Based On Fiber-coupled Laser Self-mixing Interference Effect

Laser self-mixing interference i.e. laser feedback effect or injected modulation effect, refers to a portion of light emitted from a laser source is reflected or scattered by an external object and coupled into the laser cavity. The feedback light which carries information of the external object then mixes with the light inside the cavity, and modulates the output signal of laser power. The signal characteristic of this system is similar to that of the conventional two-beam interference, thus it is called laser self-mixing interference.In previous research, many researchers analyzed the theory and observed the experiment phenomena of self-mixing interference focused on the laser diode, the vertical-cavity surface-emitting laser, the Nd: YAG laser, and the CO₂ laser, etc. All those lasers mentioned above are based on the model of F-P cavity. But so far, the research of self-mixing interference effect of distributed feedback (DFB) laser and the erbium-doped fiber laser which widely used in photocommunication field is still nearly a blank to be domestic and international. Our group focuses on the effects of self-mixing interference in fiber coupled lasers, which offer the theoretical foundation and experiment technology for the laser active sensing network based on optical feedback.In this paper, the self-mixing interference in distributed feedback lasers is theoretical analyzed based on the coupled wave equations. The emission frequency and output gain variations of the self-mixing interference inλ/4 phase shifted index coupled distributed feedback lasers, gain coulped distributed feedback lasers, and distributed Bragg reflector lasers are deduced. From the simulation we can find, their self-mixing interference signals are similar to that of F-P lasers. The self-mixing interference signal exhibits sinusoidal-like when the feedback is weak, and exhibits sawtooth-like when the feedback is stronger. One fringe of the signal corresponds to the displacement of half wavelength of the target. The characteristics obtained in simulation are verified in the experiment. The influence from the variation of attenuation and dispersion caused by the increment of fiber length are discussed. A new approach for remote reflectivity detecting based on optical feedback effect in distributed feedback lasers is presented.In addition, two modles of the optical feedback effects - internal feedback, external feedback - in linear fiber lasers and in ring fiber lasers are analyzed. The system output variations with the conditions of internal or external feedback are deduced based on the transcendental equations of fiber lasers, and compared with each other in simulation and experiment. The system output variations are discussed by changing the experiment condition, which show a good agreement with the theoretical analysis and the simulation results.