Research On Measurement Techniques For Spectral Phase Of Periodic Signal Based On Frequency Sweep Sampling

In order to meet the rapidly increasing requirements of data transmission,the rate of optical fiber communication systems is increasing,and the modulation format and multiplexing form are becoming more complex.It becomes increasingly difficult to monitor the performance of optical signals in time domain limited by the bandwidth bottleneck of electronics.The periodic optical signal is generally used to evaluate the transmission performance of optical fiber communication system and optical devices.The periodic optical signal is composed of a series of discrete spectral components which have the same frequency interval.The monitoring of transmission performance of optical signal can also be achieved by measuring the amplitude and phase of each spectral component and using the inverse Fourier transform to reconstruct the time-domain information.Compared with the time-domain method,the frequency-domain method could measure frequency-domain information with low sampling bandwidth,which is not limited by the symbol rate.Therefore,it is significant to research the method of measuring spectral information of periodic signal.In this thesis,we study the measurement techniques for spectral phase of periodic signal based on frequency sweep sampling.The research contents and results are as follows:1.A measurement technique for spectral phase of periodic signal based on frequency sweep sampling is proposed,and the simulation platform is built to verify the feasibility and robustness of the technique.The proposed technique can accurately extract the spectral amplitude and phase information of the high-speed high-order modulation format periodic optical signal at a low sampling rate,and the monitoring of signal performance can be achieved by using the inverse Fourier transform to reconstruct the time-domain information.The absolute average error of the spectral phase measured by the proposed technique is less than 0.04 rad for the three different modulation formats of OOK,QPSK and 16QAM.And the reconstructed time-domain information matches the characteristics of the modulation format of the signal under test.2.The application of the reconstructed time-domain information to chromatic dispersion monitoring is studied.The chromatic dispersion can be measured accurately by using the fractional Fourier transform with the reconstructed time-domain information.In the 28 GBaud QPSK system,the measurement absolute error is less than 60 ps/nm and the measurement relative error is less than 4%when the transmission distance is between 100 km and 500 km.3.In the original scheme,the high-order frequency mode produced by the carrier-suppression double-sideband modulation will cause error in the measurement results of spectral phase.To solve the above problem,a modulation scheme based on sawtooth wave is proposed.The modulation scheme based on the sawtooth wave could measure the spectral phase of the periodic optical signal more accurately,and its time-domain reconstruction effect is better than that of the carrier-suppression double-sideband modulation scheme.The simulation platform is built to verify the feasibility and optimization effect of the proposed scheme.4.In the original scheme,the reference clock signal is needed in the receiver to ensure sampling synchronization in order to avoid inaccurate phase measurement.In view of this problem,a scheme for spectral phase measurement of the periodic optical signal without reference clock is proposed.The new scheme realizes the accurate measurement of the second-order differential value of the spectral phase,and the spectral phase can be obtained by two cumulative calculations.The new scheme greatly reduces computational complexity of spectral phase compared with the original scheme.