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1. Stimulated generation of deterministic platicon frequency microcombs

   https://doi.org/10.1364/PRJ.459403  

   Liu, Hao ; Huang, Shu-Wei ; Wang, Wenting ; Yang, Jinghui ; Yu, Mingbin ; Kwong, Dim-Lee ; Colman, Pierre ; Wong, Chee Wei ( July 2022 , Photonics Research)

   Dissipative Kerr soliton generation in chip-scale nonlinear resonators has recently observed remarkable advances, spanning from massively parallel communications, to self-referenced oscillators, and to dual-comb spectroscopy. Often working in the anomalous dispersion regime, unique driving protocols and dispersion in these nonlinear resonators have been examined to achieve the soliton and soliton-like temporal pulse shapes and coherent frequency comb generation. The normal dispersion regime provides a complementary approach to bridge the nonlinear dynamical studies, including the possibility of square pulse formation with flattop plateaus, or platicons. Here we report observations of square pulse formation in chip-scale frequency combs through stimulated pumping at one free spectral range and in silicon nitride rings with$+55{\mathrm{fs}}^2/\mathrm{mm}$normal group velocity dispersion. Tuning of the platicon frequency comb via a varied sideband modulation frequency is examined in both spectral and temporal measurements. Determined by second-harmonic autocorrelation and cross correlation, we observe bright square platicon pulse of 17 ps pulse width on a 19 GHz flat frequency comb. With auxiliary-laser-assisted thermal stabilization, we surpass the thermal bistable dragging and extend the mode-locking access to narrower 2 ps platicon pulse states, supported by nonlinear dynamical modeling and boundary limit discussions.
2. Ultrabroadband, few-cycle pulses directly from a Mamyshev fiber oscillator

   https://doi.org/10.1364/PRJ.8.000065  

   Ma, Chunyang ; Khanolkar, Ankita ; Zang, Yimin ; Chong, Andy ( December 2019 , Photonics Research)

   While the performance of mode-locked fiber lasers has been improved significantly, the limited gain bandwidth restricts them from generating ultrashort pulses approaching a few cycles or even shorter. Here we present a novel method to achieve few-cycle pulses ($\sim 5\text{cycles}$) with an ultrabroad spectrum ($\sim 400\mathrm{nm}$at$-20\mathrm{dB}$) from a Mamyshev oscillator configuration by inserting a highly nonlinear photonic crystal fiber and a dispersion delay line into the cavity. A dramatic intracavity spectral broadening can be stabilized by the unique nonlinear processes of a self-similar evolution as a nonlinear attractor in the gain fiber and a “perfect” saturable absorber action of the Mamyshev oscillator. To the best of our knowledge, this is the shortest pulse width and broadest spectrum directly generated from a fiber laser.
3. Optical parametric oscillation in silicon carbide nanophotonics

   https://doi.org/10.1364/OPTICA.394138  

   Guidry, Melissa A. ; Yang, Ki Youl ; Lukin, Daniil M. ; Markosyan, Ashot ; Yang, Joshua ; Fejer, Martin M. ; Vučković, Jelena ( September 2020 , Optica)

   Silicon carbide (SiC) is rapidly emerging as a leading platform for the implementation of nonlinear and quantum photonics. Here, we find that commercial SiC, which hosts a variety of spin qubits, possesses low optical absorption that can enable SiC integrated photonics with quality factors exceeding${10}^7$. We fabricate multimode microring resonators with quality factors as high as 1.1 million, and observe low-threshold ($8.5\pm <\#comment/>0.5\mathrm{m}\mathrm{W}$) optical parametric oscillation using the fundamental mode as well as optical microcombs spanning 200 nm using a higher-order mode. Our demonstration is an essential milestone in the development of photonic devices that harness the unique optical properties of SiC, paving the way toward the monolithic integration of nonlinear photonics with spin-based quantum technologies.
4. Characterization of field-effect mobility at optical frequency by microring resonators

   https://doi.org/10.1364/PRJ.416656  

   Hsu, Wei-Che ; Li, Erwen ; Zhou, Bokun ; Wang, Alan X. ( March 2021 , Photonics Research)

   A novel characterization method is proposed to extract the optical frequency field-effect mobility (${\mu }_{\mathrm{op},\mathrm{FE}}$) of transparent conductive oxide (TCO) materials by a tunable silicon microring resonator with a heterogeneously integrated titanium-doped indium oxide$(\mathrm{ITiO})/{\mathrm{SiO}}_2/\mathrm{silicon}$metal–oxide–semiconductor (MOS) capacitor. By operating the microring in the accumulation mode, the quality factor and resonance wavelength shift are measured and subsequently used to derive the${\mu }_{\mathrm{op},\mathrm{FE}}$in the ultra-thin accumulation layer. Experimental results demonstrate that the${\mu }_{\mathrm{op},\mathrm{FE}}$of ITiO increases from 25.3 to$38.4{\mathrm{cm}}^2\text{⋅}{\mathrm{V}}^{-1}\text{⋅}{\mathrm{s}}^{-1}$with increasing gate voltages, which shows a similar trend as that at the electric frequency.
5. Optical beam steering by using tunable, narrow-linewidth butt-coupled hybrid lasers in a silicon nitride photonics platform

   https://doi.org/10.1364/PRJ.382852  

   Zhu, Yeyu ; Zeng, Siwei ; Zhu, Lin ( February 2020 , Photonics Research)

   Chip-scale, tunable narrow-linewidth hybrid integrated diode lasers based on quantum-dot RSOAs at 1.3 μm are demonstrated through butt-coupling to a silicon nitride photonic integrated circuit. The hybrid laser linewidth is around 85 kHz, and the tuning range is around 47 nm. Then, a fully integrated beam steerer is demonstrated by combining the tunable diode laser with a waveguide surface grating. Our system can provide beam steering of 4.1° in one direction by tuning the wavelength of the hybrid laser. Besides, a wavelength-tunable triple-band hybrid laser system working at$\sim 1$,$\sim 1.3$, and$\sim 1.55\mathrm{\mu m}$bands is demonstrated for wide-angle beam steering in a single chip.