Study Of Drive Modes And Reliability On Semiconductor Laser

Since the first semiconductor laser(laser diode) was invented in 1962, the semiconductor laser technology has changed dramatically, which greatly promoted the development of other science and technology and was considered as one of the greatest inventions in the 21th century. Semiconductor laser diode has the excellent character of high efficiency, small size, low weight, high reliability, direct modulation, but semiconductor laser diode is a kind of device with high power density and sky-high quantum efficiency. Even weak drive current and temperature change will lead to its large change of output light power and device parameters, which directly damages the safe use of laser diode, so higher request to the laser diode driver is put forward.This paper describes the model constitution and drive circuit design of high-power laser diode (LD), which works in constant current mode, constant power mode and constant voltage mode, based on the electrical characteristics of high power LD. The reliability of drive modes are analyzed and researched. By model constitution and analysis, the relations between the control voltage and the output current are set up, respectively.The function of constant current drive mode is to provide a stable drive current for laser diode. It focuses on improving the stability of drive current and obtaining the enough large drive current. The constant current drive circuit is mainly composed of voltage benchmark circuit, voltage-current conversion circuit, feedback circuit, and current-sample circuit. The control voltage unit is a high stability reference voltage source, which may provide the voltage reference for the whole circuit. In general, the reference voltage source is the core of drive circuit, which determines the stability level of drive current. The voltage-current (V-C) converting circuit is mainly composed of the operational amplifier and high-power Metal Oxide Semiconductor Field Effect Transistor (MOSFET). The maximum current of drive circuit depends on the work current of MOSFET. The feedback control unit is composed of resistor network. The feedback voltage comes from the voltage of sample resistor. The whole design idea is to use the principle of negative feedback to stabilize output current, which obtains the lowest current error and the highest current stability.The most important characteristic of laser diode is the effect of temperature on the relationship between the LD's optical output power and the injection current. When the laser diode operates in a long period, the output optical power will be variable owing to many kinds of reasons, but we hope that the laser diode can maintain relatively constant light power. Therefore, laser diode is necessary to work in the mode of constant power.The principle of constant power drive is: PD converts the change of output light power of laser diode into the change of diode current, and the change of current is feed back to voltage-current converser which adjusts output current of driver to compensate the laser diode. So, when output light power attenuates, driver will increase output current accordingly; when output light power increases, driver will reduce output current accordingly.For the semiconductor laser array, the constant-voltage drive mode is put forward. The basis of constant-voltage driving is the constant-curreent for one laser diode in the laser diode array.When one laser diode of semiconductor array has been destroyed owing to some reasons, the others laser diode will be destroyed by the very large drive current. The drive current in constant-voltage mode can be automatically adjusted by constant-voltage feedback network. The work principle is that the feedback voltage and the control voltage ensure the drive current of laser array by the negative feedback control. For the whole laser diode array, the drive mode is the constant-voltage drive. The constant-voltage drive ensures the safe use of the laser diode array.If we want to improve the drive circuits'reliability and stability, we must consider the choice of parts and solve dispersing heat. We should dispose of dispersing heat well due to the large output current of whole constant current driver. If we can't solve the heat issue, parts will change specialty because of high temperature. As we all known, high temperature also can make parts permanent invalidation owing to pole touching and semiconductor layer melting. The basic task of dispersing heat design is that we can make a heat flow circuit having the lowest heat resistance according to principle of heat transfer and we should keep parts heat be thrown off. In this way we can ensure internal knot temperature lower than allowable temperature when parts run. This paper describes the details of radiator design and how to select the method of dispersing heat.In order to preclude the possibility of the injected current exceeding the maximum safety current, especially when mode shifts of laser diode take place, the current-limit circuit is designed. Its work principle is that the limit voltage decides the maximum drive current, even if the control voltage is above the control voltage. If the maximum limit voltage is set, the maximum operating current is set by the limit voltage. That is to say, no matter how we adjust the control voltage, the operating current must not overshoot the maximum operating level.For some laser diodes, the over-current protect is necessary. If the control voltage is below the control voltage, the drive current is decieded by the controle voltage; If the control voltage is above the control voltage, the drive current is zero just now, which can ensure the safe use of the laser diode.When the laser diode works normally, we should watch for possible intermittent or unreliable connections between the laser diode and the drive circuit. In order to ensure that spikes, surges, and other switching transients are effectively eliminated, the soft start circuit is designed. Its work principle is that the drive current is on the laser diode slowly. The surge-surrendering circuit ensures eliminating the surge voltage and current.The main work in this paper is supported by the national natural sciences fund project"the super-velocity initiative mode locking optical fiber laser really self-starting and investigation into stability. The content in this paper involves in the electronics, optics and optical-electrical transform. This work mentioned in the paper has positive significance to the wide application of semiconductor laser diode, which solves key questions in the application of semiconductor laser diode.