Acousto-optical imaging using a powerful long pulse laser
Author(s):
Guy Rousseau;
Alain Blouin;
Jean-Pierre Monchalin
Show Abstract
Acousto-optical imaging is an emerging biodiagnostic technique which provides an optical spectroscopic signature and a
spatial localization of an optically absorbing target embedded in a strongly scattering medium. The transverse resolution
of the technique is determined by the lateral extent of ultrasound beam focal zone while the axial resolution is obtained
by using short ultrasound pulses. Although very promising for medical diagnostic, the practical application of this
technique is presently limited by its poor sensitivity. Moreover, any method to enhance the signal-to-noise ratio must
obviously satisfy the in vivo safety limits regarding the acceptable power level of both the ultrasonic pressure wave and
the laser beam. In this paper, we propose to improve the sensitivity by using a pulsed single-frequency laser source to
raise the optical peak power applied to the scattering medium and to collect more ultrasonically tagged photons. Such a
laser source also allows illuminating the tissues mainly during the transit time of the ultrasonic wave to maintain the
average optical power below the maximum permissible exposure. In our experiment, a single-frequency Nd:YAG laser
emitting 500-μs pulses with a peak power superior to 100 W was used. Photons were tagged in few-cm thick optical
phantoms with tone bursts generated by an ultrasonic transducer. Tagged photons were detected with a GaAs
photorefractive interferometer characterized by a large optical etendue to process simultaneously a large number of
speckle grains. When pumped by high intensity laser pulses, such an interferometer also provides the fast response time
essential to obtain an apparatus insensitive to the speckle decorrelation due to mechanical vibrations or tissues
movements. The use of a powerful long pulse laser appears promising to enhance the signal level in ultrasound
modulated optical imaging. When combined with a photorefractive interferometer of large optical etendue, such a source
could allow obtaining both the sensitivity and the fast response time necessary for biodiagnostic applications.
First experimental study of self-forming synthetic lipids by confocal laser tweezers Raman spectroscopy
Author(s):
Rajan K. Bista;
Reinhard F. Bruch
Show Abstract
We present the first experimental study of self-forming synthetic lipids, trademarked as QuSomesTM, using Raman
spectroscopy in the spectral range of 500 to 3100 cm-1. Raman spectra of these new artificial lipids composed of 1,2-
dimyristoyl-rac-glycerol-3-dodecaethylene glycol (GDM-12) and 1,2-dioleoyl-rac-glycerol-3-dodecaethylene glycol
(GDO-12) have been obtained in pure form and in aqueous suspensions with Phosphate Buffered Saline (PBS) by using
an inverted confocal laser-tweezers-Raman-microscopy system. This spectrometer works with an 80 mW diode-pumped
solid-state laser, operating at a wavelength of 785 nm in the TEM00 mode. The laser is used both for optical trapping and
Raman excitation. The two amphiphiles considered in this study, differ in their hydrophobic chain length and contain
similar units of hydrophilic polyethylene glycol (PEG) head groups. Such synthetic PEG coated lipids exist in liquid
form at room temperature and spontaneously form liposomes (nano type vesicles) upon hydration. In this work, we have
focused on the band assignments for the spectra of single QuSomesTM nano particles in pure form and in aqueous media
acquired by means of Raman spectroscopy. In particular, we have found that the most prominent peaks in the studied
spectral region are dominated by vibrational modes arising from C-C and C-H bonds. Furthermore, we have noticed
that some of the distinct peaks observed below 1800 cm-1 in pure sample are preserved in aqueous environment. These
retained intense bands are located at 1449, 1128, 1079, and 1065 cm-1. This effect might be due to the strong chain-chain
interactions, because the chains have to orient themselves and become tightly packed in the vesicles wall rather than
adopt random orientations in bulk. This technique has proven to be an excellent tool to establish the fingerprint region
revealing the molecular structure and conformation of QuSomesTM particles. The Raman spectroscopic data of these
novel lipids and its vesicles formed in suspensions confirm high stability and are therefore considered as potential
candidate for varieties of future applications including lipid based novel substances and drug delivery systems.
Temperature-controlled Raman microscopy to study the phase behavior of synthetic PEGylated lipids and nanovesicles
Author(s):
Rajan K. Bista;
Reinhard F. Bruch;
Aaron M. Covington;
Alexander Sorger;
Thoralf Gerstmann;
Alexander Otto
Show Abstract
The study of phase transitions in lipids is important to understand various phenomena such as conformational order,
trans-membrane diffusion, vesicle formation and fusion as well as drug-and protein-membrane interactions. Several
techniques, including Raman spectroscopy, have previously been employed to investigate the phase behaviour of lipids.
In this work, temperature-controlled Raman microscopy has been used to detect and analyze the phase transitions in two
newly developed synthetic PEGylated lipids trademarked as QuSomesTM and its nanovesicles in phosphate buffered
saline (PBS) suspension. The amphiphiles considered in this study differ in their hydrophobic chain length and contain
different units of polyethylene glycol (PEG) hydrophilic head groups. Raman spectra of these new artificial lipids and its
nanovesicles have been recorded in the spectral range of 500-3100 cm-1 by using a temperature-controlled sample holder
attached to a Raman microscope. The gel to liquid-crystalline phase transitions of the sample lipids, composed of pure
1,2-dimyristoyl-rac-glycerol-3-dodecaethylene glycol (GDM-12) and 1,2-distearoyl-rac-glycerol-3-triicosaethylene
glycol (GDS-23), have been detected by examining the changes in Raman spectra of the lipids caused by temperature
variation. In the liquid phase both of the studied lipids spontaneously form liposomes (nanovesicles) upon hydration. In
this study, we have demonstrated the efficacy of the temperature-controlled Raman microscope system to reveal the
main phase transition temperature (Tm) profiles of our sample lipids and its nanovesicles in PBS suspension. The phase
changes are detected by plotting peak intensity ratios in the C-H stretching region (~I2935/I2883) versus temperature. These
ratios correlate with lateral or inter-chain interactions as well as intra-molecular interactions. In particular, we have
found that phase transitions occur at a temperature of approximately 5.2°C and 21.2°C for pure GDM-12 and GDS-23,
respectively. However, the phase transition temperature becomes significantly higher for lipid nanovesicles formed in
aqueous suspensions. Such information about these PEG coated lipids might find applications in various studies
including the development of lipid based novel substances and drug delivery systems.
A new model for the anterior corneal surface using higher-order aspheric surfaces and variable eccentricity
Author(s):
Marco A. Rosales;
M. Montserrat Juárez-Aubry;
E. López-Olazagasti;
Jorge Ibarra;
Eduardo Tepichín
Show Abstract
Contact lenses manufacturers and ophthalmologists who perform laser surgery to correct visual problems depend on an
accurate model of the anterior corneal surface. Several models have been suggested in the past, going from Gullstrand's
initial idea to the aspheric profiles and to Bonnet's profile based on anatomical data. Clinical evidence shows, however,
that the anterior corneal surface is characterized by a variable eccentricity, contrary to the hypothesis on which the
current models are based. We present, in this work, a new model for the anterior corneal surface in terms of higher-order
aspheric surfaces in which the eccentricity at a given point of the cornea is a continuous function of its distance to the
optical axis. We also establish the conditions under which the different conic and Bonnet's profiles are recovered from
our model. Finally, we present our preliminary results using this model.
Fabrication and characterization of optical phantoms
Author(s):
Fatma-Zohra Bioud;
Yves Bérubé-Lauzière
Show Abstract
We discuss the fabrication of optical phantoms that will serve as calibration and test standards for a diffuse optical tomographic system developed in our laboratory. For the fabrication of a phantom's matrix, two materials are compared: polyester and epoxy resins. We investigate the capacity to use either of these two resins in the fabrication of a phantom's matrix with different shapes and thicknesses. For the absorbing agent we use India ink and for diffusing agent we choose a fine titanium dioxide (TiO2) powder. We test a collimated light measurements set-up to extract: the absorption coefficient μa of a purely absorbing medium, and the scattering coefficient μs of a purely diffusing medium. We also compare the way μa and μs add in a solution of absorbing and diffusing media.
Time-domain 3D localization of fluorescent inclusions in a thick scattering medium
Author(s):
Julien Pichette;
Éric Lapointe;
Yves Bérubé-Lauzière
Show Abstract
We introduce an improved approach in the 3D localization of discrete fluorescent inclusions in a thick scattering
medium. Previously our approach provided accurate localization of a single inclusion, showing the potential for
direct time-of-flight fluorescence diffuse optical tomography. Here, we localize various combinations of multiple
fluorescent inclusions. We resort to time-domain (TD) detection of emitted fluorescence pulses after short pulse
laser excitation. Our approach relies on a signal processing technique, dubbed numerical constant fraction
discrimination (NCFD), for extracting in a stable manner the arrival time of early photons emitted by one or
many fluorescent inclusions from measured time-of-flight (TOF) distributions. Our experimental set-up allows
multi-view tomographic optical TD measurements over 360 degrees without contact with the medium. It uses an ultra-short pulse laser and ultra-fast time-correlated single photon counting (TCSPC) detection. Fluorescence time point-spread functions (FTPSFs) are acquired all around the phantom after laser excitation. From measured
FTPSFs, the arrival time of a fluorescent wavefront at a detector position is extracted with our NCFD technique.
Indocyanine green (ICG; absorption peak = 780nm, emission peak = 830nm) is used for the inclusions. Various
experiments were conducted with this set-up in a stepwise fashion. First, single inclusion experiments are
presented to provide background information. Second, we present results using two inclusions in a plane. Then,
we move on with two inclusions located in different planes. Finally, we show results with a plurality of inclusions
(>2) distributed at arbitrary positions in the medium. Using an algorithm we have developed and tested on the
acquired data, we successfully achieve to locate the inclusions. Here, results are obtained for discrete inclusions.
In a close future, we expect to extend our method to continuous fluorescence distributions.
Three-dimensional spatial localization of thin fluorophore-filled capillaries in thick scattering media
Author(s):
Johanne Desrochers;
Patrick Vermette;
Réjean Fontaine;
Yves Bérubé-Lauzière
Show Abstract
Fluorescence optical diffuse tomography (fDOT) is of much interest in molecular imaging to retrieve information
from fluorescence signals emitted from specifically targeted bioprocesses deep within living tissues. An exciting
application of fDOT is in the growing field of tissue engineering, where 3D non-invasive imaging techniques are
required to ultimately grow 3D engineered tissues. Via appropriate labelling strategies and fluorescent probes,
fDOT has the potential to monitor culture environment and cells viability non-destructively directly within
the bioreactor environment where tissues are to be grown. Our ultimate objective is to image the formation
of blood vessels in bioreactor conditions. Herein, we use a non-contact setup for small animal fDOT imaging
designed for 3D light collection around the sample. We previously presented a time of flight approach using a
numerical constant fraction discrimination technique to assign an early photons arrival time to every fluorescence
time point-spread function collected around the sample. Towards bioreactor in-situ imaging, we have shown the
capability of our approach to localize a fluorophore-filled 500 μm capillary immersed coaxially in a cylindrically
shaped bioreactor phantom containing an absorbing/scattering medium representative of experiments on real
tissue cultures. Here, we go one step further, and present results for the 3D localization of thinner indocyanine
green labelled capillaries (250 μm and 360 μm inner diameter) immersed in the same phantom conditions and
geometry but with different spatial configurations (10° and 30° capillary inclination).
3x3 MZI with unbalanced differential detection for full range swept-source optical coherence tomography
Author(s):
Youxin Mao;
Costel Flueraru;
Sherif Sherif;
Shoude Chang
Show Abstract
Quadrature interferometry based on 3×3 fiber couplers could be used to double the effective imaging depth in Swept-
Source Optical Coherence Tomography. This is due to its ability to suppress the complex conjugate artifact naturally.
We present theoretical and experimental results for a 3×3 Mach-Zehnder interferometer using a new unbalanced
differential optical detection method. The new interferometer provides simultaneous access to complementary phase
components of the complex interferometric signal. No calculations by trigonometric relationships are needed. We demonstrate a complex conjugate artifact suppression of 27 dB obtained in a swept-source optical coherence tomography using our unbalanced differential detection. We show that our unbalanced differential detection has increased the signal to- noise ratio by at least 4 dB compared to the commonly used balanced detection technique. This is due to better utilization of optical power.
Fiber probes used in optical coherence tomography
Author(s):
Youxin Mao;
Shoude Chang;
Sherif Sherif;
Costel Flueraru
Show Abstract
Quality and parameters of probing optical beams are extremely important in optical coherence tomography (OCT)
systems both for image quality and light coupling efficiency considerations. For example, the shape, size, focal position,
and focal range of such beams could have a great impact on the lateral resolution, penetration depth, and signal-to-noise
ratio of the image. We present a design, construction and characterization of different variations of GRIN and ball fiber
lenses, for ultra-small OCT probes. Those fiber probes are made of a single mode fiber and a GRIN or ball fiber lens
with or without a fiber spacer between them. The probe diameters are smaller than 0.3 mm. We discuss design methods,
fabrication techniques, and measured performance compared with modeling results. We demonstrate swept-source OCT
images with different fiber probes.
High-resolution reflectometer for monitoring of biological samples
Author(s):
Liqiu Men;
Ping Lu;
Qiying Chen
Show Abstract
High-resolution optical low-coherence reflectometry is applied to monitor biological samples. It has been found that the
reflectivity of aged cow's milk is significantly lower than that of the fresh milk with a difference of 5.35dB. During the
process of heating the fresh milk at a constant temperature of 80°C, the reflectivity of the milk gradually decreases with
the increase of the heating duration. The technique is proved to be effective in monitoring the change in the refractive
index of the sample.
Optical design considerations when imaging the fundus with an adaptive optics correction
Author(s):
Weiwei Wang;
Melanie C. W. Campbell;
Marsha L. Kisilak;
Shelley R. Boyd
Show Abstract
Adaptive Optics (AO) technology has been used in confocal scanning laser ophthalmoscopes (CSLO) which are
analogous to confocal scanning laser microscopes (CSLM) with advantages of real-time imaging, increased image
contrast, a resistance to image degradation by scattered light, and improved optical sectioning. With AO, the instrumenteye
system can have low enough aberrations for the optical quality to be limited primarily by diffraction. Diffraction-limited,
high resolution imaging would be beneficial in the understanding and early detection of eye diseases such as
diabetic retinopathy. However, to maintain diffraction-limited imaging, sufficient pixel sampling over the field of view
is required, resulting in the need for increased data acquisition rates for larger fields. Imaging over smaller fields may be
a disadvantage with clinical subjects because of fixation instability and the need to examine larger areas of the retina.
Reduction in field size also reduces the amount of light sampled per pixel, increasing photon noise. For these reasons,
we considered an instrument design with a larger field of view. When choosing scanners to be used in an AOCSLO, the
ideal frame rate should be above the flicker fusion rate for the human observer and would also allow user control of
targets projected onto the retina. In our AOCSLO design, we have studied the tradeoffs between field size, frame rate
and factors affecting resolution. We will outline optical approaches to overcome some of these tradeoffs and still allow
detection of the earliest changes in the fundus in diabetic retinopathy.
First experimental demonstration of a Fresnel axicon
Author(s):
Kevin Gourley;
Ilya Golub;
Brahim Chebbi
Show Abstract
Nondiffracting or Bessel beams find applications in diverse fields like optical tweezers/spanners, microscopy, super-resolution
and optical coherence tomography. An axicon, energywise, is the most efficient method for generating a
diffraction-free beam. Yet one of the impediments to wide use of these optical elements is the cost related to the way
they are manufactured. Recently we proposed a novel optical element - Fresnel axicon (Opt. Lett. 31, 1890, 2006) -
which enables to overcome this problem while providing advantages such as compactness and very low bulk absorption.
Prototypes of the Fresnel axicon were manufactured. In the present work we report the first experimental results
characterising the optical properties of this novel device, which bridges the gap between diffractive axicons and their
refractive counterparts.
Spatial-domain optical coherence tomography
Author(s):
L. Langevin;
D. Gay;
M. Piché
Show Abstract
Optical coherence tomography (OCT) is a non-invasive imaging technique invented in 1991 and allowing
the observation of biological tissues with millimeter depth of penetration and a few micrometer resolution. In the
standard time-domain OCT setup (TD-OCT), a broadband light source is used with a Michelson interferometer
where one of the mirrors is replaced by the sample (which is mechanically moved transversally during data
acquisition) while the other is axially vibrating. By analyzing the temporal signal at the exit of the interferometer, a
high resolution tomographic cut of the sample can be obtained. A number of new OCT setups have been proposed
since 1991 in order to improve the data acquisition speed. In particular, Fourier-domain OCT (FD-OCT) has allowed
in vivo observation of samples by eliminating the necessity of the axial motion of the reference mirror in the setup.
We propose in this paper new OCT setups having the same potential without requiring numerical treatment of the
signal (as it is the case in FD-OCT). Because those setups are such that the axial information of the sample becomes
linearly distributed at different points of space in an interference pattern, we call them spatial-domain OCT setups
(SD-OCT). SD-OCT setups use a tilted mirror in a Michelson interferometer to produce an interference pattern
which is imaged on a CCD detector. The pattern contains all the information on the sample and is obtained without
mechanical motion or numerical treatment of the recorded signal. In order to validate the proposed scheme,
prototypes of the setups have been made in the laboratories of COPL at Laval University; biological samples such as
onion peels and phloem of trees have been tested in order to produce their tomographic images. Comparisons of
some of our results with those from a commercial setup with the same samples had notably confirmed the capacity
of ours prototypes to effectively image biological samples.
Taking control of the flagellar motor
Author(s):
Mathieu Gauthier;
Dany Truchon;
Simon Rainville
Show Abstract
Numerous types of bacteria swim in their environment by rotating long helical filaments. At the base of each
filament is a tiny rotary motor called the bacterial flagellar motor. A lot is already known about the structure,
assembly and function of this splendid molecular machine of nanoscopic dimensions. Nevertheless many fundamental
questions remain open and the study of the flagellar motor is a very exciting area of current research. We
are developing an in vitro assay to enable studies of the bacterial flagellar motor in precisely controlled conditions
and to gain direct access to the inner components of the motor. We partly squeeze a filamentous E. coli bacterium
inside a micropipette, leaving a working flagellar motor outside. We then punch a hole through the cell
wall at the end of the bacterium located inside the micropipette using a brief train of ultrashort (~60 fs) laser
pulses. This enables us to control the rotation of the motor with an external voltage (for at least 15 minutes).
In parallel, new methods to monitor the speed of rotation of the motor in the low load (high speed) regime are
being developed using various nanoparticules.
Applications of Doppler optical coherence tomography based on zero-crossing detection to flow monitoring inside a stenosis phantom
Author(s):
L. Carrion;
Z. Xu;
R. Maciejko
Show Abstract
Most of the time, arterial stenoses caused by atherosclerosis, hardening of the artery walls, or buildup of fatty deposits
prevent the blood from flowing normally. Blood flow characteristics in the vicinity of a stenosis are therefore very
important since the restriction may accelerate fatty deposits and thus quickly clog the artery. Doppler Optical Coherence
Tomography (DOCT) is a biomedical technique that allows simultaneous structural imaging and flow monitoring inside
biological tissues and materials with spatial resolution at least one order of magnitude better than ultrasound. This study
deals with the application of a Near Infrared DOCT system for imaging and monitoring of liquid flow inside a stenosis phantom inserted in a glass tube. For the measurement of the Doppler frequency, we use a numerical method based on the detection of the zero-crossing points of the OCT signal.
Two-species microparticle detection in optofluidic biochips with polymeric waveguides
Author(s):
H. Hosseinkhannazer;
L. W. Kostiuk;
J. N. McMullin
Show Abstract
The fabrication and experimental testing of polydimethylsiloxane (PDMS) optofluidic biochips with integrated solidcore
polyepoxyacrylate (PEA). optical waveguides is described. The biochips were replicated from silicon masters made
by 50-μm-deep reactive ion etching. Each biochip contained three 70-μm-wide solid-core waveguides focused on the
middle section of a 50-μm-wide, Y-shaped, microchannel. Electroosmotic flow with a voltage range of 50 to 300 volts
was used to drive fluorescent beads in the microfluidic channel. Using two excitation lasers at 532nm and 635nm with
distinct modulation frequencies, two species of microparticles with different fluorophores were identified by capturing
the fluorescence in a photomultiplier tube and analyzing the signal with a windowed Fourier transform analysis technique.
High resolution imaging with TM01 laser beams
Author(s):
Harold Dehez;
Michel Piché;
Yves De Koninck
Show Abstract
We present two optical systems that can transform a Gaussian beam into the lowest-order transverse magnetic laser
beam (the so-called TM01 laser beam). When a TM01 laser beam is focused by an objective with a high numerical aperture (NA > 0.9), theory predicts the appearance of a bright central feature at focus; the width of this feature is
smaller than that of the focal spot obtained with a Gaussian beam [1,2]. Our goal is to improve the lateral resolution of
two-photon microscopy when a TM01 laser beam is used.
Optical simulation, design, and optimization of a microchip-based flow cytometer
Author(s):
Benjamin R. Watts;
Thomas M. Kowpak;
Zhiyi Zhang;
Chang-Qing Xu;
Shiping Zhu
Show Abstract
The aim of this paper is to improve the functionality and efficiency of a microfluidic device by optically
simulating all of the components of the device and then identifying and optimizing the areas of the device
where the optics and the microfluidic components overlap. Design of the device will incorporate current
advanced methods, such as a state-of-the-art one-shot manufacturing processand noise reduction techniques
utilizing 8 parallel waveguides. A suitable material to build this device is the polymer SU-8, which has a
refractive index of 1.56 while borofloat glass, refractive index of 1.47, is used as a substrate, and an optical
adhesive (Norland Optical Adhesive 74, index of 1.52) is used to seal the device (and serve as the
waveguide cladding) by filling the gap in between waveguides reducing scattering losses and confining
higher modes. As such, simulations take into account all these parameters. Design of a photomask will
take into account three main sources of loss due to the integration of optics and microfluidics: wall
thickness, channel thickness, and input angle. Simulations have yielded behaviours and values for these
parameters. Wall thickness should be limited to 200um thick which will yield a -5.54dB attenuation (-
2.77dB at the particle) on the input (due to high angular propagation of higher order modes). Input angle of
the waveguides (which is crucial to the elimination of signal noise on the output) has been found to reduce
output signal noise to -9.60dB at an input angle of 74 degrees to the channel.
All-fiber laser beam shaping at 1.0 μm wavelength region in a single-mode fiber
Author(s):
Xijia Gu;
Waleed Mohammed;
Li Qian;
Peter W. E. Smith
Show Abstract
Laser beam shaping is an important subject in industrial and medical applications of lasers since different applications
may require different laser intensity distributions. Recently we demonstrated successfully an all-fiber laser beam shaping
device that could transform a Gaussian shaped laser beam into a uniform or ring-shaped beam in 1.5 μm wavelength
region. In this paper we present the work of the beam shaping in 1.0 μm wavelength region to make it compatible to Yb-doped
high power fiber laser. The device uses a long-period grating to couple a portion of core-mode, LP01 into a low-order
mth-radial cladding mode LP0m. Interference of the two modes could reduce field at the centre and enhance the field
in the first or second ring of the cladding mode to transform the Gaussian-shaped laser beam to an intensity uniform
beam. The design parameters that affect the beam shaping will be discussed and the results of the interference from two
cladding modes, LP03 and LP04 will be presented.
Optical low-coherence reflectometry for characterization of specialty fibers and photonic crystal waveguides
Author(s):
Yves Jaouën;
Renaud Gabet;
Phillipe Hamel
Show Abstract
The emergence of new fibers families induces considerable requirements in terms of characterization and metrology such
as group delay, chromatic dispersion, birefringence, bending losses, etc. Unlike classical characterization techniques
such as the well-known phase shift method, optical low-coherence reflectometry (OLCR) technique requires only short
fiber samples (i.e. <50cm). Characterization results concerning different types of specialty fibers including erbium-doped
fibers, few-modes fibers, photonic crystal fibers will be presented. Unique dispersive properties of higher-order mode
fibers offer novel solutions for dispersion compensation and nonlinear effects management. OLCR can allow each
LP mode characterization without the requirement of mode converters. A new method, called "Time-wavelength
mapping," based on the process of the OLCR interferogram is demonstrated as a versatile method to determine
chromatic dispersion of each guided LP mode whatever their group index. Different characterization results concerning
photonic crystal fibers with guiding based on to the conventional total internal reflection principle - high index guiding - or photonic bandgap effect - low index guiding - will be presented. Finally, we show that the versatility and deep
physical insight of OLCR technique can play a key role in the study of photonic crystal waveguides in terms of structural
disorder, losses, group delay in highly dispersive region and emphasizes the unique role of this technique in the
understanding of their properties.
Multiwavelength self-pulsating fibre laser based on cascaded SPM spectral broadening and filtering
Author(s):
Martin Rochette;
Kai Sun;
Juan Hernández-Cordero;
Lawrence R. Chen
Show Abstract
We experimentally demonstrate the operation of a laser based on self-phase modulation followed by offset spectral
filtering. This laser has three operation modes: a continuous-wave mode, a self-pulsating mode where the laser self
ignites and produces pulses, and a pulse-buffering mode where no new pulse is formed from spontaneous emission noise
but only pulses already propagating or pulses injected in the laser cavity can be sustained. In the self-pulsating and
pulse-buffering modes, the laser is multi-wavelength and continuously tunable over the entire gain band of the
amplifiers. The output pulse width is quasi transform-limited with respect to the spectral-width of the filters used in the
cavity. Overall, this device provides a simple alternative to pulsed laser source and also represents a promising approach
for signal buffering.
Microwave signal generation using an erbium-doped external cavity laser
Author(s):
Howard Rideout;
Runnan Liu;
Joe Seregelyi;
Stéphane Paquet;
Raman Kashyap
Show Abstract
The increasing demand for broadband mobile communications has generated interest in exploring new frequency bands
and modifying network structures. In such systems, photonic technologies can bring both cost reduction as well as an
increase in performance, mainly due to the low-loss properties of optical fibers. An optical source capable of producing
tunable, high-quality microwave/mm-wave signals would be of great interest not only in such communications systems,
but in fiber sensors and numerous other applications as well.
One potentially cost-effective method to fabricate such a system is via optical heterodyning. In this approach, the
difficulties in generating a high-quality signal are two-fold. The first issue is in maintaining a specific frequency
difference (i.e. microwave signal) between the lasers for an extended period of time. The second is in narrowing the
inherent linewidth of the laser from the MHz values typically produced by conventional semiconductor lasers, down to
values practical for a communications system. Both of the above requirements are facilitated by the newly developed
doped-fiber, external cavity laser (DFECL), which offers relatively stable single-longitudinal-mode operation in addition
to narrow linewidth operation.
This paper will demonstrate frequency locking of a DFECL using a delay-line discriminator. The RF linewidth, initially
10-15MHz, is reduced to levels conducive to optical PLL locking. Optical power levels are approximately -3 dBm and
unamplified microwave power output levels are typically -35 dBm, depending on photodetector responsivity. Carrier-to-noise
ratios are generally 40-45 dB. The physical mechanisms underlying the observed laser dynamics are discussed,
including laser-to-fiber alignment and thermal fluctuations.
Development of fiber long period gratings for biological sensor applications
Author(s):
Olivier L'Hénaf;
Armen Zohrabyan;
Tigran Galstian
Show Abstract
We present a fiber long period grating based sensor for biological applications. Inscribed by
using point-by-point method, the LPG has a resonant wavelength close to the emission wavelength of
biological objects of interest. The part of the light, emitted from sensing area, is collected by both fiber core
and cladding, while the majority of light is coupled into the cladding. Back coupling of light of certain
wavelength can selectively be achieved from fiber's cladding to core thanks to the LPG. Such selective
back coupling allows the increase of efficiency of remote detection of biological objects of interest, using
excitation source and detector on the same side of the fiber.
Improving the mode profile circularity of microstructured optical fibers by using an Archimedean-like cladding structure
Author(s):
Antoine Proulx;
Steeve Morency;
Claude Paré
Show Abstract
We present a novel microstructured optical fiber (MOF) structure which consists of a 7-missing-holes core surrounded
by a cladding formed by an Archimedean-like lattice of air holes, as opposed to the standard MOF cladding structure
consisting of a triangular lattice. We demonstrate that this new cladding geometry can be achieved through the standard
stack-and-draw MOF fabrication method, the main difference being the fact that the circular capillaries commonly used
in conventional MOF are replaced by hexagonal canes comprising 7 air holes disposed in a centred hexagon (forming
the so-called A7 unit cells). The Archimedean-like lattice MOF (ALMOF) is particularly interesting by the fact that it
features a dodecagonal core, which is a shape much closer to a perfect circle than the hexagonally-shaped core
characteristic of the conventional 7-missing-holes triangular-lattice MOF. As a result, we show that the improved core
circularity of the ALMOF design leads to a significantly more circular fundamental mode profile, which can prove to be
quite interesting for specific applications where the circularity of the mode profile is critical, such as precision laser
micromachining for example.
A medium-power widely tunable single wavelength fiber laser
Author(s):
Gautam Das;
Jonas Valiunas
Show Abstract
The authors report a medium-power widely tunable single wavelength fiber laser. The laser wavelength was tuned from
1530 nm to 1575 nm. The gain medium consisted of a double-clad erbium-ytterbium codoped fiber. An un-pumped
elliptical core erbium-doped fiber was used as a saturable absorber inside the cavity to reduce the laser linewidth and
mode hopping. The output power of the laser at each lasing wavelength was more than 100 mW. The linewidth of the
laser was 8 MHz, measured using a scanning Fabry-Perot spectrum analyzer of resolution 6.5 MHz. The laser was stable
at room temperature with an intensity fluctuation of less than 0.2 dB.
Feasibility of Kerr-lens mode locking in fiber lasers
Author(s):
V. P. Kalosha;
Liang Chen;
Xiaoyi Bao
Show Abstract
A mechanism of Kerr-lens mode locking in fiber laser is proposed and analyzed. It could be realized in active photonic-crystal fibers with finite number of the air holes hexagonally arranged around the core with refractive index larger than refractive index of the glass matrix and relies at decrease of the mode confinement loss for higher intensity and mode transformation from leaky to guided when refractive index in the core increases owing to Kerr self-focusing.
Analsysis of soliton interaction with local defects in fiber Bragg grating
Author(s):
Shivaji A. Pokala;
William Mak;
Banmali S. Rawat;
Pak L. Chu;
Moncef B. Tayahi
Show Abstract
The interaction of a fiber Bragg grating point like soliton with local defects has been thoroughly analyzed. The stability
of trapped solitons has also been discussed. The main finding reveals the reversal of the sign of interaction from
attraction to repulsion. It is also observed that the attraction depends on the accuracy of the numerical simulations.
Power and energy-scaling of cladding-pumped Raman fibre lasers sources
Author(s):
C. A. Codemard;
A. Shirakawa;
J.-N. Maran;
J. K. Sahu;
J. Nilsson
Show Abstract
We present results on a high-power, high-energy cladding-pumped fibre Raman laser. We first discuss fibre
requirements and give a design rule. Then, experimentally, a pulsed cladding-pumped Raman fibre laser is demonstrated
with up to 210 μJ high-brightness pulses. The fibre delivers pulses at the Stokes wavelength of 1112 nm, of 500 ns
duration and 420 W peak power, with M2 = 1.8. The linewidth is 6.5 nm without any wavelength selection. Our result is
the highest reported energy and peak power from any fibre Raman source and illustrates the power scalability capability
of such devices.
Impact of self-steepening on the dynamics of a passively modelocked fiber laser containing a long period fiber grating
Author(s):
Abdullah S. Karar;
Tom Smy;
Alan L. Steele
Show Abstract
We report on a numerical investigation of the effect of self-steepening on the dynamics of a passively modelocked
fiber laser containing a long period fiber grating. The numerical model is based on the normalized complex
Ginzburg-Landau equation and the nonlinear coupled mode equations of the grating. The nonlinear dynamics of
the laser are observed through plotting the pulse energy against the linearly increasing gain so obtaining bifurcation
diagrams. The inclusion of self-steepening was found to result in a temporal walk-off with no significant
pulse width or energy alternations, while exhibiting different regions of period doubling bifurcation.
Progress in high-power single frequency master oscillator power amplifier
Author(s):
Jean-Noel Maran;
Yoonchan Jeong;
Seongwoo Yoo;
Jayanta Sahu;
Johan Nilsson
Show Abstract
Master oscillator power amplifier (MOPA) is becoming the obvious choice in order to develop some high power single
frequency laser sources. Its simplicity, reliability, robustness have already allowed the demonstration of some
tremendous increase of the output power. In this paper we will report our latest results in the development of high power
single frequency, single mode and single polarization MOPA systems. We were able to obtain an output power as higher
as 500 W with still keeping the narrow linewidth proprieties of the source.
Kilowatt-power Er3+ doped cladding fiber amplifier
Author(s):
Galina Nemova;
Raman Kashyap
Show Abstract
A novel theoretical scheme for high-power Er3+ doped fiber amplifier assisted with a long period grating (LPG) is
presented. This device consists of an Er3+ doped cladding pumped with a high power laser at a wavelength 1480 nm and
un-doped core. The LPG imprinted into the fiber core at the beginning of the Er3+ doped region transfers a weak signal
entering the amplifier in the core-mode of a single mode fiber into a cladding mode, dramatically increasing the
effective mode-area of the signal and the threshold powers for unwanted nonlinear effects such as stimulated Raman
and Brillouin scattering. The output fiber with the large core provides a high quality output beam.
Thermo-optic switching using liquid-core waveguides in integrated Mach-Zehnder interferometers in silica-on-silicon
Author(s):
Patrick Dumais;
Claire L. Callender;
Julian P. Noad;
Christopher J. Ledderhof
Show Abstract
The use of materials with a high thermo-optic coefficient would lead to significant improvements in energy consumption
and thermal management in optical switching and sensing devices. Most liquids rank among materials having the highest
thermo-optic coefficients, along with polymers and silicon. We have developed technology to directly incorporate
liquids in integrated silica-on-silicon photonic device structures. Using this technology, we demonstrate experimentally
integrated Mach-Zehnder interferometers (MZIs) comprising a liquid-core waveguide in one of the interferometer arms.
Because of the large differential between the thermo-optic coefficients of silica and the liquid medium, the output of this
device can be modulated through the thermal control of the device chip. A high contrast ratio (more than 20 dB) in the
interferometer output modulation is obtained, demonstrating that the optical loss is well balanced between the two
interferometer paths. The temperature variation required to fully cycle the output state is less than 0.5 degrees Celsius.
Designs for low power thermo-optic switches based on these MZI structures with integrated heating electrodes are
presented. The inclusion of a second liquid-core waveguide in the "passive" interferometer arm can enable athermal and
polarization insensitive devices.
Impact of the mean nodal degree on optical networks
Author(s):
Claunir Pavan;
Rui M. Morais;
Abel R. Correia;
Armando N. Pinto
Show Abstract
We present the cost impact of establishing new links in mesh optical networks. The analysis is based on an
analytical study for quickly calculate the transmission and bandwidth management systems costs. Results show
that each network has a mean nodal degree that minimizes the total cost.
Laser oscillation in Nd:YVO4 channel waveguides fabricated by ion implantation
Author(s):
G. V. Vázquez;
M. E. Sánchez-Morales;
E. B. Mejía
Show Abstract
In this work, we report continuous laser emission at 1064 nm from channel waveguides fabricated by carbon
implantation on a Nd:YVO4 crystal. A quasi single-mode intensity profile was observed, which was caused by defects in
the cross-sectional geometry of the waveguides. An analysis of the main laser emission parameters is presented using
different output couplers in the laser cavity and the waveguide losses were calculated from these parameters. The laser
output shows high stability operating at room temperature, confirming the excellent optical properties of the yttrium
vanadate host.
Plasmonic optical waveguides in superconductive traveling-wave photodetectors
Author(s):
Behnood G. Ghamsari;
A. Hamed Majedi
Show Abstract
This paper investigates the use of plasmonic optical waveguides in superconductive traveling-wave photodetectors
(STWPDs) as a promising technique to efficiently couple the input optical field into the superconducting detecting
structures. Field analysis is employed to study the propagation of the light through the integrated device and
the coupling of optical power from the plasmonic waveguide to the superconducting film as a function of physical
dimensions of the guide. A sample plasmonic waveguide, based on the LaAlO3-YBCO-Au multilayer, will be
discussed in detail and important design rules are addressed.
Optimizing four-wave mixing performance in semiconductor optical amplifiers
Author(s):
Houssem Brahmi;
Mourad Menif
Show Abstract
The Four Wave-Mixing (FWM) effect in a bulk Semiconductor Optical Amplifier (SOA) is widely used in all-optical
communication networks for many applications such as wavelength conversion and fast optical switching.
To best achieve such optical functions and bring them into practical stage, we present in this paper some
performance criteria dealing with FWM phenomenon in both peaked and broad bandwidth gain SOA. The
SOA with a large gain profile has given better performance by increasing the conversion efficiency and signal to
background Ratio.
Optimization of antireflection coating design for multijunction solar cells and concentrator systems
Author(s):
Christopher E. Valdivia;
Eric Desfonds;
Denis Masson;
Simon Fafard;
Andrew Carlson;
John Cook;
Trevor J. Hall;
Karin Hinzer
Show Abstract
Photovoltaic solar cells are a route towards local, environmentally benign, sustainable and affordable energy solutions.
Antireflection coatings are necessary to input a high percentage of available light for photovoltaic conversion, and
therefore have been widely exploited for silicon solar cells. Multi-junction III-V semiconductor solar cells have achieved
the highest efficiencies of any photovoltaic technology, yielding up to 40% in the laboratory and 37% in commercial
devices under varying levels of concentrated light. These devices benefit from a wide absorption spectrum (300-
1800 nm), but this also introduces significant challenges for antireflection coating design. Each sub-cell junction is
electrically connected in series, limiting the overall device photocurrent by the lowest current-producing junction.
Therefore, antireflection coating optimization must maximize the current from the limiting sub-cells at the expense of
the others. Solar concentration, necessary for economical terrestrial deployment of multi-junction solar cells, introduces
an angular-dependent irradiance spectrum. Antireflection coatings are optimized for both direct normal incidence in air
and angular incidence in an Opel Mk-I concentrator, resulting in as little as 1-2% loss in photocurrent as compared to an
ideal zero-reflectance solar cell, showing a similar performance to antireflection coatings on silicon solar cells. A transparent conductive oxide layer has also been considered to replace the metallic-grid front electrode and for inclusion as part of a multi-layer antireflection coating. Optimization of the solar cell, antireflection coating, and concentrator system should be considered simultaneously to enable overall optimal device performance.
Entanglement based free-space quantum key distribution
Author(s):
C. Erven;
C. Couteau;
R. Laflamme;
G. Weihs
Show Abstract
We report on the progress of our real-time entanglement based free-space quantum key distribution (QKD)
system which uses polarization entangled photon pairs sent over a variety of free-space optical telescope links
to distribute the key. An experiment with one photon from each pair sent over a 1,325 m long free-space link
and the other photon detected locally next to the source is described. The system performs the complete QKD
protocol including all error correction and privacy amplification algorithms. Over the course of 6.5 hours of
communication at night an average raw key rate of 1,398 bits/s with an average quantum bit error rate (QBER)
of 4.58% was observed producing an average final key rate of 244 bits/s. We also performed a Bell inequality
experiment over two free-space links of 435 m and 1,325 m respectively, producing a total separation of 1,575 m
between the two detectors in the experiment. During the Bell inequality experiment we observed an average Bell
parameter of 2.51 ± 0.11.
Aging and strength improvement of silica optical fibers
Author(s):
Rochdi El Abdi;
Alexandru Rujnski;
Marcel Poulain;
Irina Severin
Show Abstract
The reliability and the expected lifetime of optical fibers used in telecommunication technologies are closely related to
the chemical environment action on the silica network. To ensure the long-term mechanical strength of the optical fibers,
a polymer coating was applied onto the fiber surface during fiber fabrication. This external coating is vital to ensure a
long fiber lifetime. Its protective action includes several functions, such as to protect glass fiber from any external
damage, to limit chemical attack, in particular that of water, and finally to ensure fatigue protection and bending
insensitivity. Since the mechanical strength of the fiber is controlled by its surface characteristics, we propose a new
method for increasing fiber strength.
Submitted to a mechanical stretching, fibers were plunged into hot water and aged for several days. Then, the fibers were
removed from the water and various weights were suspended on the fiber ends. Just before the fiber rupture, the fibers
were unloaded and subjected to dynamic tensile tests at different velocities.
Result analysis proved that the aging in hot water increased the fiber strength. The Weibull's diagram study shows a
bimodal dispersion of defects on the fiber surface and the important role of polymer coating.
Poled glasses for optical devices
Author(s):
Michael Fokine;
Fábio D. Moreira;
Isabel C. S. Carvalho
Show Abstract
Thermal poling is an efficient way to induce optical second-order nonlinearity in different types of glasses, which
typically have macroscopic inversion symmetry. In this paper we present a study on the current dynamics during thermal
poling of glasses and relate these results to the formation dynamics of the depletion region, which is closely linked to the
induced optical second order nonlinearity. Based on a simple theoretical viewpoint, supported by experimental results,
we propose that thermal poling of glasses, and space-charge formation in dielectrics in general, can be viewed as an ionic
RC circuit. This, to some extent modified view on thermal poling in glasses, opens up new opportunities to study and
control the depletion layer dynamics subsequently leading to better control of the thermal poling induced optical second
order nonlinearity in glasses.
Optimizing material properties of bulk-heterojunction polymer films for photovoltaic applications
Author(s):
Yanfei Ding;
Ping Lu;
Qiying Chen
Show Abstract
Bulk-heterojunction photovoltaic devices consisting of poly (3-hexylthiophene) (P3HT) as a donor and [6,6]-phenyl-
C61-butyric acid methyl ester (PCBM) as an acceptor are investigated in this paper. To achieve an efficient photo-induced
charge transfer, the following aspects have been studied: (1) Selection of suitable solvent to obtain good
morphology of the films and optimal absorption spectrum; (2) Determination of the donor/acceptor composition ratio
that yields good film interface and high photon absorption; (3) Thermal annealing process to enhance the photon
absorption, improve the short circuit current and the filling factor, and therefore the efficiency of the devices.
Porous silicon: electrochemical microstructuring, photoluminescence, and covalent modificaiton
Author(s):
Maxim B. Prigozhin;
Pauline Shiwsankar;
W. Russ Algar;
Ulrich J. Krull
Show Abstract
Interest in porous silicon (PS) has increased dramatically over the past two decades due to aspects such as
photoluminescence due to quantum confinement, large surface area, and micro/nanoscale architecture. In this work,
<111> p-type silicon wafers have been electrochemically etched with ethanolic solutions of hydrofluoric acid. Discrete
surface domains showing luminescence were observed. The domains were typically many tens of micrometers in size
and had a height of about 6-8 μm. Interestingly, central round wells of 10-30 μm diameter were observed to form within
domains. Investigation of luminescence in depth profile of the wells was done using confocal fluorescence microscopy,
and the results indicated that the domains were fully porous and luminescent throughout the entire depth. Spectrally, the
peak fluorescence emission was in the range of 550-750 nm and the spectra had an average FWHM equal to about 150
nm. Covalent attachment of organic monolayers to the porous silicon surfaces was done to try and passivate against
oxidation, and also to explore the possibilities of bioconjugation and tuning of the photoluminescence wavelength. A
reaction of hydrogen terminated silicon with ω-undecylenyl alcohol was done using irradiation by a UV source, and
successful derivatization was confirmed with IR spectroscopy. Bulk electrochemical etching of silicon provided a
method to generate distributed luminescent structures suitable for compartmentalization of reactions within wells of
micrometer dimensions without the use of spatially resolved fabrication methodologies such as epitaxial deposition,
lithography, or ion beam technologies.
Imaging of photonic crystal slabs with non-ideal effective refractive index
Author(s):
Guilin Sun;
Andrew G. Kirk
Show Abstract
Finite-sized photonic crystal slabs have an effective refractive index that differs from that
calculated for infinite structures. We investigate the imaging characteristics of such slabs with nonideal
effective refractive index neff, namely |neff|<1 and |neff|>1 at the 2nd band of hexagonal lattice,
and observe an approximately linear object-image relation and saturated imaging. We focus on the slab
aperture effect on imaging and analyze the mechanisms of image formation. For the finite-sized
photonic crystal slab with fixed object distance, due to beam leakage, there is a limiting aperture size
beyond which the image resolution and image distance remain almost unchanged. A larger aperture
does not necessarily lead to higher image resolution. In order to be focused by the slab with negative
refraction, the physical source or the object must contain sufficient transversal wavevectors or higher
transversal spatial frequencies. The analyses are for the cases where propagating waves dominate imaging formation.
Accurate and efficient sensitivity analysis using the beam propagation method
Author(s):
Mohamed A. Swillam;
Mohamed H. Bakr;
Xun Li
Show Abstract
We discuss a novel technique for accurately estimating the sensitivities of any desired response based on the finite
difference Beam Propagation Method (BPM). Our technique utilizes the central adjoint variable method (CAVM) for
estimating the response sensitivities. Using only one simulation of the photonic structure, the response and its
sensitivities with respect to all the design parameters are obtained regardless of their number. This approach features
accuracy comparable to that of the central finite difference approximation applied at the response level. The
effectiveness of our approach is illustrated by using different response functions and different structures. Our approach
utilizes virtual perturbations of the system matrices. Central difference scheme is utilized to calculate the sensitivity of
these matrices with respect to the designable parameters. This sensitivity is then utilized to efficiently estimate the
sensitivity of the objective function. This technique has been applied first to the scalar 2D BPM. It is also extended to
calculate the sensitivities of 3D structures using full vectorial BPM. The proposed approach achieves a significant time
saving in calculating the response and its sensitivities. The accuracy of our approach is verified through comparison
with the expensive and accurate central finite difference applied directly at the response level. We also utilized the
calculated sensitivities in gradient-based optimization algorithms to maximize the power coupling in 3D optical fiber
coupler.
A novel reconfigurable ring architecture of multiple secure private networks over EPON using OCDMA code-drop units
Author(s):
Mohammad Gharaei;
Catherine Lepers;
Ihsan Fsaifes;
Philippe Gallion
Show Abstract
A new architecture of multiple private networks independent of optical line terminal (OLT) over Ethernet passive optical
network (EPON) using ring topology is proposed. This architecture integrates the multiple private networks (PNs) with
downstream/upstream EPON. Self determining private communications between optical network units (ONUs) are
established using code-drop units. The use of optical code division multiple access (OCDMA) technique results in secure
and reconfigurable PNs in the ring. Each ONU is assigned an appropriate codeword for private network communication
and also the standard equipments for the up/downstream standard EPON communication. As an example, by using
quadratic congruent (QC) codes with (p=5) leads to four optical private networks in the ring. To demonstrate the
integration feasibility of multiple 622 Mb/s PNs over 1.25 Gb/s EPON using QC code-drop units, we analyze the
network architecture by evaluating power budget, network dimensioning and BER performances.
Optical beamforming for retro-directive array antennas
Author(s):
Mohammad Fakharzadeh;
Safiedin Safavi-Naeini;
Sujeet K. Chaudhuri
Show Abstract
In this paper we introduce a novel algorithm for the beamforming of a single channel retro-directive phased array
system. Retro-directive array antennas are the best candidate for two-way communication, however there must
be a large spectral difference between the send and receive carriers to reduce the interference and increase the
isolation. When the send and receiver RF frequencies are far apart, e.g. 10 GHz, optical beamforming provides
the unique solution to beamforming problem. Moreover single channel array antennas are hardware efficient
and cost-effective. The core of the proposed structure is a cascaded ring resonator structure with two parallel
waveguides, which can perform the roles of both a tunable optical delay line and a directional coupler. Hence,
there is no need to use an optical circulator to separate the reception path from the transmission path. The
received RF signal from the antenna is modulated with an optical carrier, ?C, and enters the delay line. The
beamforming algorithm calculates the carrier wavelength and the coupling factors between the adjacent rings to
maximize the received power from the desired source. Thermo-optics (TO) phase shifters are used to adjust the
coupling factors. The algorithm calculates the optimum coupling factors based on the instantaneous feedback
from the receiver array, hence it is robust and can compensate for the environmental changes or even the relative
motion of the source and antenna platform. The delayed signal that leaves the delay line is demodulated by
a photodiode (PD). The RF signal is amplified, filtered and delivered to the base-band receiver for decoding.
A sample of the demodulated RF signal is used as the input to the beamforming algorithm to calculate the
received power and signal to noise ratio. Based on the time-reversal property of the retro-directive arrays, the
same amount of delay is required for the transmitter antenna, so the coupling factors do not need to change.
Band gap of nanometer thick Si/SiO2 quantum wells: theory versus experiment
Author(s):
D. J. Lockwood
Show Abstract
In opto-electronics and photonics, the severe disadvantage of an indirect band gap has limited the application of
elemental silicon. Amongst a number of diverse approaches to engineering efficient light emission in silicon
nanostructures, one system that has received considerable attention has been Si/SiO2 quantum wells. Engineering such
structures has not been easy, because to observe the desired quantum confinement effects, the quantum well thickness
has to be less than 5 nm. Nevertheless, such nanometer thick structures have now been produced by a variety of
techniques. The SiO2 layers are amorphous, but the silicon layers can range from amorphous through nanocrystalline to
single-crystal form. The fundamental band gap of the quantum wells has been measured primarily by optical techniques
and strong confinement effects have been observed. A number of theories based primarily on ab initio approaches have
been developed to explain these results with varying degrees of success. In this review, a detailed comparison is made
between theoretical and experimental determinations of the band gap in Si/SiO2 quantum wells.
Slow-light plasmonic metal nano-strip resonators
Author(s):
Thomas Søndergaard;
Sergey I. Bozhevolnyi;
Jesper Jung;
Jonas Beermann;
Guiseppe Della Valle;
Alexandra E. Boltasseva
Show Abstract
Scattering resonances of metal nano-strip resonators are described as a consequence of formation of standing waves due
to counter-propagating short-range (and slow) surface plasmon polaritons and gap plasmon polaritons, which are
electromagnetic waves bound to and propagating along a nanometer-thin metal film, and a nanometer-sized gap between
metal surfaces, respectively. Scattering spectra and resonant fields are presented for single-metal-nano-strip resonators
and gap plasmon resonators with two closely spaced metal nano-strips. It is shown how strip resonators can be designed
for any resonance wavelength in the range from 600nm to 1600nm.
Extended-cavity diode laser continuously tuned with a translated varied line-space grating
Author(s):
Gilles Fortin;
Nathalie McCarthy
Show Abstract
Mode-hop-free operation of an extended-cavity diode laser is achieved with an original technique. A varied
line-space diffraction grating is used as an external coupler. Continuous tuning is obtained by a simple linear translation
of the grating. As of now, the measured continuous tuning range is as wide as 14 nm near 1568 nm with a relatively
constant output power.
Ray matrices for a varied line-space diffraction grating with curved lines
Author(s):
Gilles Fortin;
Alexandre April;
Nathalie McCarthy
Show Abstract
The focusing properties of orthogonal optical systems that include a varied line-space grating with curved lines
can be analyzed efficiently with the ray matrices presented in this paper. These matrices are obtained by comparing the
true optical path length truncated to the second order and the eikonal function (the phase of the kernel appearing in the
Fresnel-Kirchhoff diffraction integral) expressed in terms of ABCD-matrix elements.
Lens-free focusing of Gaussian beams
Author(s):
Gabrielle Thériault;
Réal Tremblay;
Nathalie McCarthy
Show Abstract
This paper studies the diffraction in the near-field of a monochromatic Gaussian beam by a sequence of parallel coaxial
circular apertures. A method to design diffraction-based and wavelength-specific focusing systems through a sequence of
circular apertures, using confocal Fresnel ellipsoids, is detailed. The results obtained with this research show that the design
method introduced here is valid and can be used to focus electromagnetic beams without traditional refractive lenses.
Critical comparison of three modal methods: bidirectional eigenmode expansion propagation method, aperiodic rigorous coupled mode analysis, and harmonic expansion method
Author(s):
Jirí Ctyroký;
Ivan Richter;
Pavel Kwiecien
Show Abstract
The performance of three bidirectional modal methods the "classical" bidirectional eigenmode expansion propagation
method, the aperiodic rigorous coupled wave analysis (known also as the Fourier modal method), and the mode
expansion method based on harmonic expansion are mutually compared using modeling tasks that include eigenmode
calculation of a relatively high-contrast planar waveguide, spectral transmittance of a one-dimensional "photonic crystal"
filter in a photonic wire, spectral transmittance of a surface plasmon based optical sensor, and a reflectance from a
double-groove structure in a high-contrast waveguide. All methods exhibit generally comparable performance, as
follows from good mutual agreement of the results and generally comparable computational time. Although all methods
use perfectly matched layers as absorbing boundary conditions, their implementation in the aperiodic rigorous coupled
wave analysis exhibits significantly stronger attenuation than that used in the other two methods. Thus, significant
improvement of the latter methods seems possible.
Spatial heterodyne planar waveguide spectrometer: theory and design
Author(s):
Miroslaw Florjanczyk;
Pavel Cheben;
Siegfried Janz;
Alan Scott;
Brian Solheim;
Dan-Xia Xu
Show Abstract
We review the theory and design of a novel type of stationary spectrometer in planar optical waveguides. These spatial
heterodyne spectrometers are based on arrayed Mach-Zehnder interferometers and offer high resolution and increased
optical throughput (etendue). A stationary Fourier technique is employed to reconstruct the input spectrum from the
Mach-Zehnder outputs. Calibration mitigates waveguide fabrication errors and can be readily implemented in the
spectra retrieval algorithm. Sensitivity to errors calibration measurements is numerically simulated.
Genetic algorithm synthesis of spectral phase OCDMA encoders and decoders
Author(s):
Moez Mathlouthi;
Mourad Menif;
Catherine Lepers;
Houria Rezig
Show Abstract
In this paper, we interest on the synthesis of spectral phase OCDMA encoders/decoders based on step chirped Fiber
Bragg Gratings to enhance their spectral and temporal efficiency. In this process, we use a real-coded Genetic Algorithm
as a synthesis technique. The encoders/decoders are formed by step chirped fiber Bragg gratings with π phase shifts
giving rise to bipolar code signatures. In fact, the device structure results from the concatenation of fiber Bragg gratings
with different nominal periods and π phase shifts inserted between the gratings to implement the code behavior. Ecole Polytechnique de Montreal
Performance comparison of coherent versus incoherent direct sequence optical code division multiple access system
Author(s):
Amel Farhat;
Mourad Menif;
Catherine Lepers;
Houria Rezig;
Philippe Gallion
Show Abstract
In this paper, we compare the performances of a coherent versus incoherent Direct Sequence Optical Code Division
Multiple Access (DS-OCDMA) system. Superstructured Fiber Bragg Grating (S-FBG) encoders/decoders are used to
implement unipolar codes such as Prime Sequence (PS) and Extended Quadratic Codes (EQC) codes. We implement the
Importance Sampling (IS) technique, which is a variant of the well-known Monte-Carlo (MC) method, to evaluate the
Bit Error Rate (BER) performances of the system. Our simulation results depict that coherent system outperforms the
incoherent one. The last system can be used but a BER floor is demonstrated due to the beat noise of the incoherent
source. We show that increasing bit rate leads to a deterioration of the BER behavior and requiring an increase of the
optical bandwidth of the signal.
Fabrication-tolerant higher order laterally coupled distributed feedback lasers
Author(s):
R. Millett;
K. Hinzer;
T. Hall;
H. Schriemer
Show Abstract
To avoid the commonly required regrowth steps in conventional distributed feedback laser fabrication, laterally-coupled
distributed feedback (LC-DFB) lasers lithographically pattern the grating out of the ridge waveguide. Using higher
order gratings increases the lithographic tolerances, resulting in lasers that are more amenable to mass-manufacturing
techniques, such as stepper lithography. We have extended the modified coupled-mode theory to a two-dimensional
cross-section, and thereby identified grating geometries that are both fabrication-tolerant and provide high performance.
Fourier decomposition methods for passive photonic device characterization
Author(s):
I. Molina-Fernandez;
J. G. Wangüemert Perez;
A. Ortega Moñux;
R. Godoy Rubio
Show Abstract
In this work the application of Fourier Decomposition Methods to analyze photonic passive devices is reviewed. The
work will specifically study the limitations of these methods to deal with discontinuous fields and recent advances of
these techniques which make them possible to deal with high contrast challenging structures, such as SoI photonic wires,
with excellent results.
Fabry-Perot temperature dependence and surface-mounted optical cavities
Author(s):
Richard W. Fox
Show Abstract
Factors that contribute to the temperature dependence of a resonant frequency in a low-expansion optical cavity are
discussed, including deformation at the cavity ends due to different coefficients of thermal expansion (CTE) of the
spacer, optically-contacted mirror substrate and coating. A model of the temperature dependence is presented that
incorporates finite-element-analysis of the cavity ends. A measurement of frequency versus temperature of a cavity
mode is used along with the model to deduce a spacer's CTE versus temperature profile. The measured profile
correlates very well with a separate experiment utilizing a temporary surface-mounted Fabry-Perot cavity fabricated on
the outside of the spacer with hydroxy-catalysis bonding.
Quasi-crystal or disordered regular photonic crystal?
Author(s):
S. R. Newman;
R. C. Gauthier
Show Abstract
Several studies have shown that the incremental introduction of disorder in photonic crystals results in the high
frequency band gaps closing followed by the lower frequency band gaps. The level and type of disorder required to
pinch off the lower band gap depends on the photonic crystal's initial dielectric layout. Our research has shown that a
rotationally symmetric 12-fold quasi-crystal structure can be reached by introducing a relatively low level of dielectric
disorder to the hexagonal array. A morphing algorithm has been developed that permits the transformation of the
hexagonal rod array photonic crystal into a 12-fold quasi-crystal. The intermediate dielectric profiles generated are used
to examine the evolution of the band gap and central defect states during the transformation. The resulting FDTD
simulations display evidence that the underlying structure of the 12-fold quasi-crystal may be closely related to the
hexagonal array.
Control of spectral aberrations in a monochromator using a chirped grating
Author(s):
A. April;
N. McCarthy
Show Abstract
A method is proposed to minimize the impact of spectral aberrations in a monochromator based on a rectilinear
translation of a plane chirped grating. The chirped grating, that has a spatially variable groove spacing, is used to diffract
and to spectrally focus the radiation. The expression of the width of the instrument line shape due to aberrations have
been developed in order to obtain the optimal rectilinear trajectory required to operate the monochromator without
significant spectral aberrations. Experimental measurements of the emission spectrum of a five-wavelength Helium-Neon laser are presented, as well as the sensitivity of the monochromator performance to different geometrical
parameters.
Multicriteria classification for photonic crystal fiber design
Author(s):
Imene Sassi;
Nabil Belacel;
Yassine Bouslimani;
Habib Hamam;
Rabah Attia
Show Abstract
The photonic crystal fibers (PCF) are considered as the future information support for the telecommunication system. In
this paper, a multicriteria method is used for the design of the PCFs with the user-defined optical proprieties. This
method combines the deductive and the inductive learning and it is introduced for the first time in the field of optical
fibers. These simulation tools will be optimized for PCF structures in order to optimize the parameters necessary for the
improvement of the communication system performances. The multicriteria decision analysis makes it possible to
evaluate the optical proprieties of PCFs by determining the effects of attenuation and distortion caused by Physics
Phenomena. This decision is done by the means of a relational model preferably. As a result, this method avoids the
recourse to distances and makes it possible to use quantitative and/or qualitative criteria. Moreover, it defeat some
difficulties encountered when data are expressed in different units. These advantages allow the new multicriteria
classification method to be employed easily to the diagnosis and to the design of photonic-crystals fibers.
Propagating arbitrarily shaped pulses in a nonlinear normally dispersive fiber using moments
Author(s):
Bryan Burgoyne;
Nicolas Godbout;
Suzanne Lacroix
Show Abstract
We use the method of moments to calculate the propagation of an arbitrarily shaped pulse in a nonlinear
dispersive fiber. By assuming that the pulse is linearly chirped, we are able to determine analytically the
evolution of the second order moments (representing the duration, bandwidth and chirp of the pulse) along
propagation regardless of the initial pulse shape. The evolution of the moments is given by an implicit equation
and several invariants. These invariants allow an easy estimation of the different pulse parameters. The linear
chirp approximation implies that the arbitrary pulse shape remains invariant along propagation but allows to
calculate the propagation in both dispersion regimes from the same solution. The solution show an oscillatory
behavior in the anomalous dispersion regime and a monotonic behavior in the normal dispersion regime. In both
regimes the calculations are compared to numerical split-step simulations and are shown to agree for propagation
over many dispersion and nonlinear lengths.
While this method describes well the evolution of the pulse duration, bandwidth and chirp, we need to proceed
differently to find the evolution of the pulse shape. From these propagation equations for the moments, we
derive an approximate implicit solution describing the propagation of a Gaussian pulse in the normal dispersion
regime. This approximate solution describes the pulse shaping toward a parabola that the pulse undergoes
along propagation. A good agreement is found between the pulse obtained from numerically solving the implicit
equation and the split-step propagation of the same pulse. Numerically solving the implicit analytical function
describing the pulse is much faster than using purely numerical simulations, which becomes time consuming for
highly chirped pulses with large bandwidths over long propagation distances. These and other results suggest
that pulse shaping along propagation is only adequately modeled by implicit functions.
Polarization compensators in silicon-on-insulator reflective interconnects
Author(s):
P. J. Bock;
R. Millett;
H. Schriemer;
T. Hall;
S. Bidnyk
Show Abstract
We report on our recent progress in polarization control and polarization compensator designs in SOI-based planar
reflective gratings for a range of silicon core thicknesses of 0.1 μm to 10 μm. The dispersion property of the silicon
slab, without a compensator region, was found to limit the applicability of SOI gratings for achieving the polarizationinsensitive
performance of wavelength division multiplexing systems based on planar gratings. We have found that in
coarse wavelength division multiplexing systems, the birefringence of the uncompensated slab becomes impractical at
core thicknesses below 1.7 μm. Our findings clearly show that shallow etched polarization compensators can effectively
eliminate polarization dependence only in thick-core gratings and only in applications requiring free spectral ranges
(FSRs) of no more than 80 nm. In silicon cores with thicknesses of less than 1.0 μm, the significantly different value of
linear dispersion strength for the two polarization states make traditional compensator designs ineffective, since only the
central wavelength can be fully compensated. We used our findings to construct a procedure for building compensators
with a flat polarization response over wide FSRs (>80 nm). The results of our study were applied to the design of a
polarization compensator in an 18-channel multiplexer for use in coarse wavelength division multiplexing. Our
simulation results show that a careful selection of the silicon core thicknesses in the slab and compensator regions is
essential for achieving low-cross talk and low insertion loss devices. The application of thin core planar silicon gratings
to building silicon interconnects is discussed.
The mass loading effect on lightweight cantilever mode frequency measurement by optical fiber sensor
Author(s):
Ziyi Zhang;
Pingyu Zhu;
Xiaoyi Bao
Show Abstract
Dynamic response of lightweight structures is affected by the mass of a transducer. The additional mass of the transducer
is defined as a mass loading for the system, which is comparable to the weight of the structures, such as composites and
thin cantilever beam/bar. In this paper, we measure the bending and torsion mode frequencies with and without mass
loading to the lightweight structures by using lightweight optical fiber sensor (OFS) and conventional accelerometer.
The frequency difference is verified by the finite element method using ANSYS software. The OFS, benefited to its
lightweight, has shown the advantage of measuring vibration frequency accurately without affecting the dynamic
response of the structure.
Temperature sensors and refractometers using liquid-core waveguide structures monolithically integrated in silica-on-silicon
Author(s):
Patrick Dumais;
Claire L. Callender;
Julian P. Noad;
Christopher J. Ledderhof
Show Abstract
Integrated optofluidic devices have many potential applications for on-chip analysis and sensing. The fabrication of
single-mode liquid-core waveguides in an integrated format allows the implementation of robust and very sensitive
interferometers that combine long optical paths (on the cm scale) with small volumes (less than a nanoliter). We have
demonstrated the monolithic integration of microchannels and liquid-core waveguides with planar silica lightwave
circuits, which allows a number of refractometer devices to be implemented. Of these, we demonstrate experimentally a
monolithic Mach-Zehnder interferometer (MZI) comprising a 20 mm-long liquid-core waveguide. The liquid-core
waveguide is quasi single mode at 1550 nm when filled with a liquid of nominal index of ~1.47 (such as toluene or an
index matching fluid). In these conditions, the output of the MZI is a pure cosine function, as a function of a linear
progression of the refractive index of the liquid medium. Furthermore, the high contrast ratio experimentally observed in
the output function allows a precise monitoring of refractive index changes by tracking the position of the transmission
minimum in the spectral domain. Refractive index variations can be measured to a precision on the order of 4x10-6. The
large differential in thermo-optic coefficients between liquid media and silica allows the structure to function as a
temperature sensor with a precision on the order of 10-2 degrees Celsius. The measurement of the spectral fringe spacing
of the interferometer response allows absolute-value measurements of temperature and refractive index.
Dramatic enhancing of fluorescent light collection efficiency from a very thin layer of polymer on a planar glass substrate
Author(s):
Jianjun Ma;
Xianzhen Li;
Huy Nguyen;
Wojtek J. Bock;
Zhiyuan Wang
Show Abstract
There is an increasing demand for the efficient collection of fluorescent light emitted from a very thin layer of polymer
material such as the specifically synthesized polymer material used in TNT explosives detection. However, the
enormous transparency of this thin film poses a severe challenge for any light detection system based on a traditional
approach. For a simple two-fiber architecture with one fiber for excitation light delivery and another for emission
collection, we report that by launching the excitation light to one corner edge of a planar glass substrate covered with a
thin layer of polymer film, we are able to simultaneously dramatically enhance the collectable fluorescent signal level
and reduce the level of stray excitation light. The proposed sensing architecture opens up an efficient way of light
coupling and collecting for fluorescent-related chemical and biological sample assay.
Characterization of 40-GHz all-optical clock recovery based on a distributed Bragg reflector self-pulsating laser
Author(s):
Xuefeng Tang;
John C. Cartledge;
Alexandre Shen;
Frederic V. Dijk;
Guang-Hua Duan
Show Abstract
We investigate the characteristics of 40-GHz all-optical clock recovery based on a distributed Bragg reflector
(DBR) self-pulsating laser. With the injection of a low timing jitter clock signal, the timing jitter characteristics
of the DBR self-pulsating laser are investigated using both time domain and frequency domain methods. The
results reveal that the cause of the timing jitter in the recovered clock signal depends on the injected clock signal
power. The system performance of the clock recovery is investigated by the injection of a 40 Gb/s return-to-zero
on-off key (RZ-OOK) signal with a 231 - 1 pseudo random bit sequence (PRBS) pattern.
Ridge waveguide Bragg grating pressure sensor
Author(s):
X. Dai;
S. J. Mihailov;
C. Blanchetiere
Show Abstract
In this work, a ridge waveguide Bragg grating pressure or touch sensor is proposed. The sensor consists of an open top
ridge waveguide Bragg grating with a pressure sensing film: polydimethylsiloxane (PDMS) on the waveguide surface.
Under pressure, the guided mode of the waveguide accesses the film by coupling of the evanescent field. A large shift
of the Bragg wavelength occurs when the effective index of the waveguide is changed by stress-indued variations in the
film refractive index that are caused by increases in pressure. By monitoring the shifts of Bragg wavelengths in TE and
TM modes, respectively, the external pressure change and the internal strain change in the film are measured. The
sensitivities of the sensor with different waveguide structures are investigated.
Pulsed quantum cascade laser based cavity ring-down and cavity enhanced spectroscopy for the detection of ethylene.
Author(s):
J. Manne;
W. Jäger;
J. Tulip
Show Abstract
We investigated the use of a pulsed, distributed feedback (DFB) quantum cascade (QC) laser centered at 970 cm-1 in
combination with cavity ring-down spectroscopy (CRDS) and cavity enhanced spectroscopic (CES) techniques for the
detection of ethylene. In these techniques, the laser is coupled to a high-finesse cavity formed by high reflectivity
mirrors. In the CRDS application, the laser frequency was tuned at a rate of ~0.071 cm-1/K by changing the heat sink
temperature in the range between -20 and 50°C. For off-axis CES, the laser was excited with short current pulses (5-10
ns), and the pulse amplitude was modulated with an external current ramp which gave a frequency scan of ~0.3 cm-1. We
utilized a demodulation approach followed by numerical filtering to improve the signal-to-noise ratio. Basic instrument
performance and optimizations of the experimental parameters for sensitivity improvement are discussed. We
demonstrated a detection limit of ~130 ppb with CRDS and ~15 ppb with off-axis CES for ethylene.
Abrupt fiber taper based Michelson interferometric deflection sensor
Author(s):
Zhaobing Tian;
Scott S-H. Yam
Show Abstract
A new compact standard single mode fiber Michelson interferometer deflection sensor was proposed, tested and
simulated. The new interferometer consists of a symmetrical abrupt 3 dB taper region with a 40 μm waist diameter, a
700 μm length and a 500nm thick gold layer coating. Compared with similar interferometric devices based on long
period gratings that need microfabrication technology and photosensitive fibers, the proposed sensor uses a much
simplified fabrication process and normal single mode fiber, and has a linear response of 1.1nm/mm.
Refractive index sensor based on etched D-fibres with wavelength adjustable operating point and resolution
Author(s):
Sameer M. Chandani;
Nicolas A. F. Jaeger
Show Abstract
Silica based fibre-optic refractive index sensors are gaining acceptance over conventional refractometers and finding
applications in chemical/biological sensing due to many of their desirable properties. Here we present an optical fibre-based
refractive index sensor that uses the power transmission through etched D-shaped fibres. The sensor's operating
point and resolution can be tailored for a specific application by selecting the correct combination of the operating
wavelength and the cladding thickness of the etched fibre. The sensor's power transmission depends on the surrounding
refractive index in which the sensor head is immersed. The sensor presented has a maximum resolution on the order of
10-6 in its "high resolution" region and on the order of 10-4 in its "low resolution" region. The refractive index at which
the maximum resolution occurs in the high resolution region can be shifted by ~0.012 and by ~0.027 in the low
resolution region. To date, such high resolutions have been reported over narrow ranges and/or for fibre Bragg grating
based sensors, which require optical spectral analysis which typically, is costly.
Lithium niobate cylinder fiber strain sensor and sonar detector
Author(s):
Philipp Kornreich;
Madhukar Bansal;
Dawit Negussey;
Ronald Drake;
Zheng-Xuan Lai;
James Flattery;
James Mandel
Show Abstract
We have developed optical fibers with a thin approximately 40 to 60 nm thick Lithium Niobate Layer
at the glass core and cladding boundary. These Lithium Niobate Cylinder Fibers (LNCF) are now in the
process of being commercialized as strain gauges for bridges, tunnels, pipe lines and aircraft components.
An application as a sonar sensor is also being investigated. LNCF strain sensors use light amplitude
detection rather than phase detection. Amplitude detection is easier to implement and is substantially less
costly. LNCF's when used as light amplitude sensing sonar detectors are over 1000 times more sensitive
than standard Single Mode Fibers. LNCFs use so called "Non Propagating" light modes rather than the
conventional propagating modes.
Phase interrogation of a planar integrated refractive index sensor
Author(s):
Galina Nemova;
Andrei V. Kabashin;
Raman Kashyap
Show Abstract
A novel theoretical scheme is presented for a surface plasmon-polariton (SPP) planar refractive index sensor based on
one of the simplest integrated optical devices available, the Mach-Zehnder interferometer (MZI), to monitor relative
phase variations in waveguides. An SPP is excited with the Bragg grating imprinted into core and buffer layers of one of
the arms of the MZI. The main principle of operation of this device is based on the large phase change of the waveguide
mode transmitted through the grating during the SPP excitation caused by the change in the refractive index of the
sensed layer in contact with the SPP supporting metal layer.
Detection of lead in brass by laser-induced breakdown spectroscopy combined with laser-induced fluorescence
Author(s):
Christian Goueguel;
Stéphane Laville;
Hakim Loudyi;
Mohamed Chaker;
Mohamad Sabsabi;
François Vidal
Show Abstract
Laser-Induced Breakdown Spectroscopy (LIBS) technique combined with Laser-Induced Fluorescence (LIF) is known
to be a high sensitivity and high selectivity analytical technique. Although sub-ppm limits of detection (LoD) have
already been demonstrated, there is still a constant and urgent need to reach lower LoDs. Here, we report results obtained
for the detection of lead trace in brass samples. The plasma was produced by a Q-switched Nd:YAG laser at 1064 nm
and then re-excited by a nanosecond optical parametric oscillator (OPO) laser tuned at 283.31 nm. Emission from Pb
atoms was then observed at 405.78 nm. The experiments were performed in air at atmospheric pressure. We found out
that the optimal conditions were obtained for an ablation fluence of 2-3 J/cm2 and inter-pulse delay of 8-10 μs. Also,
excitation energy of about 200 μJ was required to maximize the Pb(I) 405.78 nm emission. Using the LIBS-LIFS
technique, the LoD was estimated to be about 180 ppb over 100 laser shots, which corresponds to an improvement of
about two orders of magnitude with that obtained using conventional LIBS.
Spatially resolved frequency domain phosphorescence lifetime-based oxygen sensing for photodynamic therapy
Author(s):
Benjamin Lai;
Mark Gurari;
Wallace Wee;
Lothar Lilge
Show Abstract
Photodynamic Therapy (PDT) is a minimally invasive treatment that uses a photosensitive drug into convert triplet state
oxygen (3O2) to singlet oxygen (1O2) to destroy malignant tissue. A fiber-optic system based on frequency domain
detection of phosphorescence quenching by 3O2 is described which optically measures the distribution of 3O2 in the
treatment volume during PDT to permit adjustments of treatment parameters to improve outcome. A specially designed
fiber optic probe containing phosphorescent sensors embedded along its length permit spatially resolved measurements.
Each sensor is composed of a phosphorescent metalloporphyrin compound that emits a characteristic spectrum. Four
candidate sensors with high absorption at the excitation wavelength of 405nm and emission in the 650nm to 700nm
region are considered. The dependence of phosphorescence lifetime (τ) on 3O2 concentration is described by the
linearized Stern-Volmer relationship as being inversely proportional. Determination of τ, and hence 3O2 concentration,
is accomplished in the frequency domain by means of phase-modulation detection of the phosphorescence signal due to
an amplitude modulated excitation. The τ's of each sensor are recovered by performing global non-linear least squares
fit on the measured phase and modulation index over a range of frequencies and wavelengths. With the τ of each sensor
known, the oxygen concentration at each sensor's location can be determined with the Stern-Volmer relationship.
Fiber Bragg grating deflection sensor
Author(s):
Ping Lu;
Liqiu Men;
Qiying Chen
Show Abstract
A new fiber-optic sensor system consisting of a fiber Bragg grating (FBG) cantilever as a transducer is proposed and
demonstrated to realize simultaneous measurement of magnitude and direction of deflection. For the FBG mounted on a
stainless steel cantilever, a change in the bending deflection gives rise to a monotonous shift in the Bragg resonance
wavelength of the grating while the deflection direction results in either a red- or blue-shift in the Bragg wavelength due
to a stretched or shrunk state of the grating. As an application of this deflection sensor, the water flow rate was
measured, which showed good agreement with the theoretical analysis.
Fringe spacing controllable long-period grating assisted Michelson interferometer for high sensitivity refractometry
Author(s):
Jian Yang;
Chang-Qing Xu;
Yingfu Li;
John D. Brennan;
Mohammed Zourob
Show Abstract
Long-period grating assisted Michelson interferometer has been proved to be a perspective device for chemical and
biochemical sensing based on refractive index measurement. However, the phase difference between the fiber core
propagation and the fiber cladding propagation in the in-fiber Michelson interferometer is correlated to the common
path length. As a result, the fringe spacing in the reflection spectrum drops with the interferometer cavity length, leading
to reduced fringe wave length shift in refractometry measurement. In this paper, we proposed a long-period grating
assisted Michelson interferometer with the core mode and the cladding mode propagation separated. By eliminating the
residue core mode after the long period grating coupling, an interferometer arm consists of cladding mode propagation
is realized. With the cavity length of the other arm controllable, the fringe spacing in the reflection spectrum of the
Michelson interferometer can be precisely controlled. The proposed Michelson interferometer allows use of long cavity
length of the cladding mode arm to accumulate phase change and large fringe spacing for wavelength interrogation in
refractometry sensing.
Integrated optical microfluidic lab-on-a-chip
Author(s):
Arvind Chandrasekaran;
Muthukumaran Packirisamy
Show Abstract
Bio-security for health monitoring and diagnosis are the needs of the hour, for rapid detection of biological and chemical
species. This calls for a necessity to develop a cost effective miniaturized and portable biosensor device for in-situ
biomedical applications and Point-of-Care Testing (POCT). While portability of the biosensor is required for in-situ
medical detections, miniaturization is essential for handling smaller sample volumes and high throughput. Thus, the
above mentioned concerns cannot be addressed unless a fully integrated biosensor system is developed. In this work, an
integrated opto microfluidic based Lab-on-a-chip device is proposed for carrying out fluorescence based biodetection.
The input and output fibers were integrated with the microfluidic channel so as to make a robust setup. Fluorescence
detection was carried out using Alexafluor 647 tagged antibody particles and the output was measured with a
Spectrometer-on-Chip, integrated with the device. The experimental results prove that the proposed device is highly
suitable for Lab-on-a-Chip applications.
Long-period gratings in chemical sensing
Author(s):
Jack A. Barnes;
R. Stephen Brown;
Judy Cipot-Wechsler;
Cathleen M. Crudden;
Jenny Du;
Hans-Peter Loock;
Krista Plett
Show Abstract
A chemical sensor system consisting of a coated long period grating, which was spliced into a fiber loop cavity, has been
prepared and characterized. Designer coatings based on polydimethylsiloxane and nanostructured organically modified
silica (ORMOSIL) materials were prepared to provide enhanced sensitivity for a variety of key environmental pollutants.
Upon microextraction of the analyte into the polymer matrix, an increase in the refractive index of the coating resulted in
a change of the attenuation spectrum of the long period grating. The grating was interrogated using ring-down detection
as a means to amplify the optical loss and to gain stability against misalignment and laser power fluctuations. Chemical
differentiation of cyclohexane and xylenes was achieved and a detection limit of 300 ppm of xylenes vapour in air was
readily realized for PDMS coatings. Ormosil-type coatings were capable of detecting lead cations at concentrations
below 1 ppm in water.
Programmable optical microshutter arrays for large aspect ratio microslits
Author(s):
S. Ilias;
F. Picard;
C. Larouche;
R. Kruzelecky;
W. Jamroz;
L. Le Noc;
P. Topart
Show Abstract
Design, fabrication and characterization of a 16x1 programmable microshutter array are described. Each shutter controls
the light transmitted through a microslit defined on the transparent substrate supporting the array. Two approaches were
considered for the shutter array implementation: sweeping blades and zipping actuators. Simulation results and
fabrication constraints led to the selection of the zipping actuators. The device was fabricated using a surface
micromachining process. Each microshutter is basically an electrostatic zipping actuator having a curved shape induced
by a stress gradient throughout the actuator thickness. When a sufficient voltage is applied between the microshutter and
an actuation electrode surrounding the microslit area, the generated electrostatic force pulls the actuator down to the
substrate which closes the microslit. Opening the slit relies on the restoring force due to the actuator deformation.
Microshutter arrays were fabricated successfully. High light transmission through the slit area is obtained with the
actuator in the open position and excellent light blocking is observed when the shutter is closed. Static and dynamic
responses of the device were determined. A pull-in voltage of about 110 V closes the microslit and the response times to
close and open the microslit are about 2 and 7 ms, respectively.
Strain distribution and sensitivity in fiber Bragg grating sensors
Author(s):
C. Dadpay;
N. R. Sivakumar;
N. Mrad
Show Abstract
Optical Fiber Bragg Gratings (FBG) sensors have seen significant development in recent years. Such sensor
technology developed initially for the civil infrastructure is currently attracting the aerospace industry due to
the potential versatility of this technology and its measurement capability. The structural health monitoring
and the diagnostics and prognostics health management communities are excited about such development and
ready to embrace such capability. Sensors reliability and accuracy, however, continue to be two parameters
critical to the eventual implementation of the technology in high value targets. Such parameters can be
improved by different manufacturing techniques as well as optimum grating's coating selection. This paper
presents an evaluation of the mechanical behavior of the FBG strain sensors. A simulated analysis, using
finite element modeling, revealed the impact of coating material selection, coating thickness selection, and
bonding effect on the strain transfer loss. Results illustrate that metallic fiber coatings are more suitable for
improved strain transfer than their polymeric counterparts and acrylic coatings are least effective with
adhesive layer as small as possible.
Time-resolved visualization of electric fields during femtosecond laser ablation
Author(s):
Christoph T. Hebeisen;
Germán Sciaini;
Maher Harb;
Ralph Ernstorfer;
Sergei G. Kruglik;
R. J. Dwayne Miller
Show Abstract
We observe the electric fields caused by charge distributions during femtosecond laser ablation from a silicon
(100) surface. Femtosecond electron pulses passing near the ablation site serve as a probe of the electric field
generated by the emitted charges and countercharges on the sample surface. The density map of the electron pulse
downstream from the sample contains information about the charge distributions. We invert this information
by fitting the beam maps using a simple charge distribution model. Under the present excitation conditions
(390 nm, 150 fs, 5.6 J/cm2), we observe the emission of 5.3×1011 electrons/cm2 within 3 ps of the excitation
pulse, leading to self-acceleration of the emitted electrons to 2% of the speed of light. Preliminary experiments
on a metal sample display even faster dynamics.
Development of a high power femtosecond optical parametric oscillator for biomedical imaging applications
Author(s):
Anton Sharapov;
Virginijus Barzda;
Arkady Major
Show Abstract
We report on the development of a widely tunable high power optical parametric oscillator (OPO) based on
a diode-pumped femtosecond Yb:KGW laser. The laser operates at a wavelength of 1030 nm and can produce up to
3.7 W of average power in 300 fs pulses at 61 MHz repetition rate. Owing to its high peak power (>200 kW) this
laser is well suited for the development of the OPO in the near-infrared spectral region. Design considerations of the
OPO are also discussed and include the choice of the nonlinear material, its dispersive characteristics, wavelength
tuning methods and operating wavelength ranges, phase-matching properties for accurate crystal design as well as
OPO pumping configuration.
Nonparaxial transverse-magnetic laser beams
Author(s):
A. April
Show Abstract
Expressions for the fields of transverse-magnetic laser beams in free space that are rigorous solutions to
Maxwell's equations are given in a closed form. The electric and the magnetic fields are both expressed in terms of
nonparaxial elegant Laguerre-Gaussian beams that are exact solutions of the Helmholtz equation. These solutions
involve spherical Bessel functions and associated Legendre functions. Radially polarized beams of arbitrary order are
considered and the lowest-order radially polarized beam (TM01 beam) is investigated in detail.
Fabrication of photonic devices directly written in glass using ultrafast Bessel beams
Author(s):
Véronique Zambon;
Nathalie McCarthy;
Michel Piché
Show Abstract
Optical waveguides have been inscribed in fused silica by focusing femtosecond laser pulses with an axicon. The axicon
is a conical lens that allows obtaining an optical beam with a transverse intensity profile that follows a zero-order Bessel
function. This profile is invariant along a certain distance (>1 cm). The advantage of using axicon is that the beam is
focused along a narrow focal line of a few micron width. Therefore the inscription of waveguides can be done without
moving the glass sample. The waveguides so fabricated exhibit low losses and no detectable birefringence due their
excellent circular symmetry. By translating the glass sample during the inscription process, we have induced a refractive
index change along a thin plane in order to fabricate planar waveguides.
Experimental generation of spatiotemporal Bessel-Gauss beams
Author(s):
M. Dallaire;
N. McCarthy;
M. Piché
Show Abstract
We recently proposed a new class of two-dimensional (in x and t) theoretically invariant optical wave packets
characterized by a spatiotemporal Bessel function (STB beams). In these particular field distributions, a balance between
the diffraction and the dispersion of pulsed beams takes place. The solution describing the propagation of an STB beam
is independent of the propagation distance, but the infinite dimensions of this beam make it impossible to generate. The
dimensions of this beam can be limited by the use of a Gaussian envelope, resulting in a spatiotemporal Bessel-Gauss
beam (STBG beam), that we have generated experimentally. We present the experimental setup used to generate STBG
beams and experimental beam profiles which are in good agreement with those of theoretical STBG beams.
Stabilization of a mode-locked ytterbium-doped fiber laser by intracavity spectral filtering
Author(s):
Martin Laprise;
Michel Piché;
Réal Vallée
Show Abstract
In this work we explore the use of intracavity spectral filtering to enhance the performance of ytterbium-doped mode-locked fiber lasers. This technique has been experimentally demonstrated with a single-mode ytterbium-doped fiber laser operated with a ring cavity in the stretched-pulse regime. We characterized experimentally the effect of the long-wavelength filtering on the noise of a stretched-pulse cavity with a slightly negative global dispersion.
Toward attosecond electron pulses using ultra-intense lasers
Author(s):
Charles Varin;
Pierre-Louis Fortin;
Michel Piché
Show Abstract
In many countries around the world, ultra-intense laser facilities are being built. These state-of-the-art lasers are
intended for innovative medical and technological applications, as well as for basic experiments at the frontiers
of fundamental science. Laser particle acceleration is a promising new endeavor. Recently developed schemes using radially polarized beams could help in reaching unprecedentedly short electron pulse durations, well in the attosecond range and potentially in the subattosecond range.
Nonlinear effects in optical fibers using a high-power Er-doped femtosecond fiber laser
Author(s):
Karl-Alexandre Jahjah;
Louis Desbiens;
M. Piché
Show Abstract
We present new results on supercontinuum generation obtained with a high-power Er-doped femtosecond fiber laser. Our results cover many different types of optical fibers: silica, dispersion-shifted fibers, doped fibers, etc. We have obtained supercontinua covering a wide spectrum from the visible to the mid-infrared ( >2μm ). We also identified third harmonic generation phenomena and we present experimental results that may exhibit the signature of two-photon absorption in an Yb-doped fiber.
Second-harmonic generation from the longitudinal component of vectorial laser beams: a theoretical framework
Author(s):
Pierre-Yves Fortin
Show Abstract
Vectorial laser beams propagating beyond the paraxial limit exhibit an intensity profile at focus that depends
upon their field structure and the width of their plane wave spectrum. Under tight focussing conditions, the
longitudinal component of the lowest order transverse magnetic laser beam has a field amplitude that becomes
comparable to that of the transverse components of the beam; the global intensity profile is then narrower
than that produced by a Gaussian beam, thus enabling hyperresolution. With a general polarization eigenmode
approach for all propagating directions in anisotropic media, we can show that privileged propagating directions
exist, allowing preservation of the transverse magnetic polarization state despite birefringence. Using wave
functions satisfying the non-paraxial wave equation, we can also find exact expressions for the field components.
During propagation of tightly focussed beams along those privileged directions inside an appropriate anisotropic
nonlinear crystal, the longitudinal electric field component may then be used to take advantage of nonlinear tensor
terms otherwise ineffective with a paraxial beam. In this work, spectral conversion rate and power conversion
efficiency of second-harmonic generation are characterized as a function of effective and undepleted nonlinear
pumping in the case of propagation along the anisotropic axis of an uniaxial nonlinear crystal. Even if the phase
matching condition is not fully satisfied for propagation along this privileged direction, we show to which extent
the nonlinear properties are preserved for a restricted interaction volume.
Birefringence of wood at terahertz frequencies
Author(s):
Tara M. Todoruk;
Jon Schneider;
Ian D. Hartley;
Matthew Reid
Show Abstract
Fibre content of solid wood plays an important role in the wood products industry in terms of value. Additionally,
fibre structure in composite wood products such as Oriented Strand Board (OSB) and paper products plays an
important role in terms of strength properties. The effect of moisture content on wood properties is important
in the manufacturing process and final product performance, and therefore its effect on the birefringence is
of considerable interest. Since solid wood exhibits strong birefringence at terahertz frequencies, there may be
potential applications of terahertz spectroscopy to fibre content and structure sensing. There are two potential
sources for this strong birefringence: (i) form birefringence resulting from the porous structure of solid wood
and (ii) intrinsic birefringence resulting from the dielectric properties of the material itself. In this report, the
variability of birefringence within and between species, the dependence of the birefringence on moisture content
and the relative contributions from form and intrinsic birefringence are examined. In order to clarify the role
of these contributions to the measured birefringence, polarized terahertz reflection spectroscopy is examined
and compared to the results obtained in a transmission geometry. Comparison of the birefringence measured in
transmission and reflection geometries suggests that form birefringence may dominate.