| With the rapid development of internet and mobile communication and wireless communication users’ higher requirements on the speed of information transmission, the radio frequency band resources have becoming scarcer and scarcer. At present, almost all low-frequency resources have been occupied. Besides, the electronic bottleneck has made it impossible for long-distance microwave signals transmission. Therefore, it is quite difficult to generate microwave signals within the electric range and the cost of instruments will be quite high.The connection from the optical communication terminal to the user terminal is not so flexible in form now. To solve this problem, the more flexible wireless form of connection is often adopted. However, another problem we face now is that the width of the frequency band is quite limited is unable to meet the needs of multimedia communication operations. In this case, the frequency band of wireless connection is required to rise. Therefore, the current new requirement is to develop transmission frequency band(microwave frequency band) of tens of GHz. The problems existing in producing microwave signals of such frequency band through the current electronic methods are that the microwave signals generated has too low frequency band, is unstable and has too many spurious signals. However, the producing of microwave signals through optical method will be quite easy. The advantages of optical fiber communication include long distance, big band width, low wastage, etc., and the advantages of microwave communication include shot distance, flexible form of wireless connection, etc. This thesis is to make connection between optical fiber communication with wireless communication, take advantages of each and find the way to generate and transmit microwave signals within the optical range.This thesis mainly focuses on researching the optical frequency multiplication method to generate microwave frequency multiplication based on the M-Z modulator harmonic mixing. It is aimed at increasing the microwave signals of frequency multiplication and has analyzed the fundamentals and working process in detail.The optical frequency multiplication method based on the M-Z modulator harmonic mixing mentioned in this thesis takes optical wave as the carrier and modulates RF modulating signal to the continuous laser wave through the M-Z modulator. After modulation, the continuous laser wave will output spectrums ofharmonic components of each order with modulation signals. Other high-order harmonic components can be constrained by changing the bias voltage of the M-Z modulator so as to get either odd-order frequency or even-order frequency as needed.The amplitude of harmonic components of each order in the already modulated spectrum can be changed by changing the amplitude of the radio-frequency signal so as to form the highest amplitude of n-order harmonic components and constrain other harmonic components. In this way, the ideal n-order harmonic components can be filtered out. After that, using two band-passing optical filters to filter out the needed ±n-order harmonic components, after shifting the optical and electric signal through optical detector and finishing the frequency mixing, the microwave signals of relevant frequency multiplication will be finally output. Considering the limit conditions of the instruments and the influences on the transmission process, this thesis has made an analysis on the optical frequency multiplication method based on the M-Z modulator harmonic mixing.Moreover, this thesis has made simulation experiments on the optical frequency multiplication generate system based on the bias M-Z modulator harmonic mixing, has provided experimental simulation system, has made simulation experiments on microwave signals of doubled frequency, quadruplicated frequency and sextupled frequency, and has made analysis on each simulation result. The relatively ideal simulation results shows that this system has better performance in noise suppression and can get microwave frequency multiplication signals with high signal-to-noise ratio(SNR), proving the feasibility of this method. |
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