Research On Microwave Photonic Frequency Measurement Technology

Microwave photonics is an interdisciplinary research between microwave engineering and photonics,which connects the originally independent fields of microwave and optics,and has been greatly developed in recent decades.The research focus on photonic generation,processing and measurement of microwave signals,radio-over-fiber systems,opto-electronic devices working at microwave rates and optical control of microwave devices.Traditional electrical radio-frequency(RF)measurement can only provide a relatively limited measurement range due to electronic bottleneck,and the system suffers from complex structure,large volume,high cost and electromagnetic interference(EMI).It cannot meet the requirement of nowadays complex electromagnetic environment and nextgeneration wireless systems.Thanks to the inherent merits of wideband operation,low transmission loss,compact structure and immunity to EMI,microwave photonic signal measurement offers an effective solution to the performance improvement of the frequency measurement receiver.According to the requirements of the future frequency measurement system and the unique advantages provided by photonics,this dissertation investigates the microwave photonic measurement of RF signals.What follows are the detailed works:A photonic frequency measurement scheme based on frequency to power mapping is proposed and experimentally demonstrated in this dissertation.To extend measurement range and obtain high measurement accuracy simultaneously,a reconfigurable structure or a two-step operation is required,which makes the system structure complex,hard to implement and decreases the real-time performance.To solve the problem,an amplitude comparison function(ACF)is established by using one channel of a dense wavelength division multiplexer(DWDM)in our scheme.Thanks to the broadband,smooth and quasi-linear filter performance of the DWDM channel,and the use of a laser with high wavelength stability and a bias controller,measurement with high accuracy,large measurement range and long term stability is achieved without multi-step operation.In the experiment,the proposed IFM receiver can measure frequency to 0.2% of 1-40 GHz over1.5 hours.Besides,the system features compact structure and simple operation,which make the system easy to be implemented.A wideband RF subsampling and disambiguation method based on phase shift analysis is proposed in this dissertation.In traditional schemes based on multi-comb sampling,the input RF signal is subsampled by two or three pulsed optical sources and down-sampled to different intermediate frequencies.The relationship between these frequencies can be used for disambiguation through frequency recovery algorithm.However,multiple pulse-shaped lasers are required,which makes the system complex and costly.Therefore,we made an in-depth study on simplifying the structure and decreasing the cost.The principle is presented through theoretical analysis and simulation.By constructing two optical subsampling links with different optical delays and analyzing the phase shift between sampled signals,the Nyquist frequency band of the RF signal can be determined.The exact signal frequency can be recovered according to the Nyquist band and the intermediate frequency.As the scheme is based on phase shift analysis,the impact of signal-to-noise ratio(SNR)to the accuracy of phase detection is also investigated.A proof-of-concept experiment is performed,which shows an unambiguous measurement range up to 26 GHz.The system features low cost and simple operation in DSP unit.The limitation of measurement range mainly originates from the phase balance performance of the devices between the power divider and two modulators.The proposed system may find applications in modern RF signal monitoring systems.To solve the ambiguity in traditional dual-comb sampling frequency measurement,a disambiguation method based on phase analysis is proposed and experimentally demonstrated in this dissertation.In traditional dual-comb sampling methods,the original frequency of the RF signal is obtained according to the relationship between the output IF frequencies.The mathematical essence behind the subsampling theory indicates that there still exists ambiguity for dual-comb sampling frequency measurement and the unambiguous frequency measurement range is the average of the two sampling rates.Triple-comb sampling can be employed to extend the unambiguous measurement range.Nevertheless,triple-comb sampling will make the system more complicated and costly.To solve the problem,the theoretical model of dual-comb sampling system is further improved.The model indicates that the phase relationship between the IF signals and the first harmonics of two sampling rates can be used for disambiguation.A proof-of-concept experiment is performed and most of the ambiguous frequencies are successfully distinguished.The experiment results also indicate that the nonideal phase response of the system will reduce the performance of the method especially in high frequencies.Considering that it is almost impossible for the input frequencies to fall exactly at the ambiguous frequency values,an improved method,in which the variations of the calculated phases are observed to solve the ambiguity,is given so that the method is free from the calibration of the nonideal phase response.