Frequency stabilization and tuning of breathing solitons in Si3N4 microresonators

Dissipative Kerr solitons offer broadband coherent and low-noise frequency combs and stable temporal pulse trains,having shown great potential applications in spectroscopy,communications,and metrology.Breathing solitons are a particular kind of dissipative Kerr soliton in which the pulse duration and peak intensity show periodic oscillation.Here we have investigated the breathing dissipative Kerr solitons in silicon nitride(Si3N4)microrings,while the breathing period shows uncertainties of around megahertz(MHz)order in both simulation and experiments.This instability is the main obstacle for future applications.By applying a modulated signal to the pump laser,the breathing frequency can be injection locked to the modulation frequency and tuned over tens of MHz with frequency noise significantly suppressed.Our demonstration offers an alternative knob for the control of soliton dynamics in microresonators and paves a new avenue towards practical applications of breathing solitons.

Fabrication of the high-Q Si_(3)N_(4) microresonators for soliton microcombs

The microresonator-based soliton microcomb has shown a promising future in many applications.In this work,we report the fabrication of high quality[Q]Si_(3)N_(4)microring resonators for soliton microcomb generation.By developing the fabri-cation process with crack isolation trenches and annealing,we can deposit thick stoichiometric Si3N4 film of 800 nm without cracks in the central area.The highest intrinsic Q of the Si_(3)N_(4)microring obtained in our experiments is about 6×10^(6),corresponding to a propagation loss as low as 0.058 dBm/cm.With such a high Q film,we fabricate microrings with the anomalous dispersion and demonstrate the generation of soliton microcombs with 100 mW on-chip pump power,with an optical parametric oscillation threshold of only 13.4 mW.Our Si_(3)N_(4)integrated chip provides an ideal platform for researches and applications of nonlinear photonics and integrated photonics.

Enhancement of silicon sub‑bandgap photodetection by helium‑ion implantation

Silicon sub-bandgap photodetectors can detect light at the infrared telecommunication wavelengths but with relatively weak photo-response.In this work,we demonstrate the enhancement of sub-bandgap photodetection in silicon by helium-ion implantation,without afecting the transparency that is an important benefcial feature of this type of photodetectors.With an implantation dose of 1×10^(13)ions/cm^(2),the minimal detectable optical power can be improved from−33.2 to−63.1 dBm,or,by 29.9 dB,at the wavelength of 1550 nm,and the photo-response at the same optical power(−10 dBm)can be enhanced by approximately 18.8 dB.Our work provides a method for strategically modifying the intrinsic trade-of between transparency and strong photo-responses of this type of photodetectors.

Independent phase manipulation of co-and cross-polarizations with all-dielectric metasurface

Phase carried by two orthogonal polarizations can be manipulated independently by controlling both the geometric size and orientation of the dielectric nanopost.With this characteristic,we demonstrate a novel multifunctional metasurface,which converts part of the incident linearly polarized light into its cross-polarization and encodes the phase of the two orthogonal polarizations independently.A beam splitter and a bifocal metalens were realized in a single-layer dielectric metasurface by this approach.We fabricated the bifocal metalens and demonstrated that two focal spots in orthogonal polarizations can be separated transversely or longitudinally at will.The proposed approach shows a new route to design multifunctional metasurfaces with various applications in holography and three-dimensional display.

A hierarchical heterostructure of CdS QDs confined on 3D ZnIn_(2)S_(4) with boosted charge transfer for photocatalytic CO_(2) reduction

Metal sulfide based materials as photocatalysts for energy conversion are essential to produce value-added chemical fuels,but their intrinsically slow carrier dynamics and low activity are yet to be resolved.Herein,we developed a unique heterogeneously nanostructured ZnIn_(2)S_(4)-CdS heterostructure that involves zero-dimensional(0D)CdS quantum dots uniformly confined on three-dimensional(3D)ZnIn_(2)S_(4)nanoflowers,which achieves an excellent catalytic performance of CO_(2) photoconversion under visible-light irradiation.The obtained hierarchical heterostructure can significantly enhance the light harvesting,shorten the migration distance of carriers,and obviously accelerate the transport of electrons.As evidenced by the ultrafast transient absorption spectroscopy,the formed interface can effectively facilitate charge separation and transport.This work opens up a new avenue to carefully design the elaborate heterostructures for achieving optimal charge separation efficiency by lowering interfacial kinetic barriers and energy losses at the interface.