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.
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.
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 Yb<sup>3+</sup>-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.