Jialin Chen

Study of self-mode-locking in Q-switched and in all-fiber Fabry-Perot cavity ytterbium-doped fiber laser

The authors report for the first time clear and stable self mode-locked pulses with Q-switched pulse envelope in diode pumped Yb-doped Q-switched fiber lasers. Self Phase Modulation (SPM) effect is used to explain the generation of self mode-locking. On this basis, the AOM was removed and two gratings were used as the cavity mirrors. An all-fiber F-P cavity mode-locked fiber laser was realized for the first time. Similar mode-locked pulses were observed when using two ring reflectors as the cavity mirrors. SPM effect combining with saturable absorption effect is proposed as an explanation. The all-fiber F-P cavity fiber laser provides a new method to generate mode-locked pulses.

Detection of Brillouin scattering temperature signal in Brillouin optical time-domain reflectometer sensing system based on instantaneous frequency measurement technology

We present a simple and practical method for the single-ended distributed fiber temperature measurements using microwave (11-GHz) coherent detection and the instantaneous frequency measurement (IFM) technique to detect spontaneous Brillouin backscattered signal in which a specially designed rf bandpass filter at 11 GHz is used as a frequency discriminator to transform frequency shift to intensity fluctuation. A Brillouin temperature signal can be obtained at 11 GHz over a sensing length of 10 km. The power sensitivity dependence on temperature induced by frequency shift is measured as 2.66%/K. (c) 2007 Society of Photo-Optical Instrumentation Engineers.

Study of polymer thermal and mechanical properties using a fiber Bragg grating thermal sensor

A simple and practical method for the study of polymer thermal and mechanical properties using a fiber Bragg grating (FBG) sensor is presented for the first time, in which the FBG is embedded in a typical epoxy polymer. By measuring the sensitivity change of the FBG sensor, changes of the thermal-mechanical properties of the polymer with temperature and pressure can be measured. The experimental results show that this technique is capable of providing continuous in-line monitoring such properties with high sensitivity during transformation between the glassy state and the rubbery state of a polymer within the temperature and pressure range of 20 to 180°C and 0 to 15 MPa.

Mode-hopping of pi/2 phase-shifted distributed feedback fiber grating laser

During the operation of pi/2 phase-shifted distributed feedback Yb-doped fiber grating laser (YDFBL), the phenomenon of mode-hopping has been observed. It has been found that the light power incident into the fiber laser and the ambient temperature will affect the generation of mode-hopping. When the pump power changes in a wide range, i.e., from tens of milliwatts to more than one hundred milliwatts, there are only two modes dominating by turns with the consideration of different resolution error. When the ambient temperature around the fiber grating rises a little, the mode-hopping will be observed. An explanation basing on the spatial hole burning and wavelength shift induced by temperature fluctuation for this phenomenon has been given out.

Study on the characteristics of the λ/4 phase-shift DFB Yb3+-doped fiber lasers

At first, we made a approximative λ/4-shifted DFB Yb-doped fiber laser with double exposure method .The length of Yb-doped fiber is 10cm. Secondly, we processed the fiber laser by UV trimming. In addition, the running characteristics of the λ/4 phase-shift DFB Yb3+-doped fiber CW lasers were researched. The fiber laser have the following excellent characteristics: Output power of 25mW, fluctuation of less than 2%, 100% single longitudinal mode, 27dB polarization extinction ratio, 60dB signal-to-noise. What is more, the effect on the fiber lasers is also researched from several factors such as temperature, mechanism perturbation and fresnel reflection of fiber end section.