Noise reduction method for electro-optic measurement system using variable gain amplifier

This paper describes a noise reduction method for an electro-optic (EO) measurement system using a variable gain amplifier. The EO measurement system is based on Pockels effect and a laser source. When an optical bias offset in the differential EO modulated lights causes an unbalance of differential signals, the laser noise cannot be reduced. We try to reduce the laser noise with an electrical method using a variable gain amplifier before a differential amplifier. The maximum signal-to-noise ratio is obtained by changing the gain of the variable gain amplifier in accordance with DC voltage from the output signal of the differential amplifier. The noise of the EO measurement system is modeled, and a noise simulator is developed. Characteristics of the experimental results agree with those of the simulation results. The effectiveness of the noise reduction mechanism is demonstrated by the noise simulator.