Research On The Modulation Of Microwave Optical Fiber Transmission Technology

Due to the adoption of fiber communication-induced multiple advantageous including broader available network bandwidth, lower signal power attenuation, and negligible electromagnetic interference, Radio-over-fiber technology（RoF） has been an attractive scheme in recent decades. It plays a vital role in some fields, for example mobile communications, wireless local area networks, intelligent traffic systems as well as military systems. However, in RoF systems, the nonlinearity of optical modulation-induced third order intermodulation components（IMD3） have significant effects on the microwave signals and further limit the spurious-free dynamic range（SFDR） of the RoF systems. The main purpose of this thesis is thus to find the practical approaches to suppress the third order intermodulation components and to improve the SFDR of Ro F systems. The main works of this thesis can be divided into the following three parts:1) To settle the nonlinearity effects of MZ modulation, a scheme has been proposed by introducing IMD3-compensated signals at input side, and their formulas have been the theoretically explored. To accelerate the searching process of optimum value of IMD3-compensated signals, a heuristic algorithm has been proposed to optimize the theoretically-derived formulas. The numerically-simulated results shows that in the case of noise floor power being of-165 dBm, when taking radio frequency（RF） signals with their central frequencies of 18 GHz and 18.1GHz being the input signals and employing IMD3-compensated signals, the employment of IMD3-compensated signals leads to a SFDR as much as 145 d B.Hz^2/3, which equivalently introduces approximately 40 dB SFDR improvement compared with the non-compensated MZ modulation RoF system. It has been also verified that the three order transfer inhibition ratio has about 170 dB improvements compared with the non-compensation case.2) A scheme has been proposed to address the nonlinearity of phase modulation via employing IMD3- compensated signals, and heuristic algorithm has been used to simplify the corresponding theory formulas and thereby accelerating the searching process of optimum values of IMD3-compensated signals. The simulation results shows that when input RF signals at 18 GHz and 18.1GHz have the same noise floor, 20 dB SFDR increase can be observed compared to non-compensation situations. The use of the proposed scheme introduces 107 dB improvement for three order transfer inhibition ratio.3) Experimental verifications have been made for the schemes of using IMD3-compensated signals to settle the nonlinearity effects induced by MZ modulation. The measurement experiment results verify the feasibility of proposed schemes. When double-tone signals have the frequencies of 1GHz and 1.1GHz and the noise floor is-160dB/Hz, SFDR can be 105 dB.Hz^2/3.