Research On Linearization And Phase Stabilized Transmission Based On Microwave Photonic

Wide bandwidth and high resolution are the remarkable characteristics of the next generation radar.But the traditional electronic systems meet the tremen-dous technological challenges in the limited bandwidth and so on.Microwave photonic is a novel technology,which combines the microwave technology and photonic technology.Overcoming the limit of electronic bottleneck,mi-crowave photonic has been found widespread applications in multi-band radar,distributed coherent aperture radar,and deep space exploration,benefitting from its remarkable advantages such as ultra-broad bandwidth,low loss,and immunity to electromagnetic interference.Therefore,it is a new development trend of the next generation radar for handling of the broadband and high fre-quency signals.The researches of this paper are focused on the radio frequency(RF)front-end of the radar.We concentrate on the improvement of spur-free dynamic range(SFDR),stable signal phase transmission,and multi-functional signal process based on microwave photonic.The main innovations of this paper are as follows:According to the demand for high SFDR of radar receiver,a linearized microwave photonics link based on bi-directional phase modulator is presented and experimentally demonstrated.In the proposed system,two different C-band optical wavelengths are phase modulated by a bi-directional phase modulator in opposite directions.There is a natural 180° phase difference between the up and low first order optical sidebands of the optical phase modulated signal.After combining the wavelengths,a fiber Bragg grating is utilized to select the desired optical sideband(OSB)between the two directional wavelengths.The third order intermodulation distortions(IMD3)can be suppressed via subtly adjusting the optical power and modulation depth relationships between the two directional wavelengths.The experimental results indicate that the SFDR raises from 99.2 dB.Hz2/3 for a link without linearization to 119.1 dB.Hz4/5 for a link with linearization.Due to the requirement for high SFDR of radar receiver,multi-order non-linear distortions suppression in phase modulation microwave photonics link(PM-MPL)via optical spectrum vector manipulation(OSVM)is proposed and experimentally demonstrated.The theoretical relationship between nonlinear distortions and all OSBs of phase modulated signal is analyzed.Multi-order nonlinear distortions are suppressed using a closed-form solution to calculate the OSBs transmission coefficients to propose a method to highly linearize PM-MPL via OSVM.Besides,theoretical expressions of SFDR are derived when different orders nonlinear distortions are suppressed.The experimental results demonstrate that IMD3 can be suppressed to increase the overall SFDR from 100.9 dB-Hz2/3 for a link without linearization to 122.0 dB·Hz6/7 for a link with linearization.On the basis of the requirement for highly stable frequency reference signal of the individual radar of distributed coherent aperture radar,RF phase stabilized transmission over fiber based on microwave photonic phase shifter is presented and experimentally demonstrated.In the proposed system,microwave photonic phase shifter consists of a dual-drive Mach-Zehnder modulator(DMZM)and an optical bandpass filter.Both assistant RF signals are applied to drive two arms of the DMZM,respectively.And the optical bandpass filter is followed to filter out the first-order sideband of optical modulated signal.Due to the phase independence between two optical sidebands,the phase perturbation caused by fiber-length variations can be compensated automatically via controlling the direct-current bias voltage of the DMZM with the assistance of proportion-integral-differential algorithm.A 100 MHz RF signal transfer in a 155 km optical fiber is performed with a frequency stability of 9.56 x 10-14 at 1 s,and 3.05×10-17 at 10000 s averaging time.Aiming at the needs of the signal frequency conversion and phase shift of the distributed coherent aperture radar,a technology for signal frequency con-version with tunable phase shift based on microwave photonic is put forward and experimentally demonstrated.The proposed system comprises a traditional microwave photonic frequency converter and an optical path with a Hilbert transform function.Due to the Hilbert transform path,the DMZM bias in-formation,which initially influences the amplitudes of the output signals,is transferred to their phases.As a result,the frequency converter with tunable phase shift is realized without optical filter.The experimental results show that the inter-conversion between intermediate frequency(IF)signal below 4 GHz and the RF signal between 8 and 16 GHz with a 360°phase shift is performed.In summary,this thesis systematically investigates the key technologies of signal linearization,RF phase-stable transmission over fiber,and signal frequency conversion with tunable phase shift based on microwave photonic.And the performances of these methods mentioned above are experimentally demonstrated.The research results of this thesis lay a solid foundation for the application of microwave photonic in the RF front-end of the radar.