A study of a higher order FM mode‐locking laser with double phase modulators

Abstract

SUMMARYGenerating high-repetition-rate short pulses from higher order FM mode-locked lasers requires many sidebands. However, in reality, the physical limit of modulators makes it impossible to increase the modulation index. This paper proposes a novel higher order FM mode-locked laser that has two PM-I-FP sets (phase modulator, isolator, and Fabry-Perot filter) and presents an analysis of its performance. The laser uses a new technique that makes the value of the synthesized transfer function of a PM-I-FP equal in both the 0 and π phase states. This technique improves the frequency characteristics of the modulator substantially. As a result, the maximum repetition rate is doubled, and the laser also generates a chirp-free and narrower pulse train with uniform amplitude and pulse width. We also propose a system that has only one PM-I-FP. This eliminates problems that arise due to differences in the PM-I-FP characteristics when two PM-I-FP sets are used. The same effects as mentioned above are achieved.