High performance optical 90° hybrid at 2 μm wavelength range based on 2×4 MMI using Si3N4 technology

A compact and broadband optical 90° hybrid based on a 2×4 multimode interference (MMI) coupler using the Si3N4 technology is proposed. The effects of MMI length, width, and wavelength on optical power transmission are investigated. With the length of 217 μm for the 2×4 MMI coupler, this optical 90° hybrid shows a maximum phase error of 5°, an excess loss of 1 dB, and a transmission imbalance of 1 dB over a 75-nm-wide wavelength range.