Linewidth depth narrowing and control of linear cavity fiber laser based on distributed external feedback

A novel scheme to achieve linewidth depth narrowing and control of a single frequency Distributed Bragg Reflector (DBR) fiber laser based on distributed external feedback. Herein, the feedback signal can match the laser phase in real time to avoid the phase jump, thus realizing the laser mode is greatly suppressed. Moreover, it can also effectively suppress the unavoidable spontaneous radiation of the laser active medium, thus narrowing the linewidth in depth during the oscillation process. Based on this, the master laser can be regulated in an external all-optical approach by using a fiber device with controllable physical parameters. Eventually, an ultra-narrow linewidth laser with a spectral signal-to-noise ratio of 64 dB, a side mode suppression ratio of 83 dB, an output linewidth of 115 Hz. In particular, the Lorentz linewidth of the laser can be continuously adjusted from 115 Hz to 8.2 kHz by controlling the intensity of the distributed feedback signal. The proposed controllable mechanism of laser linewidth also provides a new perspective for extreme regulation of laser parameters of other types of lasers.