Switch-filter wavelength selector: simulation and experiment

A lossless programmable wavelength selector using a chain of switched optical filter cells is studied. One of N wavelength channels can be selected with log₂N switching cells, allowing a sub-linear scaling for electrode number with channel number. Each filter cell is based on the sequence of an amplifying Mach-Zehnder interferometer and an optical switch. Fine wavelength tuning and digital wavelength selection are demonstrated in a loss-compensating circuit, which allows the fast tuning of the filter pass-bands to select channels. A model is implemented and experimentally verified against an integrated circuit implementation for the case of a 200 GHz grid selector to verify the operating characteristics and study scaling. Channel selection is modelled with two different methods: pass-band selection and null-rejection. The alignment of the filter nulls to reject unwanted wavelengths is observed to improve adjacent cross-talk performance by 19 dB. This enhanced mode of operation allows a five-stage selector for a 32-channel, 100 GHz grid wavelength selector to perform with worst-case cross-talk below -25.7 dB with a control current tolerance of greater than 0.6 mA and an integrated cross-talk of -21.3 dB at the optimal control current.