Composite-cavity-mode approach to single-mode semiconductor-laser feedback instabilities.

A semiconductor laser in an external high-quality cavity is analyzed using a composite-resonator-eigenmode description of two coupled resonators. Laser threshold and lasing frequency are studied for various cavity lengths and coupling-mirror transmissions controlling the amount of light feedback into the laser. The results are valid for all values of coupling. Pronounced mode hopping is predicted, which leads to dramatic laser-frequency shifts for small variations of the external cavity length.