Investigation of $Er^{3+}$-doped fiber ring laser for gyroscope applications

Abstract

An $Er^{3+}$-doped fiber ring laser (EDFRL) was characterized to examine the possibility of gyroscope applications of a rare earth-doped fiber ring laser. The experimental setup was constructed with an erbium doped fiber, a conventional single mode fiber, directional couplers, and a wavelength division multiplexer. An argon ion laser with the wavelength of 514.5 nm or a laser diode with the wavelength of 980 nm was used as a pumping source. The ring laser operated bidirectionally in multiple longitudinal modes with stable average output power in both clockwise- and counterclockwise-propagating directions. The eigen polarization modes of the two counter-propagating laser beams were analyzed theoretically and experimentally. The analysis confirms that the gyroscope reciprocity holds in the ring laser even with a random cavity birefringence. When the two counter-propagating laser beams were combined to interfere, the output produced rotation-rate-dependent gyroscope beat signals whose frequency shifts were linearly proportional to the rotation rate according to the Sagnac effect. This indicates the possibility of a rare-earth-doped fiber ring laser gyroscope. Backscattering in the ring cavity was turned out to be the major source for the complex laser output behaviors. A coupled mode analysis for the ring cavity containing both conservative and dissipative backscattering was used to examine the laser behaviors theoretically. Owing to the contribution from the conservative backscattering, the laser output exhibited the so-called self oscillation signal whose oscillation frequency was the same as the gyroscope beat signals. The contribution from the dissipative backscattering resulted in the so-called frequency lock-in between the two counter-propagating laser beams leading to the winking phenomena. The experimental observations showed a good qualitative agreement with the theoretical results obtained from the coupled mode analysis. A push-pull phase modulation sche...