On-chip silicon photonic filters acting as spectral shapers for the input spectrum are important in various applications including optical communication, computing, and spectroscopy sensing. We used the photonics inverse design framework, aided by the Particle Swarm Optimization (PSO) algorithm, to obtain miniature and efficient filtering structures in the Silicon on Insulator (SOI) platform. These optical filters are less than 10 μm, or just a few wavelengths, in size along any dimension. The investigated structures demonstrate good light filtering characteristic, with various filter types and wavelength ranges. The performance of designed filters is comparable to widely-used mm-long Bragg grating filters, while being a tiny fraction of their size. We also study a class of filters to directly resolve the issue of removing back reflected light without using a circulator or adding a third port (as is generally done) using the optimization process. Our structures are expected to have a much wider range of applications than grating-type filters, primarily due to their miniature footprint, independence from external devices like circulators for back-reflection control, and greater tolerance to thermal effects. Our work also highlights the possibility of designing and fabricating photonic components as a next step, by inversely designing components that best match a given set of requirements instead of depending on general conventional devices.
In recent years, there has been tremendous development in photonic integrated circuits (PICs) because of the growing demand for computational power and the slowing down of transistor shrinkage. PICs are seen as a promising technology for developing next-generation technologies including the Internet of Things, on-chip data routers, and optical quantum computers due to their compatibility with the long-established complementary metal-oxide-semiconductor fabrication technology and making use of common materials such as silicon and silicon dioxide. As the size of the PICs is shrinking and considering different aspects such as modal size mismatch, fabrication/packaging cost, it has become increasingly difficult to couple light efficiently in-plane or out-of-plane among different photonic elements such as waveguides and fibers. In this study, we propose a two-layer grating coupler using a horizontally placed angle-polished single-mode optical fiber. We used the finite-difference time-domain method and optimization tools including the inverse design technique to investigate the design parameters for performance enhancement of light coupling in silicon-on-insulator (SOI) integrated circuits. We achieved a coupling efficiency of -1.54 dB (70.15%) for fiber-to-SOI chip coupling and a coupling efficiency of -0.97 dB (80%) for chip-to-fiber coupling over a wide bandwidth.
We demonstrate two-dimensional (2-D) beam-steering using only wavelength control from one-dimensional siliconbased OPA, where path differences are sequentially formed in each channel. With 79.6-μm path difference in phasefeeding lines and a 2-μm pitch in grating radiators, we achieved a continuous transversal steering about 46° and a longitudinal steering near 13° with a wavelength tuning of 90 nm. The single-beam with divergence angle of 4° was formed by phase initialization using electro-optic optic p-i-n phase shifters before beam-steering.
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