Research On Electro-optical Modulation Parameters Based On Phase Comparison

Optical communication systems are rapidly developing in the direction of large bandwidth and high speed.As the core device of optical communication systems,the frequency response characteristics of high-speed optoelectronic devices are important indicators for measuring the working speed and working bandwidth of optical communication systems.Therefore,accurately characterizing the frequency domain characteristics of optical devices has important research significance for the evaluation and optimization of the entire optical communication system.The dispersion associated with the frequency chirp of the transmission source is one of the main limiting factors of high-speed and long-distance communication systems.Mach-Zehnder modulator(MZM),which can provide low or adjustable chirp parameter,is a key component of high-capacity optical communication systems,so it is necessary to provide a wide-band,high-precision MZM chirp parameter test method.The optical field measurement method is limited by the resolution of the spectrum analyzer(0.01 nm),the resolution is poor and is affected by the line width of the light source;although the electric field measurement method has high resolution,most of them are limited to MZM with ideal or extinction,and additional calibration is needed to correct the fluctuation of photodetection response.In this thesis,two kinds of MZM chirp parameter test methods based on amplitude comparison and phase comparison are proposed,and the wide-band and high-precision test of MZM chirp parameters with finite extinction ratio self-calibration is realized.The main research contents are as follows:1.MZM chirp parameter test method based on amplitude comparison.On the basis of the acousto-optic shifting heterodyne structure,a high-frequency test of MZM chirp parameters based on amplitude comparison is proposed.By adjusting different DC bias points,the amplitude comparison of the same beat frequency electrical signal completely eliminates the influence of the photodetector uneven response and simplifies the data processing.In order to save the working bandwidth requirement of the photodetector,a high-frequency test method based on the amplitude comparison MZM chirp parameter low-frequency detection is proposed,and the high-frequency signal carrying the frequency response information of the modulator to be tested is frequency-converted to the low frequency band for detection.Both methods achieve the measurement of the MZM chirp parameter of any extinction ratio of 0-20 GHz.At the same time,both methods eliminate the measurement error introduced by the photodetector responsivity and realize the self-calibration measurement.2.Test method for chirp parameters based on phase comparison.The frequency shifting heterodyne structure is used to realize the high frequency sideband beat frequency carrying the MZM frequency response information to the low frequency band for detection,which saves the bandwidth requirement of the photodetector,and extracts the time domain waveform through the oscilloscope to realize the frequency domain to time domain mapping.Innovatively proposed a test method for the chirp parameter of MZM in the time domain.The different DC bias points are adjusted,and the MZM chirp parameter test of any extinction ratio of 0-12 GHz is realized by measuring the phase difference of the time domain waveform.The method also avoids the influence of the uneven response of the photodetector,and realizes the self-calibration and MZM chirp parameter measurement of different extinction ratios.