An Improved Two-Wavelength Phase Demodulation Method for Nanosecond Pulsed Electro-Optical Sensors

Abstract

Bias drift can always be a difficult problem in the application of electro-optical (EO) sensors based on intensity demodulation method, which may lead to the output jitter and distortion of the waveform. The bias drift problem can be avoided using a two-wavelength phase demodulation scheme, however the system noise restricts its use to low amplitude measurements. In this paper, the existing two-wavelength phase demodulation method is improved to overcome the limitation of low amplitude measurement for pulsed signals. The improved method can effectively avoid the bias drift problem compared with the intensity demodulation method and reduce the measurement limit by more than one order of magnitude compared with the phase demodulation method simultaneously. Based on the asymmetric two-wavelength EO modulation structure, we obtain the transfer function and its explicit demodulation formula without the bias term. Particularly, by adjusting the bias difference of the two lasers in the EO sensor to π/2, the modulated signal is simply proportional to the root mean square of the 2-channel outputs. To support and illustrate our method, a simulation, and a verification experiment are carried out and show that the demodulated signals have good consistency with each other.