A Thermally Tunable 1 x 4 Channel Wavelength Demultiplexer Designed on a Low-Loss Si3N4 Waveguide Platform

A thermally tunable 1 x 4 channel optical demultiplexer was designed using an ultra low-loss Si3N4 (propagation loss similar to 3.1 dB/m) waveguide. The demultiplexer has three 2 x 2 Mach-Zehnder interferometers (MZI), where each of the MZI contains two 2 x 2 general interference based multimode interference (MMI) couplers. The MMI couplers exhibit -3.3 dB to -3.7 dB power division ratios over a 50 nm wavelength range from 1530 nm to 1580 nm. The chrome-based (Cr) heaters placed on the delay arms of the MZI filters enable thermal tuning to control the optical phase shift in the MZI delay arms. This facilitates achieving moderately low crosstalk (14.5 dB) between the adjacent channels. The optical insertion loss of the demultiplexer per channel is between 1.5 dB to 2.2 dB over the 1550 nm to 1565 nm wavelength range. Error free performance (BER of 10(-12)) is obtained for all four 40 Gb/s data rate channels. The optical demultiplexer is an important tool towards building photonic integrated circuits with complex optical signal processing functionalities in the low-loss Si3N4 waveguide platform.