The characteristics of coherent coupling in Mach-Zehnder erbium-doped fiber laser cavity are experimentally studied. By virtue of a seemly controlling of length difference between two interferometric arms, the obtained comb-like spectrum of interferometer resonator with a period of 0.06 nm commendably agrees with the theory of self-organization coherence. The coherent output exits from the output mirror of a fiber Bragg grating with 4.5% reflectivity. A high coherent combining efficiency of 94% is obtained. Investigation on characteristics of the leak power opens out self-organization mechanism in Mach-Zehnder composite cavity.

Germanium doping in silica can be used as a method for nonlinearity enhancement. Properties of the enhanced nonlinearity in photonic crystal fiber (PCF) with a GeO2-doped core are investigated theoretically by using all-vector finite element method. Numerical result shows that the nonlinear coefficient of PCF is greatly enhanced with increasing doping concentration, furthermore, optimal radius of the doped region should be considered for the desired operating wavelength.

A flat high gain L-band gain-clamped erbium-doped fiber amplifier (GC-EDFA) by using backward C-band amplified spontaneous emission (ASE) is proposed. It uses two stages of EDFs pumped forward as gain media, and a broadband chirp fiber Bragg grating (CFBG) to reflect the backward C-band ASE back into the loop to control the gain, which avoids spectral-hole and relaxation oscillation due to no controlling laser exists. Compared with other similar GC-EDFAs, the proposed structure has higher and flatter clamped gain in L-band because of its optimal structure -- the length of EDFs and pump power, pump scheme, etc.. The gain is above 23 dB, the bandwidth of 3 dB is more than 36 nm, and the input signal saturation power arrives -15 dBm.

A flat high gain L-band gain-clamped erbium-doped fiber amplifier (GC-EDFA) by using backward C-band amplified spontaneous emission (ASE) is proposed. It uses two stages of EDFs pumped forward as gain media, and a broadband chirp fiber Bragg grating (CFBG) to reflect the backward C-band ASE back into the loop to control the gain, which avoids spectral-hole and relaxation oscillation due to no controlling laser exists. Compared with other similar GC-EDFAs, the proposed structure has higher and flatter clamped gain in L-band because of its optimal structure -- the length of EDFs and pump power, pump scheme, etc.. The gain is above 23 dB, the bandwidth of 3 dB is more than 36 nm, and the input signal saturation power arrives -15 dBm.

A strain-induced birefringence double-clad (DC) fiber Bragg grating (FBG) is proposed and demonstrated. The grating is fabricated in the core of rectangular inner cladding double clad fiber by using phase mask method. By applying lateral strain on the grating, the birefringence is induced. In order to detect the birefringent effect of the grating, we use it as the output mirror of a laser. When lateral strain is applied, the grating becomes birefringent. Therefore, one reflection peak of double-clad fiber Bragg grating becomes two peaks and the laser also lases in two wavelengths. The wavelength spacing of the laser can be tuned from 0 to 0.8 nm. The absolute wavelengths for the two polarizations can be tuned 1.2 and 2.0 nm, respectively.

提出了一种结构新颖的L波段环形腔掺铒光纤激光器。用掺铒光纤作为增益介质，采用980 nm激光器作为前向抽运源，利用起偏器和偏振控制器获得L波段激光，利用光环形器将后向的放大自发辐射再引入铒光纤的前端，重复利用。当抽运功率为103 mW时得到了阈值功率约为23.87 mW，输出功率达6.34 mW的激光输出，斜率效率约为8.05%,与没有重复利用后向放大自发辐射谱的掺铒光纤激光器做比较，该结构对L波段掺铒光纤激光器的性能有明显的提升作用。对于长度不合适的铒纤，在没有重复利用后向放大自发辐射谱时没有获得激光输出；而在利用后向放大自发辐射后，在阈值功率约为88 mW时得到了激光输出，从而很好地证明了上述结论。