The LDDM system is a measurement system mainly used for medium and short-range precision displacement data, especially in the field of practical engineering. In the LDDM system, the accuracy and speed of measurement system depend directly on the design of phase discriminator system. This article introduces a new high-precision digital phase detector based on FPGA hardware platform. It uses improved CIC filter and CORDIC function to design the module. Firstly two orthogonal local oscillator signals are generated, and multiply the two signals separately by the signal to be measured. After the modified CIC filter, the phase difference between the local oscillator signal and the signal containing only DC information is calculated by the CORDIC algorithm solving module. Finally, the phase difference of the signal to be measured is obtained by subtracting the phase difference between the two channels. The results of Matlab and Modelsim simulation and hardware platform experiments show that the high-precision digital phase detector designed in this article achieves a good level of measurement speed and measurement accuracy. The experimental phase error is only 1.03×10<sup>-4</sup> rad, and the accuracy reached 0.0515%.With the addition of 30dB noise, the average phase discrimination error of 20 times is 1.02×10<sup>-4</sup> rad, which achieve a high accuracy. It is important to achieve a higher accuracy displacement measurement for the LDDM system.
In order to achieve simultaneous imaging of the target. According to the principles of polarization and spectral detection, this paper proposes a laser underwater polarization detection system based on the focal plane method, which is mainly composed of imaging lens, laser, analyzer, liquid crystal tunable filter (LCTF), and focal plane polarized camera. The composition can acquire images of multiple polarization angles at the same time, and realize polarization detection of multiple spectral bands by tuning the liquid crystal tuning filter, and then perform polarization polarization fusion processing on the image by extracting polarization spectral information of the target image. The detection of underwater targets yields the expected image. Through underwater detection experiment, the effects of sediment concentration in water on polarization imaging detection are studied. The results show that the sediment concentration in water has a great influence on the polarization image acquisition.