Wide tuning range acousto-optical fiber Bragg grating filter (FBGF)

Abstract

An acousto-optical filter having a wide tuning range and a method of making the same. An acoustic transducer is provided for generating an acoustic pressure wave of a selected frequency that is propagated longitudinally along an optical fiber member. The pressure wave generates a plurality of alternating localized compressions and rarefactions in the optical fiber such that a grating (i.e., periodic changes in the fiber's refractive index) is created therein. The grating reflects optical signals of a particular wavelength depending upon its period or pitch (i.e., Bragg resonance wavelength). The acoustic pressure wave's frequency is modulated by controlling the acoustic transducer such that a variable grating pitch is obtained, thereby causing a corresponding change in the Bragg resonance wavelength of the grating. In response, a reflected optical signal selected from incoming multiplexed optical signals tunes to a different wavelength. A closed-loop controller is provided for controlling input signals to the acoustic transducer/actuator so as to modulate the tuning of the reflected optical signals.