双平行马赫-曾德尔调制器的单边带RoF系统

Generation of optical single sideband with carrier signals using the dual-parallel Mach-Zehnder modulator in the radio over fiber system

在光纤承载射频(RoF)系统中,传统单边带调制(OSSB+C)产生的光载波分量和光边带分量之间功率差较大,导致接收灵敏度较低.为此提出了一种利用双平行马赫-曾德尔调制器(MZM)产生OSSB+C信号的改进方法.通过调节该MZM调制器的直流偏压,对于任意调制指数,光载波分量和光边带分量之间的功率都能够平衡,得到最优的0dB载边比(CSR).仿真结果表明,对于小调制指数,接收灵敏度的改善高达7.8dB;对于其他情况,接收灵敏度改善0.7～1.1dB.另外,还仿真分析了直流偏压漂移对载边比和接收灵敏度的影响.结果显示,如果将偏压漂移控制在5%范围内,则接收灵敏度下降幅度甚小,因而基于所提出方法的RoF系统具有较好的稳定性.

In the radio over fiber（RoF） system,the difference in power between optical carrier and optical sideband is large using the conventional optical single sideband with carrier（OSSB＋C） modulation,resulting in lower receiver sensitivity.An improved method to generate OSSB＋C signals is thus proposed based on the dual-parallel Mach-Zehnder modulator（MZM）.By adjusting the direct current voltage of the MZM,the balanced power between the optical carrier and optical sideband is obtained for any modulation index,i.e.,the value of the carrier-to-sideband ratio（CSR） is 0 dB which is optimum.Simulation results show that the receiver sensitivity could be improved by as large as 7.8 dB for the small modulation indexes,while about 0.7 dB to 1.1 dB for the medium and large modulation indexes.In addition,the influence of the drift of direct current bias voltage on the CSR and receiver sensitivity is also analyzed by simulation.The results show that if the bias drift is controlled within the range of 5%,the receiver sensitivity degrades a little,and the RoF system based on the proposed technique has the better robustness.