Spot Size Dependence of Filtering Characteristics in Micromachined GaAlAs/GaAs Tunable Filters

We present the modeling of and experiment on the spot size dependence of the performance of micromachined GaAlAs/GaAs tunable filters. We point out that a proper design of the spot size of input light is very important for avoiding the deterioration of filter performance. We are able to reduce the spot size to 30 mum without significant penalties, which is experimentally supported. The results show the possibility of a narrow passband tunable filter with a 3 dB bandwidth of less than 1 nm.