Experimental Study On All-fiber Cascaded Raman Fiber Laser Pump Source

Raman fiber lasers (RFL) which base on the stimulated Raman scattering (SRS) effect, can generate any wavelengths output if it is pumped with an appropriate pump source and feedback elements. Cascaded Raman fiber lasers (CRFLs) have some advantages, such as longer gain medium, lower noise, broader turning, multi-wavelengths output and high coupling efficiency. The CRFLs, used as pump source in Raman fiber amplifier, can generate flat gain in a wide-band range. It is an ideal pump resource of Raman fiber amplifier. Multi-wavelengths CRFLs can be used as light source in fiber communication system, especially in WDM system. With it, the number of lasers in transmitter will be decreased.In this dissertation, SRS theory is introduced firstly. Then, a five-order CRFL is designed, including the design of CRFL resonant cavity, pump source, and the driving circuit of high power LD,which used as pump source for Yb³⁺-doped double claded fiber lasers (DCFLs). The characteristics of each part of the system are measured in laboratory and the experimental results are analyzed.The main contents of this dissertation are as followings:(1) The basic theory of SRS, the domestic and abroad research state for RFLs and Yb³⁺-doped DCFLs are introduced.(2) The transition processses between the energy states of the Yb³⁺ in Yb-doped fiber are presented. The high power DCFL, used as pump source for CRFL, is designed.(3) The drive circuit for high power LD, which used for pump DCFL is designed. The characteristics of LD are also introduced in this dissertation.(4) Bragg fiber grating is brifly introduced, and transmitiom spectra of the fiber gratings we used are experimentally measured.(5) The resonance cavity of a five-order CRFL in line style is designed. The CRFL is testd in the laboratory, and the experimental results are analysed.(6) The DCFL and the drive circuit for LD are mesured.The test results show that the driving circuit designed for high power LD is stable and fulfilled the requirement. The fifths Stokes light maximum output of the CRFL is 599mW. Reasons for high pump threshold, low light-light conversion efficiency and low slope efficiency of the CRFL are also analyzed in the dissertation.