Bidirectional Single Longitudinal Mode Er-Doped Fiber Ring Laser Using a Bandpass Filter and Cascaded Fiber Ring Filter

Bidirectional single longitudinal mode fiber ring laser have advantages and potential in optical sensing, especially angular velocity sensing. The current methods for implementing bidirectional cannot ensure complete reciprocity the path, side suppression ratio needs to be increased, while linewidth is relatively wide. This paper proposes a combined filtering structure using bandpass filter cascaded add-drop type filter. When realizing output, path fully reciprocal including polarization state reciprocity, high. of around 1.1 kHz, far lower than previous report tens kHz. proposed this does not require special devices, its theoretical system mature, which conducive subsequent application improvement laser.