Research On Decoupled Control Theory And Methodology For Laser Diode

Laser diode (LD) has been widely used, as a new light source, for its superiority of small size, light weight low driving voltage and direct modulation. Laser diode is very sensitive to environment temperature and driving current. So even the tiny fluctuations will cause remarkable changing of its output light power and parameters, and may cause serious damage of laser device. Therefore, temperature and current of laser diode should be well controlled in practical applications.To further enhance the output performance of laser diode, mathematical relationship between TEC working power and radiator equivalent thermal conductivity is derived by analyzing of thermoelectric cooler(TEC) working characteristics and using one-dimensional heat transfer equation. Temperature control efficiency could be improved by increasing equivalent thermal conductivity was proved. So that an optimization method using finned tubular radiator in LD temperature controller was presented, including theoretical foundation of radiator selection and system structure. Improvement the dirver of TEC that a comparison amplifier MOSFET-bridge circuit as PWM temperature control driver for laser diode(LD) was designed according to the characters of TEC. The low efficiency of linear driver is solved, and the MOSFET-bridge's nonstop in the traditional PWM drive circuit for TEC is avoided. By taking method as protection and isolation,mutual disturbing effect between LD's drive part and temperature control module is reduced, and consequently the system's antidisturbance ability is increased. To the question of the circuit nonlinearity, a linearization program was developed, which improve the system control precision. To increase the control precision and linearity of current by improve the constant current power, and add the constant current control mode to the system softeware. By collection device's temperature data which influenced by TEC's current and LD's current, the power-temperature coupling model of LD was built. Using feedforward decoupling compensation algorithm decoupled the model. The method can improve the temperature control effect, which was proved by analysis and simulation by Simulink. The asynchronous decoupling compensation algorithm, based on the feedforward decoupling compensation algorithm, was investigated, and the control program was designed.The experiment result indicates that the output power error of LD's driving system was successfully kept around 0.01W within 30 seconds. After using heat-pipe radiator and TEC driving circuit based on PWM comparion amplifier, the temperature error of the system was kept less than±0.1℃within 100 seconds at laboratorial enviroment. By simulating decoupled control algorithm, it was proved that the method can sucessfully improve the system performance. It was proved by the experiment that the control effect of system's output power can be improved by asynchronous decoupling compensation algorithm. In the last part of this paper, the existing problems and future ameliorations were given out.