Low-Loss and Small 2 × 4λ Multiplexers Based on 2 × 2 and 2 × 1 Mach–Zehnder Interferometers With On-Chip Polarization Multiplexing for 400GbE

Abstract

Two silicon, 4λ O-band multiplexers (MUXs) for 400GbE using two Mach-Zehnder interferometers (MZIs) having 90-degree phase shift in their output with the help of on-chip polarization multiplexing are demonstrated. By using 2 × 2 and 2 × 1 MZIs for first 3200-GHz filters, the relative position of their spectra has 90-degree phase difference, leading to significant simplification of the tuning of peak wavelength position of the two filters. The polarization MUX is done by using an on-chip polarization-splitter-rotator (PSR) based on an asymmetric directional coupler (ADC) and a TE1-TM0 mode converter (MC) using tapered rib waveguide, designed for O-band application. Two 4λ MUXs for 1.28 and 1.3 μm bands are designed, aiming to the specified wavelength range in 400GbE. Tolerance analysis shows the proposed MUX is robust to the change of waveguide width occurring in the fabrication process, compared with those of conventional multi-stage 4λ MUXs. The averaged insertion loss of eight wavelength is 1.86 dB for the fabricated device and the demonstration of 8λ (2×4λ) MUX for 400GbE based on Si-waveguide is for the first time.