Design Of Drive Circuit And Temperature Control System For Semiconductor Laser Diode

Laser technology develops rapidly in 21 st century.Currently,laser technology has been widely used in various fields such as national defense,industry,biology,medicine,communication and so on.The development of laser technology is closely related to the invention of semiconductor laser diode.Semiconductor laser diode is a device that can generate stimulated emission by using a certain semiconductor material as a working substance.As a precision optoelectronic device,whether a semiconductor laser diode has a good output depends on its input current and operating temperature.On the on hand,in the semiconductor material,the changes of the current will cause the effective refractive index different,which affect the output power of semiconductor laser diode;on the other hand,the changes of the temperature will make the cavity's length changes because of expansion and contraction,thus affecting the center wavelength of laser.Usually with the increase of temperature,the center wavelength of laser will be shifted from 0.02 to 0.2 nm/ ?.Therefore,it is very important to achieve precise control of the current and temperature for semiconductor laser diode.The design focuses on constant current driving and constant temperature control for OCLARO's LC96A74 P 980 nm pump laser diode,making its output stability.First the LC96A74 P 980 nm pump laser diode will pump the erbium-doped fiber,then passing the erbium-doped fiber laser system,which composed of two stage amplifiers.Finally the system will generate femtosecond laser,the laser's wavelength is 1560 nm and power up to 500 mw.The design of the constant current driving mainly includes the introduction of circuit design principle,the design of power supply,the selection of MCU,and the analysis and control method of the constant current drive chip.By controlling the constant current driver chip precisely,we can driver semiconductor laser diode,monitor laser current,protect the circuit,etc.The design of temperature control system mainly includes the introduction and measuring method of NTC,the principle and application of thermoelectric cooler,the analysis and control method of efficient TEC controller and the other peripheral circuits.By controlling the efficient TEC controller to realize the temperature control of semiconductor laser diode,acquisition target temperature,according to the comparison of target temperature and the setpoint temperature to cooling or heating,etc.This design uses STM32 as the control core.The CPU adjusts A/D(ADS1256)and D/A(DAC8501)precisely under the UC/OS-II operating system environment.D/A will output voltage,the accuracy of voltage is 0.1mV,and the voltage controls the linear change of semiconductor laser current;at the same time A/D collects the real-time current value of semiconductor laser diode and then feedback the value to CPU to coordinate,CPU will adjust the data according to the feedback data.In the meantime,CPU will also control the efficient TEC controller to make the temperature stable.The thermistor,compensation network and TEC will form a closed loop temperature control system,so that the semiconductor laser diode will work at constant temperature condition,ensuring the stability of the laser output.Finally,by analyzing the data of testing,the correctness and feasibility of the method which described in this paper are verified.The results show that,the design can provide 0~2A driving current for LC96A74 P series 980 nm pump laser.At the same time,the working temperature is stabled at 25 °C and the error is not more than 0.1 °C,that make LC96 P series of semiconductor laser diode produces high quality light source.