Ultra-sensitive mid-infrared single-pixel imaging method and device based on non-linear spatial modulation

Abstract

The present invention discloses a super-sensitive mid-infrared single-pixel imaging method and device based on non-linear spatial modulation. The feature is that by means of non-linear frequency up-conversion technology, the pump light is subjected to optical field spatial modulation by a spatial light modulator and then mapped into a non-linear crystal, so as to realize spatial sampling of the mid-infrared signal light carrying the information of the object to be imaged. At the same time, the mid-infrared signal light is converted to the visible light band, and the obtained visible light is focused by a lens onto a single-point silicon-based detector. The optical sum of the inner product of the modulation pattern and the real image of the object is subjected to signal conversion, and image reconstruction is carried out through an algorithm to realize super-sensitive mid-infrared single-pixel imaging. Compared with the prior art, the present invention has high-fidelity spatial modulation in the mid-infrared band and super-sensitive mid-infrared imaging with high signal-to-noise ratio, is structurally compact and integrated, improves the robustness and accuracy of the mid-infrared imaging system, and can be widely applied to military target warning, biological cell tissue imaging, topography analysis and other military, medical and civilian industrial fields.

Description

Technical Field

[0001] The present invention relates to the field of infrared imaging technology, and in particular to a super-sensitive mid-infrared single-pixel imaging method and device based on non-linear spatial modulation. Background Art

[0002] Mid-infrared imaging has the advantages of long action distance, good anti-interference ability, strong haze penetration ability, and can work all-weather and all-day. It can be applied to the reconnaissance and identification of far, medium, and short-range targets and infrared guidance in the military field. In the industrial field, since infrared electromagnetic waves can penetrate semiconductor substrates, defects (such as cracks, impurities, dislocations, etc.) inside silicon wafers can be accurately identified through infrared images, providing a fast and efficient non-destructive detection method for chip process manufacturing. In addition, the mid-infrared band contains the vibrational-rotational energy level transition spectral lines of many important molecules, which is in the molecular fingerprint spectral region and also covers multiple transmission windows of the earth's atmosphere. Therefore, the development of high-performance and super-sensitive mid-infrared imaging not only promotes the development of basic disciplines such as molecular spectroscopy and space astronomy, but also has important applications in civil and national defense fields such as remote sensing, precision agriculture, pollution monitoring, mineral exploration, and medical diagnosis.

[0003] However, traditional mid-infrared imaging devices based on narrow-bandgap materials such as mercury cadmium telluride (HgCdTe) and indium antimonide (InSb) have long faced technical problems such as slow speed, low sensitivity, and high dark noise. Their detection sensitivity is only at the sub-nanowatt level, and the corresponding equivalent noise power is 10 10 photons / second, far from achieving super-sensitive detection at the single-photon level. Usually, HgCdTe and InSb area array CCDs often need to operate at low temperature during use, which not only brings higher costs to imaging, but also greatly increases the complexity of the imaging system. Therefore, the development of super-sensitive mid-infrared imaging technology approaching the single-photon level at room temperature has always been a challenging research topic in the field of infrared measurement and control.

[0004] In recent years, single-pixel imaging systems have become a research hotspot in the imaging field due to their novel architecture that does not require an imaging array and the low cost of single-pixel sensors. Its principle lies in generating structured light illumination through a spatial light modulator to sample the spatial intensity information of the object to be imaged. The intensity information of the structured light modulated by the object is collected by a single-pixel detector. Through multiple iterative samplings, an intensity signal sequence under different structured light illumination conditions is obtained. By means of a correlation algorithm, the reconstruction of the spatial amplitude information of the object is realized. Single-pixel imaging relies on spatial structured light sampling and has relatively low requirements for spatial information at the detector end, greatly simplifying the imaging device. However, limited by the material properties and fabrication process of the spatial light modulator, currently common spatial light modulators are mostly for the visible light band and have not yet been applied in the mid-infrared band. In addition, the wavelength of the mid-infrared light field is longer than that of visible light, and the diffraction effect is more serious, posing higher requirements for high-precision spatial regulation. Summary of the Invention

[0005] The object of the present invention is to provide a highly sensitive mid-infrared single-pixel imaging method and device based on non-linear spatial modulation in view of the deficiencies of the prior art. A spatial light modulator is used to perform spatial encoding on a near-infrared pump light, and the pump light encoding information is applied to the mid-infrared light field through a non-linear sum-frequency process to achieve spatial regulation of the mid-infrared. Finally, highly sensitive mid-infrared single-pixel imaging is realized through detection by a high-performance silicon-based detector and an image reconstruction algorithm. Based on the mid-infrared non-linear spatial modulation of the above method, the limitation that traditional spatial light modulators are difficult to operate in the mid-infrared band is circumvented. At the same time, by means of the non-linear frequency conversion process, the mid-infrared signal wavelength is converted to the visible light band, and high-performance silicon-based detectors can be used to achieve highly sensitive photon detection, overcoming the problem of insufficient sensitivity of traditional mid-infrared detector devices. This mid-infrared single-pixel upconversion imaging technology has the advantages of high sensitivity and simple device, and has broad application prospects in the fields of space detection, infrared warning, biological imaging, etc.

[0006] The specific technical solution to achieve the object of the present invention is: a highly sensitive mid-infrared single-pixel imaging method based on non-linear spatial modulation, which is characterized by using a spatial light modulator to perform spatial encoding on a near-infrared pump light, and regulating the mid-infrared light field through the pump light encoding information by means of a non-linear sum-frequency process, and realizing highly sensitive mid-infrared single-pixel imaging based on non-linear frequency upconversion and detection by a single-point silicon-based detector.

[0007] The non - linear frequency up - conversion is to modulate the pump light through the set encoding matrix on the spatial light modulator, and then map it into the non - linear crystal to achieve spatial sampling of the mid - infrared signal light carrying the information of the object to be imaged. At the same time, the non - linear crystal is used to convert the mid - infrared to the visible light band. Then, the visible light obtained by non - linear frequency up - conversion is focused onto a silicon - based photosensitive detector with a sensitivity that can reach the single - photon level through a lens. Its conversion process is equivalent to taking the inner product of the modulation pattern and the real image of the object. After converting the obtained sum of light into a signal and transmitting it to the computer, after multiple operations to obtain a large number of measurement signals, and then through algorithms for computational imaging, it provides the possibility for realizing ultra - sensitive mid - infrared computational imaging at the single - photon level.

[0008] In the part of single - pixel imaging based on the non - linear frequency up - conversion process of the present invention, for the mid - infrared signal light, a 2f system is used to image the target object. By selecting a lens with an appropriate focal length, the image formed by the mid - infrared light is focused into the non - linear crystal and is slightly smaller than the pump light spot to achieve spot matching for high - efficiency non - linear conversion. In this way, the mid - infrared light can be converted to the visible light band through sum - frequency generation. At this time, the frequency of the incident mid - infrared signal light ω s and the frequency of the pump light ω p sum up to the frequency ω up of the sum - frequency light, satisfying the law of conservation of energy, as shown in the following formula (1):

[0009] ω up =ω s +ω p (1).

[0010] In addition, the intensity I up(x，y ) of the sum - frequency light is equal to the product of the light field I s_obj(x，y) of the signal light carrying the information of the object to be imaged and the light field of the encoded and modulated pump light I p_module(x，y) , which is expressed by the following formula (2):

[0011] I up(x，y) =I s_obj(x，y) ×I p_module(x，y) (2).

[0012] Through the above non - linear sum - frequency process, not only can the mid - infrared wavelength be converted to the visible light band, but from formula (2) above, it can be seen that the intensity of the sum - frequency light field is proportional to the intensity of the mid - infrared signal light field. Then, by using pump lights modulated with different matrix encodings, sum - frequency lights with different intensity values corresponding to the matrix - encoded pump lights can be obtained. Then, by collecting the intensity information of the sum - frequency light field with a single - point silicon - based detector with mature technology and good performance parameters and reconstructing the image through algorithms, ultra - sensitive two - dimensional imaging in the mid - infrared band can be realized through single - point detection.

[0013] In the single-pixel imaging section, a spatial light modulator is used to perform matrix encoding modulation on the pump light of non-linear frequency conversion. The spatially modulated pump beam undergoes frequency conversion with mid-infrared light, and spatial intensity sampling is performed on the mid-infrared signal light. Subsequently, the sum-frequency light obtained from the above process, which has been modulated and frequency-converted to the visible light band, is focused onto a super-sensitive single-point silicon-based photodetector through a relay lens. As can be seen from Equation (2) above, the intensity detection of the sum-frequency light field can directly reflect the modulation situation of the mid-infrared light field. By repeatedly refreshing the modulation matrix of the spatial light modulator, a series of modulation information can be obtained. The optical signal is converted into a digital signal through a super-sensitive photodetector and an FPGA, and then transmitted to a computer. An algorithm can be used to reconstruct the super-sensitive mid-infrared image of a single photon level of the target object.

[0014] The super-sensitive mid-infrared single-pixel imaging device based on non-linear spatial modulation has a simple structure. By multiplying the matrix encoding pattern of the spatial light modulator by the corresponding single-pixel intensity measurement, a set of weighted patterns is obtained, and then the sum is calculated to obtain the reconstructed image. Its model is shown in Equation (3) below:

[0015]

[0016] where O(x, y) is the two-dimensional image of the object to be imaged; P m (x, y) is the orthogonal mode sequence; S m is the differential intensity signal between the corresponding positive and negative patterns; M is a set of N different pattern sequences.

[0017] In principle, to reconstruct an image composed of N pixels, M = N different pattern sequence sets are required. However, if the set is a non-orthogonal mode or is interfered by noise during the measurement process, then M ≥ N is required to obtain a reconstructed image with a relatively good signal-to-noise ratio. Given an N-element orthonormal mode sequence P m (x, y) (where m is the pattern serial number), the differential intensity signal between the corresponding positive and negative patterns is S m , and they are proportional to the correlation between each pattern and the object to be imaged. Based on M matrix encoding patterns, the two-dimensional image O(x, y) of the object to be imaged can be calculated through Equation (3). For example, a common method is to use an orthogonal mode set, such as the Hadamard matrix, for spatial light modulation encoding, measure the differential intensity of each encoded pattern, and combine the measurement encoding matrix. Then, the image can be reconstructed through Equation (3) above.

[0018] A super-sensitive mid-infrared single-pixel imaging device based on non-linear spatial modulation, characterized in that the imaging device includes: pump light of a near-infrared light source, signal light of a mid-infrared source, an object to be imaged, a near-infrared spatial light modulator, a non-linear frequency conversion system, a single-point silicon-based detector, a data acquisition system, and an image reconstruction system, to achieve super-sensitive mid-infrared single-pixel imaging.

[0019] The non-linear frequency conversion system uses a spatial light modulator to control the pump light field and maps it into the non-linear medium of the frequency conversion system to achieve spatial modulation of the mid-infrared signal light, and converts the mid-infrared to the visible light band through non-linear action, and uses a single-point silicon-based detector for super-sensitive detection; the mid-infrared signal light uses a 2f single-lens imaging system to image the target object, and focuses the image formed by the mid-infrared light into the non-linear crystal through the lens, and is slightly smaller than the pump light spot to achieve spot matching and realize high-efficiency non-linear conversion.

[0020] The ultra-sensitive mid-infrared single-pixel imaging realizes the spatial modulation of the mid-infrared signal light by precisely controlling the spatial intensity of the pump light in the frequency conversion system, solves the technical problems of the fabrication process of the spatial light modulator in the mid-infrared band and material defects, and can achieve mid-infrared two-dimensional imaging detection with a single-point silicon-based detector, greatly reducing the cost and complexity of the system. Since the light intensity received by the single-point detector is the superposition of multiple pixel points of the imaging target, this value is much larger than the light intensity on a single pixel received by the traditional imaging system with point-by-point scanning or area array detector, and the signal-to-noise ratio can be further improved. In addition, the single-point silicon-based detector can use ordinary photodetectors to reconstruct mid-infrared images under strong light, or can use a ultra-sensitive silicon-based photon counting module (SPCM) for detection under weak light to achieve ultra-sensitive mid-infrared two-dimensional imaging at the single-photon level. Among them, the spatial light modulator for realizing precise spatial light control can be either an intensity modulator such as a DMD (Digital Micromirror Device), or a phase modulator such as an LCOS SLM (Liquid-crystal-on-silicon Spatial Light Modulator). Although the DMD has slightly lower efficiency, it has the advantages of high speed, wide spectrum, low cost, and being friendly to pulsed light. Although the LCOS SLM is expensive, it has the advantage of being able to conveniently realize simultaneous modulation of phase and intensity. In addition, the response rate of the spatial light modulator is very fast, and it can quickly refresh the modulation information of light, and the refresh frequency can generally reach 10k - 20kHz, so the technology proposed in the present invention can also perform real-time imaging of the target object. In addition, by using some mature algorithms such as spatial sparse aggregation algorithm (SCA), hard threshold algorithm (HTP), etc., combined with deep learning training to restore the image, and combining the integrated multi-task technology system of tracking and then imaging the moving object, it is possible to further achieve rapid positioning, clear imaging and recognition of high-speed moving targets.

[0021] The ultra-sensitive mid-infrared single-pixel imaging system of the present invention realizes mid-infrared single-pixel imaging by means of nonlinear frequency up-conversion technology, and its imaging resolution is jointly determined by the frequency conversion technology and the characteristics of the single-pixel imaging system. A 2f imaging system is adopted in the nonlinear frequency up-conversion system, and its resolution mainly depends on the emission angle of the light beam obtained by frequency up-conversion. To meet the phase-matching condition of nonlinear frequency up-conversion, there will be a certain angular limit range for the emission angle of the frequency up-converted light in the emission direction, which is mainly determined by the phase-matching characteristics and the crystal length. In fact, this angle limits the numerical aperture of the next imaging lens. Since it is usually very small (about 0.01–0.1 radians), in this case, the numerical aperture of the second lens is usually selected as sin 0.8rad = 0.72 to produce better resolution. In the part of single-pixel imaging, its imaging resolution is mainly determined by the pixel size of the coding array of the spatial light modulator. At present, the manufacturing process of the micromirror array of the spatial light modulator can reach the micron level. The spatial light modulator with high resolution and a structure of tiny mirror units can clearly and accurately display the details of the image, thus reducing the distortion generated by the pattern during the imaging process. Therefore, the resolution of the ultra-sensitive mid-infrared single-pixel imaging system mainly depends on the up-converted emission light angle that satisfies the phase-matching condition of nonlinear frequency conversion and the array size of the spatial light modulator.

[0022] More importantly, in the nonlinear frequency conversion part of the ultra-sensitive mid-infrared single-pixel imaging technology, by selecting nonlinear media suitable for broadband mid-infrared frequency conversion, such as chirped poled lithium niobate crystal (CPLN), etc., high-fidelity optical field modulation in a wide mid-infrared band range can be further achieved through precise control of the pump light, without being limited by the performance deficiency of mid-infrared modulation devices; the nonlinear media for quasi-phase matching can also select nonlinear semiconductor crystals such as oriented-patterned gallium phosphide (OP-GaP) or gallium arsenide (OP-GaAs) grown based on the oriented pattern technology, which are suitable for the mid- to far-infrared band (3-12μm), and it is expected to further expand the ultra-sensitive mid-infrared single-pixel imaging to the far-infrared band.

[0023] The present invention has the following beneficial technical effects and remarkable technical progress compared with the prior art:

[0024] 1) By adopting single-pixel imaging technology, by means of the nonlinear frequency conversion method, spatial modulation of mid-infrared signal light is achieved through precise spatial intensity control of the pump light. Combining with broadband frequency conversion nonlinear crystals, the band range of mid-infrared spatial modulation can be broadened, providing an effective way to achieve high-fidelity spatial modulation in broadband mid-infrared.

[0025] 2) The use of a spatial light modulator can achieve fast spatial light modulation and real-time imaging. Combining with algorithms and an integrated multi-task technology system that first tracks and then images moving objects, it can ultimately achieve fast positioning, clear imaging, and recognition of high-speed moving targets.

[0026] 3) By adopting the non-linear frequency up-conversion detection technology, converting mid-infrared to the visible light band, and using a room-temperature-operable ultra-sensitive silicon-based single-point detector for detection, image reconstruction is achieved through algorithms, avoiding the problems of insufficient sensitivity, low efficiency, and slow speed of existing mid-infrared imaging devices. In addition, benefiting from the mature technology and high-speed and high-performance silicon-based detectors, ultra-sensitive two-dimensional mid-infrared imaging can be achieved with a single-point detector.

[0027] 4) The single-pixel imaging system is more compact and simple in structure compared with the traditional imaging system using array detectors. In addition, combining with the non-linear frequency up-conversion technology avoids the bulky and complex structure that requires cooling for traditional mid-infrared imaging cameras. Ultra-sensitive two-dimensional mid-infrared imaging can be achieved using a single silicon-based pixel detector, further reducing the system cost and complexity, and improving the robustness and accuracy of the system. Description of the Drawings

[0028] Figure 1 Schematic diagram of a single-pixel imaging system of the prior art;

[0029] Figure 2 Schematic diagram of a single-pixel imaging system of the architecture of the present invention;

[0030] Figure 3 Schematic diagram of the process of the present invention;

[0031] Figure 4 Schematic diagram of the structure of the ultra-sensitive mid-infrared single-pixel imaging device of the present invention. Detailed Embodiments

[0032] Refer to Figure 1 , the traditional single-pixel imaging system samples the spatial intensity information of the object to be imaged through structured light illumination with a certain spatial distribution. The light intensity information modulated by the object is collected by a single-point detector. After multiple iterative samplings, a sequence of intensity signals under different structured light illumination conditions is obtained, and the spatial amplitude information of the object is reconstructed using the correlation algorithm. However, this system is currently mainly applied to the visible light and near-infrared bands. In the mid-infrared band, due to the lack of existing spatial light modulator devices, there is no mature device to directly modulate the mid-infrared signal light. In addition, in the detection part, existing mid-infrared detectors cannot achieve ultra-sensitive detection in the mid-infrared band due to problems such as low detection efficiency, high noise, and slow response speed.

[0033] Refer to Figure 2, the present invention is based on a non - linear frequency conversion structure, modulates the pump light field through spatial light encoding to regulate the mid - infrared light field, and finally realizes the ultra - sensitive mid - infrared single - pixel imaging technology through detection by a silicon - based detector with excellent performance. By means of non - linear frequency up - conversion technology, after the pump light is modulated by the set encoding matrix on the spatial light modulator, it is mapped into the non - linear crystal to achieve spatial sampling of the mid - infrared signal light carrying the information of the object to be imaged. At the same time, the non - linear crystal is used to convert the mid - infrared to the visible light band. Then, the visible light obtained by non - linear frequency up - conversion is focused by a lens onto a silicon - based photosensitive detector with a sensitivity that can reach the single - photon level. This process is actually equivalent to taking the inner product of the modulation pattern and the real image of the object. After that, the obtained sum of light is subjected to signal conversion and transmitted to the computer. After multiple operations to obtain a large number of measurement signals, calculation imaging is performed through an algorithm, providing the possibility for realizing ultra - sensitive single - pixel mid - infrared computational imaging at the single - photon level.

[0034] The single - pixel imaging system with non - linear spatial modulation proposed by the present invention is based on a non - linear frequency conversion structure. By means of a spatially light modulator in the mature and near - infrared ω p band, the pump light is precisely regulated and mapped into the non - linear medium of the frequency conversion system to achieve spatial modulation of the mid - infrared signal light ω s , solving the technical problems of the preparation process and material defects of the spatial light modulator in the mid - infrared band. Through non - linear interaction, the mid - infrared ω s is converted to visible light ω up band. In this way, an existing single - point silicon - based detector with excellent performance suitable for the ω up band can be used for ultra - sensitive detection. Through a series of modulations of the spatial encoding matrix, a series of information is obtained at the detector end. Then, through the algorithm in the following formula (3), the ultra - sensitive mid - infrared two - dimensional imaging O(x, y) can be reconstructed:

[0035]

[0036] where O(x, y) is the two - dimensional image of the object to be imaged; P m (x, y) is the orthogonal mode sequence; S m is the differential intensity signal between the corresponding positive and negative patterns; M is a set of N different pattern sequences.

[0037] Referring to Figure 3 , the ultra - sensitive mid - infrared single - pixel imaging system of the present invention includes: a near - infrared light source as the pump light, a mid - infrared source as the signal light, an object to be imaged, a near - infrared spatial light modulator, a non - linear frequency conversion system, a single - point ultra - sensitive silicon - based detector, a data acquisition system, and an image reconstruction system.

[0038] The mid-infrared source passes through the object to be imaged, and a real, inverted, and reduced image is formed by a single lens of a 2f system and enters the PPLN crystal of the nonlinear frequency conversion system. Here, the imaging satisfies the formula: 1 / d 1 +1 / d 2 = 1 / f. By reasonably selecting the focal length of the lens and the position of the object to be imaged, the imaging size in the mid-infrared range is slightly smaller than the pump spot and the crystal aperture size, facilitating subsequent frequency conversion.

[0039] Near-infrared light, serving as the pump light source for nonlinear frequency conversion, is irradiated onto the spatially light modulator encoded by a matrix and then reflected. After carrying the encoded information, the reflected pump light enters the nonlinear frequency conversion system. That is, in the nonlinear crystal, while achieving the wavelength conversion from mid-infrared to visible light, the near-infrared pump light performs spatial encoding modulation on the mid-infrared imaging. Then, through single-pixel sampling by a data acquisition system with a highly sensitive silicon-based single-point detector and an image reconstruction system processed by computer algorithms, a mid-infrared image is obtained. Finally, through this method of nonlinear spatial modulation, single-pixel hypersensitive imaging in the mid-infrared band can be achieved.

[0040] To more clearly illustrate the structure of the hypersensitive mid-infrared single-pixel imaging system, a pulsed laser with a central wavelength of 1030 nm, a mid-infrared source with a central wavelength of 3070 nm, an intensity-type spatial light modulator DMD, a highly sensitive silicon-based photon counting module, and a mask plate with a "cross" pattern are selected as the object to be imaged and a periodically poled lithium niobate crystal (PPLN).

[0041] The following further elaborates on the present invention through specific embodiments.

[0042] Embodiment 1

[0043] Refer to Figure 4 The hypersensitive mid-infrared single-pixel imaging system includes: a pump light source 100, a focusing lens 101 with f = 35 mm, a focusing lens 102 with f = 150 mm, a digital micromirror array (DMD) 103, a focusing lens 104 with f = 250 mm, a plane silver mirror 105, a focusing lens 106 with f = 50 mm, a dichroic mirror with high reflectivity at 1030 nm (high transmission in mid-infrared) 107, a signal light mid-infrared source 108, a target object to be measured 109, a calcium fluoride lens 110 with f = 50 mm, a nonlinear frequency up-conversion crystal 111, a temperature control furnace 112, a focusing lens 113 with f = 75 mm, a filter system 114, a highly sensitive silicon-based photon counting module 115, an FPGA circuit system 116, and a computer 117.

[0044] The pump light source 100 is a fiber pulsed laser that has been preliminarily amplified, with an average power reaching the order of hundreds of milliwatts and a wavelength of 1030 nm;

[0045] The f = 35mm focusing lens 101 and the f = 150mm focusing lens 102 are focusing lenses with high transmittance in the 1030nm mid-infrared range;

[0046] The digital micromirror device (DMD) 103 can, under the control of a synchronization circuit, simultaneously control the selected micromirrors to deflect by plus or minus 12°, thereby realizing the modulation of spatial light. Its digital micromirror refresh rate is 20 kHz;

[0047] The f = 250mm focusing lens 104 and the f = 50mm focusing lens 106 are focusing lenses with high transmittance in the 1030nm mid-infrared range;

[0048] The plane silver mirror 105 can reflect light with high transmittance in the 1030nm mid-infrared range to adjust the optical path direction;

[0049] The dichroic mirror (mid-infrared high transmittance) 107 with high reflectance at 1030nm can allow the mid-infrared light source to pass through while reflecting the 1030nm light;

[0050] The signal light mid-infrared source 108 is a mid-infrared pulsed laser with a central wavelength of 3070nm;

[0051] The object to be measured 109 is a "cross" hollow pattern;

[0052] The calcium fluoride lens 110 with f = 50mm has a relatively high transmittance for the mid-infrared light source;

[0053] The nonlinear frequency up-conversion crystal 111 is a periodically poled lithium niobate (PPLN) crystal;

[0054] The temperature control furnace 112 can precisely control the temperature of the crystal to meet the phase matching condition;

[0055] The f = 75mm focusing lens 113 has a relatively high transmittance for the light obtained by frequency conversion;

[0056] The filter system 114 has a relatively high transmittance for the light of nonlinear frequency up-conversion, that is, the light with a wavelength of 771nm, and has a relatively high reflectance for light in other bands, which can effectively reduce noise;

[0057] The ultrasensitive silicon-based spatial light detector 115 is an ultrasensitive silicon-based photon counting module, which can achieve ultrasensitive detection of light in the visible band;

[0058] The FPGA circuit system 116 is a high-speed intelligent acquisition and control system based on FPGA. By triggering the DMD and programming the FPGA control, the switching and data acquisition of the Hadamard matrix coding map of the DMD are realized;

[0059] The computer 117 receives the transmission signal from the FPGA and performs image reconstruction through algorithms.

[0060] The specific operations of this embodiment are as follows:

[0061] 1) The pulsed laser 100 with a wavelength of 1030 nm that has undergone preliminary high-power low-noise amplification is expanded in spot size through the beam expander system composed of the focusing lens 101 and the focusing lens 102, and is irradiated onto the digital micromirror array DMD 103 with a Hadamard matrix coding pattern, which is controlled by the FPGA circuit system 116 and the computer 117 at this time. After the reflected light carries the coded modulation information, it passes through the 4f system composed of the focusing lens 105 and the focusing lens 106. While reducing the spot size, the coded information on the DMD is imaged on the nonlinear frequency up-conversion crystal 111. Among them, the plane reflecting silver mirror 105 and the dichroic mirror 107 with high transmittance in the mid-infrared and high reflectance at 1030 nm are used to adjust the optical path direction, so that the subsequent imaging of the mid-infrared on the target object coincides with the optical path in the crystal.

[0062] 2) The mid-infrared light source 108 with a central wavelength of 3070 nm passes through the "cross" hollow pattern, that is, the target object 109 to be measured, and realizes 2F system imaging through the calcium fluoride lens 110 with f = 50 mm, satisfying the imaging formula: 1 / d 1 +1 / d 2 = 1 / f, while reducing the spot size, and the imaging scaling ratio is: ɑ = d 2 / d 1 . And it enters the PPLN crystal 111 through the dichroic mirror 107 with high transmittance in the mid-infrared and high reflectance at 1030 nm.

[0063] 3) The temperature of the crystal is accurately controlled by the temperature control furnace 112 to adjust the spot coincidence and matching of the signal light 108 and the pump light 100, and meet the phase matching conditions for nonlinear frequency conversion, so as to realize the wavelength conversion from mid-infrared to visible light and generate the sum-frequency light with a wavelength of 771 nm.

[0064] 4) The visible light with a wavelength of 771 nm generated by sum-frequency is focused onto the ultrasensitive silicon-based spatial light detector 115 through the focusing lens 113, and before focusing, it passes through the filter system 114 to filter out the noise brought by the pump light, signal light, second harmonic light, parametric fluorescence, etc. generated by frequency conversion. Then, the signal obtained by the detector 115 is transmitted to the computer 117 through the FPGA circuit system 116, and the computer performs image reconstruction through the algorithm of matrix solution. Finally, the ultrasensitive mid-infrared single-pixel imaging detection at the single-photon level can be realized.

[0065] The present invention provides a super-sensitive mid-infrared single-pixel imaging technology, and two-dimensional mid-infrared super-sensitive imaging can be achieved through a single-point silicon-based detector with excellent performance. The present invention mainly includes: a single-pixel imaging technology and a non-linear frequency up-conversion system, that is, in the non-linear frequency conversion system, a spatial light modulator is used to precisely control the pump light field to indirectly achieve spatial modulation of the mid-infrared light field. At the same time, the mid-infrared signal light is converted to the visible light band through a non-linear medium, and then super-sensitive imaging in the mid-infrared band can be achieved through a high-performance single-point silicon-based detector. Since the spatial light modulator has a fast response speed and can achieve high-speed spatial light modulation, real-time imaging can be achieved. In addition, combined with an algorithm and an integrated multi-task technology system for tracking and then imaging moving objects, fast positioning, clear imaging and recognition of high-speed moving targets can also be achieved.

[0066] The above specific embodiments are only for further illustrating the present invention, and are not intended to limit the patent of the present invention. All equivalent embodiments of the present invention should be included within the scope of the claims of the patent of the present invention.

Claims

1. A super-sensitive mid-infrared single-pixel imaging method based on non-linear spatial modulation, characterized in that Using single-pixel imaging technology, by precisely controlling the pump light field with a spatial light modulator, non-linear spatial modulation of the signal light in the mid-infrared band is achieved. The non-linear spatial modulation uses non-linear frequency up-conversion technology to modulate the pump light by the encoding matrix set by the spatial light modulator and map it into a non-linear crystal, spatially sampling the mid-infrared signal light carrying the information of the object to be imaged. At the same time, the non-linear crystal is used to convert the mid-infrared signal light to the visible light band. The obtained visible light is focused by a lens onto a single-point silicon-based detector with a sensitivity up to the single-photon level, converting the optical sum of the inner product of the modulation pattern and the real image of the object into a signal, and performing image reconstruction through an algorithm to achieve two-dimensional ultra-sensitive mid-infrared single-pixel imaging at the single-photon level. The image reconstruction is to multiply the matrix encoding pattern of the spatial light modulator by the corresponding single-pixel intensity measurement to obtain a set of weighted patterns, and then sum them to obtain the reconstructed image. The reconstructed image calculates the two-dimensional image of the object to be imaged by the algorithm of the following formula (3). : （3）； Among them, is an orthogonal mode sequence; S m corresponds to the differential intensity signal between the positive and negative patterns; M is a set of N different pattern sequences.

2. The super-sensitive mid-infrared single-pixel imaging method based on non-linear spatial modulation according to claim 1, characterized in that The spatial light modulator uses high-speed modulation to achieve real-time imaging of an object, and combines a reconstruction algorithm and an integrated multi-task technology system for first tracking and then imaging a moving object to achieve rapid positioning, clear imaging and recognition of a high-speed moving target.

3. An imaging device constructed by the super-sensitive mid-infrared single-pixel imaging method according to claim 1, characterized in that The imaging device consists of pump light from a near-infrared light source, signal light from a mid-infrared source, an object to be imaged, a near-infrared spatial light modulator, a non-linear frequency converter, a single-point silicon-based detector, data acquisition and image reconstruction. The non-linear frequency converter uses a spatial light modulator to control the pump light field and maps it into a non-linear medium to achieve spatial modulation of the mid-infrared signal light, and converts the mid-infrared to the visible light band through non-linear action, and uses a single-point silicon-based detector for super-sensitive detection; the mid-infrared signal light uses a 2F single-lens imaging system to image the target object, and the image formed by the mid-infrared light is focused into the non-linear medium through the lens and is slightly smaller than the pump light spot to achieve spot matching and realize high-efficiency non-linear conversion.

Images