Fabrication of Fiber Bragg Gratings by Visible Femtosecond Laser for Multi-kW Fiber Oscillator

Abstract

In this paper, we fabricate a pair of fiber Bragg gratings (FBGs) in large mode area double cladding fiber (LMA-DCF, core/inner cladding diameter: 20/400 µm) by visible (515 nm) femtosecond laser and phase mask for the first time to the best of our knowledge. Then this pair of FBGs are utilized to construct a high power fiber oscillator operated near 1080 nm. The maximum output laser power is more than 3.2 kW with a slope efficiency of ∼77.9%, and the beam quality factor M 2 is about 1.28. The FBGs are simply fixed on water-cooling plate without any special package, and the temperature of the FBGs is about 40 °C at the maximum output power. Our research work confirms the reliability of visible femtosecond laser in fabrication of FBGs intended to be applied in high power fiber oscillators.

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

“…Through writing FBG with femtosecond pulses into one port of the gain fiber, a spatially structured fiber oscillator with an output power of 8 kW was constructed [57]. This achievement demonstrates the prospect of FBGs inscription with femtosecond laser in improving the traditional hydrogen-carrying method and increasing the reliability of FBG resonators [58,61,62].…”

“…On the basis of cladding-pump technology, high-power multimode LDs at 790 nm and highly Tm-doped fibers, the output power of HPFLs exploiting Tm-doped fibers has exceeded the power level of Er-doped fibers gradually and a kilowatt-level output [102] has been achieved as early as 2010, representing the highest CW output power produced by Tm-doped fiber reported publicly currently. In 2018, a Tm-doped chirped pulse amplifier system with a record average power of up to 1150 W and the peak power of more than 5 GW was demonstrated, which brings exciting prospects for [46][47][48][49][50][51][52][53][54][55][56][57][58][59][60][61][62][63], c all-fiber laser amplifiers operating at ~ 1 μm [13, 14, 16-19, 35, 64-83], d all-fiber Er-doped lasers and Er-Ybco-doped lasers operating at ~ 1.5 μm , e all-fiber Tm-doped lasers operating at ~ 2 μm [94][95][96][97][98][99][100][101][102][103][104][105][106][107][108][109][110][111][112][113]. f Emission cross sections of Er 3+ , Ho 3+ and Dy 3+ ions in mid-infrared waveband [114].…”

“…2 a Schematical diagram of energy level transitions for some representative rare-earth ions. b-e Power evolution trends of some representative results for b all-fiber laser oscillators operating at ~ 1 μm[46][47][48][49][50][51][52][53][54][55][56][57][58][59][60][61][62][63], c all-fiber laser amplifiers operating at ~ 1 μm[13, 14, 16-19, 35, 64-83], d all-fiber Er-doped lasers and Er-Ybco-doped lasers operating at ~ 1.5 μm, e all-fiber Tm-doped…”

Fiber oscillator of 5 kW using fiber Bragg gratings inscribed by a visible femtosecond laser

“…In 2019, Krämer et al realized a 1.9 kW fiber oscillator by inscribing a high-reflection (HR) FBG on an LMA-YDF (with core/inner-cladding diameter of 20/400 μm) using the infrared (IR) femtosecond laser phase mask scanning technique [23] , and then a 5 kW oscillator was constructed by using a pair of FBGs in passive fibers [24] . Except these two investigations, we realized a 3.2 kW all-fiber oscillator using a pair of FBGs inscribed by a visible femtosecond laser [25] . The inscription process and the characteristics of the FBG inscribed by the femtosecond laser should be studied in detail to find out the best solution for this issue.…”