Research On High-Speed Signal Acquisition Technology Based On Photonic Time-Stretch

Analog-to-digital convertor is the critical technique for continuous analog signal to digital signal conversion and is crucial for a successful signal process system.However,due to the limitation of sampling speed and system bandwidth most electronic ADCs cannot meet the requirements of high-speed signal acquisition.Photonic timestretch(PTS),as a preprocess method,is able to lower the frequency and suppress the bandwidth of the high frequency signal before being sampled and quantized.The PTS technology enlarges the effective sample rate and analog bandwidth and a broadband digitizer is achieved.However,employing PTS system as a high-speed digital preprocessor exists the following three crucial problems.First,the envelope of the dynamically changing chirped light pulse is not flat.Thus,it introduces a dynamic distortion and deteriorates the system accuracy(evaluated by Effective Number of Bits,ENOB).Secondly,electro-optic modulator has non-linear response.And the harmonics and intermodulation signals also degrade the accuracy of digitization.Thirdly,as a microwave photonic link with high dispersion,the performance of photonic time-stretch system highly depends on dispersion.While the large time window and stretch factor will evoke the dispersion-induced frequency-dependent power fading,which will limit the system bandwidth seriously.In this thesis,in terms of the three problems above,the mathematical derivation and proof-of-concept experiment are carried out.The main contents are as follows:1.For the first two questions,complementary signals from a push-pull dual-output MZM is used to solve this problem.Based on the numerical simulation,A proof-ofconcept experiment is realized and the PTS preprocessor with a stretch factor of 8.85 and a time window of 3.57 ns is realized.The ENOB can reach 4-bit for single-tone signal input and the second-order harmonic suppression ratio is raised to 54.37 dB.It shows that PTS system based on push-pull dual-output MZM can effectively suppress non-linear distortion and dynamically eliminate envelop,resulting in a high ENOB.However,the dispersion-induced power fading limit the analog bandwidth because of the doublesideband modulation.2.In order to eliminate dispersion-induced power fading,complementary parallel single-sideband modulation architecture is proposed.Based on the numerical simulation,A proof-of-concept experiment is realized.By using this system,single-tone microwave signals in the frequency range of 2GHz-25 GHz are digitized,the maximum power degradation is about 6dB and the ENOB is larger than 3.For a single-tone at 10 GHz,the effective number of bits can achieve 3.75 and the second-order harmonics suppression ratio can achieve 16.87 dB.It demonstrates that the system can eliminate dispersioninduced power fading,remove dynamic envelop and suppress nonlinear distortion.Moreover,dispersion-induced power fading is removed totally because of working in single-sideband modulation.Although additional phase shift occurs,employing phase compensation in digital domain can solve this problem.