Study On Theory And Technology Of Pulsed Constant Current Source Applied In Semiconductor Laser

Nowadays there is a rapid development in semiconductor laser because of its characteristics: small, light, simple-constructed, cheap, easy-adjusted and long-life. It has been a core technique in nowadays optoelectronics and widely used in military, industry, transportation, medicine and scientific research and other fields. Pulsed semiconductor laser is focused on in laser field because of its special advantages. In order to make the semiconductor laser work normally, we have to offer proper, steady pulsed drive current for it. In fact, semiconductor laser is a diode. Its request for pulsed constant current source that offers it drive current is that it can produce super fast current pulse in load with low impedance. So we can see that pulsed constant current source is a current switch for the semiconductor laser. Its working load has diode's volt-ampere characteristics. The voltage on the two ends of semiconductor laser consists of the voltage of p-n junction and the voltage of series resistance, so pulsed current source can provide big enough voltage pulse as well as high-peak current pulse. What's more, when the current goes through the semiconductor laser, the temperature of its p-n junction will rise. It will lead to the going-down of the output power of semiconductor laser. So in the working mode of large pulse drive current, the shorter the rise time and fall time of pulse current are, the narrower the pulse width is, the semiconductor laser will work better. From above, we can see: in order to use semiconductor laser in reason, make good use of its potential capability, improve its work efficiency and improve the quality of output laser, we should design the pulsed constant current source that has high-peak current, narrow pulse width, short rise time and fall time and is suitable for semiconductor laser. Therefore, the study on pulsed constant current source with steady performance is an important and meaningful theory. Its development will promote the rapid development of military field, industry field, medicine field and push the social improvement and GDP forward.This dissertation focuses on the design method of pulsed constant current source applied in semiconductor laser and relevant pulse transmission theory and pulse measurement method. The specific work and innovative achievements are as follows:Pulsed constant current source is actually a device that is able to produce pulse current. Its output current is related to the following main parameters: pulse peak current, pulse width, rise time, fall time, pulse duration ratio and frequency etc. The basic pulsed constant current source includes: pulse generator, pulse amplifier and peak current adjustment, pulse width adjustment, rise time adjustment, frequency adjustment circuit etc. Among them, the key circuits are pulse generator and pulse amplifier. Further more, the core components used in the circuits are different, so are the parameters of the generated current pulse. At present, in pulse generator and pulse amplifier, the usual and core components are avalanche transistor, power MOSFET, insulated gate transistor (IGBT) and step recovery diode (SRD) etc. This dissertation analyzes the characteristics of these components and their working principles, designs some pulse circuits made up by them, analyzes the principles and characteristics of these circuits and does some simulations and experiments. This dissertation presents a method of generating a kind of high-voltage nanosecond level narrow pulse. This method uses the avalanche transistors as high-speed component and uses Marx circuit model as experiment circuit. In the simulation circuit, we obtain the output pulse with pulse width 0.81ns and pulse amplitude 28.3V. In the experiment, we obtain the narrow pulse with pulse width 2.39ns and pulse amplitude 23.3V. In the experiment, we overcome many technology problems about the generation of narrow pulse and the experiment productions can be widely used in the future. Power MOSFET has the following advantages: high input impedance, voltage control, simple control circuit, low driving power, high voltage endurance, large working current, high output power, perfect linearity of transconductance, rapid switching speed, no second breakdown phenomenon, no losing control phenomenon of the drain current etc. Because of these characteristics, in this dissertation we design a pulsed constant current source applied in semiconductor laser with power MOSFETs as core components. The dissertation introduces its formation principles, each part's function and specific circuit. We also do some simulation tests for each circuit. In the simulation tests of the core circuit, we obtain the nanosecond level pulse with peak current 21.2A. In its experiments, we obtain the nanosecond level pulse with peak current 20.0A. We can also adjust the circuit parameters according to what we need to get the current pulses with amplitudes range from 6A to 25A. By comparing and analyzing, we find that the experimental data is almost the same as the simulation results. Therefore, the purpose of generating the pulsed constant current with narrow pulse width and high-peak current is realized successfully.There will be signal transmission problems after the pulse signal appears. In this dissertation, the pulse width of the pulse current signal is in the range of nanosecond level. So its bandwidth is very wide. The frequency spectrum of the pulse can be enlarged to over 100MHz. Therefore, the transmission line effect has to be considered even though the lead is several centimeters long. The transmission line theory plays a really important role in high-speed pulse transmission. The dissertation introduces several usual pulse transmission lines'geometric figures, relevant distributing parameters and in-line transmission line's equivalent circuit. It also does the following work: (1) analyzing the transmission characteristic of the pulse signal in transmission line with Laplace transform; (2) analyzing the reflection phenomena in the transmission line with different impedance loads or joints; (3) bringing up the methods to eliminate the reflection signal.Finally this dissertation introduces some related parameters in the process of pulse measurement and several main measuring methods of pulse parameters. It analyzes the principles in selecting oscillograph and the possible errors in the process of pulse amplitude and rise time measurement when oscillograph is used to measure pulse signals. It also introduces two methods to measure pulse amplitude. These will establish the foundation for the future pulse measuring work.