Optical crystal temperature tuner based on feedforward-feedback compound control

Abstract

To tune the output wavelength of the laser, the operating temperature of the optical crystal needs to be controlled precisely in a wide range. In this paper, a temperature tuning control method for optical crystals with high temperature control precision and large temperature control range based on semiconductor refrigerator (TEC) was studied. The operating characteristics of TEC,the thermal effects and heat transfer mechanisms of optical crystals were analyzed. A temperature-current double closed loop temperature control model was established. This temperature-current double closed loop control model takes control of both the electrical characteristic's variations of working TEC and the temperature variations of the optical crystal. To overcome the inherent hysteresis characteristic of feedback control, the feedforward compensation control based on the double closed loop control was introduced. The TEC driver module based on the ARM+FPGA architecture was designed to achieve the high-frequency and high-precision PWM drive control. In conclusion, an optical crystal temperature tuning system was completed. Experimental results show that the overall temperature control accuracy of this system is better than 0.002ºC and the system can quickly stabilize at any set point temperature in a wide temperature range of -30-130ºC, and it has good robustness to abnormal environment, which meets the requirements of tunable laser for temperature range and accuracy of optical crystal.