2.58 kW Narrow Linewidth Fiber Laser Based on a Compact Structure with a Chirped and Tilted Fiber Bragg Grating for Raman Suppression

Abstract

We report a high power, narrow linewidth fiber laser based on oscillator one-stage power amplification configuration. A fiber oscillator with a center wavelength of 1080 nm is used as the seed, which is based on a high reflection fiber Bragg grating (FBG) and an output coupling FBG of narrow reflection bandwidth. The amplifier stage adopted counter pumping. By optimizing the seed and amplifier properties, an output laser power of 2276 W was obtained with a slope efficiency of 80.3%, a 3 dB linewidth of 0.54 nm and a signal to Raman ratio of 32 dB, however, the transverse mode instability (TMI) began to occur. For further increasing the laser power, a high-power chirped and tilted FBG (CTFBG) was inserted between the backward combiner and the output passive fiber, experimental results showed that both the threshold of Stimulated Raman scattering (SRS) and TMI increased. The maximum laser power was improved to 2576 W with a signal to Raman ratio of 42 dB, a slope efficiency of 77.1%, and a 3 dB linewidth of 0.87 nm. No TMI was observed and the beam quality factor M2 maintained about 1.6. This work could provide a useful reference for obtaining narrow-linewidth high-power fiber lasers with high signal to Raman ratio.

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

“…Subsequently, single-stage CT-FBG and two incorporated CT-FBGs were successfully exploited in a 5 kW tandem pumping fiber amplifier with a maximum SRS suppression ratio of above 15 dB [395]. Moreover, the SRS suppression by employing CT-FBG is also applicable for fiber lasers with other special features such as the narrow linewidth types [396] or the ability for ultra-long-distance delivery [397].…”

“…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.…”