Study Of LD Temperature Control System Based On Fuzzy-PID Control Theory

Semiconductor laser diode (LD) has wide applications in many fields such as interferometry and LD-pumped solid-state laser (DPSSL), etc. As is known that LD wavelength is temperature-tunable, research results indicate that LD wavelength drifts by ~0.3 nanometer when the LD temperature changes by 1℃. So it is essential to control LD temperature strictly. The temperature control of small or middle power LD is investigated in this thesis, and a kind of high stability LD temperature control system has been developed, which takes MCS-51 as the controller and thermoelectric cooler (TEC) as the temperature control conduct device.The thesis mainly includes five parts as follows: First, the influence of temperature on LD output characteristics is analyzed and the research status of LD temperature control techniques is investigated. Second, on the basis of the theory of automation control, the design scheme is presented and its feasibility is analyzed. Third, as the key unit of the control system, the fuzzy PID controller is designed based on the fuzzy PID control theory. The design process is as follows: Above all, the method of critical proportional band is used to get the initial value of parameters of digital PID. Then the temperature deviation and its change rate of LD are input to the controller, the three parameters of digital PID, which are proportional coefficient, integral and differential time, are modified real-time according to the fuzzy relationship. Finally, the digital controlled quantum can be produced, D/A converted, power-amplified to drive the TEC element, thus the purpose of controlling LD temperature is achieved. Forth, the hardware and software are designed. Fifth, the LD temperature control system has been established, and it has been used to control the temperature of a LD with an output optical power of one watt. The experimentally obtained results indicate that the LD temperature can be set within the range of 10℃～40℃, and thestability of temperature control system is better than 0.2℃, and the adjustive time is about 3 minutes.