Single-longitudinal-mode fiber optic parametric oscillator based on Smith predictor control scheme

Fiber optical parametric oscillators are laser sources with multiple longitudinal modes arising from their cavity length reaching several tens of meters. To reduce the noise due to multimode beating, the spacing between neighboring modes is increased using a Smith predictor internal control scheme. The Smith predictor utilizes a model of the dynamic behaviour of the system to deal with pure time delay and eliminate the effect of the delay in the overall closed-loop system. Applying the smith predictor, the system can be made to operate in a single-longitudinal mode, removing the excess modes. In this paper a linear model for operation of parametric oscillator is proposed and based on that transfer function of Smith predictor enhanced parametric oscillator is established. Numerical analysis of resulting transfer function will lead us toward single-longitudinal mode operation.