Research On Real-time Instrumentation Based On Ultrafast Optical Techniques

Real-time instrumentation is an underlying platform for a broad range of industrial,scientific,and medical applications.The ever increasing demand for higher data bandwidth is pushing the communication industry to augment the operating frequency of components and systems.Therefore,the demand for real-time instruments capable of detection and diagnostics in a very short time scale is rapidly growing.While alternative approaches based on short light essect(like stroboscopic)provide valuable information about an instant event,capture of transient and rare-occuring events,which are widespread in nature with the characteristics of instantaneity and uncertainty,will require true real-time instruments with fine time resolution and long record length.Based on dispersive Fourier transform,photonic time-stretch is a data acquisition that overcomes the speed limitations of traditional electronic digitizers and enables continuous ultrafast single-shot spectroscopy,imaging,terahertz and other measurements at refresh rates reaching billions of frames per second with non-stop recording spanning trillions of consecutive frames.This technique has opened a new frontier in measurement science unveiling transient phenomena in nonlinear dynamics such as optical rogue waves,soliton molecules and in relativistic electron bunching.It has also created a new class of real-time instruments that have been integrated with artificial intelligence for sensing and biomedical diagnostics.Under the supports of National Natural Science Foundation of China,this dissertation has launched a series of in-depth theoretical and experimental researches on real-time instrumentations based on ultrafast optical techniques.It has expanded the applications of ultrafast optical techniques in real-time device characterization,instantaneous frequency measurement and sensing.The main innovations and achievements are as follows:1.A real-time device characterization system based on photonic time-stretch is proposed and experimentally demonstrated.The system employed phase diversity with time-stretch data acquisition to eliminate the effect of dispersion penalty and extend the bandwidth of the instrument.It obtains an effective sampling rate of 2.5Ts/s,an extremely fast frequency-response acquisition time of 27 ns and an ultra-low effective timing jitter of 5.4 fs.Powered by the proposed automated DSP algorithms,the frequency responses of two commercial wide-band electronic amplifiers are tested using the time-stretch device analyzer and the results are in good agreement with the specifications provided by the respective manufacturers.The proposed instrument can measure at 3 orders faster speeds than the conventional network analyzers.2.An instantaneous frequency measurement system based on differential photonic time-stretch is proposed and experimentally demonstrated,which can perform multi-frequency measurement in real-time.Distortion of the measured frequency signal caused by the non-uniformity of the spectrum of the pulsed laser source is eliminated here by implementing differential detection,which can also significantly improve the measurement accuracy and system dynamic range.Followed by the proposed automated DSP algorithms,an IFM receiver with a frequency resolution of82.5 MHz for single-/multi-frequency measurement in the range of 3-20 GHz,and a measurement error of less than 70 MHz at a measurement speed of 100 MHz is obtained.3.A novel approach for ultrafast and temperature-insensitive strain interrogation in real-time using a polarization-maintaining photonic crystal fiber(PM-PCF)based Sagnac loop interferometer and wavelength-to-time mapping is proposed and experimentally demonstrated.The key significance of this approach is mapping the spectrally shaped waveform to the temporal domain,converting the strain-induced wavelength shift into the time shift.Compared with the traditional demodulation scheme with an OSA,it can greatly improve the interrogation speed.The system offers an ultrafast interrogation speed of 100 MHz and a strain sensitivity of-0.17ps/??.4.A novel real-time strain interrogation technique based on an SMF-TMF-SMF(STS)fiber comb filter and wavelength-to-time mapping is proposed and experimentally demonstrated.The homemade STS filter is serving as both the spectrum shaper and the sensing element,and it is formed by splicing the two-mode fiber with two single-mode fibers using core-offset structures and it has the advantages of easy fabrication and tunable wavelength spacing.Linear WTT mapping is realized by a dispersive element and the spectrally-shaped optical pulse is mapped into temporal domain and enables interrogation in real-time by monitoring the time shift.The system presents a strain sensitivity of 0.3 ps/?? and a strain resolution of 167 ?? at an ultrafast interrogation speed of 100 MHz,and the home-made sensing head also demonstrates a low thermal dependence(1.35 pm/?)in the experiment,making the system an ideal candidate for the applications where ultrafast and stable strain sensing is needed.