In order to meet the requirements of TDLAS gas measurement, a DFB laser drive and temperature control system based on STM32F103RCT6 as the main control chip was designed. On the one hand, the DDS chip AD9834 is controlled to generate a 4kHz high-frequency sine wave signal. On the other hand, the 12-bit DAC on the STM32 chip can easily generate a 20Hz low-frequency sawtooth wave signal.For the sake of filtering out the high-frequency harmonic interference in the DDS output and making the sawtooth wave smoother, a second-order Butterworth-type active band-pass filter and a third-order Butterworth-type active low-pass filter are used for sine wave signals and sawtooth wave signal respectively. And finally the laser is driven to work normally by the adder circuit and the voltage-controlled constant current source circuit. For the DFB laser used in this system, the variation coefficient of the laser center wavelength with temperature is 0.1 nm / ° C. The system is used by a current tuning method to accurately drive the DFB laser to scan the gas absorption spectrum. When the temperature is changed by the external temperature or the laser's self heating, it will cause the laser output wavelength range to change, and eventually affect the gas absorption peak and demodulated harmonics stability. Therefore, it is necessary to control the laser temperature constant. This system is designed by a bridge circuit and a differential amplifier circuit to convert the temperature. The ADC on STM32 chip implements temperature acquisition and the output is obtained through the fuzzy adaptive PID algorithm. The output voltage of the DAC on the STM32 controls the TEC power driver MAX1968 to achieve precise temperature control. In order to meet the needs of system miniaturization, this system is used by a TO package DFB laser with the center wavelength of 1653.7nm for experimental testing. The output optical power is 5mW and the maximum driving current is 70mA. The signal of the sine wave and the sawtooth wave superimposed by the in-phase adder is used as the control signal of the voltage-controlled constant current source. The actual driving current scan range of the laser is 30 \~ 60mA, and the laser temperature is adjusted so that it can output a laser of 1653.72nm. The experiments prove that the STM32-based DFB laser drive and temperature control system can stably generate the modulated current signal, which can achieve precise temperature control. The temperature control accuracy can reach ± ​​0.013 ° C, and a stable gas absorption peak is obtained. This system is designed to meet the requirements of the TDLAS gas absorption detection system for laser driving and temperature control.


Design of DFB Laser Drive and Temperature Control Circuit in TDLAS Gas Concentration Detection

Division / Sponsors: 
Aerospace, Bioengineering, Applied Mechanics, Design Engineering Division, Advanced Energy Systems, Manufacturing Engineering Division, Noise Control and Acoustics, Nondestructive Evaluation, Diagnosis, and Prognosis (NDPD), Nuclear Engineering Division, Process Industries Division, Fluids Engineering, Heat Transfer, Materials, Microelectromechanical Systems, Safety Engineering and Risk Analysis, Computers & Information in Engineering


Paper Proceedings: https://asmedigitalcollection.asme.org/IMECE/IMECE2020/volume/84478

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