Real-time Control Technique For The Laser Power In FSO

Optical wireless communication, namely Free-Space Optics (FSO), springs up again along with urgent requirement for high speed, huge capacity, low cost access in information society and the progress of the high power semiconductor lasers and optoelectronic detectors. Optical wireless communication has been widely used in many fields since it integrates the advantages of fiber communication and other traditional wireless communication technologies, such as large capacity, low cost, convenient deployment and flexibility.The design of optical transmitter is mainly concerned in this thesis and the real-time control system for the laser power is also produced. The main parts of the thesis are as follows:(1) Based on the widely learning of references, the character and applications of optical wireless communication are reviewed in the first chapter, and the research status is introduced in brief.(2) Investigations of theory and numerical simulation in regard to optical wireless communication are obtained as optical signal transmitting in the atmosphere. Performance of the system is analyzed, which is influenced by the geometrical spreading loss, the laser transmitting power, atmospheric attenuation and the link range. Then the scheme of transmitting system suiting for communication is chosen.(3) Circuits for driving semiconductor laser, temperature control and detecting are designed along with theirs advantages of simple configuration, low cost, easy realization, which can add the square-wave signal of 20MHz to the laser.(4) Since the received optical power by the receiver of optical wireless communication is very sensitive to different atmospheric attenuation, an effective power control system for the laser is put forward by comparing different schemes. This power control system can precisely inspect the atmospheric attenuation and adjust the laser transmitting power according to the weather condition.(5) The testing results are analyzed at the end of the paper, which illustrate that the system achieves the requirement of optical wireless communication on laser transmitting, signal loading, signal receiving, real-time adjustment for laser power etc.