一种新颖的基于偏振调制器的无码元走离效应的倍频毫米波光载无线系统

A novel frequency double millimeter wave radio over fiber without bit walk-off effect based on polarization modulator

为了克服基于马赫-曾德尔调制器(MZM)的倍频毫米波光载无线系统(Radio Over Fiber,ROF)中的MZM存在的直流偏置漂移问题和ROF中的码元走离效应,本文提出了一种基于偏振调制器(Polarization Modulator,PolM)的无码元走离效应的倍频ROF系统。在中心站,利用PolM产生±1阶边带信号,利用复合射频(Radio Frequency,RF)信号来驱动PolM,实现将下行数据信号仅调制在+1阶边带上。复合RF驱动信号由两路信号合成,其中一路信号由数据信号通过相位调制器调制RF驱动信号形成,另一路信号是由数据信号经电放大器进行放大形成。在基站,利用光纤光栅(Fiber Bragg Grating,FBG)反射出部分-1阶边带做上行链路的光载波,实现载波重用;利用透过FBG的±1阶边带在光检测器(Photo Detector,PD)中的拍频产生倍频毫米波信号。在误码率为10-9情况下,经20、40和60公里的传输后,下行链路功率代价分别为1dB、1.2dB和1.22dB,上行链路的功率代价分别为0.5 dB、0.8 dB和1 dB。本文设计的方案能有效地克服光纤色散导致的码元走离效应,极大地提高了系统的传输距离,在ROF系统中具有重要的应用前景。

In order to overcome the DC drift problem of the March-Zenhder modulator and the codeword walk-away effect in radio over fiber(ROF)system,in this paper a novel without codeword walk-away effect ROF system based on a polarization modulator(PolM)was proposed.At the central station,a PoIM was used to generate±1 order sideband signals,and the composite radio frequency(RF)signals were used to drive the PoIM to realize modulating the downlink data signals on the+1 order sideband only.The composite RF drive signal was constructed by combing two signals,one of which was formed by the data signal modulating the RF drive signal through a phase modulator,and the other was formed by the data signal amplified by an electrical amplifier.At the base station,a fiber bragg grating was used to reflect part of the-1 order sideband for the optical carrier of the uplink to achieve carrier reuse;the±1 order sideband through the fiber bragg grating was used to generate a frequency doubling microwave signal by beating them in the photo detector.With the BER at 10^(-9),after 20,40 and 60 km fiber transmission distance,the power penalty of downlink is 1 dB,1.2 dB and 1.22 dB,and that of uplink is 0.5 dB,0.8 dB and 1 dB,respectively.The scheme designed in this paper effectively overcomes the codeword walking away effect caused by fiber dispersion and greatly increases the transmission distance of system,which has an important application prospect in ROF systems.