Adjustable transfer function optical filter for microwave applications

Abstract

All-optical techniques for microwave and radio frequency (RF) signal processing has attracted considerable attention in recent years. An important optical component in these all-optical signal processing techniques is the optical filter. Tunable optical filters with a variety of transfer functions have been proposed. However, adjustability of the optical filter transfer function is required to provide an extra degree of control. This adjustability of the shape of the transfer function has not been addressed adequately in the literature. In this paper, we report on the theoretical basis for an all-fiber based adjustable transfer function optical filter. In particular, we model the optical filter using FO-circuit transfer matrices and Jones matrices to fully describe the state of polarization changes of the optical signals through the optical filter. The filter is based on an all fiber Michelson Gires-Turnois interferometer (MGTI). The Gires-Turnois resonators (GTRs) required for the formation of the MGTI are realized by pairs of fiber-loop mirrors (FLMs) in the two arms of the Michelson interferometer. The optical reflectivity of the GTRs is control via adjustment of the polarization in the fiber loop mirrors. We show that arbitrary transfer functions can be realized by adjusting the reflectivity of the FLMs as well as the cavity length of the fiber based GTRs.