Research On Novel Optical Modulation Scheme And Optical Millimeter-wave Generation In Radio Over Fiber System

Radio-Over-Fiber (ROF) is a technique to transmit wireless signals on optical fiber, which combines the advantages of wide bandwidth, low loss and immune to EMI of the optical communications and the advantages of mobility and access flexibility of the wireless communications, and has become a potential solution for the next generation multimedia based internet applications. Novel optical modulation and optical millimeter-wave generation are key techniques of the ROF system, and has attracted much more research interests.In this paper, firstly, we analyze the principles and key techniques of the LN-MZM based external modulation scheme, and three normally used external modulation schemes DSB, SSB and OCS are briefly introduced. Secondly, a novel SSB modulation scheme with high-order interfering harmonics well suppressed is proposed. Theoretical analysis and computer simulations are conducted compared with the conventional SSB modulation scheme. Results show that the novel SSB is immune to dispersion of the optical fiber and has higher optical modulation efficiency (OME). Thirdly, an optical millimeter-wave generation scheme, which can optionally generate millimeter-wave signals with frequency quadrupling, sextupling and octupling the frequency of the driving local oscillator, is proposed and analyzed. Results of simulations show that this new scheme can generate high frequency millimeter-wave signals with low frequency local oscillators, and the BER performance for transmission over SMF is low in power penalty. Finally, a novel optical millimeter-wave generation by frequency quadrupling and vector signal modulation scheme is proposed. Unlike the conventional optical millimeter-wave generation scheme, which simultaneously encodes data on both of the two optical sidebands, the novel scheme modulates data just on the -1 order optical sideband, with the +3 order optical sideband un-modulated. Theoretical analysis shows that the millimeter-wave signal generated by photodiode detection in the novel modulation scheme can avoid phase distortion, which would lead in severe constellation overlapping in the conventional optical millimeter-wave generation schemes. Simulation results show that the novel modulation scheme can not only generate optical millimeter-wave signal with frequency quadrupling but also modulate vector signals with no phase distortion or constellation overlapping on the millimeter-wave signal at the receiver. The novel modulation scheme has shown a great potential in the ROF link.