Computer-based digital measurement system for optical small signals

Abstract

Boxcar integrator and lock-in amplifier for the detecting of optical small signals are developed based on the virtual instrument technology of LabView. The algorithm of boxcar integrator is simple and easy-achieved. Lock-in amplifier is a powerful technique for the extracting and amplification of small signals. However, the cost of lock-in amplifier hardware is high. We develop digital boxcar integrator and lock-in amplifier in LabView platform. The performances of these two virtual measurement systems for optical small signal are exhibited and analyzed. Introduction In the biomedical detection, optical sensing and fundamental research, the measurement of optical small signals is a difficult work frequently encountered.. Optical small signals will be easy contaminated by noise, such as the environment light, the noise of photoelectric conversion, the noise of electric circuit, etc. The measurement system should minimize the effects of noise as far as possible. There are many detecting technologies, for instance correlation detection and narrow-band filter, aiming small signal measurement. Lock-in amplifier is a powerful correlation detection technique for small signal detection with high signal-to-noise ratio [1,2]. However, the cost for the hardware of lock-in amplifier is very high. When the signal is a periodic signal, time domain averaging is an effective method to extract signal from complex signals with noise [3-5]. In this paper, we develop two kinds of virtual instrument based LabView platform, digital boxcar integrator and digital lock-in amplifier, for the detecting of optical small signals. The performances of these two virtual measurement systems for are exhibited and analyzed. Modulation of Optical Signals. In optical signal measurement system, the optical signals from samples usually are very weak. Here, we realize two digital processing systems for the detection of small signals: boxcar integrator and lock-in amplifier. First of all, the optical small signals should be modulated. Figure 1 displays the using of optical chopper to modulate the signal light. The optical signals are converted to square wave by the optical chopper and then are measured by photoelectric detector, like highly sensitive avalanche photo diode (APD). The periodic signals with certain frequency are entered into conventional acquisition system undergoing amplification, filter, D/A conversion, processing and storage. Next, we mainly discuss the data processing of the complex signals of the chopped signal mixed with noise for extracting the weak effective information from sample. International Conference on Intelligent Systems Research and Mechatronics Engineering (ISRME 2015) © 2015. The authors Published by Atlantis Press 145