To obtain a predetermined power intensity without influencing the wavelength of output light by external APC, a laser beam having a predetermined plane of polarization and output from a tunable wavelength light source passes through a Faraday element and a polarizer constituting an optical...http://www.google.de/patents/US5754571?utm_source=gb-gplus-sharePatent US5754571 - Tunable wavelength light source apparatus for stabilizing power intensity by using external auto-power control 
