中文2540字Laser driver circuitSmall changes will directly semiconductor laser drive current to the output intensity fluctuation. To stabilize the output power semiconductor laser, Voltage negative feedback principle to design a constant current driving circuit comprises a soft starting and current limiting protection circuit based on; At the same time, according to the need of the light source is modulated to eliminate the influence of background light and, integrated laser modulation circuit comprises a crystal oscillation circuit and divider circuit design. Making the specific circuit and complete the relevant experimental. The experimental results show that the circuit can provide a driving current of high stability, Current stability up to 0.05%; Soft start and current-limiting protection circuit can protect the semiconductor laser and enhance the impact capability. Modulation circuit generates a carrier signal needed for laser diode modulation and direct to complete the output light modulation, The switch can be conveniently realized from 256Hz to 512kHz range of 12 kinds of commonly used modulation frequency selection.Semiconductor laser with its excellent characteristics, high efficiency, simple structure, small is widely used in scientific research, national defense, medical, and other areas of processing, its drive technology becomes more and more important. Semiconductor laser is the ideal electron - photon direct conversion devices, quantum efficiency is very high, the current small changes will lead to a great change, the output light intensity of the therefore, semiconductor laser drive current requirements is very high. Driving technology of semiconductor laser usually adopts constant current drive mode, this work, through the principle of negative feedback control loop, directly provide the effective control of the drive current. In addition, the transient current or voltage spikes, and overcurrent, overvoltage will damage the semiconductor laser drive circuit, therefore should be considered in the protection circuit against electric shock measures and special.In some applications, DC semiconductor lasers produce DC drive light in the measurement process is vulnerable to interference from ambient light slow change, which could not be separated from the environment light required DC optical signal, the signal-to-noise ratio is too small, so to carry on the modulation. When the high-speed modulated semiconductor lasers, there will be dynamic characteristics is complex, such as the relaxation oscillation, since the pulse and multi-pulse phenomena. In this paper, experiments were conducted to study the characteristics of low frequency modulation. Semiconductor laser output is stable, and can be directly modulated, it has been widely applied in optical system, is the preferred source sensor system. This paper describes the design of a high stability driving current, modulation, simple operation and low cost driving circuit for the light source of optical fiber systems.In this paper, the design of driving the semiconductor laser modulation circuit composed of four parts, including constant current circuit, a soft start, current limit protection and modulation signal generating circuit. The constant current circuit to generate a high stable drive current. Soft start is the role of eliminating surge may be present in the circuit, to prevent the harm of surge for laser. To avoid damage due to overcurrent caused by semiconductor laser can not be restored, then adding current-limiting protection in a driver circuit. Circuit to realize the modulation and frequency can be adjusted to generate a modulated signal. The constant current circuit is shown in figure 1, The in-phase end voltage reference Vr into A1 op amp, the operational control amplifier conducting level, and thus to obtain the corresponding output current. The output current generated by sampling voltage sampling resistor Rs, the sampling voltage is amplified as the inverting input voltage feedback voltage feedback amplifier A1, and voltage and the in-phase input end of comparison, Q2 to adjust the output voltage through the triode, adjustment and output current of semiconductor lasers, so that the whole closed-loop feedback system in the dynamic balance.Figure 1 Constant current mapBecause the switch instantaneous in power supply generates a voltage, current surge, as well as the surge interference effects are likely to cause the breakdown and the damage of the semiconductor laser, and therefore must be in the design of soft start circuit drive laser, namely the use of the charge and discharge of RC circuit, delay time, the specific circuit as shown in Figure 2 as shown in. Switch S1 is closed, the current through the resistor R1 and capacitor C3 to charge, the base electrode of the triode Q voltage gradually rises. As the capacitor charging and the conduction of the triode, output voltage Vo is achieved from 0 to the maxim