Self-mixing interference in distributed feedback laser diode with multiple external cavities

The self-mixing interference in distributed feedback laser diode (DFB-LD) with multiple external cavities is analyzed. Each external cavity is considered to be an optical thin film, and the equivalent reflectivity can be got from the theory of the thin film optics, the general expressions of gain and frequency in compound laser cavity are theoretically deduced. This principle is helpful to build the fiber-coupled self-mixing interference system. Considering that different parameters have influence on self-mixing interference, we make some simulation analysis at different conditions. The output of self-mixing interference is analyzed in numerical analysis, and the amplitude variations of the output gain is discussed along with different parameters, e.g., the coupling coefficient, the linewidth enhancement factor, and the reflection coefficient of external reflector.