Optical filter of adjustable finesse using a Mach Zehnder interferometer

Abstract

By adjusting the phase difference between the two arms of a Mach Zehnder interferometer inserted in the feedback path of a simple ring resonator, the finesse of an optical filter can be easily controlled over a specified range. The filter will be useful in coherent optical systems employing laser diodes, where the bandwidth has to be appropriately adjusted under varying biasing and signalling conditions.