This PDF file contains the front matter associated with SPIE Proceedings Volume 12407, including the Title Page, Copyright information, Table of Contents, and Conference Committee information.

Light-matter interaction is crucial in many application domains of nanophotonics, including biosensing, trapping at the nanoscale, nonlinear optics, and lasing. Many approaches, mainly based on photonic and plasmonic resonant structures, have been investigated to enhance and tailor the interaction, but those based on all-dielectric metasurfaces have several unique advantages: low loss, easy excitation and readout, possibility of engineering the optical field distribution with many degrees of freedom, and electric tuning. Here we show that properly designed all-dielectric metasurfaces can support silicon-slot quasi-bound states in the continuum modes resonating in the near-infrared, strongly confining light in air and, consequently, enhancing light-matter interaction. Some samples of the designed metasurface have been fabricated in a silicon-on-sapphire wafer by e-beam lithography and reactive ion etching. The optical characterization of the chip has confirmed the excitation of the quasi-bound state in the continuum resonant modes, with measured Q-factor values exceeding 700.

We use polarization-dependent gain in a twisted birefringent medium to realize a sub-megahertz linewidth optical feature. Our approach is loss-free, resonator-free, and cost-effective, offering high sensitivity and on-demand tunability.

We designed and experimentally demonstrated racetrack resonators on a 3 μm thick SOI platform with intrinsic quality factors above 10 million. The racetrack configuration consists of a combination of straight sections based on rib waveguides and bend sections based on strip waveguides following a so-called Euler curve to achieve a compact footprint. The ultra-high-Q factors were achieved through a significant sidewall roughness reduction by controlled annealing in a hydrogen atmosphere, allowing to achieve propagation losses for 3 μm wide rib waveguides down to ~3 dB/m. The process potentially enables emerging PIC applications demanding ultra-low propagation losses.

Chip-based photonic microresonators are attractive for a multitude of applications owing to their small form factors and compatibility with photonic integration and standard CMOS fabrication. Within the last decade, the ring resonator geometry has gained widespread adoption in the application of optical frequency comb generation. However, these devices often require waveguides several hundreds of nanometers thick, posing a challenge for subtractive fabrication processes where the desired pattern must be chemically etched with the use of a protective “mask” pattern. Here, we demonstrate two procedures for subtractive processing of thick SiN waveguides based on both a polymer-based “soft” photoresist mask and a chromium metallic “hard” mask as etch templates. Optical characterization of our devices fabricated with both soft mask and hard mask techniques demonstrate quality factors of 320k ± 100k and 500k ± 180k., respectively. Furthermore, this work details two reliable pathways for achieving high quality optical microring resonators and illustrates the benefits and drawbacks of these two techniques.

We demonstrate a fully packaged hybrid integrated laser and a soliton microcomb with frequency actuation bandwidth of more than 10 MHz and ultra-low laser frequency noise. The flat frequency response in the range of >1 MHz and the optical laser frequency chirp range of >1 GHz are compatible with high-resolution continuous wave frequency modulated distance ranging and distributed fiber optic sensing without any linearization or pre-distortion. The features of a novel laser system assembled in 14-pin butterfly package are enabled by the ultra-low loss silicon nitride platform and monolithically integrated piezo-electric actuators.

We present a theoretical model for describing dissipative solitons and optical frequency combs formation in a dispersive and nonlinear χ⁽³⁾-based cavity system that is phase-matched for third-harmonic generation. We consider the importance of the stability properties of the homogeneous solution in generating various types of multi-frequency combs, and demonstrate a novel type of bistable cavity solitons.

We numerically study the chaotic synchronization of microresonator frequency combs. The chaotic state of microresonators could be a key factor in optical communications because the modulation instability state (chaotic) has a larger output than the soliton state (stable), which may enable us to realize a higher signal-to-noise ratio. In addition, it will allow secure communication. We show that two microresonator frequency combs in a leader-follower configuration can be synchronized in chaotic regimes. Interestingly, the follower comb synchronizes even when some longitudinal modes of the leader comb are absent. We also show that the Turing pattern comb in the follower ring becomes chaotic and synchronizes when we inject the leader’s modulation instability comb.

Optical microresonators possessing Kerr-type nonlinearity have emerged over the past decade as reliable and versatile sources of optical frequency combs, with varied applications including in the generation of low-phasenoise radio frequency (RF) signals, small-footprint precision timekeeping, and LiDAR. One of the key parameters affecting Kerr microcomb generation in different wavelength ranges is cavity modal dispersion. Dispersion effects such as avoided mode crossings (AMCs) have been shown to greatly limit mode-locked microcomb generation, especially when pumping in close proximity to such disruptions. We present numerical modeling and experimental evidence demonstrating that using an auxiliary laser pump can suppress the detrimental impact of near-pump AMCs. We also report, for the first time to our knowledge, the possibility of the breaking of characteristic soliton steps into two stable branches corresponding to different stable pulse trains arising from the interplay of dichromatic pumping and AMCs. These findings bear significance, particularly for the generation of frequency combs in larger resonators or at smaller wavelengths, such as the visible range, where the cavities become overmoded.

A key application of Kerr optical frequency combs is ultrapure microwave generation. In this case, the intermodal radiofrequency of the comb is retrieved via photodetection. The three main challenges for the study of phase noise spectra are the determination of the various sources of noise, the understanding of how these stochastic excitations lead to microwave phase fluctuations, and finally the determination of the phase noise spectra from the nonlinear phase fluctuations. In this communication, we present our latest results and demonstrate that the phase noise spectra have two dominant contributions that can be determined separately.

Vector beams feature inhomogeneous polarization structures and have sparked significant attention in recent years. While a lot of effort has been dedicated to their generation and control, measures to quantify their vectorness are less developed. This is particularly critical for beams whose polarization distribution changes upon propagation, for which classical descriptors are not enough. Here, we describe established vectorness metrics, highlighting their advantages and limitations, as a motivation for our efforts in developing novel approaches to expand the toolkit for characterizing vector beams. We then introduce our proposed measures, presenting the pertinent theoretical background as well as experiments showing their relevance in key examples.

A new method has been developed that permits the measurement of a fully focused laser beam caustic in real-time by utilizing more of the pixelated sensor’s area. In the majority of systems, the signal to noise ratio of the spatial time slices beyond the second Rayleigh range in contrast to the first Rayleigh range is very poor and the sensor and associated software is incapable of measuring these regions with good accuracy. A unique optical concept has been implemented whereby the signal to noise ratio of the spatial time slices beyond the second Rayleigh range can be comparable that of the spatial time slices in the first Rayleigh range. This technique takes advantage of using more of the pixelated sensor’s area to get more of these spatial time slices on the sensor at the same time. Rather than using a linear array of spots, a matrix array of spatial time slices is created with a novel optical design. Previous methods achieved this using a single linear array, but the spatial time slices can be a bit crowded and therefore limit the measurements to a beam waist less than about sixty microns and requires an expensive, specialized optic. In this new approach, the beam waist can be increased to several hundred microns. This opens up a wider dynamic range of measurements with greater efficiency and less expensive optics to accomplish the task for a true easy to use, real-time M-squared measurement system.

We report on the development and setup of a beam shaping system for the Laser-Diode-Floating-Zone (LDFZ) crystal growth, a crucible-free technique used for growing high-purity crystals. The system takes a multi-kW diode laser beam with a rectangular intensity profile as an input. The intensity distribution is top-hat in the horizontal and gaussian-shaped in the vertical axis. The optical system contains a beam splitter unit, which divides the ingoing beam geometrically in 5 partial beams of equal power and size. By a two-lens imaging system, each partial beam is imaged onto the target plane by a magnification factor of 5. Adjustable mirrors of high purity fused silica allow for a radial irradiation of the sample, consequently resulting in a homogeneous heating and melting of the floating zone. After the setup and characterization, the optical system has been integrated into the existing LDFZ furnace at AIST, Tsukuba. First successful experiments on the LDFZ growth of β-Ga₂O₃ single crystals have been carried out, by which the crystal diameter could be scaled from 10 mm to 18 mm.

Since its first demonstration, spatial beam self-cleaning has been targeted as a breakthrough nonlinear effect, for its potential of extending to multimode fibers different technologies based on single-mode fibers, such as fiber lasers and endoscopes. To date, most of the theoretical descriptions of beam self-cleaning are based on scalar models. Whereas, in experiments the analysis of the polarization state of self-cleaned beams is often neglected. Here, we fill this gap between theory and experiments, by demonstrating that a self-cleaned beam eventually loses its degree of polarization, as long as linearly polarized light of enough power is injected at the fiber input. Our results are cast in the framework of a thermodynamic description of nonlinear beam propagation in multimode fibers, providing the first experimental proof of the applicability of scalar theories for the description of the spatial beam self-cleaning effect.

In this paper, we present a method for active control of thermally induced lensing in high-power lasers. We used thermal lensing to study the advantages of high-power lasers. Many delivery optics are sensitive to the thermally induced lens, which can change the focus position of the transmitted beam. To compensate for this, we used thermal lensing by pumping a crystal that had no absorption or amplification at the seed beam wavelength. By controlling the strength of the heat source, we demonstrate acute control of the focus position. Our modeling work is based on the finite-volume method (FVM) to analyse thermal effects in end-pumped solid-state crystals. This work has the potential to pave the way for active control of a thermally induced lens in high-powered laser-based applications.