We present the design and experimentally demonstrate a dual-level grating coupler with subdecibel efficiency for a 220 nm thick silicon photonics waveguide which was fabricated starting from a 340 nm silicon-on-insulator wafer. The proposed device consists of two grating levels designed with two different linear apodizations, with opposite chirping signs, and whose period is varied for each scattering unit. A coupling efficiency of -0.8dB at 1550 nm is experimentally demonstrated, which represents the highest efficiency ever reported in the telecommunications C-band in a single-layer silicon grating structure without the use of any backreflector or index-matching material between the fiber and the grating.

We report mid-infrared Ge-on-Si waveguide-based PIN diode modulators operating at wavelengths of 3.8 and 8 μm. Fabricated 1-mm-long electro-absorption devices exhibit a modulation depth of >35 dB with a 7 V forward bias at 3.8 μm, and a similar 1-mm-long Mach–Zehnder modulator has a Vπ·L of 0.47 V·cm. Driven by a 2.5Vpp RF signal, 60 MHz on-off keying modulation was demonstrated. Electro-absorption modulation at 8 μm was demonstrated preliminarily, with the device performance limited by large contact separation and high contact resistance.

In silicon photonics, the carrier depletion scheme has been the most commonly used mechanism for demonstrating high-speed electro-optic modulation. However, in terms of phase modulation efficiency, carrier-accumulation-based devices potentially offer almost an order of magnitude improvement over those based on carrier depletion. Previously reported accumulation modulator designs only considered vertical metal-oxide-semiconductor (MOS) capacitors, which imposes serious restrictions on the design flexibility and integratability with other photonic components. In this work, for the first time to our knowledge, we report experimental demonstration of an all-silicon accumulation phase modulator based on a lateral MOS capacitor. Using a Mach–Zehnder interferometer modulator with a 500-μm-long phase shifter, we demonstrate high-speed modulation up to 25 Gbit/s with a modulation efficiency (VπLπ) of 1.53 V·cm.