SMALL-SIGNAL CIRCUIT MODELING FOR A GRATING EXTERNAL-CAVITY SEMICONDUCTOR-LASER

A sinusoidal small-signal circuit model is presented for an external-cavity semiconductor diode laser with either weak or strong external optical feedback provided by a grating. It is shown that the effects of optical feedback can be modeled by two voltage sources correlated to the modulated injection current of the diode laser. The magnitudes of these two voltage sources are proportioanl to the product of the optical feedback level and the modulation amplitude. This result supports the idea of modulating a diode laser by optical injection. The small-signal intensity modulation and FM response characteristics of this circuit model are also presented. The response curves exhibit oscillations with the periods determined by the modulation feedback phase delay. These results agree with the results obtained elsewhere. For a short external-cavity limit, the response curves are reduced to the curves obtained elsewhere for a diode laser without an external cavity.