High-precision Temperature Control Semiconductor Laser Drive System

Based on the operation principle and characteristics of laser diode which are introduced in detail in this essay, a driver for pulse operating laser diode is proposed and designed. This driver consists of a pulse generating module and a temperature control module. It is capable of generating large current and narrow-width pulse as well as stabilizing the wavelength generated by laser diode, so as to ensure the safety of laser diode.Compared many ways of generating pulse, a design using the avalanche transistor as the main component of pulse generator module is established. A kind of avalanche transistor FMMT417 produced by Zetex company, which is specifically designed for avalanche mode operation is selected as the core component. The pulse generating module consists of trigger pulse grade and avalanche transistor narrow-width pulse generating grade. The trigger pulse grade uses integrated component as the pulse generating and shaping circuit. The trigger pulse is passed to the pre-avalanche composed of a single avalanche transistor, and then delivered to the Marx Bank avalanche circuit as a trigger. Thus a large current pulse with the amplitude of 1.35KV, the width of 1.85ns and the peak to peak current of 27A is obtained. The circuit has such characteristics as short rise time, large amplitude, narrow width, variable frequency, and so on.The temperature control module for laser diode is the key point of the main project, which is mainly composed of temperature sensor sampling circuit and temperature control and thermoelectric cooler driver circuit. The negative temperature coefficient thermistor is used as the temperature sensor for temperature sampling. The temperature control circuit uses the microcontroller as the key component to sample the output signal from the temperature sensor circuit to do the A/D conversion, and use the software program to make the microcontroller output controlled quantity to switch on and off MOSFET to achieve pulse width modulation. In this way, the average current goes through TEC can be precisely controlled, so the temperature of laser diode can be controlled and stable. The temperature can be set by LCD,keyboard and RS232 bus, and the temperature control module can set the maximum and minimum alarm temperature point , in case that the laser diode is operating at an abnormal state. By the experiments, the results show that the temperature control module can achieve the temperature controlling accuracy of±0.1℃。The driver for pulse operating laser diode designed in this paper can produce pulse with large current, high amplitude and narrow pulse width. In the mean time, the temperature control module can achieve high precision, and real time temperature control. Moreover, the temperature control module can control the current goes through TEC by the cooperation of pulse width modulation and power switch component, in this way the D/A chip can be saved to cut the system budget.Common components are used throughout the whole system designed in this paper, which are cheap and small,very suitable for the research institutes such colleges to research and use.