Jinbao Chen

A 100 W all-fiber linearly-polarized Yb-doped single-mode fiber laser at 1120 nm

A 100 W-class all-fiber linearly-polarized single-mode fiber laser at 1120 nm with an optical efficiency of 50% was demonstrated. The laser consists of a 4.2 m long Yb-doped polarization maintaining fiber with a core diameter of 10 μm and a pair of FBGs written in matched passive fiber. Linearly polarized output with a polarization extinction ratio of 15 dB is achieved by a cavity that selects both wavelength and polarization. Pulsed operations with square shaped pulses varying from 100 μs to 1 ms duration are achieved without relaxation oscillation.

3.15 kW direct diode-pumped near diffraction-limited all-fiber-integrated fiber laser.

We demonstrate a direct diode-pumped all-fiber-integrated fiber laser based on master oscillator power amplifier configuration at 1080 nm, producing maximum output power of 3.15 kW with corresponding optical to optical efficiency of 75.1%. Further power scaling is pump-limited and theoretical analysis demonstrates that 4 kW output power can be further achieved without stimulated Raman scattering. Near diffraction-limited beam quality (M(2) ~ 1.6 in the x and y directions) is also achieved at the maximum output power. This compact prototype laser has excellent stability and reliability, which could benefit many practical applications, such as industrial processing.

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.

20 W all fiber supercontinuum generation from picosecond MOPA pumped photonic crystal fiber

An all fiber high power supercontinuum (SC) source is demonstrated by pumping a section of photonic crystal fiber (PCF) with a picosecond MOPA laser. The core of the PCF is enlarged at the input end through a serious of PCF post processing method to match the output fiber of the picosecond laser, to ensure low loss splicing, hence high power operation of the whole system. The supercontinuum output spectrum covers the wavelength range from 650 nm to beyond 1700 nm. Limited by available pump power, 20 W super-continuum output power is obtained under 29.5 W picosecond pump power, giving a high optical to optical conversion efficiency of 67.8%.

High average/peak power linearly polarized all-fiber picosecond MOPA seeded by mode-locked noise-like pulses

The characteristics of mode-locked noise-like pulses generated from a passively mode-locked fiber oscillator are experimentally investigated. By carefully adjusting the two polarization controllers, stable mode-locked noise-like pulse emission with a high radio frequency signal/noise ratio of >55 dB is successfully achieved, ensuring the safety and possibility of high power amplification. To investigate the amplification characteristics of such pulses, one all-fiber master oscillator power amplifier (MOPA) is built to boost the power and energy of such pulses. Amplified noise-like pulses with average output power of 423 W, repetition rate of 18.71 MHz, pulse energy of 22.61 μJ, pulse duration of 72.1 ps and peak power of 314 kW are obtained. Near diffraction-limited beam is also demonstrated with M2 factor measured at full power operation of ~1.2 in the X and Y directions. The polarization extinction ratio at output power of 183 W is measured to be ~13 dB. To the best of our knowledge, this is the first demonstration of high-power amplification of noise-like pulses and the highest peak power ever reported in all-fiber picosecond MOPAs. The temporal self-compression process of such pulses and high peak power when amplified make it an ideal pump source for generation of high-power supercontinuum. Other potential applications, such as material processing and optical coherent tomography, could also be foreseen.

Efficient linearly polarized ytterbium-doped fiber laser at 1120 nm

We report a 20 W linearly polarized, spectrally clean Yb-doped fiber laser at 1120 nm with an optical conversion efficiency of 54%. An excellent polarization extinction ratio of more than 23 dB is obtained using fiber Bragg gratings (FBGs) polarization selection technique at all power levels. The results reveal that a Yb-doped fiber laser at 1120 nm could be a promising replacement compared to Raman fiber lasers.

High-Energy Square Pulses in a Mode-Locked Yb-Doped Fiber Laser Operating in DSR Region

We report the experimental observation of high-energy square pulses in all-normal-dispersion passively mode-locked Yb-doped fiber laser under dissipative soliton resonance (DSR) condition using a nonlinear polarization rotation technique. The generated square pulses are mode locked with fundamental cavity repetition rate of 1.86 MHz. The maximum output average power and the corresponding pulse energy are 62.1 mW and 34 nJ, respectively. The output square pulses are wave-breaking-free and can be tuned in pulsewidth from hundreds of picoseconds to several nanoseconds by changing the pump power. The multistability of DSR in all-normal-dispersion cavity has been first demonstrated in experiment, which is in agreement with theoretical prediction. The observed experimental results will enhance the understanding of fundamental physics of DSR phenomenon.

Comparison of fiber lasers based on distributed side-coupled cladding-pumped fibers and double-cladding fibers.

We compare both analytically and numerically the distributed side-coupled cladding-pumped (DSCCP) fiber lasers and double cladding fiber (DCF) lasers. We show that, through optimization of the coupling and absorbing coefficients, the optical-to-optical efficiency of DSCCP fiber lasers can be made as high as that of DCF lasers. At the same time, DSCCP fiber lasers are better than the DCF lasers in terms of thermal management.

1.5 kW, near-diffraction-limited, high-efficiency, single-end-pumped all-fiber-integrated laser oscillator

We report a monolithic single-end-pumped all-fiber laser oscillator with 1.5 kW power output operating at 1070 nm. The laser scheme design and fiber parameter selection are based on our theoretical analysis through one rate equation model consisting of changing pump wavelengths. The laser oscillator is pumped by 49 fiber-pigtailed 915 nm laser diodes with power of 50 W each through two stage combiners. The measured laser power is 1520 W at the pump power of 2054 W, and the corresponding optical-to-optical efficiency is 74%, in agreement with numerical simulation. Stimulated Raman scattering is observed when the laser power reaches 1030 W and the power ratio of Raman power is 4% at maximum output power. The experimental results show that the beam qualities represented by the M(2) factor are less than 1.2 at all pump power levels.