| With the development of Internet technology and the rise of high-definition video,interactive live and other new business,the user's demand for network bandwidth is growing,so higher requirements to access network technology which is the closest link to the user is put forward.Radio over Fiber(RoF)technology can effectively utilize millimeter-wave bandwidth resources and has flexible access,while Wavelength Division Multiplexing Passive Optical Network(WDM-PON)technology has an advantage of huge bandwidth and can meet a variety of business needs.To combine RoF technology with WDM-PON technology has become one of the best choices to solve the issues such as the access network transmission rate and user needs in the future.The coherent detection technique with high receiving sensitivity is applied to RoF-WDM-PON integrated system,which can further extend the transmission distance and improve the transmission performance of the system.The paper focuses on WDM-PON technology,RoF technology and coherent detection technology,so the main work and the specific research results are as follows.(1)The basic principle and key technology of RoF and WDM-PON are analyzed systematically.The principle of optical millimeter-wave signal generation using external modulator is deduced.Simulation is done for the double sideband(DSB),single sideband(SSB)and optical carrier suppression(OCS)modulations to perform three kinds of millimeter-wave signal generation.We compare the spectral structures and analyze the characteristics of the millimeter-wave signals generated by different modulations.(2)The basic principle of coherent detection technology is deduced and the characteristics of two kinds of high order modulation format,such as MPSK and quadrature amplitude modulation are analyzed and compared.Then we build a 16QAM transmission link based on coherent detection technology.We simulate the influence of the nonlinear effect in transmission and the role of each phase in the digital signal processing.(3)We propose a RoF-WDM-PON system based on polarization multiplexing and coherent detection.In this scheme,the carrier in the orthogonal polarization direction can be modulated respectively by polarization control.And at the receiving end we can complete the homodyne detection and heterodyne detection at the same time without the need to introduce a separate laser and then realize the distribution of wired and wireless signals.In addition,we can realize wavelength reuse by separating pure carriers from downlink for the uplink transmission.We also setup a simulation link to prove the feasibility of our proposed system.The analysis of the error vector magnitude(EVM)curves and constellations of the simulation link demonstrate that the signal transmission performance of our proposed system is good. |
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