This paper reports on large field-of-regard, high-efficiency, and large aperture active optical phased arrays (OPAs) for optical beam steering in LIDAR systems. The fabricated 5 mm-long silicon photonic OPA with a 1.3 μm waveguide pitch achieved adjacent waveguide crosstalk below −12dB. A relatively large and uniform emission aperture has been achieved with a low-contrast silicon nitride assisted grating (~20 dB/cm) whose emission profile can be further optimized using an apodized design. The fabricated silicon-photonic OPA demonstrated > 40° lateral beam steering with no sidelobes in a ± 33° field-of-regard and 3.3° longitudinal beam steering via wavelength tuning by 20 nm centered at 1550 nm. We have fully integrated the silicon photonic OPA device with electronic controls and successfully demonstrated 2-dimensional coherent optical beam steering of pre-planned far-field patterns. Future improvements include placement of a distributed Bragg reflector (DBR) underneath the grating emitter in order to achieve nearly a factor of two improvement in emission efficiency.

We review the state of the art and our perspectives on silicon and hybrid silicon photonic devices for optical interconnects in datacenters. After a brief discussion of the key requirements for intra-datacenter optical interconnects, we propose a wavelength-division-multiplexing (WDM)-based optical interconnect for intra-datacenter applications. Following our proposed interconnects configuration, the bulk of the review emphasizes recent developments concerning on-chip hybrid silicon microlasers and WDM transmitters, and silicon photonic switch fabrics for intra-datacenters. For hybrid silicon microlasers and WDM transmitters, we outline the remaining challenges and key issues toward realizing low power consumption, direct modulation, and integration of multiwavelength microlaser arrays. For silicon photonic switch fabrics, we review various topologies and configurations of high-port-count N-by-N switch fabrics using Mach–Zehnder interferometers and microring resonators as switch elements, and discuss their prospects toward practical implementations with active reconfiguration. For the microring-based switch fabrics, we review recent developments of active stabilization schemes at the subsystem level. Last, we outline several large challenges and problems for silicon and hybrid silicon photonics to meet for intra-datacenter applications and propose potential solutions.

We propose to monitor the spectral alignment of silicon microring resonators with an optical carrier in the 1300 / 1550 nm wavelengths by photodetecting the microring internal power using a defect-state-absorption-based silicon photodetector integrated along the microring. We can thereby adaptively tune the resonance wavelength based on the photocurrent to compensate the spectral misalignment using either an integrated electro-optical or thermo-optical tuner. Our analysis suggests that the spectral alignment can be preserved within ~±0.01 nm upon an on-chip temperature variation of 10°C or a carrier wavelength drift of ±60 pm, assuming a closed-loop operation time shorter than 900 μs and a total power consumption of ~0.65 mW for 1550 nm and ~1.1 mW for 1300 nm. As a proof-of-concept, we experimentally demonstrate monitoring the spectral alignment using the photocurrents from a silicon microring carrier-injection switch upon a 10 Gb/s data transmission in 1550 nm, while subjecting the switch to a temperature variation between 20 - 33 °C. We further analyze the feasibility of integrating such an adaptively tuned silicon microring resonator into a single-channel M-input N-output (M × N) optical switch-matrix. Our worst-case analysis suggests that a 16 × 16 switch-matrix in an estimated total footprint of ~640 μm × 480 μm imposes an estimated total power consumption of ~167 mW for 1550 nm, and a 13 × 13 switch-matrix in an estimated total footprint of ~520 μm × 390 μm imposes an estimated power consumption of ~185 mW for 1300 nm.

Silicon photonics is becoming the leading technology for photonic integrated circuits (PICs) due to large-scale integration, low cost, and high-volume productions enabled by complementary metal-oxide-semiconductor (CMOS) fabrication process. Thanks to various material and optical characteristics of crystalline silicon, the silicon-on-insulator platform has become the dominant material platform for silicon photonics. Meanwhile, monolithic or heterogeneous integration of other materials on silicon photonic chips, including the silicon nitride (SiN)-on-insulator platform and the III–V-on-silicon platform, are under rapid developments to enhance the functionalities of silicon photonics. Among the myriad of silicon photonic structures for passive and active components, integrated microresonators are promising for a broad range of applications due to their strong resonance field enhancement, narrowband wavelength selectivity, and compact footprints. In this paper, we review the state of the art and our perspectives on emerging technologies based on integrated silicon photonic microresonators in the technology domains of intradatacenter optical interconnects, integrated nonlinear and quantum photonics, and lab-on-a-chip optical biosensing. We specifically review recent progress and our original work in SOI microring-based crossbar switch fabrics; III–V-on-silicon microresonator lasers; silicon-based microresonator nonlinear and quantum sources; and SiN microresonator-based optical biosensors.

This paper investigates the opportunity and challenges of 3D silicon photonic electronic integrated circuits (3D EPICs) scaling to wafer-scale and beyond. The continuing demand for more data and information is driving new computing, communications, imaging, and information processing at higher throughput and energy-efficiency at lower manufacturing cost. The newly developed 3D silicon photonic devices including vertical U-turns and vertical lightpipes enable through-silicon-optical-vias (TSOVs) that can interconnect multiple layers of 2D silicon photonic electronic integrated circuits consistently with the industry's through-silicon-via (TSV) based 3D electronic integrated circuit manufacturing. Heterogeneous integration technology based on transfer printing allows wafer-scale (or beyond wafer-scale) heterogeneous integration of dissimilar materials (e.g. III-V semiconductor layers) on silicon at room temperature and 3D ultrafast laser inscription technologies allow arbitrary optical interfaces for high-density input/output between the 3D EPICs and many strands of multi-core-fibers (MCFs). We will discuss applications in neuromorphic computing, 3D LiDAR, photonic-integrated-interferometric-telescopes, 3D-fine-grain-memory, and 3D processor-memory realized by large-scale 3D EPICs.

While compact and low-loss optical coupling to ultrahigh-quality-factor (Q) crystalline resonators is important for a wide range of applications, the major challenge for achieving this coupling stems from the relatively low refractive index of the crystalline resonator host material compared to those of the standard waveguide coupling materials. We report the first demonstration of a single-mode waveguide structure (prism-waveguide coupler) integrated on a low-loss compact silicon nitride platform resulting in low-loss and efficient coupling to magnesium fluoride crystalline resonators by achieving the phase-matched and the mode-matched evanescent wave coupling. The coupling is characterized with 1 dB loss at 1550 nm wavelength. We further present a photonic integrated chip containing a pair of waveguides successfully coupling light into and out of the resonator, demonstrating a planar-waveguide-coupled crystalline resonator with a loaded Q of $1.9\times {10}^9$. We assemble this waveguide-coupled resonator and a distributed-feedback-laser chip into a butterfly package to realize a miniature Kerr optical frequency comb source using self-injection locking of the distributed feedback laser to the waveguide-coupled crystalline resonator.