All-polarization-maintaining linear cavity fiber lasers mode-locked by nonlinear polarization evolution in stretched pulse regime

TL;DR

This paper presents environmentally stable all-PM fiber lasers mode-locked by nonlinear polarization evolution, achieving record-short pulses below 90 fs with high repetition rates, using innovative cavity designs with non-reciprocal phase shifters.

Contribution

The study introduces two novel all-PM fiber laser configurations utilizing NPE with non-reciprocal phase shifters, enabling ultra-short pulses and high repetition rates in a stable environment.

Findings

Achieved sub-90 fs pulse duration in all-PM fiber lasers.

Demonstrated high repetition rates above 100 MHz.

Developed cavity designs that reduce mode-locking thresholds.

Abstract

Nonlinear polarization evolution (NPE) is among the most advanced techniques for obtaining ultrashort pulses with excellent optical performance. However, it is challenging to design environmentally stable NPE fiber oscillators using only polarization-maintaining (PM) fibers. Here, we use the same PM fiber and non-reciprocal phase shifter to design two different devices, which are capable of acting as effective NPE saturable absorbers (SAs) in two all-PM linear cavity fiber lasers. These two laser setups differ in the position of the non-reciprocal phase shifter, the presence of which is crucial for the proposed fiber lasers to reduce their mode-locking thresholds and achieve high repetition rates above 100 MHz. The mode-locking principle and pulse evolution in the laser cavity are investigated theoretically. The first all-PM fiber oscillator emits sub-200 fs stretched pulses with low peak powers. The second oscillator, with a simpler architecture, directly delivers stretched pulses with high peak powers, the spectral bandwidth greater than 30 nm, and the pulse duration less than 90 fs. To the best of our knowledge, 79 fs achieved in this design is the shortest pulse duration provided by PM fiber lasers using NPE mode-lockers.