Research On WDM-RoF System Based On Optical Frequency Comb

Radio over fiber(RoF)technology combines the advantages of optical fiber communication and wireless communication,which can effectively solve the problem that high-frequency microwave signals are difficult to transmit over long distances.In order to further improve the communication capacity and reduce the construction cost of the RoF system,combining the RoF system with the Wavelength Division Multiplexing(WDM)technology as the WDM-RoF system can make full use of the bandwidth resources of the fiber,which is an important means to realize the long-distance transmission and wide-range coverage of the high-frequency microwave signals in the future mobile communication system.Using optical frequency comb to provide multi-carrier optical source for WDM-RoF system can reduce the optical source cost and facilitate the expansion and reconstruction.This paper focuses on the WDM-RoF system based on optical frequency comb,researches the optical frequency comb generation technology,wireless access WDM-RoF system and WDM-RoF system for wired and wireless signals access.The specific research contents are as follows.An optical frequency comb generation technology based on a dual-parallel mach-zehnder modulator(DPMZM)and two electro-absorption modulators(EAMs)is proposed.The theoretical model was established,and simulation study was performed using the optical communication system simulation software Opti System.The influences of the center frequency of the optical source,the line width of the optical source,the power of the optical source,the frequency of the radio frequency driving signal and the EAMs bias voltage on the optical frequency comb are analyzed.By adjusting and optimizing the working parameters of the device,optical frequency comb with average power of-15.93 d Bm and flatness of 0.94 d B was generated.A WDM-RoF system with dual millimeter-wave signals based on optical frequency comb and carrier reuse is proposed.Dual millimeter-wave signals can be generated simultaneously in the base station(BS).Dual millimeter-wave signals are generated by beating the optical carrier without downlink signal and the positive and negative second-order sideband with downlink signal,which overcomes the periodic power fading effect and bit walk-off effect.The uplink signals in the BS are carried by the optical carrier reserved in the central station(CS),which realizes the BS uplink transmission without local optical source.The theoretical model was established.The optical communication system simulation software Opti System was used to study the performance of WDM-RoF system with dual millimeter-wave based on optical frequency comb and carrier reuse.The results show that the average power penalty of generating 30 GHz and 50 GHz dual millimeter-wave signals of five WDM channels carrying 5×10Gb/s downlink data after 40 km SMF transmission is 0.95 d B and 1.11 d B,respectively.The average power penalty of the uplink of five WDM channels carrying 5 × 10Gb/s uplink data after 40 km SMF transmission is 0.46 d B.Accordingly,the WDM-RoF system achieves high-efficiency transmission with low power penalty.A WDM-RoF system for wired and wireless signals access based on optical frequency comb and polarization multiplexing is proposed.Using polarization multiplexing technology,the transmission of wired and wireless signals in the uplink and downlink of one WDM channel can be accomplished by using only one optical carrier,which improves the carrier utilization.The uplink signals in the BS are carried by the optical carrier reflected by the fiber bragg grating(FBG)without local optical source,which simplifies the configuration of the BS.Wired and wireless access can be implemented in the BS at the same time,ensuring the flexibility of user access.The theoretical model was established.The optical communication system simulation software Opti System was used to study the performance of WDM-RoF system for wired and wireless signals access based on optical frequency comb and polarization multiplexing.The results show that the average power penalty of the wired access link and the wireless access link of ten WDM channels carrying 10 × 10Gb/s downlink data after 25 km SMF transmission is 0.34 d B and 0.71 d B,respectively.The average power penalty of the wired link and the wireless link of ten WDM channels carrying 10×10Gb/s uplink data after 25 km SMF transmission is 0.26 d B and 0.24 d B,respectively.Therefore,the WDM-RoF system for wired and wireless signals access has good transmission performance.