SEMICONDUCTOR LASER MODULE, LASER UNIT, AND RAMAN AMPLIFIER

摘要

PROBLEM TO BE SOLVED: To solve problems that Raman gain fluctuates as the intensity of pumping light fluctuates to cause fluctuation in the intensity of a signal light, noise of pumping light becomes noise of the signal light as it is, induction Brillouin scattering takes place eminently to lower the amplification efficiency, and the length of a depolarizer is lengthened. SOLUTION: A substantially rectangular wavelength selection filter having a transmittance spectrum is disposed in a cavity. The wavelength selection filter has a dielectric multilayer film transmitting a desired wavelength. The filter is disposed in front or rear of a semiconductor laser element. The filter is disposed between a paralleling lens and a condenser lens perpendicularly or obliquely to the optical axis. Transmission wavelength can be tuned by turning the filter. Composite resonance takes place between two or more cavities. An optical isolator is disposed closer to the optical fiber side than the cavity. The pumping light source module is built in a Raman amplifier.