Signal processing for distance measurement using laser voltage fluctuation due to self-coupling effect

When a part of the scattering light from the target is entering to the laser cavity, the terminal voltage of semiconductor laser diode slightly fluctuates. This voltage fluctuation has the information related to a distance to the target. However, the terminal voltage fluctuation has many noises. Discrimination of distance signal with many noises is almost impossible. Therefore, a statistical signal processing which utilizes the all information in terminal voltage fluctuation is newly proposed. A system is constructed using Field-Programmable Gate Array (FPGA). This system can measure the distance of 21cm to 45cm with the average error of about 2 %.