Utilizing phase-shifted long-period fiber grating to suppress spectral broadening of a high-power fiber MOPA laser system

Abstract

Suppressing nonlinear effects in high-power fiber lasers based on fiber gratings has become a hotspot. At present, research is mainly focused on suppressing stimulated Raman scattering in a high-power fiber laser. However, the suppression of spectral broadening, caused by self-phase modulation or four-wave mixing, is still a challenging attribute to the close distance between the broadened laser and signal laser. If using a traditional fiber grating with only one stopband to suppress the spectral broadening, the signal power will be stripped simultaneously. Confronting this challenge, we propose a novel method based on phase-shifted long-period fiber grating (PS-LPFG) to suppress spectral broadening in a high-power fiber master oscillator power amplifier (MOPA) laser system in this paper. A PS-LPFG is designed and fabricated on 10/130 passive fiber utilizing a point-by-point scanning technique. The resonant wavelength of the fabricated PS-LPFG is 1080 nm, the full width at half maximum of the passband is 5.48 nm, and stopband extinction exceeds 90%. To evaluate the performance of the PS-LPFG, the grating is inserted into the seed of a kilowatt-level continuous-wave MOPA system. Experiment results show that the 30 dB linewidth of the output spectrum is narrowed by approximately 37.97%, providing an effective and flexible way for optimizing the output linewidth of high-power fiber MOPA laser systems.

Mitigation of stimulated Raman scattering in a high-power fiber master oscillator power amplifier laser based on a dual-structure fiber grating

“…If a UV laser with higher output power is applied, the scanning speed can be appropriately increased. Furthermore, to improve the power durability of the dual-structure fiber grating, our proposed dual-annealing process, which combines constant-low-temperature and dynamic-high-temperature [13,21,22] , is adopted. The grating is first subjected to a temperature of 60 • C for 30 days to remove residual dissociative hydrogen molecules.…”

Functional Fibers and Functional Fiber-Based Components for High-Power Lasers

“…However, CT-FBGs have some drawbacks such as timeconsuming pretreatment and back-propagating light caused by Bragg reflection, which may seriously affect the laser output power, efficiency and beam quality [401]. Hence, the transmission grating, i.e., LP-FBG [390,393,394,[396][397][398][399][400][401][402][403][404][405], may be a better alternative. LP-FBG can eliminate SRS band by coupling the Stokes light from the core mode to the forward cladding mode, through which the reflected light could be effectively avoided [404], as illustrated in Fig.…”

“…Except for the unwanted SRS effect, other nonlinear effects (such as self-phase modulation or four-wave mixing effect) related to spectral broadening require to be suppressed as well, especially in the case of narrow-linewidth fiber lasers. Bian et al proposed to utilize a phase-shifted LP-FBG to filter the broadened spectrum in a high-power MOPA system, and the 3 dB linewidth of output spectrum was narrowed by approximately 37.97% [394], the basic principle can be found in Fig. 8d.…”