Polarization-Rotator-Free Polarization-Diversity 4 $\times$ 4 Si-Wire Optical Switch

We present a polarization-diversity 4×4 optical switch composed of silicon-wire waveguides. The proposed 4×4 switch does not require a polarization rotator, which enforces a modification in a standard complementary metal-oxide-semiconductor (CMOS) process to achieve vertical asymmetry. The switch is fabricated on a 300-mm silicon-on-insulator (SOI) wafer with argon fluoride (ArF) immersion lithography, and its footprint is 2.1 mm × 1.1 mm. The switch exhibited a 12.5-dB on-chip loss, a 1.9-dB polarization-dependent loss, and an approximately 5-ps differential group delay.