实验研究了采用一个外部调制器和一个光纤布拉格光栅(FBG)滤波器产生四倍频光载毫米波的光纤无线通信(ROF)系统。在中心站(CS), 数据和射频(RF)信号通过混频后驱动外调制器, 调节外调制器的直流偏置, 产生抑制奇数阶边带的信号, 用FBG将中心载波滤除, 两个二阶边带通过光纤发送至基站。在基站(BS), 两个边带在带宽为60 GHz的光电二极管中拍频, 产生四倍射频信号的毫米波信号。实验显示, 当射频频率为10 GHz时, 可以产生频率为40 GHz的光载毫米波信号, 得到的毫米波眼图和信号解调后的眼图效果都很好,功率代价小于1 dB。从眼图和功率代价两方面来看, 2.5 Gbit/s的数据信号可在下行链路的光纤中传输40 km以上。

A novel scheme of radio-over-fiber system to generate frequency-quadrupled optical millimeter-wave by using an external modulator and a fiber Bragg grating (FBG) filter is proposed and experimentally demonstrated. In the central station (CS), the data signal and radio frequency (RF) signal are mixed to drive the optical external modulator. We adjust the direct current (DC) bias to generate signals whose odd-order optical sidebands are suppressed. A FBG filter is employed to suppress the carrier signals, and the second-order sideband modes are transmitted to the base station (BS) in fiber. In BS, two second-order sidebands beat to generate optical millimeter-wave with quadruple frequency in the 60 GHz photodiode. The experimental results show that the 40 GHz optical millimeter-wave is generated by 10 GHz RF resource. The millimeter-wave eye diagram and the demodulated baseband eye diagram show good performance and the power penalty is less than 1 dB. The eye diagrams and power penalty result prove that 2.5 Gbit/s downstream signal can be transmitted over 40-km along fiber.