Extremely low crosstalk characteristic of semiconductor optical ADM device with deep grating

Improvement of diffraction efficiency of a vertically and contra-directionally coupled semiconductor waveguide type optical add and drop multiplexer was investigated theoretically and experimentally. Numerical calculations clarified that it was necessary to introduce a deep grating in order to attain low crosstalk characteristics required for practical application. Devices with a grating having a depth of 200 nm were fabricated by a five-step metal organic vapor phase epitaxy (MOVPE) process accompanied by reactive ion etching (RIE) and wet etching. Such a deep grating was realized by an optimization of surface treatment prior to MOVPE regrowth and growth condition. An extremely low crosstalk of -36 dB was successfully achieved.