Broad-band variable-wavelength laser beam generator
There is provided a broadly tunable laser beam generator serving as a laser beam source which utilizes a nonlinear optical effect of a silica (glass) fiber and which is broadly tunable in the near-infrared region, having ultra-broad tunability which has not been easily achieved by known tunable lasers, and generating coherent light which can be continuously swept over the entire wavelength region with a simple mechanical operation of a single wavelength selecting element and which is emitted in a constant direction independent of its wavelength. The laser beam source which utilizes a nonlinear optical effect of a silica optical fiber ( 8 ) and which is broadly tunable in the near-infrared region has ultra-broad tunability and generates coherent light which can be continuously swept over the entire wavelength region with a single wavelength selecting element ( 10 ).
1. A broadly tunable laser beam generator comprising:
a pump pulse laser;
an output-coupling half-mirror configured to pass a pulse beam emitted from the pump pulse laser therethrough;
a silica optical fiber configured to receive the pulse beam from the output-coupling half-mirror via a first collective collimator lens, the silica optical fiber having a birefringence and a cut-off wavelength from 1100 to 1300 nm; and
a single-wavelength selecting element configured to receive the beam emitted from the silica optical fiber via a second collective collimator lens and feeding back a light with a specific wavelength,
wherein the feedback light with the specific wavelength is received by the silica optical fiber via the second collective collimator lens, amplified to obtain a gain while propagating through the fiber twice, emitted from the fiber, converted into collimated light by the first collective collimator lens, and emitted from the output-coupling half-mirror as an output light beam.
2. The broadly tunable laser beam generator according to claim 1 , wherein the tunability is completely continuous to a degenerate region close to the pump light.
3. The broadly tunable laser beam generator according to claim 1 , 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 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 silica 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, the ultra-broad tunability lying from 800 nm to 1875 nm.