Apparatus for stabilizing multiple laser sources and their application

Abstract

Apparatus for stabilizing multiple laser sources having distinguishable optical characteristics, e.g., in polarization field or operational wavelength, comprises a plurality of semiconductor laser sources having respective lasing cavities capable of lasing within a narrow bandwidth of wavelengths and providing spectral outputs at their respective laser exit facets having different optical characteristics from one another. The spectral output beams of the sources may be coupled to respective optical fibers and the beams combined via a beam combiner, e.g., a polarizing beam combiner or a WDM combiner. The beam combiner combines the beam outputs forming a single beam which is launched into an output optical fiber. At least one feedback fiber grating is provided in at least one of the optical fibers with the number thereof depending upon distinguishable optical characteristics of the multiple laser sources. In the case of distinguishable optical characteristics in the form of polarization field, one grating is required and in the case of distinguishable optical characteristics in the form of operational wavelength, multiple gratings are necessary equal to the number of laser sources. The fiber grating or gratings have a reflectivity band for reflecting back a small portion of selected wavelengths of the single beam which are within the gain bandwidth of the laser sources while the remaining portion of the single beam transmitted through the grating or gratings to a final output. The grating or gratings have a reflectivity level approximately equal to or less than the reflectivity level of the laser source exit facets. The grating or gratings are positioned in the optical fiber or fibers to have an optical separation from the laser sources to cause the laser sources to operate in multiple longitudinal modes broadening the spectral output of the laser sources by several orders of magnitude.