Zengkai Shao

Ultra-low temperature silicon nitride photonic integration platform

High-quality SiNx 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 SiNx 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 SiNx 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 SiNx with properties of low loss and low stress is therefore a promising photonic integration platform for various photonic integration applications.

Realizing topological edge states in a silicon nitride microring-based photonic integrated circuit

Topological edge states in a photonic integrated circuit based on the platform of silicon nitride are demonstrated with a two-dimensional coupled resonator optical waveguide array involving the synthetic magnetic field for photons at near-infrared wavelengths. Measurements indicate that the topological edge states can be observed at certain wavelengths, with light travelling around the boundary of the array. Combined with the induced disorders in fabrication near the edge, the system shows the defect immunity under the topological protection of edge states.

Design and optimization of optical modulators based on graphene-on-silicon nitride microring resonators

In order to overcome the challenge of obtaining high modulation depth due to weak graphene–light interaction, a graphene-on-silicon nitride (SiNx) microring resonator based on graphenes gate-tunable optical conductivity is proposed and studied. Geometrical parameters of graphene-on-SiNx waveguide are systematically analyzed and optimized, yielding a loss tunability of 0.04 dB μm−1 and an effective index variation of 0.0022. We explicitly study the interaction between graphene and a 40 μm-radius microring resonator, where electro-absorptive and electro-refractive modulation are both taken into account. By choosing appropriate graphene coverage and coupling coefficient, a high modulation depth of over 40 dB with large fabrication tolerance is obtained.

Spin-orbit interaction of light induced by transverse spin angular momentum engineering

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.Harnessing both orbital and spin angular momentum in light fields enables various applications in bio-sensing and nano-photonics. Here, the authors create engineered spin-orbit coupling between orbital angular momentum and transverse spin angular momentum in light using a vortex-emitting waveguide.

Silicon Nitride Metalenses for Close-to-One Numerical Aperture and Wide-Angle Visible Imaging

SiN is an emerging semiconductor for integrated optoelectronics, due to its ultralow loss in the visible region. Developing a high-performance SiN metamaterial lens (metalens) is attractive for on-chip optical devices, but is held back by technical challenges in nanofabrication. The authors report the experimental realization of a SiN metalens that is 1 cm across and 695 nm thick, by means of CMOS-compatible fabrication. With high-quality, wide-angle visible imaging, these results point to the miniaturization of lenses for optical fibers, microendoscopes, and smart phones, as well as applications in all-sky telescopes, large-angle beam shaping, and near-eye imaging.

Orbital angular momentum assisted spin-directional coupling

Spin-directional coupling is associated with the quantum spin-Hall effect of photons, which has attracted much attention over the past few years. Here, we report orbital angular momentum (OAM) assisted spin-directional coupling and its reversal in a silicon nitride (SiNx) photonic integrated circuit. SiNx microring resonators with angular grating have been designed and realized to emit high purity circularly polarized OAM beam. In addition, utilized as an OAM receiver, photonic spin-controlled unidirectional excitation of whispering-gallery modes in ring resonator is also observed, coupling the left-hand and right-hand circularly polarized OAM beam to different channel waveguide, respectively. Our results exemplify a very promising waveguide-based OAM device such as a robust OAM assisted spin-directional coupler and may open up many new capabilities in emerging applications of on-chip chiral photonics and quantum optics.

Fabrication-friendly high-efficiency silicon nitride grating coupler

Grating coupler, as one of the key components can provide convenient on-wafer testing and packaging for integrated photonics. Silicon nitride (SiNx) grating coupler suffers from lower efficiency due to the relative low material refractive index. The efficiency of SiNx grating coupler can be improved by using high reflectivity silicon grating reflectors underneath. However, such silicon grating reflector requires several fabrication steps, including lithography, etching, high precision alignment (HPA), and chemical mechanical polishing (CMP). In this work, we demonstrate an easy-to-fabricate SiNx grating coupler only requiring a single patterning step without the need of HPA and CMP. A coupling coefficient of −2.5 dB and 1-dB-bandwidth of 65 nm have been experimentally measured.

Chirality and directional emission of a SiN x -based microring resonator with position controllable scatters

Chiral device breaking time-reversal symmetry can control the propagation direction of the light which is great significant for the information processing on chip. Here we report a new chiral structure based on silicon nitride (SiNx) microring resonator embedded with a scatterer in the evanescent region the waveguide. The simulation results show that the asymmetry backscattering of the whispering-gallery modes (WGMs) can be induced by a single scatterer and thus directional transmission observed. In addition, the dimensions and relative position of the scatterer have been optimized to obtain the strongest chirality effect, resulting in an extinction ratio of up to 10 dB. Our results open pathways towards many chiral integrated nanophotonic devices.

Integrated Orbital Angular Momentum Emitters Based on Silicon Nitride Photonic Platform

Integrated orbital angular momentum emitters have been studied widely in the past few years. Meanwhile, silicon nitride (SiNx) material provides a veritable platform for on-chip compact photonic integrated circuit. In this paper, we demonstrate integrated orbital angular momentum (OAM) emitters based on silicon nitride micro-ring resonators with angular gratings. By changing waveguide dimensions and duty cycle of gratings, several OAM emitters have been designed and fabricated. The relative high average emission efficiency was measured to be (

Hybrid Integrated Velocity Matched Travelling-wave InP/InGaAs Photodetectors with Silicon Nitride Waveguides

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