FREQUENCY CONTROL OF A LASER-DIODE BY A PHOTOTHERMAL EFFECT AND ITS APPLICATION TO FREQUENCY STABILIZATION

The frequency of an AlGaAs laser diode (LD) was controlled by using a photothermal effect. If intensity-modulated light from a heating LD is focused on the active domain of another LD, a heat spot changes the e ffective cavity length of the LD and thus modulates the lasting freque ncy. For frequency stabilization, frequency shift is detected by a Fab ry-Perot etalon, and it is compensated for by controlling the intensit y of the heating LD via a proportional-integral-derivative controller. The highest stability obtained is 2.6 x 10(-11) (tau = 10 s), which i s an improvement of 2 to 3 orders of magnitude over the free-running s tate. In this method, the concurrent intensity modulation is much smal ler than in the current modulation method.