Fiber Raman Amplifier And Fiber Raman Laser Technology Research

With the development of Internet, ISDN and multimedia techniques, the global communication services increase dramatically, the services of communication will turn to broadband services charactered by high speed IP data and multimedia data which demands that the optical fiber communication systems run with a larger capacity and a faster transmission speed than before. Then DWDM emerges as the times require, which has satisfied the demand of communications capacity and system expansion for long-distance transmission. However, DWDM brings some new problems that how to increase the capacity of fiber transmission system, introduce all optical network, increase no-relay transmission distance, and so on. Fiber Raman amplifiers (FRA) are all-optical amplifier based on Stimulated Raman Scatter generated in fibers, the pump and the gain medium of which are powerful lasers and the transmission fibers. The characteristics of FRA, such as broad gain band, high gain and distributed amplifying, have important practical meanings to the optical fiber transmission system, especially to the DWDM system. fiber Raman laser (FRL) can be a good pump of FRA. The coupling loss between FRL and the transmission fiber is very small, so the pump and the amplifier can be compatible easily. Then Yb3+-doped double clad fiber laser (YDFL) is the pump of the FRL. The gain media of YDFL and FRL are both fiber, so they can couple well.In this paper, FRA system and the modules in the system and the YDFL are analyzed theoretically, and the Raman gain fibers are discussed simultaneously from both the theory and the experiment. The main works are as follows:Firstly, FRA is introduced briefly, including the classifications, characteristics, application and the recent development about FRA. Then the pump modules of FRA, which are mainly composed of laser diodes and cascade Raman fiber lasers, are introduced.Secondly, the performances of Yb3+ doped double clad fiber laser are analyzed in theory. Using the transmission equations for the forward and the backward pumping light and the signal laser in double clad fiber, we simulate numerically the performance of Yb3+ doped double clad fiber lasers, including: evolutions of the pumping power and the forward and the backward signal power along fiber with the different fiber losses and the pumping wavelengths; relationship between the output power and the fiber length under different fiber losses, in which we obtain that there is an optimal fiber length under certain pumping power and fiber losses, when the output power is maximum; relationship between the pumping power and the output power under different fiber losses; relationship between the output power and the fiber losses with different pumping powers; relationship between the output power and reflectivities of mirrors located at output side and input side under different pumping powers and different fiber losses; and the evolutions of the gain and the threshold of YDFL along the fiber length under different fiber losses and the different fiber absorption coefficients.Finally, we analyze the Raman gain fiber which is doped by GeO2 or P2O5. For GeO2-doped fiber, according to the relationship between the spontaneous Raman gain coefficient and frequency, relationship of the Raman gain coefficient and the GeO2 concentration is deduced by using the relation of the emission cross-section and the GeO2 concentration. The performances of Raman gain fiber are numerical analyzed, including: the relationship of the fiber refractive index and the GeO2 concentration; fiber refractive index and the pumping wavelength; Raman gain of amplifier and the GeO2 concentration; and Raman gain of amplifier and the pumping wavelength. Then relationship of the P2O5 concentration and the fiber refractive index difference, loss and the Raman gain coefficient are analyzed. Furthermore, the Raman gain coefficient for frequency shift between 9 and 20 THz of the standard single mode optical fiber is measured by on-off method, in which an ASE is used as a broadband small signal probe source and a single mode laser as a pump source. The measurement principle, the experimental equipments and the experimental steps are introduced. The distribution curve of the fiber Raman gain coefficient is obtained by dealing with our experimental data, and we note that the spectrum shape measured agrees well with the theoretical value.