Pfm Optical Transmitter Design

In this paper,the design of the PFM optic transmitter is developed. It includes discussing the PFM optic transmitter's theory, introducing the way of design in detail, showing the circuit with practical worth and proving it's rationality and workability by the debug results. The work in this thesis includes several parts as follows.The structure of the transmission system in the PFM optic transmitter is designed. The transmitter transfers three lines of signal including one line of audio signal, one line of video signal and one line of data signal which are pretreated singly at first, then processed by the way of the FDM, the PFM modulation, the driving laser source and finally transformed the light pulse and feeded in the fiber to be transmitted.The laser source as the key part in the PFM optic transmitter is analyzed. We put attention to the laser here. The performance and the theory of the laser are showed. At the same time the two kinds of the main peripheral circuits are discussed. In addition, considering the requirement of the fiber transmission system for the light source, we choose rationally the light source equipments so as to gain the best effect.The PFM as the key technology in the PFM optic transmitter is discussed. The PFM technology includes two kinds modes: constant width PFM and SWFM. The SWFM mode is adopted as the modulation of the optic transmitter in the circuit's design by researching the advantages and disadvantages when the two ways are used to transmit the signals. The MC1658 which is adopted by the most designers is used to accomplish the SWFM modulation here. But the constant width PFM technology is applied in the receiver.The other two important technology, namely the FSK and FDM are presented. The FSK is used in the modulation for audio signals and the data signals. And the FDM is used to merge three lines signals.The circuits are designed and made into practicality on the basis of the rational structure. In addition, the expectant results are gained by the long time debug. The PFM modulation makes the frequency spectrum broadened and the transmitted messages depend on the exact position of the pulse edge. So the quality of the transmission will be advanced and the signal and noise ratio will be improved.