All Fiber Circulator

This proposal addresses the development of an all fiber optical circulator. Optical networks utilizing reflective elements (e.g. fiber Bragg gratings) as wavelength selective add/drop multiplexers or sensors will require optical circulators to extract the reflected signal. In addition to functioning as a circulator, the proposed device also functions as an isolator. Isolators are needed in optical networks to avoid the destabilizing effects of feedback into a laser and to avoid lasing in optical amplifiers. Tetra Tech's circulator design consists of two major components: the fiber Faraday rotator and the fused fiber polarization splitter. The Faraday rotator, based on Tb-doped fiber will be developed by Prof. Elias Snitzer at Rutgers University. Tb doping of silica fibers provides the high Verdet constant needed for an all-fiber Faraday rotator. The fiber polarization splitter utilizes a special fused taper coupler (similar to a WDM design) to split the two orthogonal linear polarization states into two separate fibers. The proposed polarization splitter is a modification of the polarization maintaining (PM) coupler currently manufactured by Tetra Tech. The specific objective of Phase I is to demonstrate an all fiber circulator with isolation of 42 dB, loss of less than 3 dB, and a bandwidth greater than 10nm.