Side-mode suppression of optical add and drop multiplexer utilizing vertically coupled InGaAsP waveguides

A sidemode suppression of a vertically and contra-directionally coupled semiconductor waveguide type optical add and drop multiplexer is investigated theoretically and experimentally, by introducing a window function to a grating width. Grating configuration dependence of device characteristics was numerically calculated for a linearly changing grating width. It was found that the sidemode suppression ratio (SMSR) could be improved to be more than 30 dB even by the simple grating structure. SMSR of 18 dB was obtained in a fabricated device, for which the grating was trimmed by a laser beam direct drawing method