PDMS) has been an excellent choice to build the optical bio-microfluidic systems because of its biocompatibility, optical properties and low cost fabrication process. In this work, we report a method to integrate the microfluidics channels and waveguides fabricated on Silica-on-silicon (SOS) and PDMS platform for the realization of a Lab-on-a-chip (LOC). Performance of the device tested by measuring fluorescence from the laser excited Quantum Dot (QD655) solution reveals that the developed device is suitable for performing the QD based biodetection and analysis efficiently.

A microfluidic device has been developed wherein single molecules in solution are electrokinetically transported along a nanochannel. The nanochannel is irradiated by two adjacently focused laser beams so that the timing of fluorescence photons induced by each beam indicates the position of a molecule along the nanochannel. This is then used to actively control the electrokinetic flow, so that the molecule may be held within the confocal volume for a prolonged time and then rapidly replaced following photobleaching or completion of the single-molecule measurement. Here we focus on Monte Carlo computer simulations of the physical processes that occur during the delivery and trapping. The simulations help in understanding the constraints imposed by experimental limitations, such as the latency of feedback, the maximum achievable speed of electrokinetic flow, and photophysical processes such as triplet crossing and photobleaching. They also aid in evaluating the effects of shot noise and photon timing error and in predicting optimum experimental operating parameters. Studies indicate that the 6 μs latency of feedback in our experiments is well below that required for stable trapping (~100 μs); for small freely diffusing molecules, a limited flow speed of ~2 μm/ms can result in ~10-20 % of molecules escaping before they photobleach; there is an optimum laser power of ~30-40 μW that provides a sufficient rate of fluorescence photons for trapping while reducing loss due to photobleaching; an increase in the spacing between the beams or increase in relative power of the down-stream beam increases the trapping time.

The field of plasmonics has shown a great promise in the enhancement of luminescence detection. Here, a simple method to enhance oxygen detection by quenching of Ru[(4,7-diphenyl-1,10-anthroline)₃]²⁺ (or Ru[dpp]2+) in a sol-gel matrix by localized surface plasmon resonance (LSPR) of gold nanoparticles (AuNP) is presented. In the experiments, AuNP (10 ± 1.5 nm diameter) were added to a sol that was prepared by hydrolysis of trimethoxysilane, octyltrimethoxysilane and ethanol in the presence of Ru[dpp]²⁺ luminophore. The resulting sol of the mixture was spincoated on glass and allowed to age in the dark for one week to form the sol-gel film. A control sample was also prepared using the procedure, except that AuNP was not added to the sol. The resulting AuNP embedded sol-gel shows 8.3 times improvement in the baseline (0% O₂) intensity (I₀) over the control. Moreover, there is a dramatic improvement in the sensitivity from 0.0011 per % O₂ in the control to 0.059 per % O₂ with AuNP, for O2 level below 15%. Signal to noise ratio also improved, thus leading to a 100-fold improvement in the detection limit. Using phaseluminometry, it was determined that there is a reduction in the luminescence lifetime when AuNP is added to the sol-gel matrix. This reduction in the lifetime can be explained by the near-field interaction between the luminophores and the AuNP.

Gold nanorods (AuNRs) efficiently absorb pulsed near-infrared (NIR) light. If the fluence is sufficiently high, then the absorption of pulsed light results in photothermal conversion to spherical morphology and a decrease in NIR absorption. In aqueous media, photothermal conversion also produces localized microbubble formation, which has the potential to kill nearby cells. Our objective was to study the potential of AuNRs to elicit cell killing effects at depth within a tissue-like phantom material. The approach was to measure photothermal conversion in phantoms with embedded inclusions representative of breast tumors. Phantoms were prepared with a homogeneous mixture of 1% Intralipid™ and 1% agarose to simulate tissue optical properties. Gold nanorod-loaded spherical inclusions 6 mm in diameter were prepared at an optical density of 0.67 at 800 nm. Inclusions were cast into the phantom material at a depth of 0, 5, 10, or 15 mm. Phantoms were then exposed to pulsed laser (800 nm, 5 ns pulse duration) for a range of fluence (17-100 mJ/cm²) and pulse count (10-1000). Each phantom was then cut longitudinally and imaged with a NIR camera. The images were analyzed for changes in contrast representative of photothermal conversion. Preliminary results indicated that photothermal conversion occurred only in spherical AuNR-loaded inclusions at or within 10 mm of the phantom surface. Based on these results, we concluded that within ANSI limits of laser exposure photothermal therapy with AuNR-based agents will be limited to lesions at or near the surface and lesions accessible with needlebased light delivery.

Currently, Minimally Invasive Surgery (MIS) performs through keyhole incisions using commercially available robotic surgery systems. One of the most famous examples of these robotic surgery systems is the da Vinci surgical system. In the current robotic surgery systems like the da Vinci, surgeons are faced with problems such as lack of tactile feedback during the surgery. Therefore, providing a real-time tactile feedback from interaction between surgical instruments and tissue can help the surgeons to perform MIS more reliably. The present paper proposes an optical tactile sensor to measure the contact force between the bio-tissue and the surgical instrument. A model is proposed for simulating the interaction between a flexible membrane and bio-tissue based on the finite element methods. The tissue is considered as a hyperelastic material with the material properties similar to the heart tissue. The flexible membrane is assumed as a thin layer of silicon which can be microfabricated using the technology of Micro Electro Mechanical Systems (MEMS). The simulation results are used to optimize the geometric design parameters of a proposed MEMS tactile sensor for use in robotic surgical systems to perform MIS.

Our group has concentrated on development of a 3D photoacoustic imaging system for biomedical imaging research. The technology employs a sparse parallel detection scheme and specialized reconstruction software to obtain 3D optical images using a single laser pulse. With the technology we have been able to capture 3D movies of translating point targets and rotating line targets. The current limitation of our 3D photoacoustic imaging approach is its inability ability to reconstruct complex objects in the field of view. This is primarily due to the relatively small number of projections used to reconstruct objects. However, in many photoacoustic imaging situations, only a few objects may be present in the field of view and these objects may have very high contrast compared to background. That is, the objects have sparse properties. Therefore, our work had two objectives: (i) to utilize mathematical tools to evaluate 3D photoacoustic imaging performance, and (ii) to test image reconstruction algorithms that prefer sparseness in the reconstructed images. Our approach was to utilize singular value decomposition techniques to study the imaging operator of the system and evaluate the complexity of objects that could potentially be reconstructed. We also compared the performance of two image reconstruction algorithms (algebraic reconstruction and l1-norm techniques) at reconstructing objects of increasing sparseness. We observed that for a 15-element detection scheme, the number of measureable singular vectors representative of the imaging operator was consistent with the demonstrated ability to reconstruct point and line targets in the field of view. We also observed that the l1-norm reconstruction technique, which is known to prefer sparseness in reconstructed images, was superior to the algebraic reconstruction technique. Based on these findings, we concluded (i) that singular value decomposition of the imaging operator provides valuable insight into the capabilities of a 3D photoacoustic imaging system, and (ii) that reconstruction algorithms which favor sparseness can significantly improve imaging performance. These methodologies should provide a means to optimize detector count and geometry for a multitude of 3D photoacoustic imaging applications.

OCT (optical coherence tomography) is generally regarded as the 6th imaging modality. This light-based system ideally suits for bio-medical diagnostic imaging applications. Outperforming to the time-domain OCT, Swept-Source OCT (SSOCT) is termed as the second generation OCT, in which, usually, thousand of individual wavelengths are sent into the system in a time sequence. The backscattered or back reflected light from the testing sample is collected by a sensor corresponding to each wavelength. The thousand received signals actually represent the Fourier coefficients in the spectrum domain. However, these coefficients only have real positive values as the sensor can only produce intensity signal. This paper describes the signal processing issues related with this intensity spectrum. Various filters, high-pass, low-pass and band-pass; spectrum decomposition; spectrum combination are discussed and demonstrated. A method for spectral synthesis of multiple light sources is presented.

Optical Coherence Tomography (OCT) is an imaging technique that could image subsurface structural details of an object. The imaging depth of OCT is ultimately limited due to multiple scattering of light. We report on the development of a numerical simulation to characterize the impact of multiple-scattered light in Swept-Source Optical Coherence Tomography. (see manuscript)

Optical coherence tomography images of arterial samples harvested from asymptomatic pigs and from lipid-rich Watanabe heritable hyperlipidemic rabbits were acquired using a fiber catheter-based swept-source optical coherence tomography system (OCT). A quadrature Mach-Zehnder interferometer based on multi-port fiber couplers and a semiconductor optical amplifier (SOA) were employed in the swept-source optical coherence tomography system. The improvement of signal to noise ratio as a result of incorporating the SOA into the configuration translated in an increase of the penetration depth. A fiber probe ending in a fiber ball lens was developed for the arterial imaging. The images acquired by this system offer the possibility to investigate anatomical details located under the surface of the artery such as the intima, media, and adventitia layers (from lumen side) of the blood vessel wall , as well as morphological features specific to artherosclerotic plaques such as lipid pools, fibrous caps, macrophage accumulations and calcified. This report indicates that our improved catheter-based swept source OCT is a potential tool for in vivo intravascular imaging.

The measurement of relative hardness of soft objects enables replication of human finger tactile perception capabilities. This ability has many applications not only in automation and robotics industry but also in many other areas such as aerospace and robotic surgery where a robotic tool interacts with a soft contact object. One of the practical examples of interaction between a solid robotic instrument and a soft contact object occurs during robotically-assisted minimally invasive surgery. Measuring the relative hardness of bio-tissue, while contacting the robotic instrument, helps the surgeons to perform this type of surgery more reliably. In the present work, a new optical sensor is proposed to measure the relative hardness of contact objects. In order to measure the hardness of a contact object, like a human finger, it is required to apply a small force/deformation to the object by a tactile sensor. Then, the applied force and resulting deformation should be recorded at certain points to enable the relative hardness measurement. In this work, force/deformation data for a contact object is recorded at certain points by the proposed optical sensor. Recorded data is used to measure the relative hardness of soft objects. Based on the proposed design, an experimental setup was developed and experimental tests were performed to measure the relative hardness of elastomeric materials. Experimental results verify the ability of the proposed optical sensor to measure the relative hardness of elastomeric samples.

We have fabricated and tested Gold Cylinder Fiber (GCF) bio sensors. The sensor fiber has a thin, approximately 3 nm to 5 nm thick, Gold alloy film layer at the glass core glass cladding boundary. One end of the fiber is etched to let the gold alloy cylinder protrude about 10 m. A Single Mode Fiber (SMF) is connected to the other end of the GCF. Light propagates through the SMF to a short section of GCF. The etched end of the GCF is dipped into the fluid to be analyzed. The reflected light from the sample returns back through the SMF to a spectrum analyzer.

Total internal reflection fluorescence microscopy is an evanescent based fluorescence microscope providing a selective visualization of cell-substrate contacts without interference from other, deeper cellular regions. Total internal reflection fluorescence microscope is used extensively to visualize cell-substrate contacts. However, quantifying these contacts - in particular the measurement of cell-substrate distances - has not been performed often. In order to quantify the cellsubstrate distances we have developed a new theoretical method which is based on a change in the penetration depth of the evanescent field by tuning the angle of incidence slightly above the angle of total internal reflection for s-polarized light. This is simpler and much more accurate in comparison to the few existing approaches.

Angular Domain Spectroscopic Imaging (ADSI) is a novel technique for the detection and characterization of optical contrast abnormalities in a turbid medium. The imaging system employs silicon micro-machined angular filtering methodology, which has high angular selectivity for photons exiting the turbid medium. The ADSI system performance was evaluated on tissue samples from a dissected mouse. Images collected with the ADSI displayed differences in image contrast between different tissue types.

There is currently considerable research underway to utilize Long-range Surface Plasmon-Polariton (LRSPP) waves, which inherently have a low attenuation, to conduct biosensing using integrated optical structures such as the Mach- Zehnder interferometer (MZI). In order for the sensor to be functional and biosensing to occur, many technological elements are required including high-quality optical waveguide structures integrated with microfluidic channels, stable low-noise interrogation optoelectronics, and external fluidic components. The processes involved in the fabrication of a variety of devices along with the devices themselves and the optical set-ups used for their interrogation are described. Measured insertion losses for uncladded, cladded and channelled devices are compared to theoretical results.

Jade is a type of rare and expensive stone. The current approaches for jade exploration and processing are blindly and wasteful. Capable of performing high resolution, cross-sectional sensing of the internal structure of materials, Optical Coherence Tomography (OCT) could be used to greatly facilitate these jade procedures. By detecting the signal intensity and analysing the internal texture, OCT system can indicate if the jade exists and what the type it could be. It provides a tool to guide the artist in designing and making the jade artworks. It also can be used for discrimination of the fake antique jade wares, as well as anti-counterfeiters on the jade market. In this paper, we present how a Swept-Source OCT system to detect and analysis the internal features of jades. Algorithms for feature extraction and classification are described and experimental results with various unearthed jades are demonstrated.

The temperature stability of fiber Bragg gratings (FBG) fabricated in SMF-28, all-silica core, and high Ge content fibers is investigated. FBG's fabricated in hydrogen loaded SMF-28 and all-silica core fiber are shown to possess high temperature stability. The magnitude of the Bragg resonance in high Ge content fiber is shown to increase with annealing temperature until, at 1000 °C, the grating slowly erases.

A full characterization of Er³⁺-Yb³⁺ co-doped fiber amplifiers (EYDFA) is done by numerically solving the simultaneous calculation of the rate and propagation equations considering the forward- and backward-amplified spontaneous emissions (ASE ± ) propagation. The effect of erbium and ytterbium codoping concentrations on the gain of the amplifier is evaluated. With optimal calculated parameters, a gain of 32.7 dB and a fiber length of 3.54 cm with pump and signal powers of 200 mWand 1 μW in optimal codoping concentrations is obtained. Simulations have been done for gain characteristic and noise figure of an erbium-doped fiber amplifier (EDFA) with parameters similar to EYDFA to compare the obtained results. The proposed model and simulation results are validated with published experimental results.

There are many applications where a very wideband phase shifter is required. Analog pre-distorters to linearize Ka-band amplifiers require a frequency-independent phase shift over at least 1 GHz. The same requirement applies to phased-array antennas or antenna feeds, as well as direct radiating array antennas. Most electrical phase shifters have a fixed operating frequency, discrete phase shift steps (e.g., 5-bit control) and some frequency and temperature dependent responses which result in sub-optimum system performance. The requirements in the 50/40 GHz band will be even more demanding where the bandwidth to be covered could extend up to 5 GHz. The use of photonic technology mitigates the limitations of electrical phase shifters. Operation over a wide range of frequencies (e.g., 4 to 50 GHz) using a single design is possible, and a flat phase response over many GHz's can be achieved. This paper discusses the use of novel microwave photonic technologies to enhance the performance of a broadband phase shifter with respect to power, mass, volume, electromagnetic interference and compatibility of future on-board satellite subsystems. The targeted phase shifter is equally applicable to analog linearizers, phased-array antennas/feeds or other smart antenna schemes where relative phase shifts are required. The results of a prototype phase shifter are presented showing a broadband response over several GHz. Limitations of this device and justification for an integrated version will be discussed. Finally, preliminary results for an integrated device are presented.

In this paper, we report a novel LiNbO3 ridge waveguide fabrication technique based on the combination of Annealed Proton-Exchanging (APE) and precise diamond blade dicing. The process is ultra compact and compatible with periodically polled LiNbO₃ (PPLN). By selecting optimized fabrication conditions, ridge waveguide with low propagation loss and single transmission mode can be formed at 1064nm and 1500nm wavelength, respectively. Such APE ridge waveguides have potential applications in optical communication, biomedical detection, and especially in nonlinear wavelength conversion.

The polymer polydimethylsiloxane (PDMS), which is used as a cladding layer in waveguide-based optical components, is sensitive to the organic compounds. In this work, a compact organic compound optical sensor with a simple fabrication is proposed by using a taped optical fiber with PDMS coating. The sensing mechanism is based on the reaction of sensing material PDMS with chemical molecules to result in the changes of PDMS cladding layer which cause the transmitted optical power of the taped optical fiber.

The surface temperature distribution of a GaAs wafer, heated under vacuum, has been measured using a digital camera. A method is proposed to remove parasitic signals from the image. The accuracy of the thermal image is validated by comparing the results with a separate measurement from absorption band-edge spectroscopy (ABES). The thermal imaging data are observed to be within the experimental error from the ABES technique for the entire surface of the wafer. We observe a radial temperature profile with a center-to-edge difference that varies as a function of the central temperature. A difference of 25 °C is observed for a central temperature of 565 °C. This difference increases with the wafer temperature, confirming that it is due to a net heat flux escaping the wafer by its edge, which is in contact with a graphite holder. Based on these results, a solution is proposed in which the graphite wafer holder is replaced by a ceramic version.

Hydrogel-coated refractive nanoparticles can self-assemble to form perfect colloidal crystalline array (CCA), which can act as a photonic sensor in visible and near-infrared region triggered by temperature. The aim of this study was to tune the lattice parameters of these CCAs made of poly-(N-isopropylacrylamide) coated silica nanoparticles and hence their sensor properties by varying various factors. The synthetic scheme of this work involves surface modification of silica nanoparticles followed by radical polymerization to obtain polymeric nanocomposites. Photon correlation spectroscopy (PCS) was used to measure the particle size of these nanocomposites with temperature variation and a sharp decrease from 1094.8 nm to 506.8 nm at the LCST (lower critical solution temperature) region was observed, which can be attributed to volume-phase transition. Atomic Force Microscopy (AFM) images complemented these results. Reflectance measurements were performed to obtain the position of photonic stop-bands as a function of temperature as well as core particle size, which can be explained with the help of Bragg's diffraction equation. With temperature increase the stop band shifted towards lower wavelength due to hydrogel collapse at elevated temperature, whereas the core particle size was directly proportional to the position of the stop band. In conclusion, self-assembly was proven to be a very simple and cost-effective approach for making photonic sensors made of polymeric nanocomposites and their sensor properties can be effectively tuned by varying certain factors.

Two sets of resonances in glass microspheres attached to a standard communication grade single mode optical fiber have been observed. It has been found that the strength of the resonances depends strongly on the polarization of the coupled light. Furthermore, the position of the resonances in the wavelength domain depends on the polarization of light in the optical fiber with maximum magnitudes shifted by approximately 45°.

In the MEMS manufacturing world, the "fabless" model is getting increasing importance in recent years as a way for MEMS manufactures and startups to minimize equipment costs and initial capital investment. In order for this model to be successful, the fabless company needs to work closely with a MEMS foundry service provider. Due to the lack of standardization in MEMS processes, as opposed to CMOS microfabrication, the experience in MEMS development processes and the flexibility of the MEMS foundry are of vital importance. A multidisciplinary team together with a complete microfabrication toolset allows INO to offer unique MEMS foundry services to fabless companies looking for low to mid-volume production. Companies that benefit from their own microfabrication facilities can also be interested in INO's assistance in conducting their research and development work during periods where production runs keep their whole staff busy. Services include design, prototyping, fabrication, packaging, and testing of various MEMS and MOEMS devices on wafers fully compatible with CMOS integration. Wafer diameters ranging typically from 1 inch to 6 inches can be accepted while 8-inch wafers can be processed in some instances. Standard microfabrication techniques such as metal, dielectric, and semiconductor film deposition and etching as well as photolithographic pattern transfer are available. A stepper permits reduction of the critical dimension to around 0.4 μm. Metals deposited by vacuum deposition methods include Au, Ag, Al, Al alloys, Ti, Cr, Cu, Mo, MoCr, Ni, Pt, and V with thickness varying from 5 nm to 2 μm. Electroplating of several materials including Ni, Au and In is also available. In addition, INO has developed and built a gold black deposition facility to answer customer's needs for broadband microbolometric detectors. The gold black deposited presents specular reflectance of less than 10% in the wavelength range from 0.2 μm to 100 μm with thickness ranging from 20 to 35 μm and a density of 0.3% the bulk density of gold. Two Balzers thin-film deposition instruments (BAP-800 and BAK-760) permit INO to offer optical thin film manufacturing. Recent work in this field includes the design and development of a custom filter for the James Webb Space Telescope (JWST) as collaboration with the Canadian company ComDEV. An overview of the different microfabrication foundry services offered by INO will be presented together with the most recent achievements in the field of MEMS/MOEMS.

Dissipative three-wave weakly coupled states, appearing within collinear and non-collinear Bragg light scattering in a two-mode square-law nonlinear medium with the linear optical losses, are uncovered. The conditions for localizing these dissipative coupled sates as well as the spatial-frequency distributions of their optical components are studied theoretically in quasi-stationary regime. Then, a set of estimations related to the realization of similar dissipative three-wave coupled states have been performed within the acousto-optical experiments in the α-quartz crystalline cells providing collinear and non-collinear geometries of interactions. The distinguishing feature of these potential experiments is the fact that the presence of linear optical losses affects both shaping these dissipative weakly coupled states and the technique for detection and identification of their optical components.

This paper summarizes the factors that limit the performance of moving-magnet galvo scanners driven by closed-loop digital servo amplifiers: torsional resonances, drifts, nonlinearities, feedback noise and friction. Then it describes a detailed Simulink® simulator that takes into account these factors and can be used to automatically tune the controller for best results with given galvo type and trajectory patterns. It allows for rapid testing of different control schemes, for instance combined position/velocity PID loops and displays the corresponding output in terms of torque, angular position and feedback sensor signal. The tool is configurable and can either use a dynamical state-space model of galvo's open-loop response, or can import the experimentally measured frequency domain transfer function. Next a drive signal digital pre-filtering technique is discussed. By performing a real-time Fourier analysis of the raw command signal it can be pre-warped to minimize all harmonics around the torsional resonances while boosting other non-resonant high frequencies. The optimized waveform results in much smaller overshoot and better settling time. Similar performance gain cannot be extracted from the servo controller alone.

The performance of optical telecommunication system is mainly limited by optical signal to noise ratio (OSNR) at the receiver, fiber dispersion and nonlinearities. The limiting factors of optical communication systems that employ pluggable XFPs are investigated experimentally by characterizing and correlating the information regarding pulses evolution of 10Gbps signals in optical fiber under the influence of dispersion and different nonlinear effects.

We investigated the use of a pulsed, distributed feedback quantum cascade laser centered at 957 cm^-1 in combination with an astigmatic Herriot cell with 250 m path length for the detection of acrolein and acrylonitrile. These molecules have been identified as hazardous air-pollutants because of their adverse health effects. The spectrometer utilizes the intra-pulse method, where a linear frequency down-chirp, that is induced when a top-hat current pulse is applied to the laser, is used for sweeping across the absorption line. Up to 450 ns long pulses were used for these measurements which resulted in a spectral window of ~2.2 cm^-1. A room temperature mercury-cadmium-telluride detector was used, resulting in a completely cryogen free spectrometer. We demonstrated detection limits of ~3 ppb for acrylonitrile and ~6 ppb for acrolein with ~10 s averaging time. Laser characterization and optimization of the operational parameters for sensitivity improvement are discussed.

Collimated beams of energetic protons are produced by the interaction of short duration high intensity laser pulses with solid foils. This field has been the subject of many studies in the last decade. This interest is motivated by the wide range of application of such beams: ion based fast ignitor schemes, probing of electromagnetic fields in plasma, isotope production or hadron therapy. The recently commissioned 200 TW laser system (5 J, 25 fs, 10¹⁰ laser pulse contrast, 10 Hz repetition rate at 800 nm) at the Advanced Laser Light Source (ALLS) facility has been used to study proton acceleration with femtosecond laser pulses. The proton spectrum was characterized using a time of flight detector. Due to the high contrast of the laser pulse, foil targets as thin as 30 nm could be studied.

Beams of X-rays of few keV energy have been produced from laser-supersonic gas jet interaction. Betatron X-ray radiation is generated when energetic electrons are accelerated and experience betatron oscillations in the ion channel produced in the wake of a high intensity femtosecond laser pulse. Experiments took place at the 200 TW laser system (5 J, 25 fs, 10 Hz) of the Advanced Laser Light source facility (ALLS). Thanks to the laser system performance these preliminary results are the first steps to an expected improvement of the X-rays beams characteristics (collimation, brightness and energy above the keV range).

Talbot self-images localization is important in many optical applications such as interferometry, metrology and nanolithography. Usually, the problem of self-images localization is reduced to the finding the planes of maximal light pattern visibility. There are several conventional techniques that determine the contrast of an intensity distribution generated by a periodical object, such as root mean square (RMS) method, and variogram-based method. In all these cases, a CCD camera is used to record the light patterns that are processed and analyzed in order to find the self-image position. Recently, it has been proposed the use an adaptive photo-detector based on the non-steadystate photo-electromotive force (photo-EMF) effect, which uses periodically oscillating light pattern to induce alternating current through the short-circuited photoconductive sample. Here we perform the theoretical analysis of the technique based on the photo-EMF effect against the conventional methods for the localization of the Talbot patterns.

The landmark measurement of human skull is fundamental to geometric morphometry of palaeoanthropology. The landmarks are geometry points which can describe anatomically the homology of species group. They play an important role in palaeoanthropology. A structured-light based method is used to measure and make the 3D digital model of skull. The distances between all pairs of landmarks and interior angles from triangulations of the landmarks can be measured fast and accurately by the digital model. Other important geometric parameters of the skull, such as curvature, surface area, volume can also be measured. In order to validate and certificate the proposed method, 9 standard balls, which are embed at the landmarks, are measured by using Coordinate Measuring Arm (CMA). The experiment shows that the measuring errors of the distances and angles are less than 0.08 mm and 5' respectively.

It is shown that an axicon telescope system preserves isotropy and scaling in both the transverse and longitudinal directions as opposed to regular lens telescopes. Also, a coherent fiber optics imaging bundle was used with an axicon lens permitting viewing with an extended depth of field as compared to using a fiber optics bundle with a regular lens.

We report in this paper the study of achieving low current threshold quantum cascade lasers (QCLs) by using highreflection (HR) coating to short-cavity QCLs. Experimental results show that the QCL current threshold (Ith) and injecting electrical power are significantly decreased with HR coatings applied to one side or both sides of a QCL. The QCL structures used in the experiment are strain balanced InGaAs/InAlAs supperlattices based on InP substrate with the emission wavelength at λ~4.8μm. QCL devices with 28 periods and 60 periods are studied. With HR coatings on both laser facets, a 28 periods QCL device cleaved with 1mm long cavity expresses a low current threshold of 70mA at cryogenic temperature and a 0.5mm long cavity device shows a current threshold of 65mA at 50K. A 0.5mm long 60 periods QCL device with both sides HR coated is found to have a current threshold as low as 30mA at 20K and still below 50mA at liquid Nitrogen cooled temperature.

In this paper, quasi-continuous-wave (quasi-CW) operation of quantum cascade lasers (QCLs) is studied. A group of strain-balanced InGaAs/InAlAs QCLs emitting around λ~4.8μm were used in the experiment. QCLs were tested at different driving conditions (i.e. pulsed mode, CW mode and quasi-CW mode) at various temperatures. Experimental measurements show that thermal effect plays an important role in deteriorating QCL performance. This is especially true at high temperatures. At low temperature (~100K), L-I curves with different pulse widths exhibit no significant difference. While at a higher temperature (~200K), we observed that the longer the pulse width, the lower the roll-over power and the worse the laser performance. At 100K, the roll-over power increases as duty cycle increases until it reaches CW operation, indicating that the thermal generation difference for quasi-CW mode and CW mode is negligible. At 200K, however, a maximum roll-over power is about 50mW at duty cycle of 65% corresponding to a CW roll-over power of 40mW. It reveals that at high temperature, quasi-CW operation generates less heat and more average output power. Therefore, quasi-CW operation is obviously a favorable way to achieve high performance operations at high temperature.

We report here on the design, fabrication and performance characteristics of 1310 nm laterally coupled distributed-feedback (LC-DFB) semiconductor lasers. We describe the epidesign of these InGaAsP/InP quantum-well ridge waveguide LC-DFB lasers, which were fabricated in a single epitaxial growth step using stepper lithography and inductively-coupled reactive-ion as well as wet chemical etching. Such a DFB fabrication process avoids the commonly required regrowth steps in conventional DFB laser fabrication processes. The lithographic tolerance has been enhanced by employing higher order gratings, yielding lasers more amenable to mass-manufacturing. In this work, uniform third-order gratings have been lithographically patterned out of the waveguide ridge built on an epitaxial structure conceived for 1310 nm lasing wavelength. We now report on L-I measurements, threshold determination and sidemode suppression ratios (SMSR) for a broad distribution of devices. These fabricated lasers achieve stable single mode lasing with SMSR as high as 54 dB under CW operation at room temperature, albeit with thresholds higher than anticipated.

We describe theoretical and experimental investigations on the spectral and temporal control of an actively mode-locked erbium-doped fiber laser equipped with a highly dispersive cavity. The laser design is based on a unidirectional ring cavity in which a pair of diffraction gratings is inserted. A direct outcome of the dispersion due to the diffraction gratings resides in the fact that the duration of a complete roundtrip in the laser cavity becomes sensitively dependent upon laser wavelength. Tuning of laser emission is then achieved by controlling the modulation frequency of the waveform applied to the loss modulator that produces mode-locked operation. Such a fiber laser enables the generation of picosecond pulses with a rapid tuning over a large bandwidth. We also incorporated a Gires-Tournois interferometer (GTI) in the laser setup in order to investigate how perturbations such as group delay ripple affect the temporal shape of the laser pulses and their spectral content, as well as the stability of the selected laser wavelength. Variation of pulse duration between 40 to100 picoseconds and continuous tuning of laser wavelength will be described.

Fiber Bragg grating based fiber lasers are promising for stable all fiber laser solutions. Standard methods for fiber Bragg gratings in fiber lasers apply germanium doped passive fibers which are connected to the amplifier section of the fiber laser with a splice. The connection is usually recoated using a low-index polymer coating to maintain guidance properties for the pump light. At high pump powers the spliced connections are affected by absorbed pump light and are prone to thermal degradation. Fiber Bragg gratings made with femtosecond laser exposure allow the direct inscription of resonator mirrors for fiber lasers into the amplifying section of the fiber laser. Such a technology has a number of advantages. The number of splices in the laser cavity is reduced. Fiber Bragg grating inscription does not relay on hydrogenation to increase the photosensitivity of the fiber. This is of special interest since hydrogen loading in large mode area fibers is a time consuming procedure due to the diffusion time of hydrogen in silica glass. Finally, one gets direct access to fiber Bragg gratings in air-clad fibers. In this paper we use a two beam interferometric inscription setup in combination with an frequency tripled femtosecond laser for grating inscription. It allows to write fiber Bragg gratings in rare earth doped fibers with a reflection wavelength span that covers the Ytterbium amplification band. Reflections with values higher than 90% have been realized.

In this paper, characteristics of the intra-cavity frequency doubled Nd:YYO₄/PPMgO:LN green laser have been studied experimentally and theoretically. Two types of green laser strucutures, namely optical contact structure and separated structure, have been packaged for low power (100 mW) and high power (~1 W) applications, respectively. Coupled mode equations are used to investigate the green laser. The effect of the thermal dephasing along the propagation direction in the PPMgO:LN due to the heat generation by the linear absorption of the fundamental wave and linear and nonlinear absorption of the second hamonic (SH) wave is analyzed theoretically. By introducing the longitudinal temperature chirp in the PPMgO:LN crystal, the temperature tuning curve is enlarged by using a uniform PPMgO:LN grating.

Among the different possible amplification solutions offered by Raman scattering in optical fibers, ultra-long Raman lasers are particularly promising as they can provide quasi-losless second order amplification with reduced complexity, displaying excellent potential in the design of low-noise long-distance communication systems. Still, some of their advantages can be partially offset by the transfer of relative intensity noise from the pump sources and cavity-generated Stokes to the transmitted signal. In this paper we study the effect of ultra-long cavity design (length, pumping, grating reflectivity) on the transfer of RIN to the signal, demonstrating how the impact of noise can be greatly reduced by carefully choosing appropriate cavity parameters depending on the intended application of the system.

A 225-μJ polarization maintaining ytterbium-doped large-mode-area multiclad fiber was designed and fabricated with an effective mode area of 450 μm² and a photodarkening maximum excess loss of ~1 dB/m at 1064 nm. The fiber index profile is based on a depressed-clad to obtain a diffraction-limited output. Optimization for low photodarkening and high conversion efficiency while maintaining a good control on the core's refractive index profile has been achieved by adjusting the ytterbium/phosphorus/aluminum concentrations in the fiber core. Concentration ratios of phosphorus/aluminum from 0.12 to 1.25 were experimentally investigated in terms of photodarkening rate and excess loss. Within this range, the photodarkening excess loss was observed to decrease by a factor of 8. The large-mode-area fiber was used in a 10-ns pulse amplifier at 1064 nm with a repetition rate of 100 kHz and 0.5-nm bandwidth. The diffraction-limited output has a measured M² value of 1.04 when the fiber is coiled to a diameter of 12 cm. The fiber amplifier slope efficiency is 70% with a polarization extinction ratio greater than 23 dB. It is shown how the phosphorus/aluminum ratio reduces photodarkening, and how a depressed-clad design improves higher-order mode filtering for reliable, efficient, and compact ytterbium-doped fiber amplifiers.

An all-fiber passively Q-switched erbium/ytterbium co-doped cladding pumped fiber laser is presented. A section of erbium/ytterbium co-doped fiber is used as both gain medium and saturable absorber, which makes the laser configuration simple and compact. By properly choosing the splitting ratio of the laser output coupler, stable Q-switching could be achieved. It has been found that the splitting ratio of the output coupler is very important for generating stable Q-switching pulses. The operation range of stable Q-switching is different for different lengths of the erbium/ytterbium co-doped fiber. Self-mode-locking effect is also observed accompanying with the Q-switched pulses. The characteristics of the laser output against the pump power and the splitting ratio of the output coupler are studied in detail.

Some ~20μm wide slots have been fabricated on Si (100) using a homebuilt 355nm nanosecond pulse laser micromachining system. The slots were characterized by fluorescence microscopy, local spectroscopy and scanning electron microscopy. A kind of microstructure like porous silicon was formed in the fabrication zone. Strong photoluminescence emission from the fabricated zone in the wavelength range between 450nm and 700nm has been detected. Furthermore, a strong decay of the PL intensity has been observed as a function of irradiation time for excitation with wavelength between 400nm and 440nm. The analysis of elemental composition in the fabrication zone shows that the fluorescence emission is in relationship with Oxygen distribution and the modified structure.

We discuss specifically elaborated approach for 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. This approach had been previously applied to rather important case of pulse generation when a single-mode semiconductor heterolaser operates in a multi-pulse regime of the active mode-locking with an external single-mode fiber cavity. In fact, the trains of optical dissipative solitary pulses, which appear under a double balance between mutually compensating actions of dispersion and nonlinearity as well as gain and optical losses, are under characterization. However, in the contrast with the previous studies, now we touch an opportunity of describing two chirped optical pulses together. The main reason of involving just a pair of pulses is caused by the simplest opportunity for simulating the properties of just a sequence of pulses rather then an isolated pulse. However, this step leads to a set of specific difficulty inherent generally in applying joint time-frequency distributions to groups of signals and consisting in manifestation of various false signals or artefacts. This is why the joint Chio-Williams time-frequency distribution and the technique of smoothing are under preliminary consideration here.

Linewidth enhancement factor (LEF) of InAs/InP quantum dot (QD) multi-wavelength lasers (MWL) emitting at 1.53 μm are investigated both above and below threshold. Above threshold, LEFs at three different wavelengths around the gain peak by injection locking technique are obtained to be 1.63, 1.37 and 1.59, respectively. Then by Hakki-Paoli method LEF is found to decrease with increased current and shows a value of less than 1 below threshold. These small LEF values have confirmed our InAs/InP QDs are perfect gain materials for laser devices around 1.5 μm.

Crystals of periodically poled KTiOPO4 (PPKTP) are considered to be promising candidates for the femtosecond OPOs when compared with conventional periodically poled LiNbO3 (PPLN) crystals that suffer from the large photorefractive effect, thermal damage and high coercive field. In order to design the poling period of PPKTP crystal and to predict the desired wavelength tuning range with required spectral characteristics an accurate calculation using the wavelength- and temperature-dependent Sellmeier equations should be carried out. Although the Sellmeier equations for PPKTP have been published and revised several times, there are still some discrepancies between the measured and the theoretical results. It was reported that a temperature shift of approximately 25 °C has to be introduced in that equation in order to match the experimental results in the near-infrared range. In our work this effect is studied in detail in both the nearinfrared and visible ranges in order to provide an accurate reference for the design of PPKTP crystals for various nonlinear frequency conversion applications.

Porous silicon is a well-known material with interesting properties for a wide variety of applications in electronics, photonics, medicine, and informatics. We demonstrate fabrication of porous silicon using a dry etching technique. We demonstrate free standing porous silicon membranes that are only few microns thick. Free standing porous silicon membranes have the ability to behave as a size-selective permeable membrane by allowing specific sized molecules to pass through while retaining others. Here, we employ the XeF2 to develop few micrometers thick suspended porous silicon membranes. The flexibility of XeF2 etching process allows the production of mechanically stable membranes of different thicknesses. By choosing the appropriate etching parameters and conditions, pore size can be tuned to produce porous silicon with optically attractive features and desired optical behaviors. The pore size, porosity and thickness of the various developed ultra-thin free-standing porous silicon membranes were characterized with scanning electron microscopy and optical transmittance measurements. The fabricated free-standing porous membrane has a typical transmission spectrum of regular silicon modulated by Fabry-Perot fringes. Porous silicon thin membranes that combine the properties of a mechanically and chemically stable high surface area matrix with the function of an optical transducer may find many used in biomedical microdevices.

Azobenzene polymer surface relief diffraction gratings were inscribed on relaxor ferroelectric Lead Lanthanum Zirconate Titanate (PLZT) thin films having a (9/65/35) composition. Resonance structures were observed in the reflected intensity spectra of a laser light beam onto these films, indicating coupling of the incident light. An ac electric field was then applied along the thickness of the PLZT films and an electro-optic modulation signal was measured as a function of the incidence angle of the laser beam. It was found that the resonance structures increased the modulation signal of the PLZT thin films at constant field amplitude.

This work focuses on the study of the modification in formation and electro-optic behavior of holographically formed polymer -liquid crystal thin film gratings doped with multiwalled carbon nanotubes. Results indicate a time delay in the evolution of the first diffraction order in the presence of carbon nanotubes when compared to ones with no nanotubes. An analysis is presented based on the modification of the diffusion kinetics in terms of photo induced phase separation. This slow down is attributed to the non-participation of the carbon nanotubes in the phase separation process, and acting as physical barriers to the counter diffusing liquid crystals. The diffusion constant of nanotubes, incorporating its shape anisotropy, is computed in such a photo polymerizable system and compared with those of the participating polymers and liquid crystals. An optimal concentration of carbon nanotube doping is arrived at which helps in improve the switching speed while maintaining diffraction efficiency. Improvement is switching speed is attributed to reduction in size of the liquid crystal droplets. Scanning electron microscopy results indicate a change in morphology of the gratings doped with carbon nanotubes. In specific, smaller droplet size and, beyond the optimal level of nanotube doping, imperfect liquid crystal phase separation with scarcity of liquid crystal droplets across the sample is seen.

Highly ordered TiO₂ nanowire arrays were prepared on the surface of Functionalized Graphene sheets (FGSs) by solgel method using titanium isopropoxide monomer with acetic acid as the polycondensation agent in the green solvent, supercritical carbon dioxide (sc-CO₂). Morphology of synthesized materials was studied by SEM and TEM. Optical properties of the nanocomposites studied by UV spectroscopy which showed high absorption in visible area as well as reduction in their band gap compared to TiO₂. By high resolution XPS, chelating bidentate structure of TiO₂ with carboxylic group on the surface of graphene sheets can be confirmed. Improvement in the optical properties of the synthesized composites compared to TiO₂ alone was confirmed by photocurrent measurements.

With the doping of Ag⁺ and Ce3⁺, the FOTURAN photosensitive glass shows not only the normal optical property but also some characteristics of metal. The photosensitive glass has been widely used in optical field for its own advantages. It is sensitive to UV light. In this paper an UV nanosecond pulse laser micro-machining system is designed and successfully performs the micro-structure machining on the FOTURAN photosensitive glass. Based on the increasing requirement in photosensitive glass shape-control fabrication, different system parameters have been tested to achieve shape-control fabrication and some satisfied microstructures are achieved finally.

High absorptivity and low thermal mass are two important requirements for coatings applied to thermal infrared detectors. Gold black coatings are very good candidates to ensure these characteristics in the broadband infrared spectral range. A specific deposition system was designed and built at INO in order to provide gold-black coatings for different broadband detection applications including the broadband radiometer (BBR) instrument for the European Space Agency (ESA) EarthCARE satellite. A parametric study targeting uniform optical absorptance within the spectral range from 0.2 μm to 50 μm was conducted. Specular reflectance lower than 10% was obtained for extended wavelength range up to 100 μm. The coating thickness ranges typically between 20 μm and 35 μm, with uniformity of about ± 3 μm over a sample surface of 10x10 mm². The deposit density was typically ~0.3% of the bulk density of gold. To singulate the blackened infrared detector pixels, a laser micromachining process was developed. The setup exhibits a 1μm positioning accuracy and allows for ablation of 3 μm to 12 μm wide channels through the gold-black thickness, while preserving the pixel and gold-black deposit integrity.

Quasi-phase matched (QPM) second-order nonlinear optical processes in compound semiconductors are attractive for frequency conversion because of their large nonlinear susceptibilities and their mature fabrication processes that permit monolithic integration with pump lasers and other optical elements. Using quantum well intermixing (QWI), we have fabricated domain-disordered QPM (DD-QPM) waveguides in GaAs/AlGaAs superlattices and have previously demonstrated continuous-wave (CW) Type-I second-harmonic generation (SHG) and pulsed Type-II SHG. CW experiments were complicated by Fabry-Perot resonances and thermal bistability. Experiments using a 2-ps pulsed system were affected by third-order nonlinear effects, group-velocity mismatch (GVM), and poor spectral overlap with the conversion bandwidth. A better evaluation of the conversion efficiency may, however, be determined by using longer pulses in order to avoid these complications. By this, the effective CW conversion efficiency and χ⁽²⁾ modulation can be ascertained. In this paper, we demonstrate SHG in DD-QPM waveguides with reduced parasitic effects by using 20 ps pulses. The waveguide structure consisted of a core layer of GaAs/Al_0.85Ga0.15As superlattice into which QPM gratings with a period of 3.8 μm were formed using QWI by As²⁺ ion implantation. For a Type-I phase matching wavelength of 1583.4 nm, average second-harmonic (SH) powers produced were as high as 2.5 μW for 2 ps pulses and 3.5 μW for 20-ps pulses. At low input powers, the SHG average power conversion efficiency of the 2-ps system was more than 10 times larger than the 20 ps system. As power was increased, the SH power saturated and conversion efficiency decreased to nearly equal to the 20-ps system which remained consistent over the same power range. This is attributed to a reduction in third-order nonlinear effects, a smaller pulse spectral width that overlaps better with the conversion bandwidth, and less pulse walkoff for the 20-ps pulses. Thus, by using 20-ps pulses over 2-ps pulses, we achieved similar output SH powers and potentially higher SH powers are possible since there was no observed saturation at high input power.

When the two-photon absorption of a high intensity pump beam takes place in a semiconductor optical amplifier there is an associated fast phase change of a weak probe signal. A scheme to realize fast all-optical XOR logic function using twophoton absorption induced phase change has been analyzed. Rate equations for semiconductor optical amplifiers, for input data signals with high intensity, configured in the form of a Mach-Zehnder interferometer has been solved. The input intensities are high enough so that the two-photon induced phase change is larger than the regular gain induced phase change. The model shows that both XOR operation and pseudorandom binary sequence generation at 250 Gb/s with good signal to noise ratio is feasible.

Ni/nSi and Pt/nSi Schottky barrier diodes have been integrated with SOI optical waveguides produced using the Local Oxidation of Silicon (LOCOS) technique. The smooth, nearly planar topography provided by LOCOS allows the Schottky metal to overlap the waveguide rib while still giving low leakage current densities (<10^-5 Acm^-2 for Ni and <10^-7 Acm^-2 for Pt at 1 V reverse bias). Correcting for input coupling loss, responsivities of 4.7 mA/W and 4 μA/W were obtained for 500 μm long Ni and Pt diodes respectively at 1310 nm. At 1550 nm the responsivity for Ni was 1.8 mA/W while Pt did not give a measureable response.

An electrooptic modulator containing a single SiGe/Si quantum-well has been designed for operation at λ_O= 1.55 μm. This single quantum-well modulator has a lower V_πL_π than the 3 quantum-well modulator recently designed and optimized by Maine et al. for operation at λ_O = 1.31 μm, for which the V_πL_π product was 1.8 V · cm. This single quantum-well modulator contains a Si_0.8Ge_0.2 quantum-well with Non-Intentionally Doped (NID) and P⁺ highly doped layers on either side. With no field applied, holes from the P⁺ layers are captured by and confined in the quantum-well and when a reverse bias is applied holes are released from the quantum well and drift to the P⁺ contact layer. Variations of the hole distribution lead to changes in the free-carrier absorption and the refractive index of each layer and subsequently to phase modulation of guided TE modes. The V_πL_π product of the single quantum-well modulator is estimated 1.09 V · cm for low voltage linear modulation and 1.208 V · cm for 0 to 1.6 V digital modulation, whereas the 3 quantum-well modulator gives a V_πL_π of 2.039 V · cm for 0 to 6 V digital modulation for operation at λ_O = 1.55 μm. Also, the optical loss in the single quantum-well (5.36 dB/cm at V = 0 V ) is lower than that of the 3 quantum-well structure (5.75 dB/cm at V = 0 V ). This single quantum-well modulator should also offer higher frequency operation than the 3 quantum-well modulator.

Metal-Semiconductor-Metal photodetectors (MSM-PDs) have been demonstrated with ease of fabrication, low capacitance, and faster responses compared to PIN photodetectors. Si and Ge are two of the CMOS compatible materials for sensing area of the photodetector. Ge, because of its higher mobility and absorption at 1.55μm wavelength is an attractive material of choice. In the outlined work, an interdigitated electrode MSM photodetector with a-Ge:H (amorphous-Ge:hydrogenated) as the sensing material has been recognized as a promising candidate for near infrared photodetection. Hydrogenating Ge generally helps improve material characteristics because it increases life time of photocarriers. Ge was sputter deposited with different H₂ concentrations of 0%, 5%, 10%, 15%, and 25% in the plasma gas. The highest hydrogen concentration showed the highest responsivity among other detectors showing that hydrogen helps to reduce the number of defects within the a-Ge film and therefore increase the life time of carriers. Results show that highest photocurrent belongs to a sample with 25% H₂ concentration in the plasma with a responsivity of 2mA/W and dark current of 11.6μA at 5v for a device area of 95×110 (μm)².

Semiconductor optical amplifiers are important for wide range of applications in 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. All optical Boolean operations such as XOR, OR, AND and NOR has been demonstrated using SOA based Mach-Zhender interferometers (SOA-MZI). A rate equation model for SOA-MZI has been developed. The model has been used to analyze the Set-Reset (S-R) latch, the gated S-R latch and the D-Flip-Flop devices. The modeling results suggest that the Flip-Flop circuits should work at high speeds.

A novel optical bistable device based on an electrically coupled semiconductor optical amplifier (SOA) and a bipolar juncture transistor (BJT) is proposed and experimentally demonstrated. The measured switching time is about 0.9-1.0 us, mainly limited by the electrical capacitance of the SOA and the parasitic inductance of the electrical connections. However, the effects of parasitic components can be reduced employing current electronic-photonic integration circuits (EPIC). Numerical simulations confirm that for capacitance values in tens of femtofarads switching speed can reach tens of GHz.

We demonstrate a silica-based tunable fiber Bragg grating (TFBG) filter with a wavelength tuning range over 60 nm. A magnetically TFBG package is employed to obtain a wide wavelength tuning range from 1540 to 1602 nm which covers the entire C band and most of the L-band. TFBG is achieved by varying an input current to a solenoid, resulting in an electromagnetic force, used as a strain (tension and compression) on the FBG. This approach is fast, has a broad band of tuning wavelengths and achieves a power reduction as no continuous supply of power is needed to maintain the set shift, due to the latch system used. This novel TFBG device can have a variety of applications in optical fiber communication systems such as programmable optical add/drop multiplexers (OADMs), dispersion compensators and tunable lasers.

Micromirrors are a typical example of Micro-Electromechanical Systems (MEMS) with many applications including optical scanners, optical switching, projection displays, etc. We have succeeded in producing MEMS micromirrors in a SiGe structural layer, which can be used to realize CMOS-integrated MEMS structures. Several pixel designs were simulated using COMSOL multiphysics and subsequently verified in hardware. They differ in mirror size, hinge length and number of attracting electrodes (two or four). One particular mirror design enables variable Pulse Width Modulation (PWM) addressing. In this design, the mirror switches between two extreme states with a variable duty cycle determined by two generic high voltage signals and two CMOS-compatible pixel-specific DC voltages applied to the four attracting electrodes. The processed arrays were subjected to Laser Doppler Vibrometer (LDV) measurements in order to verify the simulation results. The simulated and measured pull-in voltages are compared for 8, 10 and 15μm mirrors. The agreement between simulation and measurement lies within the expectations, which is an encouraging result for future designs.

The acousto-optically tuned devices are becoming quite popular in dense wavelength division multiplexing (DWDM) applications due to low insertion loss, less cross talk and freedom from the grating wavelength drift due to thermal variations. Acousto-optic cell diffracts the optical beam depending on the wavelengths and acoustic frequency. This property is used to exploit acousto-optic cell array (AOCA) for multiplex/demultiplex (MUX/DEMUX) and cross-connect applications in DWDM in optical communication. Acousto-optic diffraction grating is preferred over other systems as the directions of the deflected light beams can be controlled by changing the frequency of the drive signal and the light intensity of the beams can be adjusted by changing the power of the drive signal. This paper presents the analysis and performance of three-dimensional acousto-optic cell array system based on generalized equations. Numerical results have been obtained for optical wavelengths vs deflection angles, incident angles vs deflection angles in different directions for several stages. The wavelengths under consideration range between 1500-1600 nm and the effects of acoustic wave velocity variations have also been considered.

The gain media of the quantum dot lasers consist of InAs QDs in an InGaAsP matrix on an InP substrate. The quantum dot lasers have different free spacing ranges (FSRs) corresponding to Fabry-Pérot (F-P) cavity lengths. A silicon ring resonator and a QD laser have been combined to form comb laser. The output characteristics of the combined comb laser were investigated. The measured FSR was about 2.8nm and the extinction ratio was about 10(dB) when the FSR of the QD laser was about 0.4nm and the FSR of the ring resonator was about 0.47nm. The experimental results show that the ring resonator had a strong control on the FSR and extinction ratio of the comb laser.

Organic semiconductors with bipolar (electron and hole) transport capability play a crucial role in electronic and optoelectronic devices such as organic light-emitting diodes (OLEDs), bipolar transistors and photovoltaic cells. Recently, a considerable amount of work has been devoted to the characterization of ambipolar transport in organic materials, allowing for a better understanding of their properties as well as the physical processes, which take place in materials and devices [1-4]. The experimental methods used to obtain information about charge transport in organic semiconductors - time-of-flight (TOF) transient photoconductivity [5], charge extraction by linearly increasing voltage (CELIV) [6], current-voltage measurements in space charge limited current regime [7], and field effect transistor (FET) measurements [8, 9] are mostly focused on determination of charge carrier mobility. On the other hand, for many devices (e.g. organic photovoltaic solar cells or light emitting diodes) the knowledge of the transport and recombination characteristics of both carriers (electron and hole), and specifically their diffusion L_D = the square root of Dτ (here D is the diffusion coefficient and τ is the photocarriers lifetime) and drift lengths L₀ = μτE₀ (here μ is the carrier's mobility and E₀ is the electric dc field) is important.

The results on characterization of the main photoelectric properties of the polymer:fulleren based composite material by using the non-steady-state photo-electromotive force (p-EMF) and modulated photocurrent technique are presented. By measuring this current under different experimental conditions, important material photoelectric parameters such as drift L₀ and diffusion length L_D, photocarrier's lifetime τ ; quantum efficiency of charge generation φ can be determined. The 50% of the composite weight consists of a mixture of the hole-conducting polymer PF6:TPD (poly-hexyle-triophene:N,N'-bis(4-methylphenyl)-N,N'-bis-(phenyl)-benzidine) sensitized with the highly soluble C₆₀ derivative PCBM (phenyl-C61-butyric acid methyl ester) . Seven samples with varied polymer:sensitizer weight ratio (49:1wt.-%, 45:5wt.-%, 40:10wt.-%, 15:35wt.-%, 25:25wt.-%, 10:40wt.-%, 5:45wt.-%) where prepared. The remaining 50% were two azo-dyes 2,5-dimethyl-(4-p-nitrophenylazo)-anisole (DMNPAA) and 3- methoxy-(4-p-nitrophenylazo)-anisole (MNPAA) (25wt.-% each). Photoconductive composite film was sandwiched between two glass plates covered by transparent ITO electrodes. Two counter-propagating beams derived from a cw HeNe laser (λ = 633nm) intersected inside the detector creating an interference pattern. The output photo-EMF current (SEE MANUSCRIPT FOR EQUATION) was detected as a voltage drop by a lock-in amplifier. At polymer sensitizer ratio 25:25wt.-% the signal sign changes to the opposite revealing that the majority carriers at this and higher concentration of sensitizer are electrons. Our results show that the majority carrier's lifetime τ is only slightly affected by the variations of sensitizer concentration. Mobility-lifetime product μ_hτ_h of holes, on its turn decreases at the increasing sensitizer concentration, while μ_eτ_e of electrons keeps increasing. All this indicates that the carrier's mobility is strongly influenced by the changes on sensitizer concentrations.

Photoacoustic (PA) imaging is a non-invasive imaging modality that employs non-ionizing near infrared (NIR) laser light to obtain optical images of tissues with depth penetration and resolution comparable to ultrasound imaging. PA images are created by illuminating tissues with a short laser pulse (~10 ns), which causes optically absorbing structures to heat up slightly, but so rapidly that conditions of thermal and stress confinement are met and the structure emits a pressure wave at ultrasonic frequencies. Detection of the pressure waves at the tissue surface with an ultrasound transducer array provides the data needed to reconstruct the distribution of light-absorbing structures within the tissue. Since it is recognized that cancerous breast lesions absorb light to a greater degree than surrounding normal tissue, PA imaging is a viable candidate for detection of lesions within the intact human breast. Therefore, we have constructed a transportable PA imaging system suitable for breast imaging. The system incorporates a hand-held transducer array with 30 detector elements arranged on a ring. Laser light is delivered coaxially in relation to the ring using a fiber optic light guide. The supporting hardware includes a NIR tuneable laser, transducer cabling, 30 preamplifiers, 30 independent data acquisition channels with onboard memory, and a computer with control and image reconstruction software. Initial tests with the transducer array suggest that it has sufficient sensitivity to detect optically absorbent objects on the order of 1- mm at a depth of 2 cm. It is anticipated that a small hand-held PA imaging unit will be amenable to patient work-up and would complement standard ultrasound imaging.

A thorough analysis on the separate confinement heterostructure (SCH) designed for 1.5-μm InGaAlAs/InP multiplequantum- well (MQW) lasers is presented. Simulation results show that the enhancement rates of the threshold current and the slope efficiency of graded-index SCH (GRINSCH) drop with the increasing number of graded layers. Hence, requirement on truly graded structure may be relieved, which eases the growth process and reduces the cost. The thickness of the GRINSCH has a profound impact on the laser's performance, whereby over 25 mA reduction in threshold current was deducible by optimizing this design parameter alone. The grading energy range of the GRINSCH is found to effectively reduce the carrier leakage at elevated temperature, resulting in improved threshold current's sensitivity to the temperature. However, the increased GRINSCH energy barrier may also bring detrimental effect to the slope efficiency. To overcome this problem, a non-symmetrical SCH (NS-SCH) structure with reduced n-SCH energy barrier is proposed. Simulation results show that laser structure with NS-SCH design has better light-current performance than the laser structure with electron stopper layer. The laser structure with NS-SCH exhibits 20% decrease in threshold current and 43% increase of maximum output power as compared to those of the reference laser structure.

A Bragg grating fast tunable filter prototype working over a tuning range of 62 nm has been realized. The tunable fiber Bragg grating TFBG system is achieved by varying an input current to a solenoid, resulting in an electromagnetic force, used as a strain (tension and compression) on the FBG. However, during compression, the FBG may be subject to buckling especially when the amount of compression is large. The challenge for the FBG device is therefore to design guiding system for the FBG in order to prevent the buckling. This paper presents the design of such a guiding system. These novel TFBG devices with a guiding system can have a variety of applications in optical fiber communication systems; such as programmable optical add/drop multiplexers (OADMs), dispersion compensators and tunable lasers.

Optical design of a spectrometer for all-reflective optics based line scan Fourier domain optical coherence tomography (FD-OCT) imaging has been reported in this work for high-speed scanning. FD-OCT imaging data acquisition offers significantly improved imaging speed in the depth direction compared to conventional time domain optical coherence tomography (TD-OCT). On the other hand, line focused scanning improve imaging speed in the transverse direction compare to commonly used flying spot scanning. Combination of FD-OCT acquisition and line focused scanner can give higher imaging speed. Spectrometer is a critical submodule in FD-OCT system. Apart from the spectrometer optical resolution, and detector array resolution, the chromatic aberration should be considered to design a high-quality FD-OCT imaging spectrometer. The proposed imaging spectrometer consists of a planer reflective grating, off-axis parabolic cylindrical mirror and a CCD array detector. Mirror focusing reduces the chromatic aberration because of its insensitivity to the wavelength of the laser beam, therefore the spectrometer image quality enhanced by the reflective optics focusing. Spot profile fall-off characteristic was analyzed by using ZEMAX optical design software.

We present recent novel approaches for engineering the dispersion characteristics of guided wave structures. These approaches are highly efficient and depend mainly on the exploited numerical method for calculating the modal parameters. Using these approaches, the modal parameters and their sensitivities with respect to all the design parameters can be obtained efficiently. The computational cost is much less than that for estimating the sensitivities of these parameters using finite difference scheme. The former approach requires many additional simulations proportional to the number of design parameters. Our approaches, however, need no additional simulation for obtaining the sensitivity information. They require the construction of an adjoint problem whose solution is readily available using the original simulation.

Despite ever increasing computational power, recognition and classification problems remain challenging to solve. Recently, advances have been made by the introduction of the new concept of reservoir computing. This is a methodology coming from the field of machine learning and neural networks that has been successfully used in several pattern classification problems, like speech and image recognition. Thus far, most implementations have been in software, limiting their speed and power efficiency. Photonics could be an excellent platform for a hardware implementation of this concept because of its inherent parallelism and unique nonlinear behaviour. Moreover, a photonic implementation offers the promise of massively parallel information processing with low power and high speed. We propose using a network of coupled Semiconductor Optical Amplifiers (SOA) and show in simulation that it could be used as a reservoir by comparing it to conventional software implementations using a benchmark speech recognition task. In spite of the differences with classical reservoir models, the performance of our photonic reservoir is comparable to that of conventional implementations and sometimes slightly better. As our implementation uses coherent light for information processing, we find that phase tuning is crucial to obtain high performance. In parallel we investigate the use of a network of photonic crystal cavities. The coupled mode theory (CMT) is used to investigate these resonators. A new framework is designed to model networks of resonators and SOAs. The same network topologies are used, but feedback is added to control the internal dynamics of the system. By adjusting the readout weights of the network in a controlled manner, we can generate arbitrary periodic patterns.

The wavelength and intensity of the spectral emission of a group of quantum dots can be altered by varying the size of the quantum dots (wavelength) and the number of the quantum dots (intensity). In this way, information and be encoded into the spectral characteristics of the group of quantum dots emission. This approach has been proposed for the application of tagging thousands of biomolecules as well as replacing barcodes as a means to identify objects. The potential in this system rests in the ability to achieve a high information density. In this paper we model and measure the noise in the readout system that will contribute to the decrease of the information density. We also propose an alternate optical detector as a possibly simpler and cheaper design. Our results demonstrate that the signal-to-noise ratio for both the CCD and photodiode detectors has a linear relationship with time. To achieve comparable SNR, approximately 30dB, in both detectors we note that the CCD-based spectrometer requires integration times on the order of hundreds of milliseconds while the photodiode only requires tens of microseconds.

An analytical model for long-period grating manufactured using an electric-arc micromachining method is developed. This model takes into account the resulting modulation of the refractive index and the diameter in both the core and the cladding of the fiber structure. Based on the local-mode theory, the model introduces coupling coefficients and detuning parameters that vary longitudinally. Comparisons are made with the standard model for long-period grating manufactured using the UV micromachining method.

The paper presents an optimization analysis of the yield of high-speed 1310 nm distributed feedback lasers. Simulation results are showcased and design principles for achieving the highest possible yield of high-speed single mode devices with the side mode suppression ratio of more than 40 dB and the modulation bandwidth of over 20 GHz are outlined. The effects of the integrated Bragg grating characteristics and end-mirror reflectivities on the crucial parameters for high-speed operation are studied and guidelines for high-speed device fabrication are given.

We present an advanced approach to describing low-power trains of bright picosecond optical dissipative solitary pulses with an internal frequency modulation in practically important case of exploiting semiconductor heterolaser operating in near-infrared range in the active mode-locking regime. In the chosen schematic arrangement, process of the active mode-locking is caused by a hybrid nonlinear cavity consisting of this heterolaser and an external rather long single-mode optical fiber exhibiting square-law dispersion, cubic Kerr nonlinearity, and small linear optical losses. Our analysis of shaping dissipative solitary pulses includes three principal contributions associated with the modulated gain, total optical losses, as well as with linear and nonlinear phase shifts. In fact, various trains of the non-interacting to one another optical dissipative solitons appear within simultaneous balance between the second-order dispersion and cubic-law Kerr nonlinearity as well as between active medium gain and linear optical losses in a hybrid cavity. Our specific approach makes possible taking the modulating signals providing non-conventional composite regimes of a multi-pulse active mode-locking. Within our model, a contribution of the appearing nonlinear Ginzburg-Landau operator to the parameters of dissipative solitary pulses is described via exploiting an approximate variational procedure involving the technique of trial functions.

The question of the velocity of energy propagation in various structures is addressed and a comparison of the different definitions for this velocity is made.

Nano-scale structures have been proposed as a low cost mechanism to enhance solar cell efficiency. Computer simulations can be used to rapidly and cheaply prototype and optimize these novel designs, however the simulations are challenging due to the geometric complexity, the highly dispersive materials, and the necessity of performing broadband simulations over the solar spectrum. We show how the finite-difference time-domain (FDTD) method in conjunction with particle swarm optimization (PSO) can be used to efficiently optimize these designs. We apply the method to two specific examples: thin film silicon plasmonic solar cells and photonic crystal organic solar cells. In each case, optical enhancements of approximately 15% can be achieved. The optimization requires a few hundred simulations which can be achieved in a few hours on a good workstation. Finally, we consider the steps necessary to perform combined optical and electrical simulations to fully characterize these devices.

DPL coupling system was researched in this paper. First, the mathematic model of 3D and 2D light transmission in hollow duct was analyzed and compared. Then the 3D simulation software for all rays of the coupling system -lens duct was developed. The influence of various structural parameters of the hollow lens duct to the energy and the beam distribution were discussed with the help of developed software. The structural parameters such as the duct length, the lens radius, the size of the input and output ends were researched and were optimized to get higher efficiency and better beam distribution. Finally, the energy conversion efficiency and the beam spatial distribution of before and after optimization were compared. The results showed that the efficiency and the distribution of energy were well improved after the optimization.

In this paper, the dispersion compensation in transmission is modeled and investigated using apodized fiber Bragg grating (AFBG). The two-beam interferometer is used in AFBG manufacture. The effect of different interferometer parameters is studied for large bandwidth transmission at a zero eye closure penalty with linearly chirped gratings. The parameters under investigation for only one arm of the interferometer are d (arm length), the angle θ (beam angle) and λ (the writing wavelength). Eight different apodization profiles are studied including their effects on the performance of the compensator.

This work aims to study the improvement that has been achieved when replacing the traditional single-element (SE) receivers by imaging (IMG) receivers in line of sight (LOS) links, which can reduce the received ambient light noise, multipath distortion and co-channel interference. Also in non-directed non-LOS, the replacement of diffuse (DIF) transmitters by multi-beam (quasi-diffuse) (QDIF) transmitters has been studied; such replacement leads to reduction in the path loss. This study first based on making validation to a previous approximate and exact analysis to LOS and non- LOS links, and then a parametric study to some parameters has been made to check their effect on the link performance. We quantify the performance of the LOS and NLOS links using two main parameters; the reduction in the required transmitter power and high improvement in the signal to noise ratio (SNR).

A new method based on analysis of a single diffraction pattern is proposed to measure deflections in micro-cantilever (MC) based sensor probes, achieving typical deflection resolutions of 1nm and surface stress changes of 50μN/m. The proposed method employs a double MC structure where the deflection of one of the micro-cantilevers relative to the other due to surface stress changes results in a linear shift of intensity maxima of the Fraunhofer diffraction pattern of the transilluminated MC. Measurement of such shifts in the intensity maxima of a particular order along the length of the structure can be done to an accuracy of 0.01mm leading to the proposed sensitivity of deflection measurement in a typical microcantilever. This method can overcome the fundamental measurement sensitivity limit set by diffraction and pointing stability of laser beam in the widely used Optical Beam Deflection method (OBDM).

Surface waves on cylindrical rods with dimensions much smaller than the incident radiation experience reflection from the ends of the rods thus effectively forming a cavity. Rods with flat ends and rounded ends have been studied in the past for determination of the phase of reflection, which plays a vital role in determining the resonant frequency. In this paper we present a simpler approach to evaluate the phase of reflection from rounded end rods by considering the limiting case of a sphere. We approximate the extreme sub-wavelength sphere by a Fabry Perot (FP) resonator to derive the relation for phase of reflection which will prove useful for the design of nanorods for various applications. Optical nanorods are extensively utilized in optical antennas, optical/biological sensors, light emitting devices and other optoelectronic devices.

We propose a physically asymmetric thin film structure to support long-range surface plasmons (LRSPs), which consists of a low index medium on a metal film on a dielectric layer (membrane) over air, as a suspended waveguide. An analytic formulation is derived in 1D geometry yielding a transcendental equation that ensures symmetry of the transverse fields of the LRSP within the metal film by properly configuring the thicknesses of the metal film and the membrane. The theoretic results from the formulation agree with the transfer matrix calculations quantitatively for a candidate slab waveguide consisting of an H₂O-Au-SiO₂-air structure. These results are promising for sensors that operate with an aqueous solution that would otherwise require a low refractive index substrate to achieve LRSP guiding.

We study the polarization conversion from horizontally polarized to vertically polarized light (or vice versa) that occurs when light is incident on a cross-corrugated metal surface. The conversion is due to the optical energy exchange between the surface plasmon (SP) resonances at the metal-dielectric interface of the surface. The angular and wavelength dependence of the SP-induced polarization conversion was studied for cases where two perpendicular surface relief diffraction gratings of different pitch are used to couple the light into and out of the plasmon resonance modes. The polarization conversion occurs only when a plasmon mode is exited by one of the gratings and then the energy in this mode is out-coupled by the second grating. For various grating combinations this occurs at specific wavelength and incidence angles, otherwise no signal is obtained in a crossed polarizer set-up. An enhancement of the signal (and therefore of the surface field) is also observed when a standing wave surface plasmon is generated when one of the gratings produces counter propagating surface plasmons. A theoretical model based on graphical representations in momentum space of the travelling light beam through the specimen was developed and successfully applied to explain the experimental results.

Extraordinary optical transmission through nanohole arrays in metal films shows enhanced performance in surface plasmon resonance sensing, and efforts to develop this technology have been undertaken by many research groups worldwide. The challenge is to integrate a nanohole array sensor into a handheld design that is compact, cost effective, and capable of multiplexing. A number of implementations have been suggested, using components such as lasers and spectrometers, but these designs are often bulky, expensive and unacceptably noisy. We have developed an approach that is simple, inexpensive and reliable: an integrated handheld SPR imaging sensing platform using the nanohole array chip as the sensing element, a two-color LED source for spectral diversity, and a CCD module for multiplexed detection. A PDMS microfluidic chip made by conventional photolithographic techniques is assembled with the nanohole arrays and incorporated into the integrated module in order to transport the testing solutions, which offers the flexibility for future multiplexing. Results of preliminary tests show surface binding detection and have been promising.

The transfer matrix method and the semiclassical coupled wave theory (SCWT) are modified and applied to 1D absorptive photonic crystals. The presented treatment allows to calculate the reflection/transmission characteristics of a photonic crystal with an arbitrary shape of the refractive index on the period.

The structuring of high quality complex optical materials yields remarkable flexibility in the fabrication of nanostructures. These artificial materials can be used to manipulate light. The photonic band structure of a honey comb lattice composed of hollow shell rod with GaAs wall has been investigated by using standard Eigen mode expansion (EME) techniques. The dispersion characteristics of the dielectric material determine the tunability of the band gap as well as appearance of surface plasmon polariton (SPP) mode. Dispersion less flat band was observed for the frequency region where dielectric constant changes its sign. We demonstrate band gap tuning by applying external perturbation such as temperature change or varying external magnetic field. Using our band solver we extend the existing methodology by adjusting the dimension of the lattice to observe the desired effects. In addition to that our method studies the lacking of structural integrity due to presence of absorption.

A Long Range Surface Plasmon Polariton (LRSPP) gold waveguide supported by a thin suspended CYTOP membrane is discussed with respect to biosensing applications. This structure allows for refractive index symmetry through immersion in liquid or gaseous environments. The amorphous fluoropolymer CYTOP is used for the membrane material due to its desirable optical properties. The fabrication steps for the membranes and waveguides are described along with the membranes' mechanical properties determined experimentally through bulge testing. These structures are promising for applications in biological and chemical sensing.

This paper presents a photonic crystal fiber (PCF) refractive index sensor. The sensor structure is quite simple. It is composed of three segments of optical fibers spliced together. The multimode fibers with core diameter of 50 μm are used for light input and output. The middle fiber is a short segment of PCF, ESM-12-01. Although it has some advantages such as being able to operate in single mode for a large number of light wavelengths and has great temperature stability, it also has a common drawback of the PCFs, that is, the tiny holes will collapse when they are spliced. This paper makes use of this drawback to facilitate the generation of the surface plasmon resonance. The spliced region of a PCF actually becomes a thin silica rod that is no longer a PCF or a traditional optical fiber. For this reason once the light travels into this region it diverts in all possible directions. Thus, the splice acts as a mode converter that converts the core modes of the multimode fiber into a set of the modes spreading into the PCF cladding. Among those modes some are suitable for SPR excitation. The width and the depth of the output spectrum dip depend on the length of the sensing part and the thickness and uniformity of the gold coating, and hence these parameters affect the properties of the sensor. The developed sensor is compact in size, simple to fabricate, promising in performance, and has a potential for practical applications.

Highly nonlinear waveguides are essential components for all-optical signal processing. Many promising nonlinear waveguides utilize the Kerr nonlinearity, the strength of which is determined not only by the material properties, but also by geometrical factors, quantified by the waveguide's nonlinear effective area A_eff. In an all-optical switch, the switching threshold power is proportional to A_eff, so optimization of the nonlinear waveguide is equivalent to minimization of A_eff. Recent studies have shown that dielectric slot waveguides can confine optical energy far below the diffraction limit, with nonlinear effective areas considerably less than those attainable in total internal reflection waveguides. In this work, we instead consider the use of a gap plasmonic waveguide (GPW) for deep sub-wavelength optical confinement. Using finite element methods, we compare optimized slot waveguides with GPWs of identical geometry. We show that the GPW achieves a nonlinearity more than an order of magnitude superior to the corresponding dielectric slot waveguide, and that a further optimization of the GPW is possible.

Silver columnar thin films (CTFs) are grown by thermal evaporation combined with oblique-angle-deposition technique (OAD). The optical and structural properties of metal silver films are related to their microstructures. The surface roughness, produced during the deposition of silver metal, enables the plasmon surface wave coupling the electromagnetic light. Properties, that are interesting for several applications are found. These properties are related to the shadowing effect, films thickness and localised surface-plasmon resonance. Fundamental results related to the transition from continuous, semi-continuous to discontinuous metal films are also presented.

We have studied epitaxial lateral overgrowth of p-type silicon by Liquid Phase Epitaxy (LPE) on n-type (111) silicon substrates from a Si/In melt. The substrate had a silicon dioxide mask with a set of parallel opening windows for seed lines which were aligned along a [211]direction. The growth parameters, morphology and electrical properties of the grown crystal were studied. Two single crystalline silicon strips were formed on one single seed line, one strip on either side of the seed line, demonstrating that silicon is more likely to deposit near the interface between the silicon and the oxide. All facets of the strips are {111} planes and therefore the bottom surface has a 4 degree angle with the substrate, providing convenience for the epitaxial layer to be peeled off from the substrate and used for potential photovoltaic applications. Monte Carlo random walk model is used to simulate the epitaxial growth of the mono-crystalline strips.

Organic thin film solar cells have been researched as a low-cost alternative in solar energy technologies, but they usually have lower light harvesting efficiency. In this manuscript, a nanostructured metal film (NMF) fabricated based on self-assembly techniques is studied as a way to enhance the light absorbance in the absorbing layer, by the excitation of localized surface plasmon resonance. Finite-difference time-domain computations shows a 7-fold enhancement to the light absorbance in a 10 nm poly(3-hexylthiophene) (P3HT) layer on the NMF comparing to on flat metal. This result shows the possibility of an organic solar cell with a very thin absorbing layer and yet having a high efficiency. The NMF is also advantageous in its mass-producibility. Preliminary experimental results are also included.

In this work, a new approach for optimizing organic photovoltaics using nanostructure arrays exhibiting surface plasmons is presented. Periodic nanohole arrays were fabricated on gold- and silver-coated flexible substrates, and were thereafter used as light transmitting anodes for solar cells. Transmission measurements on the plasmonic thin film made of gold and silver revealed enhanced transmission at specific wavelengths matching those of the photoactive polymer layer. Compared to the indium tin oxide-based photovoltaic cells, the plasmonic solar cells showed overall improvements in efficiency up to 4.8-fold for gold and 5.1-fold for the silver, respectively.

Triple-junction AlGaInP/InGaAs/Ge solar cells with embedded InAs quantum dots are presented, where typical samples obtain efficiencies of > 40% under AM1.5D illumination, over a range of concentrations of 2- to 800-suns (2 kW/m² to 800 kW/m²). Quantum efficiency measurements show that the embedded quantum dots improve the absorption of the middle subcell in the wavelength range of 900-940 nm, which in turn increases the overall operating current of the solar cell. These results are obtained with 1 cm² solar cells, and they demonstrate the solar cells' low series resistance, which and makes them ideal for the current generation in commercial concentrator systems. The thermal management and reliability of the solar cell and carrier is demonstrated by testing the experimental samples under flash (up to 1000-suns) solar simulator and continuous (up to 800-suns) solar simulator. Under continuous solar illumination, the solar cell temperature varies between ~Δ3°C at 260-suns linearly to ~Δ33°C at 784-suns when the solar cell is mounted with thermal paste, and ~Δ27°C at 264-suns linearly to ~Δ91°C at 785-suns when no thermal paste is used. The solar cells experience the expected shift in open circuit voltage and efficiency due to temperature, but otherwise operate normally for extended periods of time.

Cadmium telluride thin-film solar cells are now commercially available and are being widely deployed in terrestrial, photovoltaic, power plants. However, the price of electricity from such sources would be more competitive with conventionally generated electricity if the cell efficiency could be improved without compromising the generally low-cost nature of the fabrication process. Recognizing that laboratory cells appear to have reached an efficiency limit of about 16.5%, we propose to improve on this by adding a thin-film germanium cell in a monolithic, tandem arrangement. Here we report on simulations of the photovoltaic performance of this structure, and we indicate that an efficiency improvement in excess of 20% may be attainable.

The current density-voltage characteristic of an AlGaAs/AlGaAs tunnel junction is determined by taking a time-averaged measurement across the device. A tunnelling peak of ~950A/cm² is recorded by this method. Measurements of the tunnelling peak and valley currents by the time averaging method are obscured due to the unstable nature of the negative differential resistance region of the current density-voltage characteristic. This AlGaAs/AlGaAs tunnel junction is then biased inside the negative differential resistance region of the current density-voltage characteristic, causing the current and the voltage to oscillate between the peak and the valley. The current and voltage oscillations are measured over time and then currents and voltages corresponding to the same time stamps are plotted against each other to form a timedependent curve from which a tunnelling peak of a value larger than 1100A/cm² is determined. The peak determined by this method is 11-20% larger than previously determined using the time averaged measurement. An AlGaAs/InGaP tunnel junction having no negative differential resistance region is also presented.

InAs quantum dots in a GaAs matrix are studied. Those quantum dots are used in applications to enhance the overall efficiency of multi-junction solar cells beyond 40%. Photoluminescence measurements at 77 K using a 532 nm laser have been performed on an epitaxially grown structure of self-assembled InAs quantum dots in a GaAs matrix upon a Ge substrate, where three energy levels are determined at E_n=0=1.01 eV, E_n=1=1.07 eV and E_n=2=1.13 eV. Theoretical calculations of the energy levels determine the quantum dots to be 7 nm high and have a 37 nm base diameter, which is close to atomic force microscopy measurements performed on the samples. Intensity dependant photoluminescence measurements reveal the saturation of the first excited energy level at 5×10⁶ W/m². A general model for the saturation of the first quantum dot excited energy level is then developed. This saturation model is applied to the AM1.5D solar spectrum at 297 K to determine the concentration of solar energy needed to saturate the first excited energy level within a multi-junction solar cell. Saturation was determined to be at ~1.56×10⁴ suns (where 1 sun = 1000 W/m²). Since current solar concentrations are between 500-1000 suns concentration, the saturation of such quantum dots will not occur.

Wave-optics analysis is performed to investigate the benefits of integrating photonic crystals into micromorph cells. Specifically, we theoretically investigate two novel micromorph cells which integrate photonic crystals and compare their optical performance with that of conventional micromorph cells. In the first innovative micromorph cell configuration the intermediate reflector is a selectively transparent and conducting photonic crystal (STCPC). In the second micromorph cell its bottom μc-Si:H cell is structured in the form of an inverted opal. Our results show that with the AM1.5 solar spectrum at normal incidence the current generated in a conventional micromorph cell is increased from 12.1 mA/cm2 to 13.0 mA/cm2 when the bottom μc-Si:H cell is structured in the form of an inverted opal. However, the current generated in the micromorph cell can be increased to as much as 13.7 mA/cm2 when an STCPC is utilized as the intermediate reflector. Furthermore, the thickness of the μc-Si:H opal must be relatively large in order to absorb a sufficient amount of the solar irradiance, which is expected to degrade the electrical performance of the device. In contrast, our results suggest that STCPC intermediate reflectors are a viable technology that could potentially enhance the performance of micromorph cells.

Back Amorphous-Crystalline Silicon Heterojunction (BACH)1 solar cell can be fabricated using low temperature processes while integrating high efficiency features of heterojunction silicon solar cells and back-contact homojunction solar cells. This article presents a two-dimensional modeling study of the BACH cell concept. A parametric study of the BACH cell has been carried out using Sentaurus after benchmarking the software. A detailed model describing the optical generation is defined. Solar cell efficiency of 24.4% is obtained for AM 1.5 global spectrum with V_OC of greater than 720 mV and J_SC exceeding 40 mA/cm², considering realistic surface passivation quality and other dominant recombination processes.

The first solar cells using in-situ doped polysilicon contacts to form both emitter and back surface field (BSF) regions are reported. The use of polysilicon contacts permits extremely low thermal budget processing (maximum 850°C 5 sec for dopant activation), preserving substrate properties. The effectiveness of the BSF is best seen with backside illumination, where the photocurrent under natural sunlight is found to be over 30% of that obtained with frontside illumination, even though the substrate thickness is comparable to the minority carrier diffusion length. The applicability of the structure to bifacial operation is considered.

Simulations of Al_xGa_1-xAs/GaAs (x = 0.3) and Al_xGa_1-xAs/Al_xGa_1-xAs (x < 0.2) tunnel junction J-V characteristics are studied for integration into a 2D metamorphic multi-junction solar cell model composed of GaInP/GaAs/InGaAs. A comparison of the simulated solar cell J-V characteristics under AM1.5D spectrum is discussed in terms of short circuit current density (J_sc), open circuit voltage (V_OC), fill factor (FF) and efficiency (η) for both tunnel junction designs. Using Al_xGa_1-xAs/GaAs top and bottom tunnel junctions, the metamorphic solar cell obtained values of J_sc = 12.3 mA/cm², V_OC = 2.56 V, FF = 0.81 and η = 25.5%, whereas the solar cell with the Al_xGa_1-xAs/Al_xGa_1-xAs top and bottom tunnel junctions reported values of J_sc = 12.3 mA/cm², V_OC = 2.22 V, FF = 0.81 and η = 22.1%. At open circuit voltage, energy band diagrams show minimal curvature in the electron and hole quasi Fermi levels; furthermore, the difference between the top sub-cell electron quasi Fermi level and the bottom sub-cell hole quasi Fermi level is shown to be equal to qV_OC for both designs. The energy band diagram of the complete structure is compared for both tunnel junction designs, showing the difference in energy levels that correspond to the difference in measured open circuit voltage. The observed decrease in open circuit voltage was ΔV_OC = 0.34 V, which was attributed to the difference in tunnel junction material band parameters such as bandgap, valence and conduction band offsets at heterojunctions and Fermi level degeneracies due to doping concentration differences.

Hybrid organic/inorganic photovoltaic devices have recently emerged as a possible solution to the stability, charge transfer and mobility issues that have been limiting the lifetimes and efficiencies of the organic solar cells. The purpose of the project presented here is to assess the potential of a new hybrid metal-insulator-semiconductor (MIS) photovoltaic device design developed at Carleton University. The silicon substrate is nanostructured with a wet chemical etch resulting in about 1:1 aspect ratio structures of roughly 300nm in size. The interface is passivated with a thin dielectric tunnel barrier of alumina or silica. A layer of transparent conducting polymer, Poly(3,4-ethylenedioxythiophene) (PEDOT), is added through in-situ polymerization. The structure is then completed with a printed silver/polymer composite collection electrode. The electrical current-voltage (I-V) and capacitance-voltage(C-V) characteristics along with the effect of nanostructuring the substrate on the performance of such a solar cell is explored by comparison with unstructured devices. The C-V and I-V measurements are used to estimate changes in the effective device junction due to the structuring. The quality of the insulator layer as well as its optimal thickness are studied. The fabricated structures show photovoltaic behavior with the structuring yielding a significant increase in efficiency. The test structures show promise for the use in photovoltaics and further optimization of such a structure may yield fruitful results in solar applications.

An easy process was developed to fabricate TiO₂ nanowires sensitized with CdS and CdTeS quantum dots (QDs). CdS and CdTeS nanoparticles were grown in situ by a colloidal method. No pretreatment of the TiO₂ nanowires was required prior to nanoparticle generation. Functionalization of CdS and CdTeS QDs was not needed to anchor these nanoparticles to TiO₂ surface. The resulting nanostructure assembly and composition was confirmed by transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS). The electronic structure of TiO₂ nanowires was preserved as indicated by Raman spectroscopy. The sensitization of the TiO₂ nanowires by the QDs was confirmed by photocurrent measurements. This study allows the generation of strongly anchored CdS and CdTeS QDs on TiO₂ nanowires surface without the introduction of a linker molecule which presence decreases the electron injection efficiency.

Thermoelectric power, Hall coefficient and resistivity measurements were carried out on material cut from monocrystalline ingots of CuInSe₂. The ingots were grown using a vertical-Bridgman procedure, whereby Cu, In and Se were melted and directionally cooled within a sealed quartz ampoule. When stoichiometric proportions of the starting elements were used, the material was always p-type, with hole concentrations of the order of 10¹⁷-10¹⁸ cm^-3. However, the incorporation of a sufficient amount of sodium (0.3 at. %) into the melt was seen to result in n-type material, with electron concentrations of the order of 10¹⁶. This conversion from p to n was hindered by the inclusion Se above stoichiometry into the ampoule, and more Na was required for the material to change type. The mobility of the p-type samples, with low sodium additions (0-0.2 at. %), was on average 17 cm²V^-1s^-1, and was seen to be higher for material grown from melts containing excess Se, corresponding to the chemical formula CuInSe_2.2, than from stoichiometry. SEM/EDX (Scanning electron microscope / Energy-dispersive X-ray spectroscopy) analysis of the ingots after growth indicated no sodium residing within the interior of the bulk material, but a significant amount was found on the exterior surface in the case of an ingot grown with CuInSe_2.05 and 5 at. % Na. Various deposits found within the ampoules after growth were analyzed, including a copper-rich precipitate found only in ampoules which included a high concentration of Na and a low concentration of excess Se, resulting in n-type material.

This paper presents some of the research activities on building-integrated photovoltaic (BIPV) systems developed by the Solar and Daylighting Laboratory at Concordia University. BIPV systems offer considerable advantages as compared to stand-alone PV installations. For example, BIPV systems can play a role as essential components of the building envelope. BIPV systems operate as distributed power generators using the most widely available renewable source. Since BIPV systems do not require additional space, they are especially appropriate for urban environments. BIPV/Thermal (BIPV/T) systems may use exterior air to extract useful heat from the PV panels, cooling them and thereby improving their electric performance. The recovered thermal energy can then be used for space heating and domestic hot water (DHW) heating, supporting the utilization of BIVP/T as an appropriate technology for cold climates. BIPV and BIPV/T systems are the subject of several ongoing research and demonstration projects (in both residential and commercial buildings) led by Concordia University. The concept of integrated building design and operation is at the centre of these efforts: BIPV and BIPV/T systems must be treated as part of a comprehensive strategy taking into account energy conservation measures, passive solar design, efficient lighting and HVAC systems, and integration of other renewable energy systems (solar thermal, heat pumps, etc.). Concordia Solar Laboratory performs fundamental research on heat transfer and modeling of BIPV/T systems, numerical and experimental investigations on BIPV and BIPV/T in building energy systems and non-conventional applications (building-attached greenhouses), and the design and optimization of buildings and communities.

Multi-junction solar cells are devices composed of many layers of diverse materials with varying physical properties. Understanding the operation and design of such devices is challenging because of this diversity. To support these efforts, the computer modeling and simulation study is an essential tool. The principles of two main steps in a study, conceptual modeling and simulation modeling, are presented to show their importance in dealing with many materials and their properties. Conceptual modeling deals with establishing physical mathematical models representing the physics of material behaviour. The physical models have parameters whose values are dependent on the material; often parameter models are required to establish the parameter values. Simulation models are the representation of these conceptual models within software. Examining the Sentaurus software products shows that many conceptual models are integrated within the software; proper selection of physical models must be made and parameters defined for the materials used in the device being studied. When considering new materials for improving solar cell design, typically only parameters are set for existing physical models, but it is sometimes necessary to revise the models and modify such software. Band gap modeling of dilute nitrides, in particular InGaAsN demonstrates the importance of considering conceptual modeling and how software must be capable of adapting new simulation physical and parameter models.

Amorphous silicon-crystalline silicon heterojunctions were prepared using the DC saddle-field plasma enhanced chemical vapour deposition (DCSF-PECVD) technique followed by RF magnetron sputtering of an indium tin oxide (ITO) layer on the nano-thin amorphous film. Depth dependent time of flight secondary ion mass spectrometry (ToF-SIMS) analysis was carried out in order to examine the compositional influence of the sputtered ITO on the underlying amorphous silicon layers. Three samples were analyzed: one, as deposited, a-Si:H/c-Si heterojunction; two, ITO covered a-Si:H/c-Si heterojunction; and three, similar to sample two but now dipped in 10% HCl in order to etch the ITO prior to SIMS analysis. The pre-treatment of the third sample was done to de-couple potential SIMS sputtering-induced implantation of indium, tin, and oxygen in the underlying silicon layers. SIMS analysis shows indium, tin, and oxygen below the surface of the silicon in both the etched and as-deposited samples. AFM analysis of all the samples was also done, indicating that the ITO surface has a high degree of roughness, which could make uniform etching more difficult and could potentially lead to small residual ITO spots on the surface, creating or enhancing the appearance of mixing in the SIMS results for the etched sample.

In this article, we present a novel low temperature fabrication process using focused ion beam (FIB) for CMOS compatible photovoltaic cells. Photovoltaic cells are used for scavenging light energy to power CMOS devices and integrating photovoltaic cells on the same CMOS die for self-powering integrated circuits is highly desirable. Integrating such photovoltaic cells as a post-process of the pre-fabricated CMOS die will avoid many complex assembling steps as well as unpredictable interconnect problems. To demonstrate the proof of concept, we have developed low temperature fabrication process to avoid damage to the pre-fabricated CMOS dies. We are also going to introduce focused-ion beam (FIB) as an implantation source to dope silicon wafer for desired concentration. The successfully fabricated demonstration device is tested using a solar simulator. The results obtained from the experimental data indicate that the demonstration device works perfectly as a photovoltaic cell rather with very low efficiency (0.004%).

The thermal performances of multi-junction solar cells, mounted on receivers, are studied to determine the change in device efficiency with respect to sunlight concentration under continuous illumination. Experimental characterization of the device was performed by measuring the solar cell current-voltage curve using both flash and continuous-illumination solar simulators. We are able to extract the change in efficiency and open circuit voltage with respect to the change in concentration from experiments with respect to the application of thermal paste between the receiver and the heat exchange. We show the efficiency linearly decrease at a rate of -0.0094%/°C (no paste) and -0.0043%/°C (paste). We used the calibrated numerical model to determine the solar cell temperature and incorporate the corresponding efficiency when scaled up to 2000 sun concentrations under continuous illumination.

The optical and electrical properties of bulk polymer RR-P3HT (Regio-Regular Poly(3-hexylthiophène-2,5- diyl):PCBM (Methanofullerene Phenyl-C61-Butyric-Acid-Methyl-Ester) heterojunction incorporating single wall carbon nanotubes (SWCNTs) have been already reported by a number of research groups. We investigated a new approach to functionalize CarboLex single wall carbon nanotubes (SWCNTs-e) for increasing their dispersion in various solvents. The addition of SWCNTs-e in the matrix of P3HT:PCBM improves the photovoltaic (PV) characteristics. Results show that the photovoltaic parameters depend on the concentration of SWCNTs-e. The incorporation of low concentrations of SWCNTs-e in the photoactive layer increases the current density J_sc before annealing. We attribute the improved performance to partial crystallisation of the RR-P3HT. As revealed by XRD studies and confirmed by the absorbance spectra which exhibit the characteristic 600 nm shoulder. Interestingly, we observed also that doping the P3HT:PCBM system with the functionalized SWCNTs increases V_oc from 0.583 to 0.744 V.