Design And Development Of Pulsed Laser Power Supply And Photodetection For Optical Time Domain Reflectometer

With the rapid development of optical communications, optical fiber communication technology is widely used in telecommunications, electricity, broadcasting and other fields.Optical fiber has become the most promising transmission medium. At the same time, the fiber test technology has been studied extensively in the engineering field of fiber production, laying and later maintenance, etc. Optical Time Domain Reflectometer(OTDR), also named optical backscatter tester, is an optical test device that characterizes the physical performance of fiber optic link. This device is mainly used to test the entire fiber link length, to pinpoint breakpoint location, and to calculate the fiber loss and provide the details of losses related to the fiber length. The laser power and pulse width are key factors that limits the realization of long-distance and high-precision measurements for OTDR. According to this point, a laser pulse transmitter module which enables the power and pulse width of the laser to be tunable is designed to efficiently improve the performance of OTDR.Through introducing the operating principle of OTDR, key factors that influence its performances are determined and a means of heightening the function of OTDR by designing a laser transmitter module of tunable power and width of laser pulses is proposed. The working principles of semiconductor lasers are also discussed in detail, and schemes are proposed and compared between each other, based on which the MOSFET is determined to serve as the switch component for the driving of laser pulses. The power compression technology is chosen as the guiding method to produce narrow pulse, and the design proposal of OTDR is then confirmed. The system hardware circuit is simulated and optimized with the help of Software Multisim 11 leading us to the realization of a high power and narrow width output of laser pulses. Photodetection system uses APD as the photoelectric conversion element. Finally, an FPGA-based system possessing functions of both laser pulse emission and photodetection has been successfully developed.The developed system can produce laser pulses with a minimum pulse width of 33 ns as well as a tunable peak current as low as 1A. A 1 km fiber length measurement in corporate with the laser pulse driver has been performed with the photodetection system.The result indicates that the signal of narrow width and high peak current provided by the system can greatly improve the resolution and enhance the optical time domain reflectometer dynamic range of OTDR.This design of laser driver power supply and optical detection system, not only can be used to develop a variety of OTDR equipment, but also be applied to a conventional semiconductor laser system. Its applications area can promote from a simple fiber test system to covering the entire laser length-measurement field of military and civilian. So results of this research have important application value and social value.