MONOLITHIC OPTICAL WAVEGUIDE FILTERS BASED ON FOURIER EXPANSION

摘要

A new type of monolithic optical waveguide filter comprises a chain ofoptical couplers of different effective lengths linked by differential delays ofdifferent lengths. The transfer function of the chain of couplers and delays is thesum of contributions from all possible optical paths, each contribution forming aterm in a Fourier series whose sum forms the optical output. A desired frequencyresponse is obtained by optimizing the lengths of the couplers and the delay paths sothat the Fourier series best approximates the desired response. The filter isadvantageously optimized so that it is insensitive to uncontrolled fabrication errorsand is short in length. The wavelength dependence of practical waveguide propertiesis advantageously incorporated in the optimization. Consequently, the filter is highlymanufacturable by mass production. Such filters have been shown to meet therequirements for separating the 1.3 and 1.55µm telecommunications channels andfor flattening the gain of Er amplifiers.