Study Of Laser Diode Temperature Control Technology

Now, laser diode (LD) is extensively applied in science and research, national defense, industry fields etc. When LD is applied in some precise instruments, it produces the caloric which greatly influences the characteristics of LD (for example, with LD temperature changed, the wavelength of the LD output light drifts), and so influences the accuracy and lifetime of the instrument. In this circumstance, it is needed to strictly control the changes of LD temperature. The controlled object is the temperature of small or middle power LD. Platinum thermometer is used as temperature sensor. The thermoelectric cooler (TEC) , which is free from pollution and a good cold result,is made as temperature control conduct device. The laser diode temperature control instrumen is developed on microcontroller system in series of MCS-51. Because of the uncertainty of mathematical model of the LD temperature (the LD temperature changes with the input current of LD), and the accuracy of the temperature control system is as high as 0.2℃, the traditional control method is difficult to obtain such an accuracy. So a control algorithm of combining the fuzzy theory with digital PID parameters self-tuning is adopted in the system. The process of control algorithm is as follows: First, the method of critical proportional band is used to get the parameters of digital PID control at certain temperature. Then, the digital PID parameters at some temperature and Lagrange quadratic interpolation are employed to obtain the interpolation equations of P, I and D. Finally, the system is able to self-tune the digital PID parameters of a certain temperature, and produces properly controlled quantum tocontrol the temperature of LD.In order to have better accuracy of temperature control, the whole temperature interval (10℃~40℃) is subdivided. The temperature control system takes the LD environment temperature ( room temperature) as the fussy base point, and divides the temperature control interval ( 10℃~40℃ ) into 6 fuzzy intervals. At each fuzzy interval, Lagrange interpolation is used to carry on self-turning digital PID control parameters, and the system works on the opptimum condition of temperature control. In addition, a temperature data collecting and analyzing system is designed. In the first place, the system samples temperature control data at10Hz sampling frequency, then it saves, analyses and processes the experimental data, and the system respond figure can be obained.some verification experiments have been performed using the whole temperature control system. The results of experiment mdicate that within the temperature range of 10 ℃~40℃, the resolution of the temperature measurement is 0.01℃, and the accuracy of temperature control is 0.2 ℃ (or even 0.1 ℃ at the room temperature,) and the establishing time is about 180 seconds. This temperature control system is an economical and practical system, and provides a good temperature control solution for the small or middle power LD temperature control.