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Internal optical feedback effect in fiber ring laser

The internal optical feedback effect in fiber ring lasers is similar to self-mixing interference, and the former has same phase sensitivity with the later: one fringe shifting corresponds to a target displacement of half optical wavelength λ. The optical feedback effect presented in this paper is achieved inside the laser cavity. So the feedback part becomes part of the fiber ring laser, and makes the laser not only a light source, but also a sensitive element. The similarities and differences between optical feedback in fiber ring lasers and self-mixing interference in semiconductor lasers are analyzed, which offers the theoretical foundation and experiment technology for fiber active sensing applications. The internal optical feedback system based on fiber ring lasers satisfies the need of microminiaturized sensing device and the interrogation demand of optical fiber. This system can easily perform noncontact and remote measurement of velocity, vibration, displacement, etc.