Qirong Xiao

Bidirectional pumped high power Raman fiber laser

This paper presents a 3.89 kW 1123 nm Raman all-fiber laser with an overall optical-to-optical efficiency of 70.9%. The system consists of a single-wavelength (1070nm) seed and one-stage bidirectional 976 nm non-wavelength-stabilized laser diodes (LDs) pumped Yb-doped fiber amplifier. The unique part of this system is the application of non-wavelength-stabilized LDs in high power bidirectional pumping configuration fiber amplifier via refractive index valley fiber combiners. This approach not only increases the pump power, but also shortens the length of fiber by avoiding the usage of multi-stage amplifier. Through both theoretical research and experiment, the bidirectional pumping configuration presented in this paper proves to be able to convert 976 nm pump laser to 1070 nm laser via Yb3+ transfer, which is then converted into 1123 nm Raman laser via the first-order Raman effect without the appearance of any higher-order Raman laser.

High-power all-fiber superfluorescent source with fused angle-polished side-pumping configuration

We report high-power operation of a broadband superfluorescent source with an all-fiber configuration. The superfluorescent source yields an amplified spontaneous emission (ASE) output of 43.2 and 25.1 W from both ends, respectively. The maximum combined ASE output is 68.3 W with a slope efficiency of 78.6%. The wavelength bandwidths (FWHM) of the counterpropagating and copropagating ASE output are 31.5 and 18.9 nm, respectively. The fused angle-polished side-pumping coupler is applied to set up the all-fiber configuration. Furthermore, the influence of reflectivity on the laser threshold of the ASE sources is studied theoretically. The experimental results agree with the theoretical analysis.

Tapered fused fiber bundle coupler capable of 1 kW laser combining and 300 W laser splitting

A high efficiency 7 × 1 multimode fiber coupler using the method of fusion and tapering is reported. This coupler can be applied to combine laser power, ad it can be used as a 1 × 7 splitter with reversible simultaneously. In the experiment, for combiner, coupling output power of 1032 W is obtained with the input power of 1066 W. The total coupling efficiency is 96.8%. The average insertion loss of each input fiber is 0.14 dB at ∼150 W input power. To splitter, the sum of 7 output ports power is 294 W with the input power of 341 W, and the insertion loss is about 13.8%. This fiber coupler can be applied in pumping all-fiber double clad fiber laser, as well as power combination and splitting of fiber lasers.

A Side-Pump Coupler With Refractive Index Valley Configuration for Fiber Lasers and Amplifiers

A side-pump coupler with a refractive index valley was investigated theoretically and experimentally. The high pump coupling efficiency and the suppression of backward light propagation due to the refractive index valley are illustrated. Based on the analysis, the (2+1) × 1 pump and signal coupler with both pump coupling efficiency and signal transfer efficiency of > 96% and the BR of 2.82 was implemented, which accompanied with the maximum pump power of 398 W. And based on these couplers, an all-fiber bi-directionally pumping MOPA laser with an output power of 256 W and optical-optical efficiency of 80.5% was achieved in the experiment.

Tapered Fiber Bundle 7

A high efficiency tapered fiber bundle (TFB) 7 × 1 end-pumping coupler with a handle pumping power of 3.01 kW and a coupling efficiency of 99.4% was reported. The coupling efficiency of the TFB 7 × 1 end-pumping coupler is calculated by the 3-D beam propagation method. According to the theoretical results, the excellent TFB 7 × 1 end-pumping coupler is manufactured successfully in experiment.

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In this paper, a 933 W amplified spontaneous emission (ASE) source with a full width at half maximum (FWHM) of 50.4 nm is presented. The broadband source is generated by a 1271 W ASE amplifier together with 140m ordinary passive fiber for nonlinear transformation. With multi-wavelength rate equations and a nonlinear Schrödinger equation (NLSE), spectral evolution of the ASE source is analyzed theoretically.

1 End-Pumping Coupler Capable of High Power CW Operation

Ytterbium-doped fiber lasers are attractive in many fields due to their high output power and good beam quality. Meanwhile, fiber fusion splicing—a necessary and inevitable process in building a fiber laser—could affect not only the output power but also the output beam quality of a fiber laser. The influences of fusion splicing on laser beam quality are studied and discussed in this paper. A model based on the beam propagation method and computation of the M2 factor is employed to research the effects of fiber splicing. Different cases of spatial deviation during fusion splicing, including shifting and tilting, are simulated. Fiber splicing with drift in one and two dimensions is investigated as well, the results of which show good agreement with the simulated ones. Furthermore, the effects of splice shifting and tilting on laser beam quality are compared to select the most critical one. Beam quality variations under different circumstances, such as deviation direction, fiber type, and input beam quality, are also discussed.

933 W Yb-doped fiber ASE amplifier with 50.4 nm bandwidth

A pump/signal fiber coupler with functions of pump light coupling and high-order-mode suppression is reported. This coupler is composed of pump fibers and a double-clad fiber (DCF) with high pump-coupling efficiency. The core of DCF is microdeformed in the coupling region, which serves mode selection. Theoretical analysis and experimental results verify these functions. In the experiment, the pump-coupling and signal-transmitting efficiency of the coupler were ~98% and ~96%, respectively. This coupler can prevent mode distortion with fundamental mode launching, and improve the fiber laser beam quality with high-order-mode launching.

The influence of fusion splicing on the beam quality of a ytterbium-doped fiber laser

A pump-signal combiner with a new processing method is reported in this paper. The core deformation of the signal fiber can be avoided by this method, and an 8+1 to 1 pump-signal combiner with 100 μm core-signal fiber feed-through is fabricated. The pump and signal coupling efficiencies are 96.8% and 98.0%, respectively. Furthermore, this pump-signal combiner is applied to a CW large mode area fiber laser with a counter pump configuration. The output power of the laser is 87 W.

Fiber coupler for mode selection and high-efficiency pump coupling.

This Letter presents a high-power 1018 nm ytterbium-doped fiber laser (YDFL) with optimized parameters. A record output power reaching 805 W was achieved, along with a light-to-light efficiency of 64.9% and a beam quality factor of M2=1.80. Further, a higher efficiency of 82.8% of 1018 nm YDFL pumped by wavelength-stabilized laser diodes for the first time, to the best of our knowledge, was shown. At last some attempts were made in bidirectional pumping structure. In this Letter, all the measured spectra showed strong amplified spontaneous emission suppression, and the power curves indicated the potential for further power scaling.