Research On Technique For Digital Correlation Detection In Measurement For Low-loss Parameter

More and more attention is paid on the low-loss parameter of light scattering rate and low transmission ratio caused by the super smooth optical surface, which has become one of the basic and key problems for studying the optical element. So, the detection for the weak light signal under strong yawp becomes very significant. After studying the digital correlation detection technology in this paper, the accurate measurement of the low loss parameter is realized.A kind of measuring system used for detecting low loss parameter of optical element (scattering rate, low transmission rate) was researched in the paper. The system is made up of light path, integrating sphere, photoelectric detector, data acquisition and control, the software for correlation detection algorithm.etc. In order to improve the integrated level of system and reduce the cost of measurement, a high cost-effective and accurate measurement for the light scattering parameters is realized by using software phase lock algorithm to replace the hardware lock-in amplifier in the measuring system. The design for the software system is based on Lab VIEW, which consists of four modules as follows, synchronous data acquisition module, the phase shift module, data splicing module and correlation module, the correlation is the core algorithm of the software phase-locked amplifier, the measurement results were output ultimately by using a series of operations for signal, such as multiplication, filtering, square, additive and open radical sign.The measurement error is 0.1% with frequency of 0.2 kHz, amplitude of 1.0 V and the noise amplitude of 0.5V. The results of simulation proved that to realize digital orthogonal related detection technology by the software is completely feasible. Then the practical measurement data verify the correctness and feasibility of the algorithm, and the experimental results show that the time constant corresponding to the sampling points and along with the increase of sampling points measurement result error smaller and smaller. And the phase control problem of hardware phase-locked amplifier is ignored. Finally, the influences on test results of sampling points, noise and filter parameters were discussed.