Broad-band variable-wavelength laser beam generator

A broadly tunable laser beam generator serving as a laser beam source which utilizes a nonlinear optical effect of a silica optical fiber and which is tunable in a broadband in the near-infrared region, having ultra-broad tunability, and generating coherent light which can be swept over the entire wavelength region with a single wavelength selecting element and which has a collinear emittance directivity, wherein the silica optical fiber is a single mode fiber in which birefringence remains and whose cut-off wavelength lies preferably from 1100 to 1300 nm, and wherein, by coupling a pulse laser beam source with an end face of the fiber so as to input a pulse laser beam having a short wavelength very close to the cut-off wavelength into the end face of the fiber as pump light, stimulated Raman scattering and stimulated parametric four-lightwave mixing occur in the single fiber so as to provide a gain spectrum continuously extending over both shorter and longer wavelength regions with respect to a wavelength of the pump light, and consequently to provide ultra-broadband tunability.