Design For The High Precision Temperature Control System Of External Cavity Semiconductor Laser

Currently, external cavity semiconductor laser has many advantages such as lowthreshold, long life, small size, high reliability and high conversion efficiency, so it iswidely used in the field of scientific research, communications, defense, precisionmeasurement and old atom physics. External cavity semiconductor laser is very sensitiveto temperature change. The caloric generated in its own work seriously affected the outputcharacteristics. Therefore, we designed and developed a high-precision external cavitysemiconductor laser temperature control system which is based on the C8051F seriessingle chip processor controller．Firstly, we detailedly analyze the influence of temperature on the output characteristicsof external cavity semiconductor laser, the characteristics of temperature control, as wellas the current domestic and foreign common temperature control methods. Thistemperature control system uses a negative temperature coefficient thermistor as thetemperature sensor. We analyze the mathematical model of the negative temperaturecoefficient thermistor, accurately establish a correspondence table among of the thermistorvalues, temperature values, and the sampling voltage values.Secondly, we completed the design of temperature control system circuit withC8051F021microcontroller as the core. Temperature acquisition circuit has flexible andaccurate characteristics, can real time adjust temperature sampling value and eliminate thereference voltage drift and volatility impact on the sampling results. In the drive circuit,we use a thermoelectric cooler (TEC) as the actuator, which is small size, pollution-free,high temperature-controlled precision. In order to control the TEC heating or cooling, themicro-controller outputs the pulse width modulation (PWM) to drive the bridge circuit, toachieve the fast, two-way, low-power requirements.Finally, in the software design, we use the more mature digital PID control algorithm. Inorder to make the system’s temperature control more accurate, faster response, smallerovershoot, we must improve the digital PID control algorithm such as variable speedintegral, incomplete differential and algorithm calibration optimization processing. The experimental results show: The measurement resolution of this system is0.01℃.The temperature control accuracy is about±0.04℃. The set-up time of thesystem is about5~7minutes.