This PDF file contains the front matter associated with SPIE Proceedings Volume 11987, including the Title Page, Copyright information, Table of Contents, and Conference Committee listings.

Convolutional neural networks (CNNs), inspired by biological visual cortex systems, are a powerful category of artificial neural networks that can extract the hierarchical features of raw data to greatly reduce the network parametric complexity and enhance the predicting accuracy. They are of significant interest for machine learning tasks such as computer vision, speech recognition, playing board games and medical diagnosis. Optical neural networks offer the promise of dramatically accelerating computing speed to overcome the inherent bandwidth bottleneck of electronics. Here, we demonstrate a universal optical vector convolutional accelerator operating beyond 10 Tera-OPS (TOPS - operations per second), generating convolutions of images of 250,000 pixels with 8-bit resolution for 10 kernels simultaneously — enough for facial image recognition. We then use the same hardware to sequentially form a deep optical CNN with ten output neurons, achieving successful recognition of full 10 digits with 900 pixel handwritten digit images with 88% accuracy. Our results are based on simultaneously interleaving temporal, wavelength and spatial dimensions enabled by an integrated microcomb source. We show that this approach is scalable and trainable to much more complex networks for demanding applications such as unmanned vehicle and real-time video recognition.

For several decades there has been much discussion within the liquid crystal laser community that a semiconductor-based pump source would offer a significant improvement compared to the typical method of Q-switched laser pumping in terms of cost, size and commercial viability of liquid crystal lasers. By combining specialist driver electronics with a high-power 445 nm laser diode and using in-house fabricated liquid crystal laser cells, we demonstrate the first diode-pumped liquid crystal laser capable of producing linewidths ≤ 1.5 nm in the blue, green, yellow and red regions of the visible spectrum. Using the same 445 nm laser diode pump source, a spinning liquid crystal laser set-up is presented, enabling an average output power of 10 μW at a repetition rate of 20 kHz – the highest repetition rate published to-date. We also present the design of the first portable diode-pumped liquid crystal laser prototype device, with spinning and wavelength selectivity capabilities. We anticipate this improvement in pump source, repetition rate and form-factor will offer a major step forward in bringing applications of this relatively unexplored area in photonics closer to realization, such as in fluorescence microscopy and laser-based displays.

We propose a theoretical analysis of the effect of noise on the dynamics of miniature optoelectronic oscillators (OEOs) based on whispering-gallery mode resonators. Our approach is based on Langevin equations for the modal optical fields, coupled with a Langevin equation for the noisy photodetector. This model successfully allows to determine some of the noise properties in the optical and microwave signals.

Dynamically stable resonators have a stationary TEM00 beam waist inside the laser rod (w₃₀), which is minimal throughout the stability interval and insensitive to changes in pump power. For a given set of resonator parameters (mirror radii and distances between mirrors and rods), the stability interval parameters, which are the limits of the stability interval in terms of the rod’s thermally induced focusing length are determined. In linear resonators, these stability interval parameters cannot be changed independently only by varying resonator distances, and mirrors of different curvature have to be employed. However, our group showed recently that for a symmetric ring resonator containing a pair of curved mirrors, the width of stability interval and the stability interval limit at maximum rod’s focal length can be adjusted continuously and independently only by varying resonator distances once the mirror radius of curvature has been fixed. In this work we demonstrate a project of an adaptive ring resonator that allows the TEM00 - mode resonator to be continuously tuned throughout the whole range of pump powers utilizing standard electromechanics to move the mirrors. Additionally for a given value of pump power, w30 can be varied, thus allowing different beam qualities to be obtained from the same resonator.

Achieving a high-quality (Q) factor for microresonators at a longer wavelength, e.g. longwave infrared (LWIR) with a wavelength from 8 to 14 um, will trigger new development in integrated non-linear optics and sensing on a chip. Although there are both powerful integrated light sources like solid-state quantum cascade lasers (QCLs) and strong driving force from chip-based sensing applications in the LWIR atmospheric transparent window, the Q factors of the microresonators are only several thousand, due to limited choices of low-loss materials and complicated fabrication procedures. Here, we report on the realization of a germanium (Ge) whispering gallery mode microresonator from a facile non-epitaxy fabrication process of high-quality Ge material with an ultra-smooth surface. By coupling the output of a QCL at 7.8 um into a partially suspended Ge on glass waveguide, an intrinsic Q of 2.5 ×105 are reported. Compared with the previous study, our work shows the importance and great promise of maintaining high-quality material for integrated photonics at LWIR.

Adiabatic frequency conversion (AFC) in microresonators comes without phasematching restrictions and does not depend on light intensity, i.e. it can reach 100 % conversion efficiency even at the single-photon level. The AFC is experimentally achieved in various configurations since 2007. However, compared with their nonlinear-optical counterparts, they still lead a life on the edge of obscurity. Despite of some impressive proof-of-concept demonstrations, there seems to be only little interest to employ adiabatic frequency converters for real-world applications. We demonstrate an electro-optically driven adiabatic frequency converter based on a millimeter-sized whispering gallery resonator made out of a lithium niobate crystal. The electric field is applied with a self-built ultra-fast high-voltage pulse generator. It consists of a push-pull stage with two fast-switching 600-V GaN power transistors and a control unit. This enables us to generate pulses with voltages of up to 600 V, slew rates of up to 150 V/ns and repetition rates reaching 1 MHz. Considering 100 µm resonator thickness, this enables electrically-controlled frequency shifts of up to 100 GHz. We combine this frequency converter with a system for multi-wavelength digital holography. Here, interferograms are recorded at slightly different laser frequencies. Calculating the difference phase of the interferograms numerically, interferograms at the beat frequency of the respective wavelength pairs can be created that correspond to phase data at the difference frequency. Cascading this process, a large unambiguity range paired with a high axial resolution becomes possible. A single laser combined with an adiabatic frequency converter is very appealing to provide sequentially the many, exactly spaced laser frequencies needed here, replacing a series of stabilized fixed-frequency lasers.

The evolution of pathogens has increased the demand for a sensing and detection platform, capable of qualifying constituents in real time. Whispering Gallery Mode Resonators provide an ideal biochemical sensing platform due to their low cost, high sensitivity, and low impact on the analyte. These resonators have high quality factors and possess the ability to detect minute changes in the local environment, as the light traveling on the surface of the resonator, when at resonance interacts with the surrounding medium for interaction lengths on the order of ~10-100cm’s . These changes in physical properties are captured through shifts of the resonance wavelength, resonance dip intensity, and/or quality factor. In this work, we provide our design of a 3-D printed microfluidic cell that is compatible with our taper and sphere coupling scheme developed from our previous work. Initially, the baseline performance of the resonator fluidic system was established by measuring the resonance wavelength shift due to refractive index change from water to phosphate buffered saline (PBS). Next, we showcase our biofunctionalization procedure and measure the accumulation of pathogens, such as E. Coli and Influenza A, on the resonator’s surface. The presence of these biological analytes results in small changes in the resonator’s diameter and refractive index, which manifests in real time as a red shift of the resonance wavelength on the picometer scale. Finally, we develop the foundation for a silicon integrated circuit chip resonator system, resulting in a further reduction of our system’s footprint.

By combining the requirements on the angular random walk and the bias stability of an optical passive resonant gyroscope, we end up with simple expressions of its minimum diameter and the maximum power it should be probed with. These design parameters depend only on the propagation losses, the mode size and the Kerr properties of the cavity material. We applied these results to passive miniature resonant optical gyroscope based on state-of-the-art performances of photonic integrated circuit and whispering gallery mode technologies. We show that tactical grade gyroscope performances can be achieved with a diameter of a few cm provided the detrimental influence of the Kerr effect is mitigated using, for instance, an active control of the unbalance in the intensities. We further extend the analysis to medium performance gyroscope and give some hints on the efforts to be made to potentially demonstrate a miniature resonant optical gyroscope with this level of performance.

Microresonator frequency combs have rapidly evolved in the last years and have become a hot topic in integrated photonics. These combs are typically generated relying on the χ⁽³⁾ nonlinearity via degenerate and non-degenerate four wave mixing. More recently, the idea of comb generation based on the χ⁽²⁾ nonlinearity has also started to be explored as it might provide new potential benefits like accesing new wavelength ranges. In this direction, we investigate the generation of χ⁽²⁾ frequency combs based on optical parametric oscillation in a lithium niobate whispering gallery resonator. By pumping at 532 nm and driving the optical parametric oscillation to degeneracy at 1064 nm, we observe two 1-THz-wide combs centered around these wavelengths. This scheme can directly be transferred to other materials to generate combs in the mid-IR region by pumping at telecom wavelengths.

All-dielectric metasurfaces have attracted increasing attention due to their negligible losses and sharper resonances compared to their metallic counterparts. In this work, we numerically studied the optical performance of a novel alldielectric metasurface based on complementary split-ring resonators (CSRRs), in which ultrathin slots were periodically etched in a thin silicon layer. The proposed CSRR metasurface exhibits two multipolar resonances in the near-infrared (NIR) window. Moreover, a quasi-bound state in the continuum (quasi-BIC) with an ultra-high quality factor can be excited by breaking the symmetry of the structure. Taking advantage of the high-quality factor quasi-BIC mode and its sensitivity to the superstrate medium refractive index (S = Δλ_res/Δn), we design an ultra-high figure of merit (FoM = S/FWHM) refractive index sensor for biomedical applications. By three-dimensional finite element method (3D-FEM), we evaluate the sensitivity of the sensing device to the variation of the superstrate refractive index in the range 1.31-1.33, which is typical for aqueous solutions. Our simulations reveal that a sensitivity of S ~ 155 nm RIU^-1 and an extraordinary FoM ~ 387500 RIU^-1 can be achieved using the ultra-narrow quasi-BIC resonance in the CSRR metasurface structure. The proposed approach opens new paths to develop flat biochemical sensors with high accuracy and real-time performance.

We present an adaptive optical system to stabilize the position of a laser beam passed through the turbulent atmosphere. The system uses two tip-tilt mirrors and is controlled by an FPGA to increase the bandwidth. An internal FPGA structure is presented. FPGA reads the error signal from the sensors formed by quadrant photodiodes and calculates the voltages to be applied to the piezo-driven tip-tilt mirrors by the control units.

Narrow-linewidth lasers are building blocks of coherent communication systems, as lower linewidths enable higherorder modulation formats with lower bit-error rates. For this purpose, diode lasers are in high demand due to their low power consumption, compactness, and potential for mass production. In field-testing scenarios, their output is coupled to a fiber, making them susceptible to external optical feedback (EOF), which is notoriously detrimental to their stability. This challenge is traditionally combated by using, for example, angled output waveguides and optical isolators. The approach reported in this work makes use of EOF in a new way, to reduce and stabilize the laser linewidth. Whereas research in this field has focused on EOF applied to only one side of the laser cavity, this work gives a generalization to the case of feedback on both sides. It is implemented using photonic components available via generic foundry platforms, thus creating a path towards devices with high technology-readiness level. It is numerically observed that the double-feedback case can lead to improved performance with respect to the single-feedback case. In particular, by correctly tuning the phase of the feedback from both sides, a broad region of stability is discovered. This work paves the way towards low-cost, integrated and stable narrow-linewidth integrated lasers.

In recent studies, high-speed optical coherence tomography (OCT) systems are gaining attention and are in high demand due to the need for a wide range of real-time in-vivo imaging applications. This report presents a stretched-pulse mode-locked (SPML) laser providing ~20 MHz A-line rate for rapid OCT imaging at a center wavelength of 1.06 μm and optical bandwidth of 92 nm. The OCT performance of the laser design was investigated in a Scotch band phantom. The proposed laser may have significant potential in OCT imaging modality, especially in OCT angiography applications.

A bimorph deformable mirror with a diameter of 320 mm, including 127 control electrodes, has been developed and investigated. The flatness of the initial surface of the mirror RMS = 0.16 μm was achieved due to mechanical adjustment in the system of fixing the mirror substrate in the frame. An adaptive system with deformable mirrors and a ShackHartmann-type wavefront sensor was installed in a 4.2 PW Ti: Sa laser. Correction of the wavefront made it possible to obtain a record radiation intensity in the focusing plane of 1.1x10²³ W/cm², while the Strehl ratio was 0.84.

While the high index contrast between silicon and silicon dioxide in the silicon-on-insulator photonics platform permits unprecedented device density, it also leads to high sensitivity to fabrication variations. In silicon microring and microdisk resonator devices, fabrication variations can substantially change the target resonance wavelength. Silicon’s high thermo-optic coefficient allows for correction of these fabrication variations and stabilization of the device resonant wavelength through thermal tuning. Metal and doped silicon integrated heaters are commonly used to perform this tuning and have become an essential feature of silicon microring and microdisk modulators. Metal heaters are typically placed in a layer above the silicon devices, while doped silicon heaters are placed in the same silicon waveguide layer, adjacent to the devices. The advantage of doped silicon heaters over metal heaters is due to proximity of the heater to the optical device, leading to greater efficiencies. However, for active devices using p-n junctions such as modulators, parasitic junctions can form between the doped heater and the modulator junctions, resulting in highly unstable and substandard device performance. Here, we present a detailed simulation framework for heater design in resonant silicon microdisk modulators, supported by experimentally measured device performance, which emphasizes tuning efficiency while eliminating parasitic diode formation. Simulations were conducted in Ansys Lumerical HEAT, CHARGE, and MODE to model parasitic junction behavior between the heater and modulator, in addition to the heater’s thermal response and its effect on the resonant wavelength of the microdisk.

We introduce a formalism, inspired on the perturbation theory for nearly-free electrons in a solid-state crystal, to describe the resonances in optical ring resonators subjected to a perturbation in their dielectric profile. We find that, for small perturbations, degenerate resonant modes are split, with the splitting proportional to one specific coefficient of the Fourier expansion of the perturbation. We also find an expected asymmetry in the linewidths (and Q factors) of the split modes. Experimental transmission spectra from rings with specially designed perturbations show a qualitative match with the formalism predictions.

Generation of coherent frequency combs in optical microresonators at normal GVD is a challenging task. It is well known that they can be generated in the form of the flat-top solitonic pulses, platicons, via controllable mode interaction or modulated pump. However, such methods are rather complicated, requiring either sophisticated mode interactions, complex two-cavity systems or high-frequency modulators. Recent investigations have shown that the self-injection locking effect provides interesting possibilities for frequency comb generation. It has been shown that this effect not only provides laser stabilization due to the resonant backscattering of laser radiation from the high-quality-factor microresonator but also leads to the nontrivial nonlinear dynamics in the same microresonator. First, this has been demonstrated for bright solitons with an ordinary laser diode as a pump source. Recently, it has been shown experimentally that such approach is also applicable for platicon generation and does not require additional equipment. In our work we study this process in detail and identify different generation regimes depending on the combination of the pump power and the backscattering coefficient providing the self-injection locking effect. The range of parameters necessary for the efficient platicon generation is found. We also report a novel mechanism of platicon generation based on the thermal effects inevitable in real-life systems. We show that it is possible if thermal effects are negative (the direction of the thermal shift of the microresonator resonance is opposite to the direction of the nonlinear shift) and the ratio of the thermal relaxation time to photon lifetime is small enough. Different generation regimes are found, and the possibility of the turn-key operation regime is demonstrated.

A high-quality flat wavefront is usually used to calibrate the Shack-Hartmann wavefront sensors. The article discusses the possibility of calibrating sensors with spherical wavefronts. Special attention is paid to the consideration of calibration in standard laboratory conditions. The mathematical apparatus and the scheme of the experiment are considered. A statistical analysis of the calibration accuracy of the Shack-Hartmann wavefront sensor is carried out. Spherical wavefronts from a point source were used as references. As a result, the parameters of the wavefront sensor were determined: the focal length and the dimensions of the digital camera pixel. This calibration method is considered in comparison with the traditional calibration using flat wavefronts.

In this paper we demonstrate the results of implementation of B-spline surface approximation algorithm for Shack-Hartmann wavefront sensor. We compared the efficiency of reconstruction of simple simulated wavefronts, represented by the single aberrations, such as defocus, coma, astigmatism, trefoil, spherical aberration, etc. by means of Zernike and B-spline polynomials. We also demonstrated the efficiency of the use of B-spline approximation of the complex wavefronts: Franke surface (RMS of the initial and the reconstructed surface was equal to 0.38 and 0.39 um, respectively) and wavefront of the thin ring-shaped detail (outer/inner diameter of the ring was 114/95 mm) with the peak-to-valley of approximately 3.5 um.

A fast adaptive optical system, operating at frequencies up to 2000 Hz (frames per second), was used to analyze turbulence created in the laboratory by using a fan heater. The turbulent distortion bandwidth was approximately 100 Hz. The expansion of the wavefront in terms of Zernike polynomials was used when processing the raw data. Then the statistical analysis was performed separately for each polynomial. As a result, the degree of predominance of definite aberrations in the wavefront of laser radiation was obtained. Taylor's hypothesis is confirmed: low-order aberrations are slower than high-order ones. The dependence of the correction quality on the number of corrected Zernike polynomials is also shown.

For laser beam control in different scientific and industrial tasks adaptive optics tools are widely exploited. Any adaptive optical system parameters are mainly determined by wavefront corrector properties such as stroke, operating speed, resolution of control elements, accuracy performances. Stack-array deformable mirror wavefront corrector made of multilayer piezoceramic combs is proposed as low-cost and reliable alternative to conventional ones. Such design allows to increase spatial resolution and first resonant frequency. Moreover, proposed deformable mirrors will be distinguished by high cost-effectiveness that is key parameter for this type of wavefront correctors.

The paper presents an analysis of designing an optical-electronic imaging system designed to operate in a turbulent atmosphere. The optoelectronic system design is based on hill-climbing and phase conjugation technique using a bimorph adaptive mirror and a Shack-Hartmann-type wavefront sensor. The system corrects the wavefront distortion of the laser radiation passing through the test object and an inhomogeneous medium that simulates a turbulent atmosphere. Criteria for restoring the geometric characteristics of the test object are analyzed using the proposed hybrid algorithm, including spatial-frequency analysis of the recorded spectrum.