Research On Mid-infrared Single-photon Upconversion Imaging Based On Multi-dimensional Nonlinear Engineering

The mid-infrared(MIR)corresponds to the characteristic vibration-transfer energy leap spectral lines of many molecules and atoms,and is an important fingerprint spectral region.At the same time,it covers several transmission windows of the atmosphere,with advantages such as long acting distance,strong ability to penetrate the haze and good anti-interference.In addition,MIR also has good penetration of materials such as semiconductors,which can realize nondestructive detection of precision devices such as silicon wafers.Based on the above characteristics,MIR detection has a wide range of applications in civil and military fields such as biomedical imaging,environmental monitoring,industrial inspection and infrared guidance.However,due to the small photon energy in the MIR band,there are many challenges to achieve high-precision and highly sensitive detection and modulation.For example,in the field of MIR detectors,the traditional detectors based on semiconductor materials such as mercury cadmium telluride usually require low-temperature cooling,and face technical bottlenecks such as difficult preparation process,high cost,and large dark count,as a result,the current MIR detection has large noise,slow response,and can not achieve high-resolution imaging and other problems.In terms of MIR optical modulation devices,due to the fact that many materials have absorption bands in the MIR range,only a few transparent materials can be used as substrates,resulting in the existing MIR optical imaging components,phase modulators,intensity modulators,etc.still have a significant gap in core performance compared to visible or near-infrared devices.Currently,high-precision phase modulation and intensity modulation in the MIR cannot be achieved.For a long time,the development of wide-band,highresolution,high-efficiency,and highly sensitive MIR modulation technology and detector devices has been a frontier topic in the field of infrared detection research.To address the above problems,this paper conducts a multi-dimensional modulated MIR single-photon imaging study based on nonlinear frequency upconversion technology,and specifically explores new mechanisms and techniques for ultra-sensitive MIR detection and high-precision MIR modulation.Firstly,a precision-controlled MIR frequency upconversion detection system is built,which can convert MIR photons to visible wavelengths and realize ultra-sensitive detection at the single-photon level in MIR wavelengths by combining with the excellent performance of silicon-based detectors.Then,based on the nonlinear frequency upconversion system,it further organically combines the nonlinear modulation technology to realize the ultrasensitive MIR photon edge enhancement imaging based on phase modulation,and demonstrate the MIR photon single-pixel imaging based on intensity modulation,which provides an effective means for the measurement and control of infrared photons at room temperature.The details and innovations are summarized as follows:1.The time-stretching dispersive Fourier transform technique was used to reveal the transient mode-locked state of soliton lasers,providing a new perspective to investigate the mode-locking mechanism and dynamics process of lasers.Besides,a fully polarization-maintaining dual-color output fiber mode-locked laser with a common cavity structure was built to achieve highly stable and high-precision ultrashort pulse synchronization by cross-phase modulation effect.Through the intracavity dispersion compensation and fiber Bragg grating,the precise timefrequency control of ultrafast laser pulses was realized,which provided a basic light source for high-efficiency nonlinear frequency conversion.2.A nonlinear frequency conversion scheme based on coincidence pumping technique has been developed to achieve high efficiency and low noise MIR upconversion detection and imaging.Thanks to the laser system with precise time-frequency domain control,the narrow spectral width was easier to meet the phase matching conditions,and the ultrashort pulse could suppress the parametric fluorescence noise within an extremely narrow time window.As a result,it helped to improve the sensitivity of the MIR frequency upconversion imaging detection and broke through the limitations of large dark count noise in traditional infrared array detectors.Finally,ultra-sensitive imaging at the MIR single-photon level was achieved.3.A new method of ultra-sensitive MIR frequency upconversion edge enhanced imaging based on nonlinear phase modulation was proposed.For the first time,the imaging wavelength of spiral phase contrast was extended to the MIR,achieving MIR single-photon edge enhanced imaging.By loading the pump optical field with a spiral phase to form a vortex light field,and imprinting its phase onto the MIR fourier spatial spectrum with high fidelity,the phase modulation of the MIR was achieved,and the MIR was spectrally converted to the visible region at the same time.The current lack of the MIR phase modulator fabrication process and materials was circumvented,and highly sensitive MIR edge enhanced imaging could be obtained by a silicon-based camera.4.A new technique of ultra-sensitive MIR frequency upconversion single pixel imaging based on nonlinear intensity modulation was realized.The intensity modulation and wavelength conversion of the MIR signal in a nonlinear crystal has been achieved,with the precise control of the pump optical field encoding in the time-space domain.So that the highly sensitive MIR two-dimensional imaging at the single-photon level could be achieved by using a silicon-based single-pixel detector,which solved the two major problems of highly sensitive detection and high-fidelity modulation in the MIR.Further,by combining compressed sensing and machine learning algorithms,ultra-sensitive MIR compressed imaging with high signal-to-noise ratio could be obtained under sub-Nyquist sampling conditions.