Abstract:

Aiming at the problem of seed-source mode-locked stability monitoring of picosecond lasers, a digital measurement system of laser pulse repetition rate based on field programmable gate array (FPGA) is designed. The system uses multiple phase-shifted high-frequency standard clock signals generated by the phase locked loop (PLL) of FPGA to count and measure the time gate generated by the input optical pulse signal, and uses the method of amplitude limiting filter and arithmetic average filter to obtain more accurate and stable frequency measurements to strengthen the anti-jamming ability of the system. The proposed system measures the signal to be measured at 80 MHz, the theoretical measurement accuracy can reach 31.7 Hz, and the relative accuracy can reach 3.96×10^-7. According to the experimental test results, the actual accuracy is about 18 Hz, and the relative accuracy is 2.25×10^-7, the system design is verified to meet the accuracy requirements. The result shows that the proposed system can accurately sense the repetition frequency change of picosecond seed laser pulse in MHz, which provides a basis for further judgment and control of mode-locked stability, and also has significant reference value for other industrial frequency measuring devices design.

Key words: picosecond mode-locked laser, pulse repetition rate, field programmable gate array (FPGA), equal precision periodic measurement, filter processing