Single-longitudinal-mode fiber ring laser using internal lasing injection and self-injection feedback

A single-longitudinal-mode (SLM) fiber ring laser is demonstrated by introducing internal lasing injection and self-injection feedback. Internal lasing, generated in an auxiliary cavity, interacts with the laser oscillation in a main cavity to suppress mode hopping. Self-injection feedback loops are incorporated in the main cavity to serve as laser mode filters. Neither an ultra-narrow bandpass filter nor a precise control for laser cavity length is required in achieving stable SLM operation.