NOVEL REALIZATION OF MONOTONIC BUTTERWORTH-TYPE LOWPASS, HIGHPASS, AND BANDPASS OPTICAL FILTERS USING PHASE-MODULATED FIBEROPTIC INTERFEROMETERS AND RING RESONATORS

A novel realization of monotonic Butterworth-type lowpass, highpass, and bandpass optical filters (from their electrical digital filters characteristics) by cascading the all-pole and all-zero resonators is presented. A graphical method for fast deriving the transfer functions, quick inspection of the resonance effects and important characteristics of any photonic circuits is described. It is shown that incorporation of the optical amplifiers and optical phase modulators into the delay lines of two basic optical resonators, whose pole and zero can be adjusted independently of each other, provides great design flexibility which would otherwise not possible by the conventional passive optical resonators. Possible applications of these realized optical filters as optical pulse equalizers and receiver shaping filters in long-haul coherent lightwave transmission system are discussed. Possible application of the basic resonators comprising optical phase modulators as tunable optical filters for spectrum analyzers is also considered.