Stimulated Brillouin Scattering In Fiber

Stimulated Brillouin scattering (SBS) is a nonlinear process that can occur in the optical fibers. It manifests through the generation of a backward-propagation Stokes wave that carries most of the input energy, once the Brillouin threshold is reached,which is harmful to the optical systems.In this thesis, the impacts of the SBS effects on the ytterbium-doped fiber amplifiers (YDFA) are analyzed firstly. The main contents are as follows:⑴The output characteristics of the high-power and narrow-linewidth YDFAs under the backward pump are numerically studied by solving the propagation-rate equations including SBS, stimulated Raman scattering(SRS), and amplified spontaneous emission(ASE). The relationship between signals and Brillouin-stokes waves with different orders and the influences of Brillouin-stokes waves on the YDFAs are investigated, respectively. The simulated results show that the SBS will deform the output signal pulses in both the time domain and the spectrum domain.⑵The influences of the pump power, the signal linewidth, the fiber length, and the fiber-core diameter on the output characteristics of the YDFAs are studied in detail. Calculating results show that the SBS can be suppressed effectively by using an ytterbium-doped fiber with length shorter than 0.68 m and fiber-core diameter larger than 26μm, or broadening the signal linewidth to a critical value of 0.04 nm.On the other hand, SBS effects in optical fibers can be applied in the fields of the optical buffing and the optical information processing, Therefore, the SBS effects also attract large attention in the field of fiber optics. The SBS-based tunable pulse delays in the fibers are investigated. The main contents are as follows:⑴Pulse delays and pulse broadening of the signals with different pulse durations and peak powers are investigated, respectively. The simulated results show that long time delays and small pulse broading can be achieved by using the long-duration signal pulses with the low peak powers.⑵The differences of the Brillouin gain spectrum and the group index are analyzed at the pump lights with different bandwidths. The simulated results show that gain spectrum bandwidth is approximately normal linewidth(~35MHz), when the bandwidth of the pump light is smaller than the Brillouin linewidth; and the gain spectrum can be extened by employing a broadband pump at a decreased SBS gain coefficient.⑶The tendence of the Brillouin gain spectrum is investigated at the pump lights with high power and broad bandwidth. Calculating results show that Stokes gain spectrum and anti-Stokes absorption spectrum appear at different Brillouin frequency shifts, when the bandwidth of the pump is smaller than the Brillouin frequency shift, and the spectrum bandwidth is linear to the pump bandwidth; when the bandwidth is equal to the Brillouin frequency shift approximately, Stokes gain spectrum and anti-Stokes absorption spectrum overlap atδv=0, and the bandwidth of the gain spectrum is smaller than the pump bandwidth, when broadening the bandwidth of the pump light.