Dual-parallel Mach-Zehnder modulator based microwave photonic down-conversion link with high dynamic range
Authors: Wang Yun-Xin  , Li Hong-Li  , Wang Da-Yong  , Li Jing-Nan  , Zhong Xin  , Zhou Tao  , Yang Deng-Cai  , Rong Lu  ,   College of Applied Sciences, Beijing University of Technology, Beijing 100124, China;,   Beijing Engineering Research Center of Precision Measurement Technology and Instruments, Beijing University of Technology, Beijing 100124, China;,   Science and Technology on Electronic Information Control Laboratory, Chengdu 610036, China
Published: December 2020

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 1st local oscillator sideband, and two RF signals are fed to the MZM-b to form the 1st 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/Hz2/3. 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.