Stabilization of an FM active harmonic mode-locked fiber laser at high repetition rates

Abstract

A new and simple approach was optimized for stabilizing a harmonic active mode-locked fiber laser at 40GHz. A computer tunes the modulation frequency in a 500kHz band near 40GHz to follow variations in the optical cavity length. A second approach based on a Proportional-Integral ( PI) controller and a piezo fiber stretcher was also developed and optimized. This approach uses a circuit-controlled piezo (PZT) device to physically counteract optical cavity length variations. The optimized circuit-controlled and computer-controlled approaches were compared to draw conclusions on their performance. Results for the pulse characteristics, the side mode suppression ratio and the time jitter show that both approaches provide an efficient method for stabilizing a harmonic FM active mode-locked fiber laser at 40GHz. Finally, the versatility of both approaches was used to attempt to generalize the two methods for use at any modulation frequency up to 40GHz.