Passive optimization of pump noise transfer function by narrow band-pass filtering in femtosecond fiber lasers

Peng Qin,Youjian Song,Minglie Hu,Sijia Wang

doi:10.1017/hpl.2019.38

Abstract

Fluctuation of pump power is one of the major sources of temporal and intensity noise in femtosecond fiber lasers. In this work, the transfer functions between the relative intensity noise (RIN) of the pump laser diode (LD) and the output RIN, between the RIN of the pump LD and timing jitter of femtosecond fiber lasers are systematically studied. It is demonstrated, for the first time to our knowledge, that the amplitude of the pump RIN transfer function can be effectively decreased by an intra-cavity narrow band-pass filter. In particular, for normal-dispersion lasers, the 3-dB bandwidth of the transfer function can also be narrowed by two-thirds, with a steeper falling edge. Furthermore, with the narrow band-pass filtering, the transfer function is almost independent of the net intra-cavity dispersion due to amplifier similariton formation. The proposed scheme can effectively isolate the pump-induced noise without the need of complex active pump LD control and intra-cavity dispersion management, thus providing an easy way for practical high-power, high-stability femtosecond fiber laser design and related high-precision applications outside the laboratory.

Highlights

IntroductionDue to the limited lifetime of the gain medium, the mode-locked laser can function as a low-pass filter
Mode-locked fiber lasers generate trains of femtosecond pulses with equal pulse width, intensity and timing interval, making them ideal sources in pump–probe experiments[1], laser ablation[2], timing synchronization[3] and precise metrology[4]
It can be seen that even 3-mW power fluctuation, which corresponds to 1.25% of the total pump power, could lead to a significant rise in the low-frequency relative intensity noise (RIN) of the laser output

Summary

Introduction

Due to the limited lifetime of the gain medium, the mode-locked laser can function as a low-pass filter. Considering the dominant role of laser dynamics in the pump noise response of femtosecond fiber lasers, the transfer function between the pump and the output can be expected to be further optimized by improving the cavity design. Under various intra-cavity net dispersion and spectral filtering conditions It is demonstrated, for the first time to our knowledge, that the incorporation of a band-pass filter can effectively decrease the amplitude of the pump noise transfer function. The proposed scheme can effectively isolate the coupling between the pump power fluctuation and the output noise of femtosecond fiber lasers without the need for complex active pump LD control and intra-cavity dispersion management, demonstrating the potential for practical high-power, high-stability laser design and related high-precision applications outside the laboratory

Experimental setup and results

Findings

Conclusion