Microwave Photonics Frequency Conversion Method Based On Dual-Parallel Mach-Zehnder Modulator

The microwave photonics,as a new discipline,is a combination of microwave and photonics technology.Due to the increasing demand in enormous application including wireless communication,satellite communications,radar detectionetc,the low-frequency microwave can't meet the actual need,and the K and Ka microwave with high frequency has become attractive.The detector with limited bandwidth cannot directly process these high-frequency microwave signal at the receiver.The microwave photonics down-conversion link supplies a well solution,and can transform the microwave signals from high frequency to intermediate frequency.As the microwave signals with increasing frequenciesare required in applications such as electronic warfare,radar,there for it is necessary to convert low-frequency microwave signal into high-frequency microwave signal at the transmitter.The microwave photonics frequency multiplication technology utilizes the modulator to mix the frequency signals,and optical carrier microwave signal is produce and delivered through optical fiber.Then the frequency multiplication signal is generated by photoelectric conversion and finally launched though the antenna.In this paper,the microwave frequency down-conversion and frequency multiplication approaches are proposed through theoretical derivation and experimental analysis.The work of this thesis is mainly as follows:1.The microwave photonics frequency multiplication method based on a dual-parallel Mach-Zehnder modulator is studied to produce high-purity RF signal with frequency quadrupling.The principle and performance parameters of the frequency quadrupling system are analyzed and simulated by theory.Then the frequency quadrupling link is built based on the dual-parallel Mach-Zehnder modulator.The DC bias of the DPMZM is operated on the carrier suppressed double sideband modulation mode,and the performance of link is tested.The upper arm of the dual-parallel Mach-Zehnder modulator is driven by radio frequency at 6GHz.The experimental results show that the link can produce the frequency quadrupling signal of 24GHz.The optical carrier suppression ratio of the frequency quadrupling link is34.56dB,and the radio frequency sideband suppression ratio is-5.06dBm whenthe radio power is 26dBm.In order to further improve the radio frequency sideband suppression ratio of the frequency quadrupling link,the microwave frequency quadrupling link based on the dual-parallel Mach-Zehnder modulator and the optical filter is built.The experiment results show that radio frequency sideband suppression ratio is up to 34.77dB whenthe radio frequency power is26dBm,and has been improved by 39.83dB comparing with thefrequency quadrupling link without theoptical filter.2.The microwave photonic down-conversion method based on an integrated dual-parallel Mach-Zehnder modulator is proposed.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 DC bias of the DPMZM is adjusted to output the high carrier suppressed double sideband signal,and then the system performance is tested.The experimental result demonstrates that the conversion efficiency is 7.43dB,spurious free dynamic range is 110.85dB/Hz^2/3 and the working frequency band can cover the frequency range of 5GHz to 18GHz.In comparisonto the traditional cascaded intensity modulators microwave photonic link,conversion efficiency and spurious free dynamic range?SFDR?are improved by25.72dB and 22.10dB,respectively.The proposed linkis simple and easy to be implemented,and is a good alternative for improving the conversion efficiency and spurious free dynamic range.