Study On Stimulated Brillouin Scattering And Its Applications In Optical Fibers

Stimulated Brillouin scattering (SBS) is a nonlinear interaction between the pump and Stokes fields through an acoustic wave. SBS is the major nonlinear optical phenomena in optical fibers because the threshold powers are much lower than those needed for stimulated Raman scattering (SRS). SBS has wide applications in phase conjugation, optical fiber sensors, microwave photonics, controllable slow light and fiber lasers.Slow light based on SBS has already becomes a hot topic in the research of slow light, as it has many advantages such as low Brillouin threshold power, easily controllable group velocity, tunable wavelength and it is easy to be integrated with existing telecommunications. Tunable multiwavelength Brillouin erbium-doped fiber laser (MWBEFL) takes the advantages of Brillouin amplification in optical fibers and high gain from the erbium-doped fibers amplifier (EDFA). It has the merits of equal-wavelength spacing, narrow linewidth and high output uniformity over the channels at room temperature.With the subjects supported by the Tianjin Natural Science Foundation (Grant No.08JCYBJC14400), the Tianjin Key Project of Applied and Basic Research Programs (Grant No.07ZCKFGX00200), the National Natural Science Foundation Project (Grant No.60572018), the main contents of this paper are as following:1. The advancements on controllable slow light and multiwavelength erbium-doped fiber lasers based on SBS are introduced systemically. The physical principle of SBS in optical fibers is presented and the SBS slow and fast light in optical fibers are theoretically studied from the SBS coupled wave equations. The analytic solutions of SBS slow light delay time are theoretically studied in the case of stable state with small-signal.2. The highly nonlinear photonic crystal fiber used as SBS slow light medium is studied. Through theoretical analysis, the photonic crystal fibers with small mode field areas can improve the delay efficiency of the slow light system. This is demonstrated by the experiment. The Brillouin gain of 33 dB is achieved when a highly nonlinear photonic crystal fiber is used as slow light medium, which results in 30 ns time delay of 50 ns signal pulses. The delay efficiency of this kind fiber is 0.0046 ns/mW/m, which is about 13.7 times larger than the single mode fiber.3. A new type of simple tunable multiwavelength Brillouin/erbium fiber ring laser is presented. It is proposed that two ports of a 3dB optical coupler is employed to connect the gain medium, in combination of a fiber loop mirror in another port to form feedback and realize cascade. This configuration reduces the insertion loss and complexity of the fiber laser. The threshold power is greatly reduced and the generation of multiwavelength is enhanced by the bidirectional pumping scheme. With the maximum 1480 nm pump power of 110 mW,21 average output channels with 13 nm tuning range are achieved.4. A tunable multiwavelength Brillouin/erbium fiber laser based on highly nonlinear photonic crystal fiber is presented. The ring cavity is very simple, in which one coupler launches the Brillouin pump signal into and takes the multiwavelength signals out of the cavity. The laser with shorten cavity length is easy to be integrated due to a 70-m low loss highly nonlinear photonic crystal fiber (HNL-PCF) used as the Brillouin gain medium. The laser provides a tuning range of 25 nm and 3 output channels at the Brillouin pump power of 3 dBm and the 1480 nm pump power of 30 mW. At the maximum 1480 nm pump power of 110 mW,10 stable output channels with 10 nm tuning range are achieved.5. Widely tunable multiwavelength Brillouin/erbium fiber sources with ring and linear cavity are demonstrated. The structure is proposed that the Brillouin Stokes signals return back to the linear cavity owing to the effect of SBS. The influence of the self-lasing cavity modes is effectively eliminated. The tuning range of the fiber sources is only limited by the bandwidth of erbium-doped fiber amplifier and the tuning range of Brillouin pump signal. The threshold power of the linear fiber source is effectively reduced by the double-pass Brillouin pump preamplified technique. The fiber sources provide a tuning range of 40 nm from 1530 nm to 1570 nm.