Spatial hole burning in erbium fiber lasers using Faraday rotator mirrors

Abstract

Erbium-doped fiber amplifiers (EDFAs) seem to be promising candidates for constructing rapidly tunable, widely tunable, single-frequency, single-polarization 1.55 /spl mu/m sources. However, simultaneously attaining all these characteristics has proved to be difficult. Much work has avoided using polarization-maintaining (PM) EDF to enhance affordability, availability, and flexibility. The observation that the Faraday rotator mirrors (FRM) can compensate for the effects of fiber birefringence suggests that the state of polarization (SOP) is orthogonal to the input SOP everywhere in the fiber (referred to as orthoconjugate). This led many to conclude that spatial hole burning could be eliminated by using a FRM in an EDFA. Unfortunately, the orthogonality of so-called orthoconjugate waves are based on a change of coordinate system. To analyze spatial hole burning a fixed coordinate system is required to properly add any coincident electromagnetic fields. To show the effects attributed to interference of counterpropagating waves within a gain fiber are not eliminated by using an FRM, two single-polarization ring laser configurations are compared.