Research On Optical Millimeter-waves Generation And Transmission For Radio-over-fiber System

Radio over Fiber utilizes optical fiber link for transmitting highfrequency wireless signal, it coalesces high-capacity and low loss offiber-optic communications, efficiency and flexibility of wirelesscommunications. It has been widely studied. At the same time,orthogonal frequency division multiplexing (OFDM) has the advantagesof large transmission capacity and high spectral efficiency. It is widelyused in broadband wireless LAN,3G mobile communication and otherfields.The mix of ROF and OFDM technology becomes4G researchhotpot.The paper studies deeply optical millimeter-wave generation andtransmission technologies for Radio over Fiber. The main researchachievements are as follows:Firstly，we have proposed a system for generation and transmissionof OCS-DPSK mm-wave using phase modulation along with optical filter.In the center station, after a phase modulator is driven by a mixed signalof DPSK signals and RF signal, an optical double-sideband (DSB)-DPSK)signal is generated. After the center carrier of the DSB-DPSK signal wascarried by optical filter, the output of the optical filter is an optical carriersuppressed (OCS)-DPSK format.When DPSK signals were modulated, itjust happened phase shift.Compared to ASK signals, DPSK signals notonly can avoid the occurrence of distortion after modulation andtransmission, but also can enhance the ability of anti-Gaussian noise andanti-Inter-Symbol Interference (ISI). Compared to double-drive MZMand single-drive MZM, the phase modulator don’t need to bias voltage,its system structure also is simple and high stability. Except setting ROFmodel, the paper also have analyzed fiber dispersion and input opticalpower’s effect for the performance of the system.Theoretical analysis andexperimental results showed that the system can overcome effectivelyfiber dispersion and extend transmission distance.Secondly，it proposed a system of the optical carrier OFDM signalgeneration and transmission based on phase modulator, and analyzedfiber dispersion influence on phase and Peak-to-Average-Power (PAPR)problem of OFDM signal and PAPR influenced for the whole system.In the center station, double-sideband suppressed-carrier(DSB-SC) opticalmillimeter wave signal generated utilizing phase modulator along withoptical filter.Then two sideband signals of the DSB-SC signal weresplited by interleaver multiplexer. Intermediate frequency OFDM signalis modulated only onto one of the two optical carriers using double-driveMZM. After modulated intermediate frequency OFDM signal coupledwith another sideband and transmited to base station. A generation andtransmission system of optical OFDM millimeter-wave signal based onphase modulator may reduce the complexity of the system, improve theperformance of the system and resist effectively fiber dispersion. Theexperimental results showed the system’s constellation chart and eyechart is very clear in30GHz-ROF, after10Gb/s baseband OFDM signaltransmited over95km along optical fiber.