Anolog Signal Processing Based On Polarization-Modulated Photonic Microwave Phase Shifting

Handling of broadband waveforms is an important feature and core capability of the next generation of multi-functional and integrative RF systems.However,limited by the well-known “electronic bottleneck”,it is extremely difficult for electrical systems to process signals with high frequencies and large bandwidths.Thanks to the intrinsic broad bandwidth characteristic brought by photonic technologies,microwave photonic signal processing is regarded as the tendency and solution of current signal processing,which can break the limitations of the electrical systems on transmission loss,operational bandwidth,electro-magnatic interference and amplitude-phase coupling.The basis of microwave signal processing is how to manipulate the magnitude and phase of the microwave signals.Since the magnitude can be easily tuned by an optical attenuator or amplifier,photonic microwave phase shifting is considered as a fundamental and key technical enabler for many microwave photonic signal processing functions.In this thesis,a new microwave photonic phase shifting technology based on polarization modulation is proposed.The technology features flat phase response,fast tuning speed and power independent phase shifting.Different phase shifting stuctures,i.e.,frequency fundamental,frequency multiplied and frequency mixed microwave photonic phase shifters,are demonstrated.The impacts of the device parameters on the performance of the phase shifting systems are studied.Broadband analog signal processing functions enabled by microwave photonic phase shifting are explored and realized,including high-speed phase coding,broadband linear frequency modulating,tunable filtering,optically controlled beamsteering and image-reject mixing.The detailed contexts are as followed.Firstly,microwave photonic phase shifting mechanism based on orthogonally circularly polarized wavelengths is developed.A theoretical model is built based on the mechanism.The phase shifting performance of the model is investigated by using analytical simulations.The novel microwave photonic phase shifting mechanism can solve the amplitude-phase coupling problem caused by the well-known K-K relations.Seondly,frequency fundamental,frequency multiplied and frequency mixed microwave photonic phase shifting are implemented based on polarization modulation.With polarization modultion and sideband filtering,orthogonal circularly-polarized wavelengths are generated,based on which,a microwave photonic phase shifter is realized.The phase shifter can obtain full-range phase shifting over 10-40 GHz while the magnitude maintains unchanged.To increase the operational bandwidth and the flexibility,cascaded polarization modulations are employed to decrease the lower boundary to 1.7 GHz,and polarization division multiplexing dual-parallel Mach-Zehnder modulation(PDM-DPMZM)is employed to increase the upper boundary to 184 GHz.In addition,frequency multiplication and frequency mixing can also be realized by the PDM-DPMZM based phase shifter.The influence of the unideal parameters of the devices on the performances of the microwave photonic phase shifters are investigated.Finally,broadband analog signal processings enabled by the novel phase shifting technology are demonstrated.In the transmitter,method for reconfigurable waveform generation is proposed by manipulating the phase of microwave signals according to different electrical driven waveforms,and high speed phase-coded signals and broadband linear frequency modulated(LFM)signals are successfully generated.Thanks to the peoriodicity of the phase,the time-bandwidth product(TBWP)of the generated LFM signal is improved by more than 500 times by splicing the driven baseband waveforms into multiple pieces.In the receiver,a microwave photonic filter is implemented thanks to the good scalability of the polarization-based phase shifter.The frequency response of the filter and the beam direction of the beamformer can be tuned by adjusting the phase of each signal.An image-reject mixer is also realized thanks to the opposite phase shifting experienced by the wanted IF signal from the RF signal and the unwanted IF signal from the image component.The image rejection ratio of a 4-GHz LFM signal is about 20 d B.