Research On Semiconductor Laser Control System Applied To Seawater Velocity Measurement

The 21 st century is the century of the ocean,and a maritime power is an important measure in our country’s modernization process.Seawater velocity is one of the important marine dynamic parameters.Laser velocity measurement has become a research hotspot of a new generation of seawater velocity measurement technology due to its advantages of high precision and sensitivity,non-invasive measurement and no electromagnetic interference.In the laser velocimetry system,the optical stability of the laser is the key to ensure the accuracy of seawater velocity measurement.Based on the theory of luminescence of semiconductor lasers,the optical stability of the laser is closely related to the injection current and operating temperature.At present,although commercial lasers have good performance in the control accuracy and stability of current and temperature,their large size and high-cost make it difficult to meet the needs of in-situ velocity measurement of seawater.Based on the above problems,this paper develops a small and low-cost semiconductor laser driver and temperature control system.Based on the analysis of the working principle and characteristics of the semiconductor laser,the relationship between the output optical characteristics and the injection current and the operating temperature is summarized.According to the domestic and foreign research status and project requirements to determine the technical indicators and design scheme,which mainly includes constant current drive and temperature control.In the constant current drive part,the 16-bit digital-to-analog converter chip DAC8501 is used to set the control voltage,and ATLS250MA106 is used as the constant current driving chip to realize the high precision constant current driving of semiconductor laser.Perfect protection measures are designed for semiconductor laser,including anti-surge shock,delay soft start and current limiting protection.In the temperature control part,ADN8835 is used as the temperature control chip,and the temperature value is preset by the upper computer.The temperature information of the semiconductor laser is collected by the 24-bit analog-to-digital converter chip ADS 1255.The temperature set value and acquired voltage are processed by the fuzzy PID algorithm in the central processing unit of STM32.The processing results are converted by DAC8501 to drive the H-bridge circuit integrated in AND8835,so as to control the current strength and direction of TEC,so as to ensure the temperature stability of the semiconductor laser.According to the above design schematic drawing and PCB design,the size of the control system is 120 mm*65 mm is realized.The control system are tested and analyzed,and the results show that the driving current and control voltage have good linearity,and the current stability was tested at 550 mV,750 mV,and 950 mV for two hours,the maximum fluctuation of current was 0.104 mA.The stability was tested at 15℃,25℃,and 35℃ for one hour,with a maximum temperature fluctuation of 0.007℃.The output optical power and wavelength of the laser were tested,the output optical power fluctuated within 0.3 mW and the wavelength fluctuated within 6 pm in two hours.The design was integrated into the flow velocity measurement system for testing,and the water flow velocity signal in the tank was measured.This design achieves miniaturization and low cost under the condition of satisfying the design index,and realizes application innovation.