Effect of uni-directional and bi-directional cavity structure on the performance of Brillouin fiber laser

We experimentally investigates the effect of uni-directional and bi-directional cavity structure on the performance of the Brillouin fiber laser for the first and the second Stokes signals. The laser cavities; unidirectional and bidirectional are tested under the same experimental conditions using different SMF lengths. We observed that in both cavities, the first Stokes threshold was almost same in values within all the selected fiber spools due to the Brillouin amplification effect. In addition, in a bidirectional cavity, the second Stokes signal threshold exhibits low threshold values within the SMF range as compared to its values in unidirectional cavity at which no Brillouin amplification effect is occurred. Moreover, the maximum power of the first and the second Stokes signals are tested using different SMF length for both cavities. An additional gain of 3.88-1.09 dB is observed at the SMF range for the first Stokes power in unidirectional cavity as compared to its values in bidirectional cavity; while, an additional gain (2.37-0.49) dB is observed at the same SMF range for the second Stokes power in bidirectional cavity.