Xueping Cheng

Single-Longitudinal-Mode Erbium-Doped Fiber Ring Laser Based on High Finesse Fiber Bragg Grating Fabry–PÉrot Etalon

We present a simple and stable single-longitudinal-mode (SLM) erbium-doped fiber laser. It consists of an apodized fiber Bragg grating (FBG) and a high finesse FBG-based Fabry-Perot (FP) etalon in the ring cavity. The apodized FBG acts as a wavelength discriminative component selecting a few oscillation modes while the FP etalon serves as narrow bandwidth bandpass filter to further discriminate and select SLM efficiently. Stable SLM laser output at 1.55 m with linewidth about 2.5 kHz is acquired. Furthermore, continuous wavelength tuning over 8 nm is achieved by simultaneously applying strain to the FBG and the FP etalon.

High-energy wave-breaking-free pulse from all-fiber mode-locked laser system.

We demonstrated an all-fiber mode-locked laser system which generated high-energy wave-breaking-free pulses with low repetition rate. The system included a passively mode-locked fiber laser which acted as a master oscillator and an Yb-doped fiber amplifier. By increasing the cavity length of the laser, pulse energy could be significantly increased. According to different cavity length, wave-breaking-free pulse with 2.9 nJ-6.9 nJ pulse energy and 870 kHz-187 kHz repetition rate has been achieved from the master oscillator. Over 4 microJ pulse can be obtained after amplification.

Analysis of linearly tapered fiber Bragg grating for dispersion slope compensation

We demonstrate that linearly tapered fiber Bragg gratings (FBGs) display nonlinear group delay under strain or stress. The nonlinear group delay of the tapered FBG is analyzed theoretically. Experimental results show a good agreement with the analysis. We are the first to find that linearly tapered FBGs can be used in dispersion slope compensation.

Design and fabrication of flat-band long-period grating

A method to realize the practical flat-band long-period fiber grating (LPG) fabrication is proposed. Based on the results obtained from the layer-peeling method, we have analyzed the structure of the designed flat-band LPG. We found that the designed LPG is an apodized LPG with sinc-like envelope and a constant period, while there exists a /spl pi/ phase shift at each zero point of the apodization profile. For the first time, a flat-band LPG is realized in fabrication. The experimental result shows a good match with our theoretical analysis.

All-Fiber Q-Switched Erbium-Doped Fiber Ring Laser Using Phase-Shifted Fiber Bragg Grating

We propose a unique all-fiber Q-switched erbium-doped fiber ring laser. It consists of a phase-shifted fiber Bragg grating (FBG) and an apodized FBG reflector. By using the piezoelectric transducer (PZT) to periodically stretch the apodized FBG and detune it with the phases-shifted FBG, the cavity loss of the fiber ring laser is switched between high and low states to achieve Q-switching. This Q-switched fiber laser has advantages of narrow spectral bandwidth, stable oscillation wavelength, and the repetition rate of the Q-switched pulses can be double of the PZT modulation frequency. A numerical model is developed and presented to simulate and analyze this FBGs-based Q-switched fiber ring laser with consideration of the dynamic response of FBGs during Q-switching. We experimentally demonstrate 10 and 20 kHz Q-switching operation with 10 kHz PZT modulation frequency. The experimental result is similar to the simulation result.

Wavelength-Tunable High-Energy All-Normal-Dispersion Yb-Doped Mode-Locked All-Fiber Laser With a HiBi Fiber Sagnac Loop Filter

We experimentally demonstrate a broadly wavelength-tunable high-energy Yb-doped mode-locked fiber laser without any dispersion compensation. Wide tunability and filtering effect are simultaneously obtained using a fiber Sagnac loop filter in an all-fiber laser mode-locked by a semiconductor saturable absorber mirror. The Sagnac loop filter is constructed with a segment of a high birefringence (HiBi) fiber, a 3-dB coupler, and a polarization controller. By optimizing the HiBi fiber length and adjusting the polarization controller within the loop, the wavelength of the output pulse with 3 nJ pulse energy could be continuously tuned over the range from 1032 to 1052 nm. The heating of the HiBi fiber also led to wavelength shifting of the output pulse with a sensitivity of approximately -0.3-nm°C.

Influence of Sidelobes on Fiber-Bragg-Grating-Based

We analyze the influence of sidelobes on fiber-Bragg-grating (FBG)-based Q-switched fiber laser. Simulation results show the sidelobes of uniform FBG introduce undesired multiple peaks and decrease the output peak power. The experimental results confirm the simulation results.

Q

We demonstrate a novel approach to increase the Q-switching repetition rate of the fiber ring laser. This Q-switched fiber laser integrates an apodized fiber-Bragg-grating (FBG) reflector and a Fabry-Perot (FP) etalon constructed from cascaded chirped FBGs into the cavity. The apodized FBG reflector acts as wavelength discriminative component for oscillation, while the FP etalon is tuned periodically using the piezoelectric transducer (PZT) and functions as a Q-switching component. By adjusting the tuning range of the FP etalon, we obtain 3.5-, 7-, and 14-kHz Q-switched pulses train with constant PZT modulation frequency of 3.5 kHz.

-switched Fiber Laser

Blackening aluminum alloy with alumina surface now can be achieved in a cost-effective way with a nanosecond pulse fiber laser at 1064-nm wavelength, putting aside the traditional bulky, expensive femtosecond or picosecond pulse lasers. The surface blackening effect is numerically studied by the International Commission on Illumination L* value and it is found that the laser power fluence needs a proper control to obtain the shining black color effect. The surface profile and optical properties of the surfaces with or without laser treatment are analyzed. The nanostructures and microstructures layer formed beneath the alumina surface is discovered, and it is suggested to be the cause for the structural black color. This letter provides progress to a broader understanding on the nanosecond laser-induced blackening of Al with alumina surface. This nanosecond pulse fiber laser-induced blackening technique is useful for light power sensing, antireflective surface, and surface decoration applications.

All-Fiber

High efficiency, good robustness, and low amplified spontaneous emission are among the key factors of the high power ytterbium-doped pulsed fiber laser. In this letter, we propose an optimized pulsed pumping design for the nanosecond ytterbium-doped fiber laser with tunable pulse repetition rate and pulsewidth. For the pulsed pumping, the pumping power is kept at the maximal reachable power level and the pumping duration is modulated according to the pulsewidth. At each pulsewidth, the pumping duration is fixed for every seeding pulse. The performance of this laser at 130- and 20-ns seeding pulsewidth is experimentally analyzed. Simulation results are provided with the same configuration of the experiments. The results show that better performance of the laser is achieved. This technique is meaningful and strongly recommended for the design of high power nanosecond ytterbium-doped fiber laser.