基于双平行马赫-曾德尔调制器的大动态范围微波光子下变频方法

为了提高微波光子下变频链路的性能,提出了基于集成双平行马赫-曾德尔调制器的微波光子下变频方法.通过理论推导和数值仿真分析了系统的增益和无杂散动态范围,实验搭建了基于双平行马赫-曾德尔调制器的下变频链路,控制直流偏置电压使双平行马赫-曾德尔调制器工作在高载波抑制的双边带调制模式,并对链路进行了性能测试.实验结果表明:该下变频链路的增益为7.43 d B,无杂散动态范围达到了110.85 d B/Hz2/3,工作频段可覆盖5—18 GHz的宽频范围.基于双平行马赫-曾德尔调制器的下变频方法可优化设计输出频谱,系统结构简单、易于实现,为微波光子下变频链路提供了有效的解决方案.

Dual-parallel Mach-Zehnder modulator based microwave photonic down-conversion link with high dynamic range

With the rapid development of the microwave photonic communication technology, the frequency of the microwave signal is expanded to the Ka waveband, since most of low frequency bands are occupied. However, the current commercial detectors and signal processing modules are limited by bandwidth. Therefore, the traditional method of directly detecting the microwave signals cannot meet the actual demands. It is essential to achieve the microwave photonic down-conversion from the high frequency microwave signal (~10 GHz) to the lower frequency signal (~100 MHz). Meanwhile, the down-conversion low frequency signal can be processed by the existing mature technology and low cost devices. The microwave down-conversion link can effectively avoid leaking the local oscillator, and it possesses many advantages such as high bandwidth and spurious free dynamic range, low loss and low noise. In this paper, a microwave photonic down-conversion system is presented based on the integrated dual-parallel Mach-Zehnder modulator (DPMZM) to increase the spurious-free dynamic range as well as conversion efficient of microwave photonic link. The integrated DPMZM is mainly comprised of two intensity modulators (MZM-a and MZM-b), and a phase shifter. The radio frequency (RF) signal is loaded into DPMZM to modulate the optical signal. The local oscillator is loaded into the MZM-a to produce the 1^st local oscillator sideband, and two RF signals are fed to the MZM-b to form the 1^st RF signal sideband. The direct current bias of the DPMZM is adjusted to output a high carrier suppressed double sideband (DSB) signal. The erbium-doped fiber amplifier is used to increase the power of light to match the power range of the detector. The RF signal sideband and local oscillator sideband are mixed to produce the beat frequency, and the frequency down-conversion can be achieved. The principle of frequency down-conversion is elaborated by theoretical analysis. The conversion efficiency and spurious free dynamic range are analyzed and simulated. On this basis, the microwave photonic link of frequency down-conversion is built. The performance of the system is tested. The ratio of optical carrier power to sideband power of the DSB signal is 26 dB. The experimental result shows that the conversion efficiency is 7.43 dB and spurious-free dynamic range is 110.85 dB/Hz^2/3. The down-conversion method based on the DPMZM can optimize the output spectrum of the sideband. The structure of system is simple and easy to implement, so it is a good option for improving the conversion efficiency and spurious-free dynamic range.