Coupled-cavity analysis of the resonant loop mirror: closed-form expressions and simulations for enhanced performance lasing.

A coupled-cavity analysis of the resonant loop mirror with a signal flow graph technique is presented. Use of this technique has resulted in simple closed-form expressions for reflectance, transmittance, critical coupling, bandwidth, finesse, gain threshold, and mode splitting. Application of this device to enhance the single longitudinal mode operation of a fiber laser is also proposed. Detailed simulation results show a dramatic reduction in bandwidth and a threefold enhancement of the free spectral range by use of the vernier effect. The formulas and results obtained would also be useful in laser sensors and filters.