This PDF file contains the front matter associated with SPIE Proceedings Volume 12871, including the Title Page, Copyright information, Table of Contents, and Conference Committee information.

On-chip coherent light generation has wide-ranging applications in metrology, spectroscopy, quantum optics, etc. In this study, we demonstrate the generation of coherent light from a silicon-nitride microring resonator using cascaded nonlinear processes. This involves a telecom pump laser and its efficiently generated second harmonic through the coherent photogalvanic effect. By leveraging second- and third-order nonlinear effects such as harmonic generation, (stimulated) four-wave mixing, and optical parametric oscillation, we achieve the generation of UV, visible, and near-infrared light. This study highlights the potential of silicon nitride integrated photonics in producing broad-spectrum light sources at wavelengths beyond the capabilities of conventional lasers.

We investigate the dynamics of Kerr cavity solitons in the normal dispersion regime, under the influence of intracavity phase modulation. When increasing the strength of the parabolic phase modulation, dark solitons undergo a transformative shift into high-order bright solitons. We characterize this phenomenon and show that it is associated with a transition from a collapsed snaking bifurcation structure for dark solitons, to a multimode resonance structure for the high-order bright solitons case. This study may offer a comprehensive exploration of cavity dynamics, unveiling an avenue to access new multi-stable states by controlling the phase modulation.

Adiabatic Frequency Conversion (AFC) in microresonators is independent of the intensity of laser light, and it is free from phase matching restrictions. It even allows for changing the frequency of single photons. The AFC has been experimentally investigated for more than a decade in different configurations. However, despite of some impressive proof-of-concept demonstrations, adiabatic frequency converters remain relatively obscure compared to their nonlinear-optical counterparts. So far, adiabatic frequency converters for applications were a curiosity due to lack of experimental investigation. We demonstrate linear frequency chirps between 0 and 690 MHz around 1.5 μm wavelength generated by electro-optically driven AFC. This is achieved by applying linear voltage chirps between 0 and 20 V on a 300-μm-thick whispering gallery resonator made of lithium niobate with 1.2 mm major radius. The frequency chirps have less than 2 % rms deviation from perfect linearity at chirp times as low as 130 ns. We apply these chirps for frequency-modulated continuous-wave LiDAR as a proof for a practical application of AFC. We successfully determine distances between 0 and 6 m. The distance resolution is of the order of 10 cm and just limited by the chirp bandwidth. Our proof-of-concept demonstration shows that laser light from adiabatic frequency converters is useful for applications. The performance of the AFC-based FMCW LiDAR system can be improved by integrating the resonator on a chip since the same voltage provides higher electric fields. Here, electro-optically-induced frequency shifts of 10 GHz and more have already been demonstrated. This would increase the distance resolution by more than one order of magnitude.

Quantum microcombs are nonclassical states of light generated when twin-photons are excited via spontaneous four-wave mixing in a microresonator. In general, intrinsic losses are overlooked and the theoretical description of these systems implicitly assumes that the quantum microcombs are pure states. In this communication, we propose a density operator theoretical framework that is valid in the general case of a lossy resonator.

Whispering-Gallery Mode (WGM) microresonators have become popular in photonic systems thanks to their ease of fabrication, high optical Q-factor and ultra-small mode volume. Here, we illustrate the modelling and experimental activities derived from light coupling mechanisms to passive WGM microresonators based on free-space scattering without using any prism or fiber waveguide. This has been carried out for cavities made of liquid and solid materials, for which we report applications and potential use in optical sensing, machine learning and spectroscopy. In particular, angular momentum matching, i.e. light coupling via scattering, is obtained only in a strict interval of alignment conditions exhibiting WGM spectra populated with a variety of peaks with diverse quality factors. We devised an optical feedback loop based on a spatial light modulator that tailors the phase of a laser beam and, thanks to a random algorithm optimizes the alignment maximizing the scattered light-ring pattern. This allows to harness the strong mode confinement and power amplification of the microresonator to observe opto-mechanical and radiation-pressure effects. Free-space WGMs is also an appealing platform for artificial intelligence architectures. Taking a further step from this optical setup, we started implementing a photonic learning machine whereby the SLM acts as an optical encoder while the WGM spectrum provides the optical readout. Finally, we developed a novel room-temperature radiation sensor based on a free-space laser locked on the resonance of a silica microsphere. Thanks to silica strong absorption in the IR, we showed that the microsphere element enables detection of electromagnetic radiation from the mid-IR (MIR) up to the THz spectral range proving also suitable for absorption spectroscopy.

Thin Film Lithium Niobate (TFLN) photonic integrated circuits offer several improvements over other platforms in terms of material loss, energy efficiency, and operational bandwidth. We review our recent demonstration of quadrature phase shift keying in an ultrasmall TFLN photonic crystal-based IQ modulator. Our modulator features a footprint of 40 × 200 μm² along with quality factors approaching 105 providing it with a Vπ = 1.16 V [H. Larocque et al. CLEO 2023, paper STh1R.3; H. Larocque et al. arXiv:2312.16746]. We discuss an extension to and optimization of quadrature amplitude modulation encoding schemes tailored to the device’s voltage response, including the use of a deep neural network for streamlining bit error rate minimization.

Narrow line width lasers with high stability are a key enabling technology in high-impact applications such as quantum technologies and laser surgery. On the one hand, stabilizing such lasers implies the design of efficient Proportional-Integral-Derivative (PID) controllers. On the other hand, high end applications require PID controllers with very high regulation bandwidth, relocking feature and easy to adjust parameters. In order to tackle these challenges, we designed and enhanced a PID controller using the pipeline technique. This allowed us to improve the sample rate at which the controller operates. The designed PID has been successfully used in a VBG based external cavity for laser stabilization with ultra-narrow line width.

Dissipative Kerr solitons in microring resonators have the potential to enable precision measurements with optical frequency combs in an integrated photonics package. However, the small volume of these resonators makes them highly susceptible to thermorefractive effects. We present a system of two coupled resonators that reduces the effect of thermal shifts on comb states through controllable mode crossings and fast detuning control of the pump laser. Both methods aim to beat the thermal timescale of the resonator to stabilize a dispersive Kerr soliton. Using soliton lifetime as a metric, we find increased resilience to thermorefractive effects when the pump laser is swept faster than the thermalization timescale of the cavity and when mode frequencies in the auxiliary resonator at or near the pumped mode are tuned towards degeneracy with the main resonator (i.e. the resonator with the soliton). The lifetime near an auxiliary resonator-main resonator mode crossing shows a three order of magnitude increase from the native soliton lifetime set by the thermalization time of a single resonator. These results suggest that both methods can be used to reduce thermorefractive phase noise in soliton microcombs.

A significant challenge faced by Wireless Optical Power Transfer (WOPT) using the Resonant Beam Charging (RBC) method is the restrictive alignment requirement. In this study, we examine the utilization of a diverging angular dispersion beam and active beam steering to enhance the likelihood of identifying and maintaining a resonant link. The system exhibits significant improvements compared to conventional systems that utilize pencil beams. This enhancement is observed during the initial search for the receiver position, and it contributes to maintaining resonance cavity between the two beam types. These findings highlight the potential of utilizing diverging angular dispersion beams for real-time charging applications in future research.

Employing two novel beam attenuation and ghost suppression schemes, a compact, high-power laser beam CMOS-based profiler has been realized. The traditional method of attenuation employs a multitude of crossed polarized wedge prism pairs along with other mirror and neutral density filters to get the intensity of the laser beam on the CMOS without overexposing the sensor. In general, the CMOS requires low microwatts of power to avoid over exposure of the sensor. This means that for 1 kilowatt of continuous wave laser power, the attenuation, prior to the sensor, needs to be in the -8 to -9 optical density range. A pair of uncoated, fused silica wedge prisms have an equivalent optical density of about -2.8. Therefore, three pairs of wedge prisms would be required for an -8 to -9 optical density equivalent. The implementation of three sets of wedge prisms requires a long optical path with no less than six optics to achieve the desired attenuation. In the current work, the number of optics required is only 3 to achieve the same level of attenuation and is a fraction of the size in contrast to the traditional method.

We report on the development of inhibited-coupling hollow-core photonic crystal fiber with record-low transmission loss of ⪅50 dB/km at 266 nm, and solarization-free. 2 meter-long patchcords with SMA terminations were made and their UV handling and lifespan were tested. A laser beam from a 266 nm wavelength laser-source emitting 1 ns wide and 30 μJ energy pulses was injected into the hollow-core fiber patchcord, achieving a total transmission rate of 93%. The laser beam was kept continuously coupled to the patchcord for over 100 hrs. The results show excellent stability in transmitted power (fluctuations of less than 2.6%) and in mode quality. To our knowledge this the first fiber guidance of DUV laser that combines high energy handling and long lifespan. The results mark a major milestone in the adoption of fiber UV laser beam delivery by the industrial community.

We present a highly efficient method for generating multiple beam spots through the multimode interference within Single Mode Fiber – Square Core Fiber (SMF-SCF) structures. By adjusting the length of SCF, we can achieve diverse beam spot configurations in a square lattice, such as 4×4, 3×3 and 2×2, providing unparalleled flexibility. Through simulations and experimental validations at a wavelength of 1060 nm, our study unveils significant potential for applications in photonics and laser technology.

Spatial beam self-cleaning in graded-index multimode fibers involves a nonlinear transfer of power among the fiber modes, which leads to robust bell-shaped output beams. The resulting output mode power distribution can be described by statistical mechanics arguments. Although the spatial coherence of the output beam was experimentally demonstrated, there is no direct study of modal phase evolution. Based on a holographic mode decomposition method, we reveal that nonlinear spatial phase-locking occurs between the fundamental and its neighboring low-order modes, in good quantitative agreement with theoretical predictions.

We report a new reference-free method for measuring the complex Transmission Matrix (TM) of a Multimode Fiber (MMF), without the need of an interferometric setup, employing a two-step supervised machine learning framework. By using a deformable mirror at the proximal end of the MMF, and a camera at its distal end, we first retrieve the TM of the MMF that predicts the intensity pattern of the output beam. In a second step, with only some random additional images of the output far field, the TM is corrected to predict the true complex field at the distal end of the MMF. We experimentally validate our method by controlling the output optical field from a standard 50/125 step-index multimode fiber with 140 LP modes per polarization, using a segmented deformable mirror of 952 actuators at 1064 nm. We demonstrate the validity of the retrieved complex transmission matrix by tailoring the laser beam from the MMF simultaneously at two distal planes. These results open new avenues for complete control of the optical field using solely intensity measurements, which could be of major interest for endoscopic or telecommunication applications.

A filament forms through a balance of self-focusing (Kerr effect) and plasma self-defocusing. The heat generated as the electron-ion recombine produces a cylindrical shock wave behind which a low-density channel is formed. High-energy UV filaments are used to study the shock wave by shadowgraphy. The shock is seen to start supersonic, before transitioning after microseconds to a constant velocity acoustic wave. Computational models of the gas-dynamics evolution are presented that agree with a well known empirical formula for shockwave velocity, as well as with experimental observations. We determine the profile of induced changes to the refractive index of air due to these thermal effects. We then simulate a vortex filament creating a parabolic index of refraction that can serve as a waveguide for successive filaments.

We experimentally reveal a so-far unnoticed high-power limit to spatial beam self-cleaning in graded-index nonlinear multimode optical fibers. As the optical pulse power is progressively increased, we observed that the initial Kerr-induced beam clean-up and associated improvement of the spatial beam quality are eventually spoiled. Based on a holographic mode decomposition of the output field, we show that this beam degradation can be described in a thermodynamic approach to wave propagation as a manifestation of “high-temperature” thermalization, which depletes the fundamental mode in favor of a highly multimodal power distribution.

Control over the parameters of a laser beam such as intensity and phase provides an important basis of modern photonics. Established control schemes, however, cover only a limited parameter range. We employ intense ultrasound fields in ambient air, enabling control of laser light in extreme parameter regimes. We acousto-optically modulate ultrashort pulses at 1030 nm with a peak power of 20 GW efficiently (⪆ 50%) in ambient air. Further, we show excellent beam profile conservation and separability of diffracted and transmitted beams. Finally, our approaches show that light control can prospectively be translated from solid-state media to the gas phase by means of intense ultrasound, considerably widening the scope of established light control methods.

Laser locking is a crucial tool in various scientific applications, especially in the field of atomic physics, where the laser's frequency must be stable with respect to the frequencies of atomic transitions. This work aims to leverage the advantages of 3D printed push-fit slots to achieve an inexpensive, compact, and highly customizable optical setup for locking lasers to the frequency of transition between two excited, and thus unpopulated, electron states of a neutral atom. In our approach, the optical components are mounted in custom 3D printed slots instead of traditional optical posts to decrease costs and overall size. The error signal is then created by an Electromagnetically Induced Transparency (EIT) signal in a Two-Photon Dichroic Atomic Vapor Laser Lock (T-P DAVLL), corresponding to the 6S_1/2, 6P_1/2, and 8S_1/2 states of Cesium.

Atmospheric turbulence causes refractive index fluctuations that introduce extra distortions to the wavefront of the propagated radiation. It degrades the resolution of the telescope for imaging applications and reduces the radiation power density in focusing applications. One of the possible ways of research the impact of the turbulence is to numerically simulate the spectrum of refractive index fluctuations, to reproduce it using a wavefront corrector and to measure the resultant wavefront using a Shack-Hartmann sensor. In this paper, we developed turbulence simulator software that generates the sequence of phase screens with Kolmogorov spectra. We reconstructed the generated set of phase screens using a stacked-actuator deformable mirror.

A multispectral wavefront sensor can be used to perform a single-shot spatio-temporal characterization of a laser pulse. In order to measure the spatio-spectral electric field, a laser pulse can be spectrally modulated, separated and measured by a wavefront sensor. In order to simplify the experimental setup and hardware control, the single wavefront sensor can be used. In this research we discuss the development of the multi-channel wide-aperture high-resolution Shack-Hartmann sensor for multispectral wavefront sensing. The whole sensor area of 15×15 mm was divided into four logical apertures, each for separate laser beam. The development and calibration procedure are described. The wavefront sensor control software is developed and tested.

In this paper the efficiency of the heat sink for various configurations of the stacked-actuator wavefront correctors with thermostabilization of the mirror substrate through piezoactuators body was investigated. The simulation of the thermomechanical behavior of the mirrors under influence of the continuous-wave laser radiation with power of 10 kW was performed. Stacked-actuator deformable mirrors with diameters of 50, 78, 120 mm and 19, 55, 121 actuators, respectively, were used as wavefront correctors. Also, the alternative design of actuators with individual metal housing of control elements was proposed.

This paper presents the automated system for minimizing the deviation of the path of passage and the divergence of a secondary radiation source with similar parameters of the main beam of a high-power Ti:Sa laser using mirrors in kinematic mounts on the motorized stages. As an alignment laser, the diode laser with a fiber output was used with radiation characteristics coinciding with the parameters of the main beam (wavelength, beam diameter). The successive approximation algorithm was used to minimize the beam deflection. The deviations of the main alignment parameters from ‘live’ to ‘pilot’ beam are following positioning accuracy (X axis – 0.96 μm, Y axis – 0.96 μm), pointing accuracy (X axis – 8.78 μm, Y axis – 6.14 μm), beam size matching (X axis – 0.96 μm, Y axis – 0.96 μm), wavefront curvature (P-V = - 0.072 μm).