Phase coherence length in silicon photonic platform

Abstract

We report for the first time two typical phase coherence lengths in highly confined silicon waveguides fabricated in a standard CMOS foundry's multi-project-wafer shuttle run in the 220nm silicon-on-insulator wafer with 248nm lithography. By measuring the random phase fluctuations of 800 on-chip silicon Mach-Zehnder interferometers across the wafer, we extracted, with statistical significance, the coherence lengths to be 4.17 ± 0.42 mm and 1.61 ± 0.12 mm for single mode strip waveguide and rib waveguide, respectively. We present a new experimental method to quantify the phase coherence length. The theory model is verified by both our and others' experiments. Coherence length is expected to become one key parameter of the fabrication non-uniformity to guide the design of silicon photonics.