The relationship between the intensity modulation depth of light source and the modulation frequency and injection current of laser diode (LD) is studied in a LD interferometer with a photothermal modulation which is used for optical fine measurement.

Based on the physical model of a laser diode (LD) modulated utilizing photothermal effect, the relations of the photothermal intensity modulation depth of the LD with the modulation frequency and injection current are theoretically and verify experimentally deduced.

At present, the researches emphasis on the sensor are based on light intensity modulation, which makes sensor have low accuracy and poor stability because light source and optical path disturbance have a great impact on light intensity modulation.