The Study Of Weak Optical Signal Measurement System Based On Pseudo-random Sequence

Optical signal in optics application and optical fiber performance testing is very weak and easily mixed with interference and noise in signal transmission. How to detect the weak optical signal precisely is increasingly arousing people’s attention. Therefore, employing new detection technology is the key to solve the problem. With the development of science and technology, researchers study on detection methods of useful signal submerged in noise ceaselessly and try to make these methods advanced, convenient and widespread.A new method of detecting weak optical signal which can eliminate interference and noise is proposed in this thesis on the basis of spread spectrum communication and the correlation property of pseudo-random sequence. The thesis consists of the following parts:Firstly, the properties of pseudo-random sequences are elaborated. The correlation between noise and weak signal is analyzed, which provides theoretical basis for reducing noise interference over signal. One of the pseudo-random sequences-m sequence-is analyzed in detail and it can be generated by linear feedback shift register.Secondly, the principle of pseudo-random sequence and spread spectrum communication are studied. The theories provide foundation for weak optical detection system. The relationship between correlation peak and signal intensity and its impact on SNR(signal to noise ratio).Thirdly, the spread spectrum modulation model of signal and pseudo-random sequence is established in DSP Builder software. The detailed design is studied and the desired signal can be obtained by setting model parameters.Finally, The hardware circuit design is completed by designing the synchronization and despreading module of the proposed detection system in Multisim software. The test and simulation of the circuit are conducted and the experimental results verify the feasibility of the usage of pseudo-random sequence in weak optical signal detection. The technology has strong application value and it is suitable for the detection of common light signal and weak optical signal.