Research On The Microwave Signal Processing By Using Optoelectronic Oscillation Mechanism

Microwave signal detection and processing play an important role in the microwave receiving system.The increasingly complex electromagnetic environment imposes ever-increasing requirement on the signal receiving ability of the system.The pure electronic technology is generally insufficient in terms of operation frequency band,processing bandwith,dynamic range and anti-electromagnetic interference capability.It is urgent to investigate new techniques to break through the limitation.Therefore,the microwave photonic technology comes into being.By combining the advantages of the microwave thechnology and the photonic technology,the microwave photonic technology exhibits promising applications in generating,transmitting and processing microwave signals.By converting the microwave signals into the optical domain,the predominant capability of optical fiber communication technology,such as broad frequency band,large bandwidth,low loss and high capacity of anti-electromagnetic interference,can be fully exerted.As well as the advantages of the microwave technology,including the wide coverage,high mobility and flexibility,can be utilized.Therefore,the microwave photonic technology provides a new way to enhance the capability of signal transmission and processing systems.The optoelectronic oscillators(OEOs),as one of the main microwave photonic systems,have evolved from the initial microwave signal generation to optical sensing,clock signal recovery,signal detection,frequency conversion,and so on,taking the advantages of microwave photonic technology.In this thesis,we focus on the microwave signal detection and frequency down conversion by utilizing OEO mechanism.Firstly,the model of microwave signal detection with OEO system is established according to the theory of the microwave photonic link and the classical optoelectronic oscillation mechanism.The theoretical model of the traditional Yao-Maleki phase noise is modified,which paves the way for the research work.A low-power microwave signal detection scheme by using frequency identifiable OEO is proposed.The optically carried microwave signal is amplified in optical domain by virtue of the cyclic oscillation gain mechanism.At the same time,the frequency of the detected signal can be estimated by using the frequency tunable capability of OEO.In the experiment,the detection of the low-power microwave signals from 1.5 to 5 GHz is measured with the gain of about 10 dB.The detection sensitivity is about-91 dBm,and the frequency measurement error is within±100 MHz.For the application of narrow bandwith signal detection,the QPSK modulation signal is input to the OEO detection system.The detection sensitivity of-83 dBm is obtained for the synchronous speech signal.The gain by the OEO detection system based on the conventional phase modulation is realitively low due to the large optical carrier to sideband ratio(OCSR).To overcome this shortcoming,a new equivalent phase modulation(EPM)based OEO scheme is proposed with an adjustable OCSR.The gain can be greatly enhanced by suppressing the power of optical carrier to decrease the OCSR of EPM signal.In the experiment,the EPM is realized by using a dual-parallel Mach-Zehnder modulator with the proper DC biase control.The low-power signals from 2 to 18 GHz is detected with the detection sensitivity of about-87.7 dBm.Compared with the OEO based on the conventional phase modulation,the detection sensivity of the EPM based OEO is increased about 9 dB.The detection performance of the EPM based OEO is comprehensivelly investigated,and the solution for improving the detection capability is provided.For further processing the received wide frequency band signal,a frequency down conversion scheme without the external local oscillator(LO)is proposed.It utilizes the polarization multiplexed dual-loop OEO system as the LO signal generator and the frequency down convertor simultaneously.The high quality and frequency tunable LO signals can be generated by the proposed OEO.The frequency down conversion is realized directly in the OEO loop without the external LO and additional modulator.In the experiment,the frequency tunable microwave signal from 2.5 to 7 GHz is generated with the sidemode suppression ratio of 56 dB and the phase noise of-109 dBc/Hz at the frequency offset of 10 kHz.By using the generated LO signal,the microwave signals from 3.5 to 8 GHz are down converted to the same intermediate frequency of 1 GHz.The spurious free dynamic range of the frequency down conversion system is 102.2 dB·Hz2/3.For the real applications of communication,the frequency down conversion of the microwave signals with different modulation rate and different signal to noise ratio is also studied with confirmative results.The work in this thesis demonstrates the feasibility and advantages of the OEO mechanism for low-power microwave signal detection and frequency down conversion.It provides an efficient solution for the microwave photonic signal detection and processing.