Research On Key Techniques Of OSSB Modulation And Optical Millimeter-wave Generation In RoF System

Radio over Fiber(RoF)system has the advantages of low loss,large bandwidth,strong anti-electromagnetic interference ability,low construction and maintenance cost and easy dynamic allocation of service capacity.Therefore,it has a wide application prospect in future mobile broadband communication and Internet of Things.This thesis is devoted to investigating the optical carrier-to-sideband ratio(OCSR)optimization of optical single-sideband modulation(OSSB)signal and optical generation of the millimeter-wave signal with tunable multiplification factor,based on theory,simulation and experiments.Moreover,a full-duplex optical link for RoF system is built.The main achievements and innovative research efforts are summarized as follow:1.The influence that transmission pulse type of the data signal has on the system performance in conventional OSSB modulation is studied emphatically.It is found that,Return-to-Zero(RZ)pulse and the None-Return-to-Zero(NRZ)pulse are most suitable for short distance(l<10km)transmission and long-haul stable signal transmission,separately.To solve the problem of time shift of code edges due to the fiber chromatic dispersion,an improved scheme is proposed,which only modulates data on the optical carrier.Compared with the original scheme,the time shift of code edges is eliminated.Besides,the performance of the system can be upgraded greatly.It is also found that RZ transmission pulse is the most suituable pulse for the improved scheme.2.A single channel OSSB-RoF scheme with large range and continuous tuning of optical carrier sideband ratio(OCSR)is proposed and demonstrated.This scheme make uses of a uniform fiber Bragg grating based acoustic optical tunable filter(UFBG-AOTF).The primary and first secondary transmission peaks of the UFBG-AOTF are aimed to attenuate the optical carrier and the first-order sideband of the OSSB signal simultaneously.Based on the numerical results,a conclusion can be drawn that the OCSR can be continuously tuned from-20.12dB to 29.04dB.A UFBG-AOTF is fabricated and applied to the proposed scheme.The research results show that the sensitivity of the RoF link can be improved by about 3.7 dB while the OCSR is reduced from 13.96 dB to 0.47 dB.3.An optical fiber Sagnac loop based on a single polarization maintaining fiber is fabricated experimentally and applied to both the generation and the OCSR optimization of OSSB modulation signal of multi-channel.The scheme utilizes the slope of the Sagnac loop's transmission spectrum to apply different degrees of attenuation on the optical carrier,the upper and lower sidebands of the multi-channel ODSB signals.As a result,the ODSB signal is converted to an OSSB signal in each channel,and the OCSR of the signal is optimized from 4.40 dB to 1.13 dB.The scheme eliminates the periodic fluctuation of the RF power caused by the fiber dispersion and the crosstalk between the channels,at the same time,the receiver sensitivity of the optical link is improved by 2.16dB.4.A scheme of generating millimeter-wave signal with tunable frequency multiplication factor(FMF)by employing the UFBG-AOTF is demonstrated.Tunable FMFs can be easily achieved by adjusting frequency of the applied acoustic wave on the UFBG.The proposal employs the Mach-Zehnder Modulator(MZM)with simple structure,thus it has the merits of low cost and convenient operation.Two homemade UFBG-AOTFs are used in the proposed system,resulting in the generation of millimeter-waves with the FMF of 2 and 4,separately.5.A full-duplex Radio-over-Fiber system is proposed,which provides both the generation of millimeter-wave signal with tunable FMF and the wavelength reuse for uplink data.FBG-AOTFs driven by two AW signals(0.572MHz and 1.145MHz)are experimentally fabricated and further applicated in the proposed scheme.By simulation,millimeter-wave signals with FMF of 2 and 4 are generated using these two FBG-AOTFs.Results of the research indicate that the 2-Gbit/s data can be successfully transmitted over 25km single mode fiber for bidirectional full-duplex channels with power penalty of 2.42dB and 2.58dB for the downlink.For the uplink,the power penalty is 0.12dB and 0.58 dB,respectively.