Optical frequency bistability and power bistability in semiconductor lasers

Optical frequency bistability and power bistability in semiconductor lasers biased from below to above threshold are presented using the unified description of semiconductor lasers with external light injection. A new method is given to calculate the bistable frequency and power loop widths. When the bias current of a laser is fixed, there is a lowest power for the external light to realize optical frequency bistability. And this lowest power reaches its minimum just at threshold. The optical injection level (defined as the ratio of the injected power to the power emitted by the free-running laser) must be larger than a certain value to obtain the bistability. This level may be larger than unity for a laser biased below threshold. On the other hand, for a given bias current, there is a lowest frequency detuning between the electric field of the laser and the injected field to achieve the power bistability. And this detuning must be negative for any bias current (below or above threshold) of the laser. The results are in good agreement with experiments