Jiangming Xu

High-power 1018 nm ytterbium-doped fiber laser and its application in tandem pump.

In this paper, we present our experimental results of a high-power 1018 nm fiber laser and its usage in tandem pump. A record output power of 476 W 1018 nm fiber laser is obtained with an efficiency of 78.2%. Utilizing a specially designed gain fiber, a one-stage high-power monolithic fiber amplifier tandem pumped by six 1018 nm fiber lasers is assembled. A 110 W 1090 nm seed is amplified to 2140 W, and the efficiency is as high as 86.9%. The beam quality factor M2 is measured to be 1.9. Limitations and possible solutions for purchasing higher output power are discussed.

Power scaling of narrowband high-power all-fiber superfluorescent fiber source to 1.87 kW.

We demonstrate a high-power narrowband all-fiber superfluorescent fiber source employing three-stages master oscillator power-amplifier chain. Narrowband seed light is selected from a broadband-amplified spontaneous-emission source by a spectrum filter combing with fiber circulator and fiber Bragg grating. In the main amplifier, the maximal output power is 1.87 kW with an optical-to-optical conversion efficiency of 77.4% and a full width at half-maximum (FWHM) linewidth of 1.7 nm. The corresponding power fluctuation is ±1.4% in 100 s operation, and no parasitic oscillation or self pulsation is observed. A beam quality of M(2)=1.71 is measured at 1.4 kW output power. This manuscript investigates the spectral evolution in high-power amplification. The central wavelength shifted from 1079.5 nm to 1080.7 nm, and the FWHM linewidth narrowed from 2 nm to 1.7 nm at full power, respectively. These effects could be inferred as hybrid effects of many factors, such as wavelength shifting of pump LD, nonoptimized length of gain fiber, and enhancement of temperature level of gain fiber. The narrowband-maintained characteristic in spectral domain under high-power amplification is significant for applications such as spectral beam combination, and further power scaling is available as the output power is only limited by the pump power.

1.01 kW superfluorescent source in all-fiberized MOPA configuration

We present a high power all-fiberized master oscillator power amplifier (MOPA) structured superfluorescent source based on dual-cladding ytterbium-doped fiber. The seed source is a 0.814 W homemade amplified spontaneous emission (ASE) source. Two-stage high power fiber amplifier is utilized to boost the seed power to 1.01 kW with a beam quality of M(x)(2) = 1.688 and M(y)(2) = 1.728. The central wavelength of the output light is 1074.4 nm, and the full width at half maximum (FWHM) linewidth is about 8.1 nm. No self pulsing or relaxation oscillation effect is observed and the power fluctuation is less than 2% in 100 seconds continuous operating. In additional, spectral evolution effects of central-wavelength-drifting and linewidth-narrowing of broadband amplification in high power superfluorescent source system are investigated. To the best of our knowledge, this is the first demonstration of an all-fiberized superfluorescent source with output power exceeding kilowatt.

Incoherently pumped high-power linearly-polarized single-mode random fiber laser: experimental investigations and theoretical prospects

We present a hundred-watt-level linearly-polarized random fiber laser (RFL) pumped by incoherent broadband amplified spontaneous emission (ASE) source and prospect the power scaling potential theoretically. The RFL employs half-opened cavity structure which is composed by a section of 330 m polarization maintained (PM) passive fiber and two PM high reflectivity fiber Bragg gratings. The 2nd order Stokes light centered at 1178 nm reaches the pump limited maximal power of 100.7 W with a full width at half-maximum linewidth of 2.58 nm and polarization extinction ratio of 23.5 dB. The corresponding ultimate quantum efficiency of pump to 2nd order Stokes light is 86.43%. To the best of our knowledge, this is the first demonstration of linearly-polarized high-order RFL with hundred-watt output power. Furthermore, the theoretical investigation indicates that 300 W-level linearly-polarized single-mode 1st order Stokes light can be obtained from incoherently pumped RFL with 100 m PM passive fiber.

Narrow-linewidth Q-switched random distributed feedback fiber laser.

A narrow-linewidth Q-switched random fiber laser (RFL) based on a half-opened cavity, which is realized by narrow-linewidth fiber Bragg grating (FBG) and a section of 3 km passive fiber, has been proposed and experimentally investigated. The narrow-linewidth lasing is generated by the spectral filtering of three FBGs with linewidth of 1.21 nm, 0.56 nm, and 0.12 nm, respectively. The Q switching of the distributed cavity is achieved by placing an acousto-optical modulator (AOM) between the FBG and the passive fiber. The maximal output powers of the narrow-linewidth RFLs with the three different FBGs are 0.54 W, 0.27 W, and 0.08 W, respectively. Furthermore, the repetition rates of the output pulses are 500 kHz, and the pulse durations are about 500 ns. The corresponding pulse energies are about 1.08 μJ, 0.54 μJ, and 0.16 μJ, accordingly. The linewidth of FBG can influence the output characteristics in full scale. The narrower the FBG, the higher the pump threshold; the lower the output power at the same pump level, the more serious the linewidth broadening; and thus the higher the proportion of the CW-ground exists in the output pulse trains. Thanks to the assistance of the band-pass filter (BPF), the proportion of the CW-ground of narrow-linewidth Q-switched RFL under the relative high-pump-low-output condition can be reduced effectively. The experimental results indicate that it is challenging to demonstrate a narrow-linewidth Q-switched RFL with high quality output. But further power scaling and linewidth narrowing is possible in the case of operating parameters, optimization efforts, and a more powerful pump source. To the best of our knowledge, this is the first demonstration of narrow-linewidth generation in a Q-switched RFL.

Powerful linearly-polarized high-order random fiber laser pumped by broadband amplified spontaneous emission source

A great deal of attention has been drawn to Random fiber lasers (RFLs) for their typical features of modeless, cavity-less and low coherence length. However, most previously reported high power RFLs employ narrowband fiber lasers as the pump source, thus inducing the self-pulsing transferring from pump source to output Stokes. In this contribution, linearly-polarized RFL pumped by broadband amplified-spontaneous-emission (ASE) is demonstrated and continuous-wave (CW) high order Stokes can be obtained.With 30.6 W pump injected into the half-opened cavity, 23.51 W the 2nd order Stokes centered at 1178 nm with a full width at half-maximum linewidth of 1.73 nm and polarization extinction ratio of about 25 dB can be obtained. The standard deviation and peak-vale value of the 2nd order Stokes light at maximal output power is just 0.47% and 4.10%, which indicates the good power stability. Significantly, the corresponding quantum efficiency of the 1st and 2nd order Stokes light is about 87% and 85%, and almost all pump photons are converted into Stokes photons. As far as we know, it is the highest power ever reported from linearly polarized RFL, and further power scaling is available in the case of more powerful pump source and optimization of system parameters.

Investigation of stimulated Raman scattering effect in high-power fiber amplifiers seeded by narrow-band filtered superfluorescent source

In this paper the stimulated Raman scattering (SRS) effect in high-power fiber amplifiers seeded by the narrow-band filtered superfluorescent source (SFS) is firstly analyzed both theoretically and experimentally. Spectral models for the formation of the SFS and the spectral evolution in high-power fiber amplifiers seeded by filtered SFS are proposed. It is found that the SRS effect in high-power fiber amplifiers depends on the spectral width of the filtered SFS seed. The theoretical predictions are in qualitative agreements with the experimental results.

Laser diode-pumped dual-cavity high-power fiber laser emitting at 1150 nm employing hybrid gain

We demonstrate a laser diode-pumped dual-cavity high-power fiber laser emitting at 1150 nm. The laser employs Yb and Raman gains simultaneously. The fiber laser with a simple structure achieves high-efficiency operation while efficiently suppressing the amplified spontaneous emission and parasitic oscillation. The maximum output power at 1150 nm is 110.8 W, with an optical-to-optical efficiency of 57%. Further power scaling at 1150 nm is expected with the optimization of the system design.

Ultra-stable high-power mid-infrared optical parametric oscillator pumped by a super-fluorescent fiber source

The longterm stability of the laser system is very important in many applications. In this letter, an ultra-stable, broadband, mid-infrared (MIR) optical parametric oscillator (OPO) pumped by a super-fluorescent fiber source is demonstrated. An idler MIR output power of 11.3 W with excellent beam quality was obtained and the corresponding pump-to-idler conversion slope efficiency was 15.9%. Furthermore, during 1h measurement at full power operation, the peak-to-peak fluctuation of idler output power was less than 1.9% and the corresponding standard deviation was less than 0.4% RMS, which was much better than that of a traditional single mode fiber laser pumped OPO system (10.9% for peak-to-peak fluctuation and 1.8% RMS for the standard deviation) in another experiment for comparison. To our knowledge, this is the first demonstration on a high-power, ultra-stable OPO system by using the modefree pump source, which offered an effective approach to achieve an ultra-stable MIR source and broadened the range of the super-fluorescent fiber source applications.

2.53 kW all-fiberized superfluorescent fiber source based on a compact single-stage power-scaling scheme

In this paper we demonstrate an all-fiberized superfluorescent fiber source that has a maximal output power of 2.53 kW and is based on a single-stage power amplification configuration. The seed source is a broadband-amplified spontaneous emission source with a full output power of 27.6 W. A single-stage dual-clad fiber amplifier is used, in which the maximal optical-to-optical conversion efficiency is 81.47%. A beam quality of M 2 = 1.53 is measured at an output power of 1 kW. At maximum output power, the central wavelength and full width at half maximum linewidth of the amplified light are 1082.08 nm and 6.32 nm, respectively. No conspicuous spike was observed at the stimulated Raman scattering wavelength. The corresponding power fluctuation is 2.97%, which indicates the good power stability of the broadband high-power superfluorescent fiber source (SFS) system. This kilowatt-class high-power all-fiberized SFS system which has high conversion efficiency and good power stability and is based on a compact single-stage power-scaling scheme, is an alternative and competitive solution for industrial precision processes and special stabilized pumping. To the best of our knowledge, this is the highest power SFS ever reported, and the first demonstration of a high-power SFS with a kW-level output power in a compact single-stage power-scaling scheme.