Double-ended output near-single-mode quasi-continuous wave monolithic fiber laser

Abstract

Quasi-continuous fiber lasers have a broad application prospect in the industrial field. However, the current research on quasi-continuous wave (QCW) fiber lasers only uses the single-ended output structure. A double-ended output fiber laser oscillator only needs one resonator to realize two laser outputs. Compared with single-end output laser, it has a lower cost, smaller volume and higher work efficiency. It is expected to learn higher power laser output through double-end output beam combining. Therefore, the double-ended output QCW fiber laser is proposed and studied in this paper. The steady-state rate equation established a theoretical model of a QCW fiber laser oscillator with two ends, considering the stimulated Raman scattering (SRS) and amplified spontaneous emission (ASE). The output power, time domain and nonlinear effects of this type of laser are simulated. The results show that the overshoot effect caused by relaxation oscillation will produce a large amount of thermal deposition and ultra-high peak power in the fiber. It will reduce the nonlinear threshold and limit the power increase of the QCW fiber laser. Prolonging the pump rise time can effectively suppress the relaxation oscillation and obtain a stable pulse output during the pulse duration. In addition, compared with the single-ended QCW laser, the double-ended output structure changes the energy distribution in the fiber and reduces the accumulation of nonlinear effects in the gain fiber, thus inhibiting SRS. Then, the ytterbium-doped fiber (YDF) with a core/cladding diameter of 20/400 μm was used to achieve the first double-ended QCW laser output with a peak power of 3 kW. The peak power at both ends was 1218 W and 2220 W, respectively. The corresponding beam quality factor M<sup>2</sup> was 1.34 and 1.27. The optical-to-optical conversion efficiency was ~60%. The pulse width was 100 μs, and the repetition frequency was 1 kHz. This paper verifies the feasibility of high power and high beam quality output by double-ended output QCW fiber laser, which provides support for small volume, low cost, high power and high brightness QCW fiber laser. Further breakthroughs in the research and application of high-power fiber lasers are expected to be made by continuing to optimize experiments, increasing pump power, and improving the laser’s output power and conversion efficiency.

2 × 4.5 kW bidirectional output near-single-mode quasi-continuous wave monolithic fiber laser

“…In Ref. 28 , wavelength-stabilized LDs of 981 nm were used to achieve a bidirectional QCW laser output with a total peak power of 3 kW for the first time, and the peak power at both ends was 1218 W and 2220 W, respectively. However, the absorption cross section at 981 nm is small.…”

“…The peak power scaling of the above experiments is also limited by SRS. In order to suppress SRS, the effect of fiber length on SRS intensity was studied based on the theoretical model of bidirectional output QCW fiber laser, using the modified steady-state rate equation 19 , 24 , 28 , 29 , 33 , 34 . The main simulation equations are ( 3 )–( 5 ).…”

Novel Bidirectional Output Ytterbium-Doped High Power Fiber Lasers: From Continuous to Quasi-Continuous

“…Figure 6 shows the schematic diagram of the structure of a QCW BOFL-OS [ 52 ]. Based on this structure, the QCW BOFL-OS has been validated for the first time.…”

“… Experimental results of a QCW BOFL. ( a ) The output spectrum at the maximum output power; ( b ) beam quality at end A; ( c ) beam quality at end B; ( d ) comparison of output spectra between a BOFL and UOFL [ 52 ]. …”