Two-Dimensional Grating-Based Silicon Mach–Zehnder Modulator Featuring a Polarization Insensitive Behavior

We present dual-polarization silicon Mach-Zehnder modulators based on central-symmetric two-dimensional apodized grating couplers to address the polarization sensitivity issues of optical transmitters. For comparison, both “balanced-arm” and “unbalanced-arm” devices were fabricated and characterized. The former is designed to evaluate the polarization dependent loss (PDL) and demonstrate broadband optical modulation. It features a measured PDL below 0.3 dB across the C-band, fiber-to-fiber insertion loss (IL) of about 10 dB, and a large optical bandwidth of 60 nm for modulation. The latter is more suitable for evaluating the modulation efficiency, EO bandwidth, and modulation speed. The modulation efficiency is about 1 V·cm and the maximum EO bandwidth, obtained at a reverse bias voltage of 5 V, is 35.4 GHz. It can operate at a speed of up to 80 Gb/s and eye diagrams show superior polarization insensitivity with 3-tap FFE enabled. This work presents a novel device structure to realize polarization insensitive optical modulations in pure silicon and other material waveguide platforms.