Spectral width of parametric amplification in fiber waveguides

Single-frequency and biharmonic laser pumping of a few-mode fiber waveguide was used in a study of the spectral width of parametric amplification under conditions of intermode phase matching. It was found that this width was governed by the pump power and by imperfections of the fiber waveguide. Experimental values of the spectral width of parametric amplification were used to estimate variation of the diameter of a fiber along its length. The results indicated that under intermode phase matching conditions the region of spectral tuning of a narrow-band anti-Stokes wave obtained as a result of biharmonic pumping corresponded to the spectrum of parametric amplification in the case of single-frequency pumping.