The investigations on optical angular momenta and their interactions have broadened our knowledge of light’s behavior at sub-wavelength scales. Recent studies further unveil the extraordinary characteristics of transverse spin angular momentum in confined light fields and orbital angular momentum in optical vortices. Here we demonstrate a direct interaction between these two intrinsic quantities of light. By engineering the transverse spin in the evanescent wave of a whispering-gallery-mode-based optical vortex emitter, a spin-orbit interaction is observed in generated vortex beams. Inversely, this unconventional spin-orbit interplay further gives rise to an enhanced spin-direction locking effect in which waveguide modes are unidirectionally excited, with the directionality jointly controlled by the spin and orbital angular momenta states of light. The identification of this previously unknown pathway between the polarization and spatial degrees of freedom of light enriches the spin-orbit interaction phenomena, and can enable various functionalities in applications such as communications and quantum information processing.

High-quality SiN_x films with controllable low stress and low optical loss are deposited at ultra-low temperature (75 °C) using inductively coupled plasma chemical vapor deposition (ICP-CVD). Two kinds of integrated photonic structures have been demonstrated that exemplify its viability as a photonic integration platform. A microcavity consists of two distributed Bragg reflectors (DBR) formed by alternating a total of 49 layers of SiN_x and SiO₂ with a total thickness of about 11.5 μm is grown without any cracks, confirming the excellent stress control in the process. Microring resonators are also fabricated in as-deposited planar SiN_x waveguide layer using electron-beam lithography (EBL) and plasma etching. Average waveguide loss of 0.79 ± 0.22 dB/cm has been achieved in the range of 1550-1600 nm for ring radii larger than 40 μm. The ultra-low temperature grown SiN_x with properties of low loss and low stress is therefore a promising photonic integration platform for various photonic integration applications.

Cylindrical vector vortex (CVV) beams, complex light fields that exhibit a vector nature and carry quantized orbital angular momentum (OAM) states, have been widely investigated due to their rich applications. Current technologies to generate CVV beams using individual polarization and spatial phase manipulations suffer from bulky size and low configurability. In this Letter, we propose and experimentally demonstrate an approach to generate CVV beams with a single integrated device based on a silicon nitride microring resonator and embedded top-gratings. The device allows the manipulation of both the polarization and OAM degrees of freedom of light, and enables the generation of both radially and azimuthally polarized CVV beams. In addition, we develop a method to fabricate the devices of shallow-etched top-gratings with only one-step etching. To the best of our knowledge, this novel method provides new capabilities to develop on-chip integrated devices with great ease and flexibility.

The chip-fiber grating coupler is a fundamental building block in integrated photonics, providing convenient on-wafer testing and packaging. Couplers based on a silicon nitride (${\mathrm{SiN}}_x$) material platform can achieve wider bandwidths than silicon-based couplers, but suffer from lower efficiency due to the relative low material refractive index. The efficiency of the ${\mathrm{SiN}}_x$ grating coupler can be improved by using high-reflectivity silicon grating reflectors underneath. However, such a silicon grating reflector requires several fabrication steps, including lithography, etching, high precision alignment (HPA), and chemical mechanical polishing (CMP). In this Letter, we demonstrate an easy-to-fabricate ${\mathrm{SiN}}_x$-on-SOI transverse-electric mode grating coupler requiring only one patterning step (grating alone), and without the need for HPA and CMP. A coupling coefficient of $-2.5\mathrm{dB}$ and 1-dB-bandwidth of 65 nm has been experimentally measured.

We report very low-loss deuterated silicon nitride (SiN_x:D) micro-ring resonators fabricated by back-end CMOS compatible low-temperature plasma-enhanced chemical vapor deposition (PECVD) without annealing. Strong confinement micro-ring resonators with a quality factor of > 2 million are achieved, corresponding to a propagation loss in the 1460-1610 nm wavelength range of ∼ 0.17 dB/cm. We further report the generation of low-noise coherent Kerr microcomb states including different perfect soliton crystals (PSC) in PECVD SiN_x:D micro-ring resonators. These results manifest the promising potential of the back-end CMOS compatible SiN_x:D platform for linear and nonlinear photonic circuits that can be co-integrated with electronics.