Optical EngineeringFrequency control of a laser diode by a photothermal effect and its application to frequency stabilization
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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 effective cavity length of the LD and thus modulates the lasting frequency. For frequency stabilization, frequency shift is detected by a Fabry-Pérot etalon, and it is compensated for by controlling the intensity of the heating LD via a proportional-integral-derivative controller. The highest stability obtained is 2.6x 10-11 (π = 10 s), which is an improvement of 2 to 3 orders of magnitude over the free-running state. In this method, the concurrent intensity modulation is much smaller than in the current modulation method.