High-sensitivity Phase-noise Measurement Based On Dual-parallel Coherent Microwave-photonic Phase Detection And Cross-correlation Processing

The signal noise draws more attention to the higher-frequency signal in communication systems and radar detection due to the increasing carrier frequency of the signal.Phase noise affects various indicators of the above systems and it also plays an instructive role in designing architecture of various systems,so accurate phase noise measurement can effectively improve the system performance.Nowadays,with the great development of microwave oscillation technology,signal generation with extremely low phase noise can be realized.It is difficult to take accurate measurement with traditional phase noise measurement system,which is based on microwave instruments.Microwave photonics has been widely applied due to its characteristics of high repetition rate and low time-jitter.For example,a multi-band broadband radar receiver based on photonic analog-to-digital converter(PADC)can directly receive the radar signals,which effectively improve the imaging performance of the broadband radar.In this paper,we propose a phase-noise measurement scheme based on microwave-photonic phase detection and cross-correlation processing.The reference signal in this paper is high-repetition-rate optical pulse trains generated by active mode-locked laser(AMLL).The phase detection is conducted by a dual-output Mach-Zehnder modulator(DOMZM).The cross-correlation processing is used in the backend to suppress the introduced noise by the measurement devices.The proposed measurement provides high-sensitivity phase noise measurement for high-frequency signal under test(SUT).Main contents of the thesis are summarized as follows:(1)We discuss the principle of three main phase noise measurement.We demonstrate the advantages and disadvantages of each principle.The current examples of phase noise measurements are also discussed.Considering the limitations of the measurement methods based on microwave devices,the measurement based on photonic technology offers a solution to the phase-noise measurement of high-frequency SUT.(2)We propose the measurement scheme.The advantages of high-repetition-rate optical pulse train working as reference signal are analyzed.We also explain the microwave-photonic phase detection based on the principle of optical sampling and cross-correlation processing used to suppress the introduced noise in detail and the feasibility of the proposed experimental scheme in this paper is analyzed.(3)Based on the theoretical analysis and formula derivation,we discuss two factors that affects the measurement results: the noise introduced by the measurement devices and the number of times of cross-correlation algorithm processing(M)that are performed.Simulations are also performed to reveal the influences by the introduced noise and cross-correlation processing on the results.We summarize the relationship between M and the suppression effect and offer a solution to optimize the measurement.(4)This proposed scheme is used to measure the phase discrimination coefficient and the phase noise of a 20-GHz SUT generated by the microwave signal generator.Better suppression effect and more accurate measurement results are achieved by increasing M.Comparing the measurement results of this paper with those of commercial instruments,higher accuracy at low offset frequencies is achieved.We design a measurement scheme to measure the noise floor,and the phase-noise measurement sensitivity of-80 d Bc/Hz at 10 Hz and150d Bc/Hz at 1MHz are realized.