Stimulated Raman scattering excited in a silica optical fiber by Q-switched Nd:YAG laser beam is investigated. The optical fiber used are (a) multimode, (b) two-mode, (c) single mode fibers and datum are obtained mainly from the single mode fiber 120 m long, where 900 watt coupled laser power is used.
In this experiment Raman Stokes lines are found at 1.12 ㎛, 1.18 ㎛, 1.24 ㎛ and the Stokes lines beyond the longest wavelength of 1.24 ㎛ are buried in a continuum, which extends up to 1.45 ㎛. The pump power dependent Stokes Raman profiles are measured in detail and the effect of polarization of the coupled laser power (99.0% deg. of polarization) is investigated. As the optical fiber is circular the polarization in the fiber waveguide becomes degenerate and the degree of polarization of the output beam, which is the sum of Stokes lines and laser beams, is found to have 50.0%. The first Raman Stokes begins to be observed above 95 watt and the critical power is about 185 watt.
In the same experiment 4-photon mixing signal is also detected at λ = 1.039 ㎛, 1.054 ㎛, 1.075㎛ and 1.090 ㎛. These signals at 4 wavelengths are satisfied the phase matching condition by using waveguide dispersion.
