Silicon photonics has experienced phenomenal transformations over the last decade. In this paper, we present some of the notable advances in silicon-based passive and active optical interconnect components, and highlight some of our key contributions. Light is also cast on few other parallel technologies that are working in tandem with silicon-based structures, and providing unique functions not achievable with any single system acting alone. With an increasing utilization of CMOS foundries for silicon photonics fabrication, a viable path for realizing extremely low-cost integrated optoelectronics has been paved. These advances are expected to benefit several application domains in the years to come, including communication networks, sensing, and nonlinear systems.

Silicon has been the material of choice of the photonics industry over the last decade due to its easy integration with silicon electronics, high index contrast, small footprint, and low cost, as well as its optical transparency in the near-infrared and parts of mid-infrared (MIR) wavelengths (from 1.1 to 8 μm). While considerations of micro- and nano-fabrication-induced device parameter deviations and a higher-than-desirable propagation loss still serve as a bottleneck in many on-chip data communication applications, applications as sensors do not require similar stringent controls. Photonic devices on chips are increasingly being demonstrated for chemical and biological sensing with performance metrics rivaling benchtop instruments and thus promising the potential of portable, handheld, and wearable monitoring of various chemical and biological analytes. In this paper, we review recent advances in MIR silicon photonics research. We discuss the pros and cons of various platforms, the fabrication procedures for building such platforms, and the benchmarks demonstrated so far, together with their applications. Novel device architectures and improved fabrication techniques have paved a viable way for realizing low-cost, high-density, multi-function integrated devices in the MIR. These advances are expected to benefit several application domains in the years to come, including communication networks, sensing, and nonlinear systems.

A 16-element optical phased array integrated on chip is presented for achieving two-dimensional (2D) optical beam steering. The device is fabricated on the silicon-on-insulator platform with a 250 nm silicon device layer. Steering is achieved via a combination of wavelength tuning and thermo-optic phase shifting with a switching power of $P_{\pi }=20\mathrm{mW}$ per channel. Using a silicon waveguide grating with a polycrystalline silicon overlay enables narrow far field beam widths while mitigating the precise etching needed for conventional shallow etch gratings. Using this system, 2D steering across a $20°\times 15°$ field of view is achieved with a sidelobe level better than 10 dB and with beam widths of $1.2°\times 0.5°$.

The past two decades have witnessed the stagnation of the clock speed of microprocessors followed by the recent faltering of Moore’s law as nanofabrication technology approaches its unavoidable physical limit. Vigorous efforts from various research areas have been made to develop power-efficient and ultrafast computing machines in this post-Moore’s law era. With its unique capacity to integrate complex electro-optic circuits on a single chip, integrated photonics has revolutionized the interconnects and has shown its striking potential in optical computing. Here, we propose an electronic-photonic computing architecture for a wavelength division multiplexing-based electronic-photonic arithmetic logic unit, which disentangles the exponential relationship between power and clock rate, leading to an enhancement in computation speed and power efficiency as compared to the state-of-the-art transistors-based circuits. We experimentally demonstrate its practicality by implementing a 4-bit arithmetic logic unit consisting of 8 high-speed microdisk modulators and operating at 20 GHz. This approach paves the way to future power-saving and high-speed electronic-photonic computing circuits.

An ultracompact silicon electro-optic modulator was experimentally demonstrated based on silicon photonic crystal (PhC) waveguides for the first time to our knowledge. Modulation operation was demonstrated by carrier injection into an $80\mu \mathrm{m}$ -long silicon PhC waveguide of a Mach-Zehnder interferometer (MZI) structure. The $\pi$ phase shift driving current, $I_{\pi }$ , across the active region is as low as $0.15\mathrm{mA}$ , which is equivalent to a $V_{\pi }$ of $7.5\mathrm{mV}$ when a $50\Omega$ impedance-matched structure is applied. The modulation depth is 92% operating at $1567\mathrm{nm}$ .

We present the design, fabrication and characterization of a compact and highly sensitive integrated photonic electromagnetic field sensor based on a silicon-organic hybrid modulator driven by a bowtie antenna. Slow-light effects in the electro-optic (EO) polymer refilled silicon slot photonic crystal waveguide (PCW), together with broadband electric field enhancement provided by the bowtie antenna, are utilized to enhance the interaction of microwaves and optical waves, enabling an ultra large effective in-device EO coefficient over 1000 pm/V and thus a high sensitivity. The EO polymer refilled slot PCW is designed for low-dispersion slow-light propagation, high poling efficiency, and high optical mode confinement inside the slot. The bowtie antenna acts not only as a receiving antenna, but also as poling electrodes during the fabrication process. A bowtie antenna integrated on doped silicon slot PCW is demonstrated to have a broad operational bandwidth, with a maximum resonance at the frequency of 10 GHz. The strongly enhanced broadband electric field is used to directly modulate the phase of the optical waves propagating through the slot PCW embedded inside the feed gap of the bowtie antenna. The phase modulation is then converted to intensity modulation using an external reference arm to form a Mach-Zehnder interferometer in our experimental setup. The sensing of electromagnetic field at 8.4 GHz is experimentally demonstrated, with a minimum detectable electromagnetic power density of 8.4 mW/m ² , corresponding to a minimum detectable electric field of 2.5 V/m.