Research On Hyperfine Optical Vector Analysis And Wideband Signal Acquisition Based On Microwave Photonic Technology

Microwave photonics is an interdiscipline that studies the interaction between light waves and microwaves in media,which combines the respective advantages of microwave technology and photonic technology.On one hand,through taking advantage of the large bandwidth and low transmission loss of optical technology,microwave photonic technology can realize the generation,transmission,processing and reception of broadband microwave signals in the optical domain.Besides,due to the wideband tunability and the reconfigurable characteristics of a microwave photonics system,it can be potentially applied in software-defined radar,wireless communications,electronic countermeasures and other fields.On the other hand,through taking advantage of the high precision and flexibility of microwave technology,microwave photonics technology can realize high frequency resolution,multi-dimensional optical measurement or sensing system.Based on the characteristics of microwave photonics,this dissertation focuses on the study of high-precision optical vector analysis technology and broadband microwave signal acquisition technology.The main contents of this dissertation are listed as follows.1.To meet the demand of the spectral response measurement of ultra-high Q optical bandpass filters,a high-resolution optical vector analysis scheme based on two-tone probing is proposed.By using Electro-optical modulation,a two-tone optical signal with an extremely small frequency interval can be generated.The two-tone optical signal is used to probe ultra-high Q optical bandpass filters and the signal-to-noise ratio of the measurement signal is largely enhanced.The proposed scheme solves the problem that the optical vector analysis solution based on optical single-sideband modulation（or optical double-sideband modulation）cannot measure ultra-high Q optical bandpass filters.In the experiment,the magnitude responses and group delays of a fiber Fabry-Perot tunable filter and a fiber Fabry-Perot interferometer are measured,whose bandwidths are1.5 GHz and 60 MHz respectively.Furthermore,high-order harmonics are utilized to improve the single measurement bandwidth of the system.In the experiment,a single measurement bandwidth of 100 GHz was achieved through using microwave signals with a frequency sweep range of only 12.5 GHz.2.To meet the demands of measuring the spectral response of optical devices with high speed,an ultrafast and wideband optical vector analysis scheme based on complementary optical linear frequency modulation wave and frequency-shifted dechirping process is proposed.The proposed method solves the problem of slow measurement speed of optical vector analysis schemes based on optical single-sideband modulation（or optical double-sideband modulation）.By modulating a linearly frequency-modulated microwave with a high linearity and a fast frequency scanning speed into the optical domain,the proposed scheme can achieve high-speed optical domain scanning.Compared with optical vector analysis schemes based on optical single-sideband modulation（or optical double-sideband modulation）,the single measurement time of the proposed scheme can be reduced by 4 orders to tens ofμs.Besides,the proposed scheme utilizes a frequency-shifted dechirping structure to solve the frequency aliasing problem after the complementary swept frequency optical signal is dechirped.Therefore,the single-shot measurement bandwidth is expanded by 2 times.In the experiment,a linear frequency modulation microwave with a pulse width of 20μs and a bandwidth of 18 GHz was used to realize an ultrafast optical vector analyzer with a single-shot measurement time of 20μs and a single measurement bandwidth of 36 GHz.The measurement resolution and the measured dynamic range are tested as 10 MHz and about 45 d B,respectively.3.To meet the demands of measuring the optical time delay with high accuracy and high speed,an ultrafast and high-precision optical time delay measurement scheme based on complementary optical linear frequency modulation waveform and frequency-shifted dechirping process is proposed.Compared with traditional optical time delay measurement methods based on optical linear frequency modulation waveform,the proposed method solves its problem of low speed and low accuracy.By modulating a linearly frequency-modulated microwave with high linearity and fast frequency scanning speed into the optical domain,a complementary optical linear frequency modulation waveform with high linearity and high scanning speed is generated,which can reduce the single-shot measurement time to tens ofμs.Besides,an optical phase noise suppression algorithm is proposed,which combined with the frequency shift dechirping structure can greatly suppress the optical phase noise in the dechirping photocurrent.Therefore,the proposed scheme can realize ultrafast and high-precision optical delay measurement,whose measurement accuracy is 1 order higher than that of traditional schemes.In the experiment,a linear frequency modulation microwave with a pulse width of 20μs,a period of 30μs,and a bandwidth of 4 GHz is modulated into the optical domain through electro-optical modulation,and a complementary optical linear frequency modulation wave is generated,which is used to probe the delay of 1-km single-mode fiber.When the average time is 30μs and 4.17 ms,the time delay measurement errors are 0.52 ps and0.04 ps,which correspond to relative measurement accuracies of 1×10^-7 and 4×10^-9,respectively.4.To meet the demand of simultaneously testing multiple optical devices,a multi-point optical vector analysis scheme based on optical linear frequency modulation wave and Kramers-Kronig receiver is proposed.Through utilizing the Kramers Kronig receiver,the spurious signals generated by multiple measurement optical signals beating with each other are eliminated,thereby improving measurement accuracy.In the experiment,a narrowband phase-shifted fiber Bragg grating and a fiber Mach-Zehnder interferometer were simultaneously measured.By constructing the minimum phase signal,the Kramers Kronig receiver is used to suppress the spurious signal in the photocurrent by about 20d B.Therefore,the fluctuations in the measurement results are eliminated.5.A novel photonic time-stretch analog-to-digital converter（ADC）based on complementary optical single sideband modulation is proposed to meet the requirements of broadband microwave signal acquisition.The proposed scheme can simultaneously solve three major problems of the photonic time-stretch system,e.g.,dispersion-induced power penalty,uneven pulse envelope distortion,and nonlinear modulation distortion.thereby achieving high-precision acquisition of broadband microwave signals.In the experiment,a time-stretch ADC based on the proposed scheme is set up,with an equivalent sampling rate of 87.7 GS/s,an analog bandwidth of 25 GHz,and an effective number of bits greater than 3.4 bits.A simulation model is established to study the impact of non-ideal devices on the performance of the proposed scheme.In addition,a broadband real-time time-stretched oscilloscope prototype based on the proposed scheme has been developed.