Study On Double-clad Fiber Lasers And Amplifiers

One well known advantage of the double-clad geometry is that facilitates pumping by high-power laser diodes. Fiber lasers and amplifiers using the cladding-pumping method are able to handle very high optical power. The studies on the double-clad fiber lasers and amplifiers will undoubtedly promote the development of many applications, such as medical, military, industrial processing and modern optical telecommunication. These also need the perfect of the fiber lasers and amplifiers in cavity structure, laser stability, laser line-width and output power.According to the project of the "Natural Science Foundation of China under Grant No: 60137019", and "the national High Technology Programme of China under No: 2003AA312100", the main contents are listed as follows:1. We hydrogen-loaded the double-clad fiber firstly, and then experimental study ofthe photosensitivity of the fiber. Variation of the amplitude of reflective-index modulation and effective reflective index with the UV exposure time is observed. The evolution of the grating reflectivity and the Bragg wavelength shift during the growth of fiber Bragg grating (FBG) can be estimated by these relations.2. Depend on the photosensitivity relations of hydrogen-loaded double-clad fiber, wefabricate diversiform reflectivity of double-clad fiber Bragg gratings with phase mask method, the best reflectivity of the grating is 99.9%. We make a Moire fiber grating in the core of double-clad fiber with double exposure method. Using this Moire fiber grating, a two wavelengths Yb -doped double-clad fiber laser is fabricated.3. Using the experimental data obtained, we modeled the thermal decay characteristics according to the anneal thermal. These results are more significative for estimate the properties of the grating, such as thermal, wavelength and anneal time.4. The resonant nonlinearity of double-clad fiber Bragg grating is theoretically andexperimentally investigated. By using the strong residual pumping power, we observe the resonant nonlinearity in the Yb -doped double-clad fiber Bragg grating.5. A strain-induced birefringence double-clad fiber Bragg grating is proposed and demonstrated. The grating is fabricated in the core of rectangular inner cladding double clad fiber employing phase mask method. By applying lateral strain on the...