The three-wave equations that describe broadband microresonators with a nearly quartic dispersion are briefly derived. They are then applied to describe recent experimental results in which interleaved frequency combs are generated, from which a single broadband frequency comb can be generated under the right conditions [1,2].
1. G. Moille, et al., “Kerr-induced synchronization of a cavity soliton to an optical reference,” Nature 624, 267–274 (14 Dec. 2023) [doi: 10.1038/s41586-023-06730-0].
2. G. Moille, et al., “Ultra-broadband Kerr microcomb through soliton spectral translation,” Nat. Comm. 12, 7275 (2021) [doi: 10.1038/s4146-021-27469-0].
KEYWORDS: Photodetectors, Quantum efficiency, Temperature distribution, Indium gallium arsenide, Electric fields, Electrical conductivity, Temperature metrology
We present an approximation method to compute the temperature distribution in photodetectors under steady-state optical excitation. The derived temperature profile assesses the impact on performance metrics like quantum efficiency, bandwidth, and phase noise. Our numerical study reveals that assuming constant room temperature leads to overestimated output current and quantum efficiency and underestimated bandwidth. In contrast, a varying temperature model closely aligns with experimental values. InGaAs’s low thermal conductivity impedes heat dissipation, leading to temperature accumulation. Changing optical excitation while maintaining constant output current results in nonlinear changes in bandwidth, phase noise, and quantum efficiency. These findings aid in understanding and optimizing thermal management in photodetectors under strong optical excitations.
Subwavelength moth eye structures are the nanostructures arranged uniformly whose feature size is less than the incident optical wavelength. These structures are promising to reduce the reflection of any material by creating a refractive index gradient profile at the interface surface. Mid-wave infrared (MWIR) is an important wavelength to investigate the moth eye structures for various applications like photovoltaic, solar cells and display technologies. In this paper, we fabricated two different moth eye structures Nano pillars and Nano holes using the simple and robust lithography technique. Using silicon dioxide as a hard mask, structures are transferred onto gallium arsenide substrate using different etching conditions. We compared the transmission of nanoholes and nanopillars structures and find out that nanoholes structures shows better transmittance in MWIR. We also obtained theoretical transmission data using rigorous coupled wave analysis (RCWA) which agrees with our experimental data. Moreover, Nano holes structures has an advantage over nanopillars structure as the former are resistant against contamination which therefore will not lead to decrease in transmission performance. The characterization results of the structures are obtained from SEM which shows the morphologies of the structures. Our approach is reproducible and can be easily applied to any optical devices which require antireflective property.
We demonstrate that a dissipative Kerr soliton comb tooth can be captured by another injected pump laser, resulting in Kerr induced synchronization. This regime is highly significant for metrology applications, where the soliton can passively lock onto a reference clock laser. The dynamics of the system also enable other forms of locking, where the comb tooth is captured at a fixed offset from the reference laser, entering the syntonization regime. Similar to breather entrainment, we establish that the syntonization frequency offset correlates with the soliton's repetition rate.
We show that in the Kerr-Induced Synchronization (KIS) regime, an external reference pump laser allows for the control of the opposite (in frequency) Dispersive Wave (DW) power and frequency, through self-balancing of the cavity soliton. We report an increase of more than 20~dB of the DW of an octave-spanning comb at 780 nm, with a reference pump in the telecom C-band, while tuning of the DW over three comb teeth. Our work paves the way for significant improvement of the carrier-envelope offset frequency detection of octave-spanning combs.
We initially developed an efficient solver to study photodetectors composed of multiple semiconductor layers with varying thicknesses and doping concentrations. Subsequently, we employed it as the forward solver for three different numerical optimization methods aimed at designing Si-Ge photodetectors with larger bandwidth, higher quantum efficiency, and lower phase noise. Our work offers new insights into the design of high-performance photodetectors—a challenging task due to computation time, design constraints, and the complexity of estimating sensitivity to design parameters.
We present a study on the accuracy of three neural network architectures, namely fully-connected neural networks, recurrent neural networks, and attention-based neural networks, in predicting the coupling response of broadband microresonator frequency combs. These frequency combs are crucial for technologies like optical atomic clocks. Optimizing their spectral features, especially the dispersion in coupling to an access waveguide, can be computationally demanding due to the large number of parameters and wide spectral bandwidths involved. To address this challenge, we employ machine learning algorithms to estimate the coupling response at wavelengths not present in the input training data. Our findings demonstrate that when trained with data sets encompassing the upper and lower limits of each design feature, attention mechanisms achieve over 90% accuracy in predicting the coupling rate for spectral ranges six times wider than those used in training. This significantly reduces the computational burden for numerical optimization in ring resonator design, potentially leading to a six-fold reduction in compute time. Moreover, devices with strong correlations between design features and performance metrics may experience even greater acceleration.
We present the demonstration of elastic collisions between dissipative Kerr solitons at different repetition rates in an integrated microresonator. Their periodic collision results in a periodic inter-exchange of their repetition rate. We observe this phenomenon experimentally, and support it with numerical simulations, with each comb tooth is impacted by the periodic soliton collision, producing an interwoven frequency comb.
We present the creation of a two-dimensional frequency comb in a single integrated microring resonator through its dual pumping. We demonstrate experimentally and theoretically that dual-pumping allows for the creation of a multi-color soliton with a single group rotation velocity yet multiple phase rotation velocities, yielding multiple soliton eigenfrequencies (i.e. colors). We show that, thanks to the material's nonlinearity, its eigenfrequencies can cascade through four-wave mixing, creating a comb. Because this dimension is orthogonal to the azimuthal mode number dimension, the extracted frequency comb is ultimately a two-dimensional one.
KEYWORDS: Frequency combs, Pulsed laser operation, Monte Carlo methods, Systems modeling, Solitons, Latex, Laser development, Fiber lasers, Laser systems engineering, Doping
Key issues in the design of any passively modelocked laser system are determining the parameter ranges within which it can operate stably, determining its noise performance, and then optimizing the design to achieve the best possible output pulse parameters. Here, we review work within our research group to use computational methods based on dynamical systems theory to accurately and efficiently address these issues. These methods are typically many orders of magnitude faster than widely used evolutionary methods. We then review our application of these methods to the analysis and design of passively modelocked fiber lasers that use a semiconductor saturable absorbing mirror (SESAM). These lasers are subject to a wake instability in which modes can grow in the wake of the modelocked pulse and destroy it. Even when stable, the wake modes can lead to undesirable radio-frequency sidebands. We demonstrate that the dynamical methods have an advantage of more than three orders of magnitude over standard evolutionary methods for this laser system. After identifying the stable operating range, we take advantage of the computational speed of these methods to optimize the laser performance over a three-dimensional parameter space.
We review recent work in which we developed a phase-matched model to study the transverse mode instability (TMI) in high-energy laser amplifiers. The standard models for TMI have contributions that vary rapidly compared to the beat period between the fundamental mode and the higher-order modes in the problem. In the phase-matched model, we neglect these rapidly varying contributions. We consider a realistic example with a Yb-doped fiber amplifier that is similar to the amplifier that was considered by Naderi et al. [Opt. Exp., 21(13), 16111 (2013)], but with a more realistic 10-m length. In this example, only one higher-order mode is present. We show that the computational speedup of the phase-matched model is on the order of 100 with no loss of accuracy even in the highly-saturated nonlinear regime.
Nano-arrays are an important structure for building chemical filters, photonic crystal waveguides, antireflection, or transmission devices. There are different methods of lithography to produce these nano-arrays, which include contact and projection photolithography, E-beam direct writing, and X-ray lithography. Contact photolithography is the most widely used method due to its simplicity and good for time and cost-saving. However, there are penalties that come with these benefits which include problems of generating Newton rings and difficulties of transferring patterns faithfully for situations at and beyond the diffraction limit.
In this work, we fabricated nano-arrays for high power antireflection applications using contact photolithography. Fortunately for the antireflection application, pattern periodicity is more important than obtaining the exact shape of the nanostructure. The fabricated structure, even though not the same as the original pattern, can still produce promising antireflection results. We have studied how the range of the distance between the mask and the photoresist affects the shapes of the produced patterns including holes, posts, and cones. The experimental results with different shapes and periodic patterns produced by different diffraction distances are explained with simulation results involving Fourier transformation and Fresnel diffraction of the mask patterns.
The development of negative curvature fibers is an exciting advance in optical fiber technology that combines relatively low loss over a broad bandwidth with relatively high tolerance for fabrication imperfections. Tolerance of fabrication imperfections is particularly important for chalcogenide fibers, and negative curvature geometries have made it possible to fabricate hollow-core chalcogenide fibers that can transmit light at 10 μm with a loss of 2.1 dB/m. We review theoretical and experimental work that we have carried out to determine the performance limits and to design and fabricate chalcogenide negative curvature fibers.
KEYWORDS: Surface plasmons, Life sciences, Fluorescent markers, Cameras, Digital imaging, Biological research, Tissues, Current controlled current source
Distinguishing between intact cells, dead but still whole cells, and cell debris is an important but difficult task in life sciences. The most common way to identify dead cells is using a cell-impermeant DNA binding dye, such as propidium iodide. A healthy living cell has an intact cell membrane and will act as a barrier to the dye so that it cannot enter the cell. A dead cell has a compromised cell membrane, and it will allow the dye into the cell to bind to the DNA and become fluorescent. The dead cells therefore will be positive and the live cells will be negative. The dead cells later deteriorate quickly into debris. Different pieces of debris from a single cell can be incorrectly identified as separate dead cells. Although a flow cytometer can quickly perform numerous quantitative, sensitive measurements on each individual cell to determine the viability of cells within a large, heterogeneous population, it is bulky, expensive, and only large hospitals and laboratories can afford them. In this work, we show that the distance-dependent coupling of fluorophore light to surface plasmon coupled emission (SPCE) from fluorescently-labeled cells can be used to distinguish whole cells from cell debris. Once the fluorescent labels are excited by a laser, the fluorescently-labeled whole cells create two distinct intensity rings in the far-field, in contrast to fluorescently-labeled cell debris, which only creates one ring. The distinct far-field patterns can be captured by camera and used to distinguish between whole cells and cell debris.
Optical beam spread and beam quality factor in the presence of both an initial quartic phase aberration and atmospheric turbulence are studied. We obtain the analytical expressions for both beam radius-squared and the beam quality factor using the moment method, and we compare these expressions with the results from Monte Carlo simulations, which allow us to mutually validate the theory and the Monte Carlo simulation codes. We then analyze the first- and second-order statistical moments of the fluctuating intensity of a propagating laser beam and the probability density function versus intensity as the beam propagates through a turbulent atmosphere with constant Cn2. At the end, we compare our analytical expression and our simulations with field test experimental results, and we find a good agreement.
We simulate the propagation of both a partially spatially coherent infra-red (IR) and a visible laser beam through a turbulent atmosphere, and we compare the intensity fluctuations produced in the simulation to the intensity fluctuations that are observed in both maritime and terrestrial environments at the US Naval Academy. We focus on the effect of the level of turbulence and the degree of the beam's spatial coherence on the receiver scintillations, and we compare the probability density function (PDF) of the intensity in our simulation to the experimental data. We also investigate the effect of optical beam spreading on the coherent and partially coherent laser beams along the propagation path.
KEYWORDS: Digital signal processing, Monte Carlo methods, Atmospheric turbulence, Turbulence, Atmospheric optics, Atmospheric propagation, Gaussian beams, Solids, Free space optical communications, Laser beam propagation
Optical beam spread and beam quality factor in the presence of both quartic phase aberrations and atmospheric turbulence is numerically analyzed. We obtain analytical expressions for both the mean-square beam radius and the beam quality factor using the moment method, and we compare these expressions to the results from Monte Carlo simulations, which allows us to mutually validate the theory and the Monte Carlo simulation codes. We also discuss the reason for the discrepancy between the classical approach for calculating the ensemble-averaged mean-square beam radius in a turbulent atmosphere that is described by Andrews and Phillips and by Fante versus using the moment method.
Recent computational work to optimize the output spectrum of As2Se3 and As2S3 chalcogenide photonic crystal fibers is summarized. Design procedures for both maximizing the output bandwidth and maximizing the power spectral density in the 3-5 μm range are described. With a 2.5μm pulsed pump source, it is possible to obtain a bandwidth of 4 μm in As2Se3 fibers, and, with a 2.0 μm pulsed pump source, it is possible to shift 25% of the input power to the 3-5 μm range in As2S3. With a source at 2.8 μm, it is possible to obtain an output power spectral density in As2S3 that extends between 2.5 μm and 6.5 μm. The single-shot output power spectral density exhibits rapid 10-20 dB fluctuations as the wavelength varies. Moreover, when the pump pulse duration and peak power vary, there are substantial shot-to-shot fluctuations in both the output bandwidth and spectral power density. With 10% variations of the pump pulse duration and peak power, the output spectrum averaged over 5000 shots exhibits less than 5 dB of variation in the intermediate wavelength range of 2.8-4.6 μm and has a reproducible bandwidth of slightly less than 3 μm. The average over 5000 shots yields the same output spectrum with 106 shots, indicating that the spectrum has converged.
We review our experimental and simulation-modeling studies on optoelectronic oscillators (OEOs). The OEO can have
an intrinsic quality factor, Q that is orders of magnitude higher than that of the best electronic oscillators (i.e. Poseidon).
However, our experimental results show that the OEO's current phase noise level is still worse than that of the Poseidon.
This is caused by many noise sources in the OEO which reduce the "loaded-Q" in the loop system. In order to mitigate
these noise sources, we have systematically studied such phenomena as the laser RIN, Brillouin and Rayleigh scattering
in the fiber, vibration, etc. These noise sources are convoluted in both optical and electrical domains by many different
physical effects; hence, it is very difficult to experimentally separate them, and only the dominant phase noise is
observed in each offset-frequency. Therefore, we developed a computational model to simulate our experimental
injection-locked dual-OEO system. By validating the model with our experimental results from both individual
components and OEO loops, we can start to trace the individual phase noise sources. The goal is to use the validated
model to guide our experiments to identify the dominant phase noise in each spectral region, and mitigate these noise
sources so that the OEO can reach its full potential.
Most system analyses of CW high-power lasers propagating in the atmosphere assume a simple additive linear relation of the impact of thermal blooming and optical turbulence in the atmosphere to the propagated laser beam spreading. In other words, both effects are treated as if they would follow Gaussian statistics in an RMS sense.
While the statistics of optical propagation in a turbulent atmosphere can be modeled as Gaussian to first order, thermal blooming is a deterministic nonlinear optical phenomenon. To the best of our knowledge, there is no reason for adding linearly the beam spreading due to these two optical effects. In fact, assuming no interplay in the presence of a strong nonlinear optical interaction is
counter-intuitive. As a result, we have performed extensive numerical Monte-Carlo optical wave-propagation simulations, >50,000 realizations, in the presence of thermal-blooming and
atmospheric turbulence to varying degrees. During the propagation, the amplitude and the phase of a high power laser
field are coupled by the interplay of diffraction, refractive turbulence and thermal blooming. In some cases, we have
observed in our numerical experiments a strong coupling between turbulence and nonlinear thermal blooming.
An analysis of the parametric interaction and the initial fiber geometry to achieve wavelength conversion
from common laser sources operating in the 1030-1064nm spectral band into the 900-950nm wavelength range has
been performed. The preliminary analysis shows that new fiber designs involving fibers with cores engineered with
crystal-like shapes and also pulsed fiber sources operating at wavelengths in the 1030-1064nm will be required to
achieve efficient emission within the desired wavelength range. Both the fiber required for phase-matching the
parametric nonlinear process and the pulsed fiber laser pump source are within reach of current technology. They both
require engineering efforts to produce a packaged, rugged and compact source.
Spectral broadening of single-frequency laser pulses by optical cross-phase modulation (XPM) with chaotic laser pulses in birefringent single-mode optical fibers is investigated numerically and results are compared with experiments. By this process we have generated laser pulses of variable bandwidth (1 - 25 angstrom) at the fundamental wavelength (1053 nm) for amplification in high power solid-state Nd:glass lasers used for inertial confinement fusion research. Simulations indicate that a temporally smooth XPM pulse can be generated with intensity fluctuations of less than 10% and spectral width greater than 50 angstrom using a short length (approximately 5 m) of special low dispersion and low birefringence fiber, e.g., D equals 10 ps/nm-km (normal dispersion) and (Delta) n equals 2 X 10-5. Readily available fibers of similar length, with parameters of D equals 40 ps/nm-km and (Delta) n equals 6 X 10-5, can give spectral widths exceeding 25 angstroms, but the noise will range from 25 to 60%. Broadband laser pulses generated by XPM are now routinely used at Lawrence Livermore National Laboratory for active smoothing of the laser irradiance on targets by the technique of smoothing-by-spectral dispersion.
Access to the requested content is limited to institutions that have purchased or subscribe to SPIE eBooks.
You are receiving this notice because your organization may not have SPIE eBooks access.*
*Shibboleth/Open Athens users─please
sign in
to access your institution's subscriptions.
To obtain this item, you may purchase the complete book in print or electronic format on
SPIE.org.
INSTITUTIONAL Select your institution to access the SPIE Digital Library.
PERSONAL Sign in with your SPIE account to access your personal subscriptions or to use specific features such as save to my library, sign up for alerts, save searches, etc.