Abstract: A laser apparatus is disclosed combining polarized light beams from two optical emitters into a combined beam of light with controllable degree of polarization (DoP). The laser apparatus includes a polarization combiner for combining the polarized beams into the combined beam, an optical tap for separating out a portion of the combined beam, and a photodetector electrically coupled to a laser controller for providing a feedback signal. The controller distinctively modulates the polarized radiation of each of the emitters, detects modulation signals in the photodetector output and adjusts an output power ratio of the optical emitters for maintaining the DoP of the combined beam at a pre-determined level. The invention can be used for minimizing the DoP of pump radiation in Raman and EDFA pump laser modules combining multiple pump laser diodes.

Abstract: A single-frequency Brillouin fiber ring laser with extremely narrow linewidth comprises a single-frequency narrow-linewidth rapid-tunable pump laser, a temperature-controlled acoustically-damped package for Brillouin fiber ring laser cavity, and an auto-tracking feedback electronic loop with novel configuration for active stabilization. The Pound-Drever-Hall frequency-locking technique is employed to keep pump laser frequency in resonance with one of the Brillouin fiber ring cavity modes. Instead of changing cavity length of Brillouin fiber ring laser, the pump laser frequency is rapidly tuned in the auto-tracking feedback electronic loop. This enables extremely narrow linewidth radiation emitted from a Brillouin fiber ring laser without stretching the fiber ring.