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- Front Matter: Volume 8236
- Resonators
- Beam Shaping I
- Beam Shaping II
- Beam or Mode Diagnostics
- Adaptive Optics
- Microcavity Lasers and Applications I
- Parametric Processes in Microresonators
- Integration of Microresonators and Photonic Circuits
- Microcavity Lasers and Applications II
- Microresonator-Based Sensors I
- Microresonator-Based Sensors II
- Microresonator-Based Sensors III
- Resonant Opto-Mechanics
- Resonant Four-Wave Mixing and Applications
- Doped Microresonators
- Coupled Microresonators and Effects
- Poster Session
Front Matter: Volume 8236
Front Matter: Volume 8236
Show abstract
This PDF file contains the front matter associated with SPIE Proceedings Volume 8236, including the Title Page, Copyright information, Table of Contents, Introduction, and Conference Committee listing.
Resonators
A comparison of passive coherent beam combining architectures: experimental results
Show abstract
Modal properties of two architectures for coherent beam combining are theoretically analyzed and experimentally
verified. The supermodes of a two-laser spatially filtered cavity exhibit two distinctly different types of behavior
depending on the path length error. When the error is small, the two modes present different cavity loss values and can
be differentiated by gain. However, cavities containing path length errors greater than a critical value produce modes
with identical losses and different resonant frequencies. A diode-bar side-pumped plano-concave Nd:YAG laser cavity is
built for experimental verification of the theory. Experiments have shown two distinct regions as predicted by theory. In
the small path length error region, the cavity runs in one single mode; however, when the path length error goes beyond
a critical value, the cavity lases in two modes simultaneously or alternates between two modal states. Detailed loss
versus phase error curves are presented and compared to theory. The modal behavior in this spatial filtering architecture
is quite different from that found in a superposition architecture for coherent beam combining where the fundamental
mode always has smaller loss per round trip than the second mode. The modal curves for a superposition architecture are
provided for comparison with those from spatial filtering.
1121 nm resonator properties and impact on the design of a 1178 nm sodium guidestar laser
L. J. Henry,
J. Grosek,
G. Moore,
et al.
Show abstract
A dual seeded (pump at 1069 nm and second Stokes at 1178 nm) Raman laser system involving amplification of the
second Stokes in a Raman resonator having high reflector Bragg gratings tuned to the first Stokes at 1121 nm is
proposed. This system has the potential of generating 50 W of output power at 1178 nm. Because the laser is seeded
with the desired output wavelength (second Stokes), outputs having narrow or broad linewidths can be achieved. Highly
efficient Raman conversion is achieved in a short Raman fiber (< 20 m) due to high 1121 nm circulating power levels in
the Raman resonator. Stimulated Brillouin Scattering, the 1121 nm circulating power level, and the effects of modal
instability are constraints on the design of a narrow linewidth system. Length of the resonator cavity, power level of the
1069 nm pump, and power level of the 1178 nm seed are parameters that can be adjusted to optimize the design. Usage
of germanosilicate fiber improves the performance of the system. Finally, because of the low power level of available
1178 nm seeds, a two stage system (low and high power stages) is necessary to achieve 50 W of 1178 nm output power.
Comprehensive analysis of thermal lensing effects on the coaxial resonator of a high power RF-Excited CO2 laser
Show abstract
The influence of a variety of parameters, such as the gas composition, pressure and lateral variation of Joule heat release
of the discharge at employed frequency, are taken into account to derive a distributed thermal lensing expression and to
numerically calculate the focal length as a function of position within the inter-electrode gap. The process of widening of
the beam inside the resonator is investigated by means of complex ray methodology. The findings are incorporated into
the optimization process of the optical resonator in the stable direction and the impact on the beam quality and power
stability is verified by experimental results.
Unstable resonator with high magnification and low output coupling
Show abstract
The application of standard unstable resonators does not allow for an independent adjustment of the resonator
magnification and the output coupling. Either you get a high magnification together with a high output coupling, or
vice versa. Certain laser types, like e.g. thin-disc lasers or chemical oxygen iodine lasers, permit only quite low
optimum output couplings. The corresponding low resonator magnification is equal to a poor beam quality. In order
to apply unstable resonators with a high magnification also to low gain media an additional mirror surface
retroreflects a part of the out coupled radiation back into the cavity. The output coupling is reduced efficiently,
whereas the resonator magnification stays high. Accordingly low gain media can be operated with high power
extraction in combination with a good beam quality. Numerical and experimental investigations are shown. The
experiments are performed with a chemical oxygen iodine laser operating at a wavelength of 1.315 μm and
demonstrate the feasibility of this resonator design.
Beam Shaping I
Effect of ring width on ring generated Bessel beam
Show abstract
In this work we study the effect of the ring width on the performance of a ring generated Bessel beam. Experimental
results and simulation model for ring generated Bessel beams are investigated and compared. The simulation model is
based on Fourier optics. The effect of varying the ring radius and the ring width on the Bessel beam parameters like the
axial intensity and the detected output power transported by the beam passing through the ring is studied. A good
agreement is found between the simulation model and the measurements. Larger ring width led to higher efficiency
(output power) but to less beam quality.
Efficient beam splitting with continuous relief DOEs and microlens arrays
Show abstract
Diffractive optical elements (DOEs) are of rising importance for many industrial laser applications, especially for laser
beam shaping and laser beam splitting. Typically, such applications require high damage threshold of the diffractive
optical elements as well as high diffraction efficiency. Usually DOEs with multilevel (step-like) phase profiles are made
microlithographically and suffer from "quantisation" errors and scattering on profile derivative discontinuities. The steplike
structure lowers the DOE damage threshold compared to the intrinsic material values.
LIMO's microoptical technology is suitable for the production of high-precision free programmable continuous surface
profiles in optical glasses, crystals and metals. It can be applied for manufacturing of microlens and micro-mirror arrays
as well as for manufacturing of diffractive optics with continuous reliefs. Both the arrays and DOEs with continuous
relief are suitable for high efficiency laser beam splitting. However, the design approaches to obtain a desirable solution
for the corresponding continuous phase profiles are different.
The results of the wave-optical simulations made by LIMO's own program and by VirtualLab software, and
experimental studies for a 1 to 11 beam splitter with a continuous profile for the wavelength of 532 nm are presented.
Continuous phase profiles for the DOEs were designed by a procedure based on the theory of beam splitting by a phase
grating. Comparative theoretical and experimental studies were also done for splitting with a double-sided microlens
array. For both types of beam splitting the efficiency can be very high (> 98%). The DOEs show especially high
homogeneities of the resulting intensity distribution, however, they are much more sensitive to wavelength variations.
The microlens arrays demonstrate even weaker ghost orders as the DOE splitters and their surface profiles are simpler.
However, the efficiency and homogeneity suffer on interlens gaps.
Beam Shaping II
Gaussian-to-top-hat beam shaping: an overview of parameters, methods, and applications
Show abstract
Direct laser patterning of various materials is today widely used in several micro-system production lines like inkjet
printing, solar cell technology, flat-panel display production, LEDs, OLEDs, semiconductors and medicine. Typically
single-mode solid state lasers and their higher harmonics (e. g. 266, 355, 532 and 1064 nm) are used especially for
machining of holes and grooves. The striking advantages of flat top intensity distributions compared to Gaussian beam
profiles with respect to the efficiency and quality of these processes were already demonstrated. Here we will give an
overview of parameters, methods and applications of Gaussian-to-top-hat beam shaping. The top hat field size can start
from about 30 μm with no upper size limitation in the far field of the optics. Beam shaping for various wavelengths were
realized with field geometries of squares, rectangles and circles. With LIMO's compact Gaussian-to-top-hat converter an
inhomogeneity better than 5% contrast was reached. Special focus is put on the integration of Gaussian-to-top-hat beam
shapers in fast scanning systems employing Galvo mirrors and a specially developed f-Theta lens to avoid destruction of
the top hat profile within the scan field. Results with a 50x50μm2 top hat size (inhomogeneity down to <10%) in a scan
area of 156x156mm² are presented. The minimal distortions of the top hat observed within the scan area make LIMO's
compact Gaussian-to-top-hat converter excellently suited for industrial scanning applications, e.g. for the processing of
solar panels.
Wavefront reconstruction using computer-generated holograms
Show abstract
We propose a new method to determine the wavefront of a laser beam, based on modal decomposition using
computer-generated holograms (CGHs). Thereby the beam under test illuminates the CGH with a specific,
inscribed transmission function that enables the measurement of modal amplitudes and phases by evaluating the
first diffraction order of the hologram. Since we use an angular multiplexing technique, our method is innately
capable of real-time measurements of amplitude and phase, yielding the complete information about the optical
field. A measurement of the Stokes parameters, respectively of the polarization state, provides the possibility to
calculate the Poynting vector. Two wavefront reconstruction possibilities are outlined: reconstruction from the
phase for scalar beams and reconstruction from the Poynting vector for inhomogeneously polarized beams. To
quantify single aberrations, the reconstructed wavefront is decomposed into Zernike polynomials.
Our technique is applied to beams emerging from different kinds of multimode optical fibers, such as step-index,
photonic crystal and multicore fibers, whereas in this work results are exemplarily shown for a step-index fiber
and compared to a Shack-Hartmann measurement that serves as a reference.
Variable beam shaping with using the same field mapping refractive beam shaper
Show abstract
Modern laser scientific techniques and industrial technologies require not only simple homogenizing of a beam but also
more freedom in manipulation of intensity profile and generating such profiles like super-Gaussian, inverse-Gaussian,
skewed flattop and others. In many cases the task of variable beam shaping can be solved by refractive beam shaping
optics of field mapping type which operational principle presumes saving of beam consistency, providing collimated
output beam of low divergence, high transmittance and flatness of output beam profile, extended depth of field; another
important feature is negligible residual wave aberration. Typically the fields mapping refractive beam shapers, like
πShaper, are designed to generate flattop intensity profile for a beam of pre-determined size and input intensity profile.
Varying of the input beam diameter lets it possible to realize either super-Gaussian (smaller input) or inverse-Gaussian
(bigger input) intensity profiles of output beam that are important in pumping of solid-state lasers, hardening, cladding
and other techniques. By lateral shift of a beam with respect to a πShaper the output flattop profile gets a skew in
direction of that shift, the skew angle corresponds to the shift value. The skewed profile is important, for example, in
some acousto-optical techniques where compensation of acoustic wave attenuation is required. All variety of profiles can
be provided by the same beam shaper unit.
This paper will describe some design basics of refractive beam shapers of the field mapping type and techniques to vary
the output intensity profile, experimental results will be presented as well.
Propagating aberrated light
Show abstract
We outline a theory for the calculation of the laser beam quality factor of an aberrated laser beam. We provide closed
form equations which show that the beam quality factor of an aberrated Gaussian beam depends on all primary
aberrations except tilt, defocus and x-astigmatism. The model is verified experimentally by implementing aberrations as
digital holograms in the laboratory. We extend this concept to defining the mean focal length of an aberrated lens, and
show how this definition may be of use in controlling thermal aberrations in laser resonators. Finally, we look at
aberration correction and control using a combination of spatial light modulators and adaptive mirrors.
Beam or Mode Diagnostics
Continuous single pulse resolved measurement of beam diameters at 200 kHz using optical transmission filters
Show abstract
We present a novel laser beam measurement setup which allows the determination of the beam diameter for each
single pulse of a pulsed laser beam at repetition rates of up to 200 kHz. This is useful for online process-parameter
control e.g. in micromachining or for laser source characterization. Basically, the developed instrument combines
spatial transmission filters specially designed for instantaneous optical determination of the second order moments
of the lateral intensity distribution of the light beam and photodiodes coupled to customized electronics. The
acquisition is computer-based, enabling real-time operation for online monitoring or control. It also allows data
storage for a later analysis and visualization of the measurement results. The single-pulse resolved beam diameter
can be measured and recorded without any interruption for an unlimited number of pulses. It is only limited by
the capacity of the data storage means. In our setup a standard PC and hard-disk provided 2 hours uninterrupted
operation and recording of varying beam diameters at 200 kHz. This is about three orders of magnitude faster
than other systems. To calibrate our device we performed experiments in cw and pulsed regimes and the obtained
results were compared to those obtained with a commercial camera based system. Only minor deviations of the
beam diameter values between the two instruments were observed, proving the reliability of our approach.
Discerning comb and Fourier mean frequency from an fs laser based on the principle of non-interaction of waves
Show abstract
The key objective of this article is to underscore that as engineers, we need to pay close attention in repeatedly validating
and re-validating the underlying physical processes behind a working theory that models a phenomenon we are using to
create tools and technologies. We use the test case, the prevailing mode-lock theory, to illustrate our views by identifying
existing contradictions and showing approach towards their resolution by identifying the relevant physical processes.
The current theory tells us that the Fourier summation of all the allowed cavity modes directly produces the train of
pulses. It effectively assumes that electromagnetic (EM) waves are capable of re-organizing their spatial and temporal
energy distribution to generate a train of temporal pulses while preserving the spatial mode energy distribution. The
implication is that EM waves interact with each other by themselves. Even though the theory is working, we have three
logical problems. First, in the real world, in the linear domain, waves never interact with each other. On careful analysis
of all types of interference experiments, we will recognize that only in the presence of some interacting material medium
can we observe the physical superposition EFFECT. In other words, detectors carryout the superposition effect we call
interference phenomenon, through the summation of their multiple simultaneous linear stimulations and then absorbing
energy proportional to the square modulus of the sum total stimulation. Second, a Fourier monochromatic wave, existing
in all space and time, is a non-causal hypothesis. Just because our theories are working does not mean that we have
understood the real physical interaction processes in nature. We need to build our theories based upon space and time
finite EM wave packet containing a finite amount of energy, which is a causal approach. Third, in spite of staggering
successes of Quantum Mechanics, we do not yet have a self consistent model for space and time finite model of a
photon. QM only predicts that EM energy emission (spontaneous and stimulated) takes place only in a discrete amount at
a time from atoms and molecules. It does not give us recipe about how to visualize a propagating photon as it expands
diffractively. However, Huygens-Fresnel's classical diffraction integral gives us a rigorous model, which is the
cornerstone of modeling evolution of laser cavity modes, CW or pulsed. In this paper, we highlight the contradictions
that arise out of the prevailing mode-lock theory and resolve them by using causal models, already underscored above.
For example, there are now a wide range of very successful technological applications of the frequency comb extracted
out of fs lasers. If the Fourier summation were the correct physical process, then all the cavity modes would have been
summed (converted) into a single mean frequency around the gain line center for perfectly mode-locked systems.
Further, sending such fs pulses through an optical spectrometer would have always displayed a transform limited fringe,
centering on the mean Fourier frequency, rather than generating the comb frequencies, albeit instrumentally broadened.
Output pulse train from a phase locked laser is functionally produced due to the oscillatory time-gating behavior of the
intra-cavity phase-locking devices. So, we need to pay more attention to the fast temporal behavior of the materials we
use for achieving very fast time-gating, since this material imposes phase locking on the cavity modes to enhance its own
high-contrast time-gating behavior.
Real-time monitoring of thermal lensing of a multikilowatt fiber laser optical system
Show abstract
A laser beam waist analyzer system has been developed that permits the real time focal spot measurement of a high
power fiber laser in excess of ten of kilowatts and the ability to monitor thermal lensing of a laser and its optical system.
The analyzer can provide a laser's spatial profile, circularity, centroid, astigmatism and M-squared values inclusive of
the optics used in the process application. The system is very compact, measures in real time with no moving parts by
incorporating an all passive optical design to obtain spot diameter, M-squared, Rayleigh length, beam waist position at
power levels in excess of 20 kW in less than one second from laser off to laser on.
Comparison of two modal decomposition techniques
Show abstract
Higher oder modes in multi mode fibers determine fundamental beam properties. Hence, the knowledge about
the modal content becomes essential to understand the underlying physical effects. Therefore, different modal
decomposition techniques have been developed. In this paper we present a comparison of two methods. At
first the modal decomposition by a correlation filter method (CFM) and secondly using a numerical phase
retrieval algorithm. Limitations of both techniques are demonstrated and theirs overcoming by combining both
is presented.
Adaptive Optics
Active mirrors for intra-cavity compensation of the aspherical thermal lens in thin-disk lasers
Show abstract
With the development of the thin-disk laser, thermal lensing issues have been drastically reduced. However,
fundamental mode operation at high output powers is still limited by severe efficiency reductions due to diffraction
losses introduced by the temperature gradient at the boundary of the pump spot. To countervail these aspherical
wavefront deformations, high-power laser mirrors featuring deformable surfaces have been developed. The surface
of these mirrors resembles the shape of the thermally induced change of optical path length in the pumped laser
crystal. The magnitude of the surface deformation can be actively controlled to provide optimal compensation
at different power levels.
New deformable mirror technology and associated control strategies for ultrahigh intensity laser beam corrections and optimizations
Show abstract
When ultra high intensity lasers facilities were in their early development, the only concern was getting laser pulses with
the right energy and pulse duration. As facilities are orienting toward the end users, they are now required to deliver a
laser beam with additional qualities like a focal spot with constant quality. That is why Adaptive Optics is now a
standard feature for the current ultra high intensity lasers facilities to correct for the aberrations of the beam exiting the
laser chain. However, the very last optical components, like the off axis parabola to focus the beam induce aberrations
that cannot be directly corrected as they are located after the wavefront sensing.
We present a new technology of deformable mirror and a new correction strategy to get optimal focal spot in the
experiment chamber as well as measurement of the actual beam quality in the chamber while the beam is used for
experiments. These deformable mirrors were designed taking into account needs of ultra intense laser applications. They
provide exceptional stability, optical quality and innovative features like scalability and maintenance of the reflective
surface. The method of correction proposed uses usual adaptive optics loop to correct for all the aberration from the laser
chain, as well as additional steps to get an optimal focal spot in the experiment chamber on a non amplified beam, and to
correct and measure the actual beam quality on the amplified beam while it is used for experiments.
New Hartmann wavefront sensor for high power CO2 lasers
Show abstract
This paper presents the two types of Hartmann wavefront sensors to measure the aberrations of CO2 laser radiation. One
sensor is baser on commercially available IR camera while the second one - on so-called thing film sensors. We discuss
both positive and negative attributes of these sensors and the possibility to use them in the real laser systems.
Microcavity Lasers and Applications I
Unidirectional-emission, single-mode, whispering-gallery-mode microlasers
Show abstract
Unidirectional-emission microlasers are greatly demanded for photonic integrated circuits and optical interconnection. In
this paper, the mode characteristics of circular and coupled-circular microresonators with a bus waveguide are
numerically simulated by finite-difference time-domain technique. For a circular microresonator connected with a bus
waveguide, coupled-mode between two whispering-gallery modes can have high mode Q factor for realizing
unidirectional-emission lasing. In addition, symmetry and antisymmetry coupled modes are analyzed for the coupledcircular
microresonator with a middle bus waveguide. Furthermore, the output characteristics of a coupled-circular
microlaser, which is fabricated by standard photolithography and inductively-coupled-plasma (ICP) etching techniques,
are reported. Single mode operation is realized for the coupled-circular microlaser with a radius of 20 μm and a 2-μmwidth
bus waveguide.
Whispering-gallery-mode resonators for miniature optical clocks
Nan Yu,
Lukas M. Baumgartel,
Yanne Chembo,
et al.
Show abstract
Crystalline whispering gallery mode (WGM) resonators are small and structurally monolithic, yet capable of ultra-high
quality factors and dramatically enhanced optical nonlinearities. These properties can be exploited in developing
miniature optical clocks. Several studies have explored using WGM resonators as frequency reference cavities, and there
also exists great research interest in using WGMs for frequency comb generation. In this paper, we will describe our
efforts in pursuing laser stabilization using WGM reference cavities with both passive and active temperature
stabilization schemes. We will also present our latest analysis and experimental results in frequency comb generation in
WGM resonators.
Exploring the frequency stability limits of whispering gallery mode resonators for metrological applications
Yanne K. Chembo,
Lukas Baumgartel,
Nan Yu
Show abstract
Whispering gallery mode (WGM) resonators are attracting increasing interest as possible frequency reference
cavities. Unlike commonly used Fabry-Perot cavities, however, WGM resonators are dielectric resonators lled
with a bulk medium whose properties have a signicant impact on the stability of its resonance frequencies.
Thermal and other refraction index
uctuations of the medium induce additional frequency instability that
has to be reduced to a minimum. On the other hand, a small monolithic resonator provides opportunity for
integration and immunity against vibration and acceleration disturbances. This feature is essential when the
cavity operates in a non-laboratory environment. In this paper, we report a case study of vibration sensitivity
reduction for a crystalline resonator and discuss a pathway towards the inhibition of vibration- and acceleration-
induced frequency
uctuations.
Parametric Processes in Microresonators
Monolithic optical parametric oscillators
Ingo Breunig,
Tobias Beckmann,
Karsten Buse
Show abstract
Stability and footprint of optical parametric oscillators (OPOs) strongly depend on the cavity used. Monolithic
OPOs tend to be most stable and compact since they do not require external mirrors that have to be aligned. The
most straightforward way to get rid of the mirrors is to coat the end faces of the nonlinear crystal. Whispering
gallery resonators (WGRs) are a more advanced solution since they provide ultra-high reflectivity over a wide
spectral range without any coating. Furthermore, they can be fabricated out of nonlinear-optical materials like
lithium niobate. Thus, they are ideally suited to serve as a monolithic OPO cavity.
We present the experimental realization of optical parametric oscillators based on whispering gallery resonators.
Pumped at 1 μm wavelength, they generate signal and idler fields tunable between 1.8 and 2.5 μm
wavelength. We explore different schemes, how to phase match the nonlinear interaction in a WGR. In particular,
we show improvements in the fabrication of quasi-phase-matching structures. They enable great flexibility
for the tuning and for the choice of the pump laser.
Photonic microwave receivers based on high-Q optical resonance
Show abstract
The quest for low power and high frequency electro-optical modulator has been one of the important endeavors in
microwave photonics. The advent of microdisk electro-optic modulator created a new domain in optical modulator and
photonic microwave receiver design by exploiting the unique properties of high quality (high-Q) Whispering-Gallery
Mode (WGM) optical cavities. High-Q crystalline WG cavities were the first devices used as compact and low power
resonant electro-optical modulators and gradually semiconductor and polymer based microdisk and microring
modulators emerged from this core technology. Due to its small size, high sensitivity and limited bandwidth, originally
microdisk modulator was developed with the objective of replacing the conventional microwave wireless receiver frontend
with a sensitive photonic front-end. Later it was shown that the electro-optic microdisk modulator could also
function as a microwave frequency mixer in optical domain. Starting from fundamentals of resonant electro-optic
modulation in high-Q WGM cavities, in this paper we review the development of high sensitivity microdisk modulators
and the recent progress toward more efficient modulation at higher frequencies. Next related topics such as singlesideband
modulation, all-dielectric photonic receiver, and semiconductor microring modulators are briefly discussed.
Finally, photonic microwave receiver configurations that employ high-Q optical resonance for modulation, filtering and
mixing are presented. We will show that high-Q optical resonance is one of the promising routes toward the general idea
of an all-optical microwave receiver free of high frequency electronic transistors, mixers and filters.
Integration of Microresonators and Photonic Circuits
Coupling approaches and new geometries in whispering-gallery-mode resonators
Show abstract
In order to fully exploit the unique properties of micro-optical resonators with whispering gallery modes (WGMs), both
for fundamental investigations as well as for practical applications, a critical point is an efficient, controllable, and robust
coupling of the light to the cavity WGMs. We present the results of our studies on phase-matched evanescent field
couplers, with particular reference to the coupling to high-index crystalline resonators like lithium niobate disks. We
focus on couplers based on different types of waveguide configurations and include demonstration of optical coupling to
high-Q lithium niobate resonators from integrated planar waveguides as well as from angle polished waveguides. These
systems are all in guided optics architectures. We also briefly present our recent achievements in the development of
microbubble resonators fabricated from silica capillaries. We show that, as high-Q hollow 3-D cavities with intrinsic
microfluidics, these resonators represent a promising biochemical sensing platform.
Microcavity Lasers and Applications II
Dynamic multi-mode analysis of passive Q-switched lasers
Show abstract
Passive Q-switched lasers are constructed using saturable absorbers (SA). One characteristic of these lasers is
that they are built with small dimensions. There are difficulties in designing lasers with a given pulse repetition
rate or pulse energy using saturable absorbers. Numerical simulation of Q-switches facilitates the design and
production of such lasers and helps to reduce development time and cost. This paper presents a new simulation
method which calculates beam quality, maximal output power, pulse-width and pulse energy.
Improvements in monoblock performance using external reflector
A. D. Hays,
John Nettleton,
Nick Barr,
et al.
Show abstract
During the past few years the Monoblock laser has become the laser-of-choice for Army laser range-finders. It is eyesafe
with emission at 1570 nm, high pulse energy, simple construction, and high efficiency when pumped by a laserdiode
stack, providing advantages that are not available with other laser types. Although the divergence of the
Monoblock output beam is relatively large, it can be reduced to <1 mR using a telescope with a large magnification.
This solution, however, is not acceptable for applications where the laser and telescope size must be kept to a minimum.
In this paper we present a simple and compact technique for achieving significant reduction in the Monoblock beam
divergence using a partial reflector that is placed a short distance from the optical parametric oscillator (OPO). Using
an ultra-compact 38 mm Monoblock with a 10 mm long KTP OPO, we achieved a beam divergence of <4 mR,
corresponding to a >2.5 X reduction from the unmodified laser. Performance using this technique with various feedback
and etalon spacings will be presented. Laser diode array and VCSEL pumping were both investigated with similar
results.
Characterization of the longitudinal Gouy phase branches in cascaded optical systems
Show abstract
The Gouy phase is an important phase, however rather poorly understood. It has been shown recently that
it can be used to control the frequency of a ring laser and can help in achieving a control over mode-locking
problem of ring laser gyro. It is demonstrated now that with the help of the Gouy phase one discovers further
characterization of a laser involving cascaded optics in terms of what may be called longitudinal Gouy phase
branches. On such a Gouy phase branch one can tune the laser in a manner described elsewhere. It is noted that
the longitudinal Gouy-phase-branches play significant role in cascaded optical systems as well as have potential
characterization feature in several ring configurations that get naturally selected in a random lasing medium.
The concept is further clarified with Collins chart diagrams of several cascaded optics lasers.
Microresonator-Based Sensors I
Nonlinear modes of plasmonic microcavities: theoretical analysis and device applications
Show abstract
High fabrication costs of complex photonic nano-devices make it imperative to have access to high-performance
computational tools, which can greatly accelerate the device design process by reducing the design-fabricationtesting
cycle. To this end, in this article we briefly review a numerical method based on the multiple scattering
algorithm, which we used to describe the second-harmonic generation in plasmonic nanostructures. Then, by
using specific examples, we illustrate how this method can be employed to characterize the nonlinear optical
modes of microcavities made of plasmonic nanowires. In particular, we show that such plasmonic microcavities
have three distinct types of modes, namely, plasmonic cavity modes, multipole plasmon modes generated via
the hybridization of modes of single nanowires, and whispering gallery modes. We also show that due to the
sensitivity of the nonlinear plasmonic cavity modes to the changes in the environment, they are ideal candidates
for nano-scale sensing devices, e. g., plasmonic sensors.
Silicon microring sensors
Show abstract
Due to its closed-loop structure, the silicon microring resonator can have a very high quality factor value and its output
intensity is very sensitive to different wavelengths. These characters, plus the potential in CMOS compatible fabrication
process, are making the silicon microring resonator a key building block of photonic integrated circuits for the
applications of filtering, switching, modulation, and wavelength conversion. In parallel, the silicon microring resonator
has also been proposed as a compact and highly sensitive optical sensor. In recent years, microring sensing related
research and development has been growing consistently and rapidly for the purposes of environment monitoring, health
diagnosis, and drug development. This article will firstly review the recent development in silicon microring sensors,
which are mainly concentrated in two areas: to improve the sensitivity and to enhance selectivity. In order to have better
understanding of this class of sensors, the basic structure of the microring sensors, its working principle, and its unique
properties will be described. Then, our own works, in particular, the methods to improve dynamic range, sensitivity, and
stability of the silicon microring sensors, will be presented. By studying the fundamental optical properties of the
coupled microring resonators, novel silicon microring sensors with better and more reliable sensing performance are
constructed. Finally, through studying the interactions between chemistry and optics, acceleration and optics, the specific
applications in glucose sensing and seismic sensing are discussed.
Microresonator-Based Sensors II
On-chip whispering-gallery-mode lasers for sensing applications
Show abstract
Whispering-Gallery-Mode (WGM) microresonators have shown great promise for ultra-sensitive and label-free chemical
and biological sensing. The linewidth of a resonant mode determines the smallest resolvable changes in the WGM
spectrum, which, in turn, affects the detection limit. The fundamental limit is set by the linewidth of the resonant mode
due to material absorption induced photon loss. We report a real-time detection method with single nanoparticle
resolution that surpasses the detection limit of most passive micro/nano photonic resonant devices. This is achieved by
using an on-chip WGM microcavity laser as the sensing element, whose linewidth is much narrower than its passive
counterpart due to optical gain in the resonant lasing mode. In this microlaser based sensing platform, the first binding
nanoparticle induces splitting of the lasing line, and the subsequent particles alter the amount of splitting, which can be
monitored by measuring the beat frequency of the split modes. We demonstrate detection of polystyrene and gold
nanoparticles as small as 15 nm and 10 nm in radius, respectively, and Influenza A virions. The built-in self-heterodyne
interferometric method achieved in the monolithic microlaser provides a self-referencing scheme with extraordinary
sensitivity, and paves the way for detection and spectroscopy of nano-scale objects using micro/nano lasers.
Polymer microring resonators for high sensitivity, broadband, wide-directivity ultrasound detection and high-resolution imaging
Show abstract
Optical detection of ultrasound is an emerging technique based on the interaction of strain field and optical field,
modulating the optical properties of the resonance cavity for sensitive detection. Such a detection scheme can have
several unique advantages, such as broadband response and size-independent sensitivity, compared with conventional
piezoelectric transducers. Detector's high sensitivity is essential for deep penetration depth, especially for highresolution
imaging because of the strong attenuation of high-frequency ultrasound. Besides, small element size has the
advantage of realizing wide acceptance angle of ultrasound detection. Previously we have demonstrated optical-based
ultrasound detectors using polymer microring resonators, showing flat spectral response from dc to high frequency, over
90 MHz at -3-dB. By improving the fabrication process, we are able to achieve a new generation device with higher
sensitivity and smaller element size. An ultralow noise-equivalent pressure of 21.4 Pa over 1-75 MHz range has been
achieved using a fabricated detector of 60 μm diameter. We will mainly demonstrate its applications to photoacoustic
imaging, including photoacoustic computed tomography and photoacoustic microscopy. The new generation device can
also be applied to other ultrasound-related imaging and detection.
Fiber optic resonator sensors based on comb synthesizers
G. Gagliardi
Show abstract
Over the past several years, fiber-optic resonators have been successfully used as mechanical probes by virtue of their
intrinsic sensitivity to length changes. In a recent work, we devised a diode-laser system for strain interrogation of a
high-finesse fiber Bragg-grating cavity, achieving a 10-13 resolution in the infrasonic and acoustic frequency ranges,
thanks to the exceptional stability of an optical frequency comb (OFC). A Pound-Drever-Hall (PDH) frequency locking
technique is implemented for low-noise and wide dynamic range readout of the sensor keeping the interrogating laser
always linked to the OFC reference. In this way, the low-frequency strain noisefloor is free from laser noise and possibly
limited by thermodynamic phase fluctuations or other thermal effects in the fiber.
Microresonator-Based Sensors III
Porous wall hollow glass microsphere as an optical microresonator for chemical vapor detection
Show abstract
Optical microresonators have been proven effective for developing sensitive chemical and biological sensors by
monitoring the changes in refractive index or mass near the resonator surface. The rotationally symmetric structures
support high quality (Q) whispering gallery modes (WGMs) that interact with the local environment through the
evanescent field. The long photon lifetime of the high-Q resonator (thus the long light-material interaction path) is the
key reason that a microresonator can achieve very high sensitivity in detection. In this paper, we present our recent
research on using porous wall hollow glass microsphere (PW-HGM) as an optical microresonator for chemical vapor
detection. The diameter of the PW-HGM ranges from 10μm to 100μm. The wall thickness is about 2μm and the pore
size is about 20nm. The Q-factors and free spectrum ranges (FSR) of PW-HGMs were measured by coupling light into
the PW-HGM using a single mode fiber taper. Various types of chemical vapors were used to characterize the PW-HGM
resonator. The resonant wavelength shift was measured as a function of vapor concentration. Comparisons between a
PW-HGM and a solid glass microsphere indicated that a PW-HGM can effectively adsorb vapor molecules into its nanosized
pores, providing a direct and long light-material interaction path for significant sensitivity enhancement for
chemical vapor detection.
Sensitivity of long-wave infrared intracavity laser absorption vapor detector
Show abstract
A quantum cascade laser at IR wavelengths with an open external cavity presents an opportunity for spectral sensing of
molecular compounds that have low vapor pressure. The sensitivity of such a system is potentially very high due to
extraordinarily long effective optical paths that can be achieved in an active cavity. We demonstrate here an external
cavity mid-IR QCL molecular absorption sensor using a fixed Fabry-Perot etalon as the spectrum analyzer. The system is
sensitive to the water vapor present in the laboratory air with an absorption coefficient of just 9.6 x 10-8 cm-1. The system
is sensitive enough to detect the absorption coefficient of TNT vapor at room temperature.
Resonant Opto-Mechanics
Whispering gallery mode resonators as tools for non-linear optics and optomechanics
Show abstract
In principle, a microspherical resonator pendulum can be trapped using the optical forces produced by two
simultaneously excited whispering gallery modes of a photonic molecule, comprising two microspherical cavities. The
cavity-enhanced optical force generated in the photonic molecule creates an optomechanical potential that can trap the
pendulum at an equilibrium position by carefully choosing the excitation laser frequencies. In this paper, we study the
mechanical characteristics of microsphere pendulums by evanescently detecting the pendulum motion. Nonlinear effects
like electromagnetically induced transparency and absorption, and Fano resonances have also been observed using a
microsphere-fiber taper system and the results are presented here.
Surface acoustic wave frequency comb
Show abstract
We investigate opto-mechanical oscillation (OMO) and subsequent generation of acoustic wave frequency combs
in monolithic crystalline whispering gallery mode (WGM) resonators. The OMO is observed in resonators made
of electro-optic (lithium tantalate), non-electro-optic birefringent (magnesium fluoride), and non-birefringent
(calcium fluoride) materials. The phenomenon manifests itself as generation of optical harmonics separated by
the eigenfrequency of a surface acoustic wave (SAW) mechanical mode of the same WGM resonator. We show
that the light escaping the resonator and demodulated on a fast photodiode produces a spectrally pure radio
frequency (RF) signal. For instance, we demonstrate generation of 200 MHz signals with instantaneous linewidth
of 0.2 Hz.
Effects of spatial confinement of electromagnetic field on optical forces due to whispering-gallery modes
Show abstract
Using ab initio approach to the theory of electromagnetic interaction of a small particle and spherical whispering
gallery mode resonator, we derive the optical forces experienced by the particle and it's resulting motion. The
form of the forces differs from that expected by the traditional gradient/scattering approach due to the modification
of the field by the particle. The main effect of the confinement of the field in a cavity consists in making
the component of the optical force usually interpreted as gradient, manifestly non-conservative, and hence not
presentable in the gradient form. It is shown how the standard gradient/scattering formalism can be modified
for the cavity confined optical field.
Evanescent light coupling and optical propelling of microspheres in water immersed fiber couplers
Show abstract
We study the propulsion of polystyrene microspheres along water immersed silica tapered fibers. We observed a nearly
linear increase of the propulsion velocity with the sphere diameter increasing from 3 to 20 μm. By measuring the fiber
transmission spectra we demonstrate efficient evanescent coupling of light to whispering gallery modes (WGMs) in large
(>10 μm) polystyrene spheres. For 20 μm spheres we observed the depth of resonant dips ~ 3.5 dB in combination with
the Q-factors ~ 103. Due to small losses in the fiber ~1-2 dB we are able to determine the power in the tapered region and
to characterize quantitatively the optical propelling forces. The maximum value of the propelling velocity was 260 μm/s
and was observed for 15 μm spheres with guided power of only 43 mW. Such velocities are nearly an order of magnitude
higher than those observed for similar powers on waveguide structures. Using simple physical arguments we show that
for spheres with diameters larger than 10 μm the experimentally observed velocities of propelling are too high to be
explained by the conventional nonresonant scattering forces. We propose that these high velocities indicate that the
optical forces are enhanced in such cases due to resonant coupling effects.
Resonant Four-Wave Mixing and Applications
Nonlinearities in silicon photonics: something to exploit or to counteract?
Show abstract
In the 1550-nm wavelength range, silicon waveguides exhibit a plethora of non-linear phenomena arising when the
optical power is sufficiently intense. Inside optical resonators the efficiency of wave mixing effects is largely enhanced
and can be effectively exploited for on-chip all-optical signal processing. By cascading silicon microring resonators, we
demonstrated the concept of travelling-wave resonant four-wave mixing (FWM) and we realized a 630-μm-long
wavelength converter with a conversion gain 28-dB higher than a bare waveguide of the same physical length. Both the
conversion efficiency and the bandwidth of the device are enhanced with respect to a single silicon resonator. However,
one of the major impairments associated with nonlinearity in silicon is the TPA-induced local heating of the waveguides.
In coupled resonator architectures, this produces not simply a rigid red-shift of the spectral response, but a resonance
spread disrupting the frequency response of the devices. Active thermal control of the individual resonators is proposed
as a viable strategy to adaptively compensate for intensity-dependent distortions and cross-talk increase in silicon
coupled resonator filters, demonstrating that device performance can be preserved regardless of the aggregate power
transmitted through the waveguide.
Linear and nonlinear effects of electron paramagnetic resonance in high-Q cryogenic sapphire microwave resonators
Daniel L. Creedon,
Karim Benmessai,
Warwick P. Bowen,
et al.
Show abstract
Cryogenic sapphire resonators operating in Whispering Gallery Modes have very high Q-factors (> 109) at
microwave frequencies . Such a property makes them useful for a host of applications, which are only possible due
to the additional inclusion of residual paramagnetic impurities that annul the frequency-temperature dependence
of sapphire. More recently, residual Fe3+ impurities with parts-per-billion concentration within the lattice have
been shown to create a three level system corresponding to the spin states of the ion. By pumping at 31.3 GHz, a
stable 12.04 GHz maser signal (stability of parts in 1014) has been created without any stabilization circuitry. In
addition, we have observed the fundamental thermal noise limit near 4 K by operating such masers in a bimodal
conguration. Annealing one resonator in air has led to conversion of Fe2+ ions in the lattice to Fe3+, leading
to an orders of magnitude increase in active ion concentration. At the post-annealing Fe3+ concentration of 150
ppb , we observe nonlinear eects such as a degenerate four-wave mixing due to a χ(3) magnetic nonlinearity as
well as stable frequency comb generation.
Ab initio theory of nonlinear effects in individual and coupled microdisk resonators
Show abstract
Ab initio approach to description of nonlinear dynamics of individual and coupled microdisk whispering-gallerymode
resonators is developed for the nonlinearities of Kerr type. Distinction between scattering resonances and
eigenfrequencies, which is important for resonators with moderate quality factors is discussed. Properties of
various parameters important for nonlinear dynamics, such as coupling to external radiation, linear inter-disk
coupling parameter, nonlinear mode overlap coefficients are discussed from the point of view of the ab initio
formulation.
Doped Microresonators
Hybrid microspheres for nonlinear Kerr switching applications
Show abstract
Electronic Kerr effect in a polyfluorene derivative is used to reversibly switch near infrared probe beam resonantly
coupled to a hybrid polymer-silica microspherical resonator. NIR pumping at 780 nm in pulsed laser regime is used for
non-linear switching of the WGM resonances that shift as much as 2 GHz for 50 mW of average pump power, compared
to a shift of 250 MHz for the same average pump power at CW regime. The absence of temporal drift and the magnitude
of this shift confirm the Kerr nature of the switching, ruling out thermooptical effects.
Spherical resonators coated by glass and glass-ceramic films
Show abstract
Coating of spherical microresonators is a very promising technique for optimizing their optical
properties. Optical coatings are constituted by glasses, polymer, and glass ceramics, passive or
activated by luminescent species, Glass ceramic activated by rare earth ions are nanocomposite
systems that exhibit specific morphologic, structural and spectroscopic properties allowing to
develop interesting new physical concepts, for instance the mechanism related to the transparency,
as well as novel photonic devices based on the enhancement of the luminescence. At the state of art
the fabrication techniques based on bottom-up and top-down approaches appear to be viable
although a specific effort is required to achieve the necessary reliability and reproducibility of the
preparation protocols. In particular, the dependence of the final product on the specific parent glass
and on the employed synthesis still remain an important task of the research in material science.
Looking to application, the enhanced spectroscopic properties typical of glass ceramic in respect to
those of the amorphous structures constitute an important point for the development of integrated
optics devices, including coating of spherical microresonators. Here we present a review regarding
spherical microresonators coated by glass and glass-ceramic film activated by Er3+ ions. Er3+ ions
appear to be embedded in a crystalline or amorphous environment and the lifetime dynamic is
influenced by the geometry and by the morphology of the system. Photoluminescence results and
morphologic properties are discussed for both amorphous and glass ceramic films.
Composite micro-sphere optical resonators for electric field measurement
J. Stubblefield,
D. Womack,
T. Ioppolo,
et al.
Show abstract
Polymer-based, multi-layered dielectric microspheres are investigated for high-resolution electric field
sensing. The external electric field induces changes in the morphology of the spheres, leading to shifts
in the whispering gallery modes (WGMs). Light from a distributed feedback (DFB) laser is sidecoupled
into the microspheres using a tapered section of a single mode optical fiber to interrogate the
optical modes. The base material of these multi-layered spheres is polydimethylsiloxane (PDMS).
Three microsphere geometries are investigated: (1) cores comprised of a 60:1 volumetric ratio of
PDMS-to-curing agent mixture that are mixed with varying amounts of barium titanate (BaTiO3) nano
particles, (2) cores comprised of 60:1 PDMS that are coated with a thin layer of 60:1 PDMS that is
mixed with varying amounts of barium titanate and (3) a composite Carbon Black-BaTiO3 prototype.
The outermost layer for all sphere geometries is a thin coat of 60:1 PDMS which serves as the shell
waveguide. Light from the tapered laser is coupled into this outermost shell that provides high optical
quality factor WGM (Q ~ 106). The microspheres are poled for several hours at electric fields of ~ 1
MV/m to increase their sensitivity to electric field. Preliminary results show that electric fields of the
order of 100 V/m can be detected using these composite micro-resonators.
Coupled Microresonators and Effects
Silicon photonic resonator sensors and devices
Show abstract
Silicon photonic resonators, implemented using silicon-on-insulator substrates, are promising for numerous applications.
The most commonly studied resonators are ring/racetrack resonators. We have fabricated these and other resonators including
disk resonators, waveguide-grating resonators, ring resonator reflectors, contra-directional grating-coupler ring
resonators, and racetrack-based multiplexer/demultiplexers.
While numerous resonators have been demonstrated for sensing purposes, it remains unclear as to which structures
provide the highest sensitivity and best limit of detection; for example, disc resonators and slot-waveguide-based ring
resonators have been conjectured to provide an improved limit of detection. Here, we compare various resonators in
terms of sensor metrics for label-free bio-sensing in a micro-fluidic environment. We have integrated resonator arrays with
PDMS micro-fluidics for real-time detection of biomolecules in experiments such as antigen-antibody binding reaction
experiments using Human Factor IX proteins. Numerous resonators are fabricated on the same wafer and experimentally
compared. We identify that, while evanescent-field sensors all operate on the principle that the analyte's refractive index
shifts the resonant frequency, there are important differences between implementations that lie in the relationship between
the optical field overlap with the analyte and the relative contributions of the various loss mechanisms.
The chips were fabricated in the context of the CMC-UBC Silicon Nanophotonics Fabrication course and workshop.
This yearlong, design-based, graduate training program is offered to students from across Canada and, over the last four
years, has attracted participants from nearly every Canadian university involved in photonics research. The course takes
students through a full design cycle of a photonic circuit, including theory, modelling, design, and experimentation.
Longitudinal mode selection in laser cavity by moiré volume Bragg grating
Show abstract
A Fabry-Perot etalon, consisting of two π phase shifted reflecting volume Bragg gratings, is presented. These gratings
are obtained as a moiré pattern resulting from sequential recording of interference patterns with different periods in
photo-thermo-refractive glass and called moiré volume Bragg gratings (MVBGs). A detailed investigation of the
fundamental operating principles and measurement techniques for phase shifted gratings is shown. Experimental results
demonstrating a MVBG with a 15 pm bandwidth and 90% transmission at resonance are presented. The use of the
MVBG for longitudinal mode selection in a laser resonator is shown.
Beam tapering effect in microsphere chains: from geometrical to physical optics
Show abstract
By using polystyrene microspheres with index n=1.59 as a model system we study light focusing and transport
properties of chains formed by spheres with diameters varying from 2 to 30 μm. We used techniques of imaging based
on light scattering perpendicular to the axis of the chain to visualize and study periodically focused beams in such
structures. The results demonstrate good agreement with geometrical optics modeling for sufficiently large spheres,
D>>10λ, where D is the sphere diameter and λ is the wavelength of light. For mesoscale structures with 4<D/>><10 we
observed two effects which cannot be explained by geometrical optics. One is a "beam tapering" effect which is stronger
in normalized units than it is theoretically possible in the limit of geometrical optics in short chains. Another effect is
reduced power attenuation in sufficiently long chains which is found to be smaller than it is possible in the limit of
geometrical optics. Both effects are ascribed to the increased role of physical optics properties. We can also suggest
some role of the microjoints developing between polystyrene microspheres in self-assembled structures. The results are
important for developing applications requiring focusing of multimodal beams such as mid-infrared laser surgery.
Accurate analytical estimates of eigenfrequencies and dispersion in whispering-gallery spheroidal resonators
Show abstract
In several applications of optical whispering-gallery resonators, in particular for Kerr frequency comb generation,
a possibility to calculate accurately the eigenfrequencies and geometry dependent dispersion is an important prerequisite
for device optimization. While these calculations with significant time consumption may be performed
numerically, analytical approximation are still quite desirable for theoretical considerations. Spheroidal geometry
can fit the form of most types of whispering gallery resonators that are in use today. We propose and check
numerically new accurate approximations for the frequencies and geometrical dispersion of fundamental and
transversal modes of oblate and prolate spheroids using both the eikonal approximation and WKB analysis. We
also suggest approximations for the distribution of optical fields in a spheroidal resonator.
Poster Session
Generalized model for beam-path variation in ring resonator and its applications in backscattering coupling effect
Show abstract
A generalized model for beam-path variation analyzed with vector method in square ring
resonators is established. The model can be applied to analyze beam-path variation in various ring
resonators induced by all the possible perturbation sources. The generalized model is useful for the
cavity design, cavity improvement, alignment of planar ring resonators and research on backscattering
coupling effect. Backscattering coupling effect in square ring resonator has been chosen as examples to
show its application. Backscattering coupling coefficient r is obtained as a function of mirror's axial
displacements. Some novel results of backscattering coupling effect have been acquired. The results
indicate that r can not be reduced to zero because of the initial machining errors of surfaces of plane
mirrors. However, r can be reduced to zero almost when stabilizing frequency of laser gyro by take the
suitable values of axial displacements of plane mirrors. These results are important for high precision
laser gyro.
Performance of the smoothing of small target spots in frequency-tripled high-power laser
Xiujuan Jiang,
Jinghui Li
Show abstract
The uniform irradiation performance of the small target spots for indirect-drive inertial confinement fusion is
studied. A lens array and the technique of smoothing by spectral dispersion are included in the frequency-tripled
high-power laser driver. The intensity distributions of the target spots are simulated and their spatial power
spectra are analyzed. The results show that spots of clear envelopes can be obtained with a lens array and
smoothing by spectral dispersion has obvious effects in eliminating high-contrast intensity modulation inside
the spots, even in the cases they are very small. With the two methods of beam smoothing, performance of
indirect-drive experiments is expected to be evidently improved.
About some possibilities of influencing the energetic relief of metals in order to favor micro-joining processes
Show abstract
The energetic relief depends on the nature of the considered element which has its own internal energy, cohesion,
structure and other characteristic parameters.
Former experiences has shown that we could appreciate how and when a metal part was cut, with the aid of an electron
counter system - in a determined period of time.
To join or aggregate metal parts - or particles like powder - we must reduce or eliminate the influence and effect of the
energetic relief between the considered parts or particles. Different types of fields or energy may be applied in order to
do that.
Authors experienced some kind of energies and studied the resulting plasma with the magnetohidrodynamic theory. They
found that the variation of plasma density and the intensity of the magnetic field appears in a time interval which is under
- or comparable - with the wave lenght at this was the start point to develope further research. The experiences were
made with the aid of an original device. Of course, after measuring and studying the main obtained data, authors have
designed installation and devices, for industrial use.
One of the - economical - conclusion, was that is possible to influence the energetic relief in order to diminish costs of
all type of aggregation processes, like sintering, welding a.s.o. In the same time, the processing time, may be reduced.