A single-pixel ultraviolet optical imaging system based on quantum dot down-conversion

Abstract

The present invention belongs to the field of computational imaging technology, and specifically is an ultraviolet single-pixel computational optical imaging system based on quantum dot down-conversion. The system of the present invention includes an ultraviolet emission module, an ultraviolet down-conversion module, a spatial light encoding module, and a single-pixel imaging module. Under the conditions of the unique photoelectric characteristics of quantum dots, the present invention can achieve high-efficiency wavelength conversion in a wide spectrum range, thereby converting ultraviolet wavelengths into visible light wavelengths; based on a digital micromirror array spatial light modulator, it can perform binary phase modulation on light, thereby transmitting light-encoded information; based on single-pixel imaging technology, it can achieve imaging with a wider dynamic range and higher sensitivity. Compared with traditional area array detection imaging methods, the present invention can use only a single-pixel detector without spatial resolution to record image information, and can image under complex conditions of low light and scattering in the detection path.

Description

Technical Field

[0001] The present invention belongs to the technical field of computational optical imaging, and in particular relates to a computational optical imaging system for invisible ultraviolet light. Background Art

[0002] Photodetectors are photoelectric devices that convert non-conductive charges into conductive charges under the action of light radiation. Visible light detection devices are already very mature, but for the ultraviolet spectrum, there are problems such as ultraviolet light being easily absorbed and difficult to detect. Quantum dots are a type of nano-fluorescent material. By applying a certain light pressure to this nano-material, light of a specific frequency can be emitted. By adjusting the size of the quantum dots, the switching of light frequencies can be easily achieved. This characteristic can be used to convert ultraviolet light that is not easily detected directly into visible light, so as to achieve ultraviolet light detection.

[0003] Traditional optoelectronic imaging technology was developed in the industrial age. It is based on geometric optics and plays an important role in both civil and military applications. Traditional optoelectronic imaging technology is designed to obtain images that meet the requirements of human or machine vision. Usually, it is necessary to ensure the acquisition of high-quality image data during image acquisition. The way this technology obtains information leads to the loss of light field information such as phase, polarization, and spectrum, so that the detector only obtains a single physical quantity information of the two-dimensional intensity image, making it difficult to achieve the imaging requirements of "higher imaging resolution, longer detection distance, larger imaging field of view, smaller power consumption and smaller size". Based on the above factors, computational optical imaging technology will become one of the key technologies for future imaging scenarios.

[0004] Computational optical imaging technology is a type of information acquisition and processing method that is different from traditional optical imaging. It adopts the imaging method of "modulation first, then shooting, and then demodulation". It is a new cross-technology that integrates optics, mathematics, and signal processing. Through the collection and calculation of light field information, it achieves information utilization and interpretation that traditional imaging technology cannot achieve. This technology integrates lighting, optical medium transmission, optical system, detection imaging and display, and systematically describes optical imaging. Controllable coded information is artificially introduced through the lighting and imaging system, with the aim of modulating more essential information of the object or scene into the original image signal that can be captured by the sensor. In the demodulation stage, based on the theoretical foundations of geometric optics, the process of optical system imaging through the detector is established into an accurate forward mathematical model, and finally reconstruction is achieved by solving the "inverse problem" of the forward imaging model. Summary of the invention

[0005] The purpose of the present invention is to propose an ultraviolet single-pixel optical imaging system based on quantum dot down-conversion to overcome the problem that invisible ultraviolet light is difficult to image.

[0006] The ultraviolet single-pixel computational optical imaging system based on quantum dot down-conversion provided by the present invention has a structure as shown in Figure 1 As shown, it includes an ultraviolet emission module, an ultraviolet down-conversion module, a spatial light encoding module and a single-pixel imaging module; wherein:

[0007] The ultraviolet emission module is composed of a power supply and an ultraviolet light-emitting diode (UV-LED); the power supply limits the voltage to below 12V and provides a current of 60mA to light up the ultraviolet light-emitting diode (UV-LED), and obtains the excited ultraviolet light according to the working principle of the light-emitting diode. As the light source of the present invention, the wavelength range of the ultraviolet emission module spans 260nm-370nm, and is represented by 265nm, 305nm and 365nm ultraviolet light-emitting diodes;

[0008] The ultraviolet down-conversion module is composed of cadmium selenide (CdSe) quantum dot material and a glass sheet; specifically, cadmium selenide powder quantum dots are dissolved in volatile oily substances such as toluene, and then scraped on one side of a glass sheet (such as one inch), and after volatilization, a quantum dot film is formed to achieve fluorescence excitation of the quantum confinement effect, and according to the nonlinear optical changes of the quantum dots, high-energy ultraviolet photons can be converted into visible light photons with lower energy;

[0009] The spatial light encoding module is a digital micromirror array; the number of micromirrors is in the tens of millions, and each micromirror rotates independently at a certain angle; one micromirror corresponds to one pixel; by changing the flip state of each micromirror, the intensity and direction of the modulated light are modulated to perform pixel-level modulation, thereby achieving high-speed, efficient and reliable spatial light ON:OFF encoding; according to the principle of digital micromirror array spatial light modulator, each micromirror is independently controlled to achieve spatial modulation of the light passing through;

[0010] The single-pixel imaging module is composed of a high-performance workstation, a convex lens and a high-speed response photodiode (PD). The convex lens converges the light intensity of the detected object and the spatially modulated light after superposition. The converged light beam is received by the high-speed response photodiode. The light intensity received by the photodiode is converted into an electrical signal to obtain the modulated light signal intensity, and the back-end image reconstruction is performed.

[0011] Further:

[0012] In the present invention, the ultraviolet emission module, the ultraviolet light source excited by the working principle of the light-emitting diode (the system has a mature technology and is used in most ordinary occasions or environments), specifically includes: fixing the ultraviolet light-emitting diode on the heat dissipation part of the printed circuit board, limiting the voltage to below 12V and the current of 60mA through the lead and the external power supply, using the characteristics of the semiconductor material to inject carriers into the PN junction between the P-type semiconductor and the N-type semiconductor, and releasing the excess energy in the form of light after compounding with the majority of carriers, and finally converting the electrical energy into light energy to realize the electroluminescence phenomenon; specifically, a semiconductor material with a large band gap width can be selected to obtain light emission in the wavelength range of UV-A (400-315nm), UV-B (315-280nm) and UV-C (280-100nm). In order to better select the wavelength in the ultraviolet wavelength region, we use a bandpass filter for wavelength selection, and the bandpass filter is adjacent to the filter of the cutoff band on both sides of the transmission band, which can effectively select the wavelength. The light source is an optical device that emits wavelengths in the solar-blind region. From the perspective of reducing the size of the device, a laser diode or a light-emitting diode can be selected as an ultraviolet emission module device.

[0013] In the present invention, the ultraviolet down-conversion module utilizes the principle of quantum dot fluorescence to absorb high-energy photons, and the electrons in the quantum dots are transitioned to a higher energy level. The electrons gradually return to their original energy level and release photons, and the released photon energy is determined by the size of the quantum dots. The module utilizes semiconductor materials to a certain critical size, and the movement of electrons on the three-dimensional structure is limited, thereby showing a quantum local effect, which causes the electronic energy level near the Fermi level to change from a continuous state to a discrete state, and can excite fluorescence. In this module, we use cadmium selenide (CdSe) as a quantum dot material, and cadmium selenide powder is dissolved in volatile oily liquids such as toluene. After the quantum dot material is sucked off with a dropper, it is dripped on one side of a transparent glass sheet, and after rotating and smearing and waiting for volatilization, a layer of quantum dot film will be condensed on one side of the transparent glass. The ultraviolet light beam emitted by the ultraviolet emission module is collimated by a convex lens and then passes through the glass sheet coated with a quantum dot film. After the quantum dots are stimulated, the down-conversion is realized to convert ultraviolet light into yellow-green light.

[0014] In the present invention, the spatial light encoding module realizes a programmable binary transmission mask through a digital micromirror device, in which the elements take values ​​of "0" and "1" and obey the encoding method. Subsequently, the above transmission mask is projected onto the scene to realize structured lighting. Among them, the flip state of each micromirror is changed by an array composed of tens of millions of tiny mirrors that can rotate independently at a certain angle in the digital micromirror device, thereby modulating the intensity and direction of the light, and performing pixel-level modulation, wherein "0" means that the micromirror is reversely flipped -12°, and "1" means forward flipping, thereby realizing high-speed, efficient and reliable spatial light ON: OFF encoding. After the ultraviolet light carrying the detection object information passes through the ultraviolet conversion module, the object information is recorded on the light wave of the excited fluorescence band, and is collimated by the lens and then shot into the digital micromirror array to realize the spatial encoding of the visible fluorescence band light beam, thereby obtaining the spatial encoding module matrix to encode and modulate the target information, and finally obtain the encoded target information.

[0015] In the present invention, in a single-pixel imaging module, the micromirror is flipped according to the spatial light encoding module to realize matrix encoding, thereby encoding and modulating the information in the target scene, obtaining the encoded target signal, and collecting the light intensity by a high-speed response photodiode. Different masks in the spatial encoding module cause the intensity of the target signal light to change, and the light irradiates the photodiode to cause the current to change, thereby realizing the conversion of the light signal into an electrical signal and realizing intensity detection. The image information is separated into two parts: a two-dimensional image of the object and a mask image with spatial resolution; a two-dimensional image of the target object The target image contains N = n1 × n2 pixels. Assuming that a series of modulation mask patterns with spatial resolution are transmitted through the spatial light coding module, the modulation mask sequence of the spatial light coding module is expressed as Where M represents the number of codes implemented by the spatial light coding module. The modulation mask of the i-th frame is used; the corresponding M total light intensity values ​​are obtained after the modulation mask interacts with the two-dimensional image of the target object. The total light intensity is expressed as The above light intensity is captured by the photodetector (photodiode). The two-dimensional image of the target object can be expressed as The modulation mask of the spatial light coding module is expressed as You can get:

[0016] HI=p, (1)

[0017] The single-pixel imaging module uses the modulation mask sequence H of the known spatial light encoding module and the signal sequence p captured by the photodetector to reversely solve the two-dimensional image of the target object. Simply multiply both ends of formula (1) by the inverse matrix of H to solve I and achieve image reconstruction:

[0018] I=H -1p,(2)

[0019] The ultraviolet single-pixel computational optical imaging system based on quantum dot down-conversion provided by the present invention has the following working process:

[0020] (I) Provide the light source conditions required for imaging through the ultraviolet emission module, and realize ultraviolet irradiation of the target image; limit the voltage to below 12V and the current to 60mA through the lead and external power control, light up the ultraviolet light-emitting diode, the wavelength range spans 260nm-370nm, select 265nm, 305nm and 365nm ultraviolet light-emitting diodes to irradiate the target to obtain the spatial coding information of the target under ultraviolet light.

[0021] (ii) The spatial information carried by the invisible ultraviolet light is converted into visible light through an ultraviolet down-conversion module while maintaining the spatial information; cadmium selenide powder is dissolved in volatile oil liquids such as toluene, spread evenly and wait for evaporation, and then condensed into a quantum dot film on one side of the transparent glass. The ultraviolet light carrying the target spatial information irradiates the quantum dot film to stimulate fluorescence and carry the detection target information and transmit it.

[0022] (iii) A series of modulated mask patterns with spatial resolution are combined with the fluorescent target image through a spatial light encoding module; a digital micromirror array performs matrix encoding, and the spatial light encoding is realized by flipping the micromirrors at different angles to realize whether the light is reflected or not. The target spatial information converted into fluorescence after the ultraviolet irradiation quantum dots is collimated by a lens and then shot into the digital micromirror array to realize the spatial encoding of the visible fluorescent band light beam, and finally the encoded target information is obtained.

[0023] (IV) Through the single-pixel imaging module, the photodetector receives the light signal to realize the reconstruction of the invisible ultraviolet target image. The light intensity of the encoded target signal is detected by using a high-speed response photodiode (PD), and the target signal information is reversed by combining the detection of the total light intensity with the known spatial encoding of the digital micromirror array.

[0024] The ultraviolet single-pixel computational optical imaging system based on quantum dot down-conversion proposed by the present invention converts ultraviolet light into visible light bands through quantum dots, uses a photodetector (photodiode) without spatial resolution capability, detects the light intensity in the light transmission system, and associates the intensity with the structured light of the modulation mask sequence for calculation, thereby realizing image reconstruction of invisible ultraviolet light. In the present invention, quantum dot luminescence technology is used to realize conversion into visible fluorescence (yellow-green light) in the wavelength range of invisible ultraviolet light UV-A (400-315nm), UV-B (315-280nm) and UV-C (280-100nm); by using modulation devices such as digital micromirrors, multiple high-speed digital light reflection switch arrays are rotated within a certain angle range, thereby realizing information encoding of two-dimensional spatial images of visible light after light conversion; based on single-pixel imaging technology, high time resolution, light detection efficiency and detection bandwidth can be achieved through photodetectors (photodiodes), better detection can be obtained in complex environments such as scattering and weak light, and the target image can be quickly reconstructed according to the intensity of the light signal obtained after detection.

[0025] The present invention has the following advantages:

[0026] (1) The present invention is based on quantum dot down-conversion technology, which can convert invisible ultraviolet light into visible light for regulation. This regulation method can better utilize existing visible light modulation, detection and other devices, and can achieve a modulation method with lower cost, faster frame rate and higher modulation rate.

[0027] (2) The present invention is based on single-pixel imaging technology. Compared with array detectors, single electrical detection devices have better detection characteristics, higher detection efficiency and sensitivity, and can achieve imaging detection effects in weak light and scattered scenes. In addition, by combining signal processing algorithms such as compressed sensing and machine learning, the imaging efficiency can be effectively improved, and higher resolution can be obtained in the time dimension. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 This is a structural block diagram of the ultraviolet single-pixel computational optical imaging system based on quantum dot down-conversion of the present invention.

[0029] Figure 2 The diagram is a structural diagram of the ultraviolet single-pixel computational optical imaging system based on quantum dot down-conversion of the present invention.

[0030] Figure 3 This is an imaging principle diagram of the ultraviolet single-pixel computational optical imaging system based on quantum dot down-conversion of the present invention.

[0031] In the figure, reference numerals 101 are ultraviolet emission modules, 102 are ultraviolet down-conversion modules, 103 are spatial light encoding modules, and 104 are single-pixel imaging modules. DETAILED DESCRIPTION

[0032] The present invention will be further described below with reference to structural block diagrams and technical principle diagrams.

[0033] The ultraviolet single pixel imaging system based on quantum dot down-conversion proposed in the present invention has a structure as shown in Figure 1 It includes an ultraviolet emission module 101, an ultraviolet down-conversion module 102, a spatial light encoding module 103, and a single pixel imaging module 104; wherein:

[0034] The ultraviolet emission module 101 switches ultraviolet rays of different wavelengths according to different application scenarios to achieve illumination of the target image. In the ultraviolet light emitting diode, electrons transition to an excited state after voltage is applied, but the electrons cannot be maintained in this state. When they transition back to a low-energy state, they release energy and emit photons to obtain invisible ultraviolet rays. Since the ultraviolet LED has a large divergence angle, it is necessary to converge the light beam in the field of optical imaging to achieve better information utilization. The present invention places a convex lens with a large numerical aperture in front of the ultraviolet LED to collect invisible ultraviolet light to improve the utilization of the light beam, thereby obtaining more information. After the large numerical aperture on the right side of the ultraviolet emission module 101 obtains more light beam energy, it irradiates the target image. After the ultraviolet light beam obtains the spatial information of the target, the light beam is collimated by two convex lenses and irradiated onto the ultraviolet down-conversion module 102 with a parallel light beam.

[0035] In the ultraviolet conversion module 102, when the semiconductor material is reduced to a certain critical size, the movement of electrons in three dimensions is restricted, showing a quantum confinement effect. This effect causes the energy level of electrons near the Fermi level to change from continuous to discrete energy levels or the energy gap to widen, and discrete energy structures with molecular characteristics can be stimulated to emit fluorescence after being excited. The invention adds a narrow-band filter before a cadmium selenide (CdSe) quantum dot film to select the wavelength of invisible ultraviolet light. The filter allows light signals to pass through in a specific wavelength band, while light signals on both sides outside the wavelength band are blocked. The wavelengths of 365nm, 305nm and 265nm can be selected in UV-A (400-315nm), UV-B (315-280nm) and UV-C (280-100nm) respectively, so that the light transmitted into the quantum dot film is invisible ultraviolet light of a specific wavelength, thereby achieving the effect of converting ultraviolet light to excite visible fluorescence. A long-wave pass filter is added after the cadmium selenide (CdSe) quantum dot film to transmit visible light greater than 450nm, cut off light signals less than 450nm, and filter out ultraviolet light that may pass through, so as to ensure that the light passing through the ultraviolet conversion module converts invisible ultraviolet light into visible fluorescence.

[0036] The spatial light coding module 103 uses an array of digital micromirror devices, such as a plurality of high-speed digital light reflectors, and uses a rotating small aluminum reflector to realize the opening and closing of the optical switch. The number of lenses is determined by the display resolution, a small lens corresponds to one pixel, and the conversion rate can reach several thousand times per second or higher. When the digital micromirror device is in the "on" state, the reflector will rotate to +12 degrees, and when the digital micromirror device is in the "off" state, the reflector will rotate to -12 degrees. Combined with the digital micromirror device, the reflector will selectively reflect or leave the light-transmitting hole for the visible incident light after passing through the ultraviolet conversion module, so that the reflector in the "on" state looks very bright, and the reflector in the "off" state looks very dark, thereby realizing ON: OFF coding. The present invention performs optical switching of the prepared coding format, thereby realizing spatial coding modulation of visible light.

[0037] The single pixel imaging module 104 flips the micromirror according to the spatial light encoding module 103 to achieve structured illumination, thereby encoding and modulating the fluorescence signal obtained by the UV conversion module 102. The spatially encoded target signal finally obtained is collected by the high-speed response photodiode for light intensity. The image information is separated into two parts: a two-dimensional image of the object and a mask image with spatial resolution; assuming that the two-dimensional image of the target object The target image contains N=n1×n2 pixels; assuming that a series of modulation mask patterns with spatial resolution are transmitted through the spatial light coding module in claim 4, the modulation mask sequence of the spatial light coding module is expressed as Where M represents the number of codes implemented by the spatial light coding module. The modulation mask of the i-th frame is used; the corresponding M total light intensity values ​​are obtained after the modulation mask interacts with the two-dimensional image of the target object. The total light intensity is expressed as The above light intensity is captured by the photodetector. The two-dimensional image of the target object can be expressed as The modulation mask of the spatial light coding module can be expressed as You can get:

[0038] HI=p, (1)

[0039] The single-pixel imaging module uses the modulation mask sequence H of the known spatial light encoding module and the signal sequence p captured by the photodetector to reversely solve the two-dimensional image of the target object. Simply multiply both ends of formula (1) by the inverse matrix of H to obtain the solution:

[0040] I=H -1 p, (2).

Claims

1. A single-pixel ultraviolet computational optical imaging system based on quantum dot down-conversion, characterized in that: It includes an ultraviolet emission module, an ultraviolet down-conversion module, a spatial light encoding module and a single-pixel imaging module; wherein: The ultraviolet emission module is composed of a power supply and an ultraviolet light-emitting diode (UV-LED); the power supply limits the voltage to below 12V and provides a 60mA current to light up the ultraviolet light-emitting diode (UV-LED), and obtains the excited ultraviolet light according to the working principle of the light-emitting diode; the wavelength range of the ultraviolet emission module is 260nm-370nm; The ultraviolet down-conversion module is composed of cadmium selenide (CdSe) quantum dot material and glass sheets; according to the nonlinear optical changes of quantum dots, high-energy ultraviolet photons are converted into visible light photons with lower energy; The spatial light encoding module is a digital micromirror array; each micromirror in the array rotates a certain angle independently; one micromirror corresponds to one pixel; by changing the flip state of each micromirror, the intensity and direction of the light are modulated, and pixel-level modulation is performed to achieve spatial light ON:OFF encoding; according to the principle of digital micromirror array spatial light modulator, each micromirror is independently controlled to achieve spatial modulation of the light passing through; The single-pixel imaging module consists of a workstation, a convex lens and a photodiode (PD). The convex lens converges the light intensity after the detection object and the spatially modulated light are superimposed. The converged light beam is received by the photodiode and converted into an electrical signal to obtain the intensity of the modulated light signal and perform back-end image reconstruction.

2. The optical imaging system according to claim 1, characterized in that: The ultraviolet conversion module is made of cadmium selenide powder quantum dots dissolved in a volatile oily substance, which is then scraped and coated on one side of a glass sheet to form a quantum dot film after volatilization to achieve fluorescence excitation of the quantum confinement effect.

3. The optical imaging system according to claim 2, characterized in that: In the spatial light encoding module, a programmable binary transmission mask is realized by a digital micromirror array, and the elements thereof take values ​​of "0" and "1" and obey the encoding method; then, the transmission mask is projected onto the scene to realize structured lighting; wherein, the flipping state of each micromirror is changed by the micromirrors in the digital micromirror array that can independently rotate at a certain angle, thereby modulating the intensity and direction of light, and performing pixel-level modulation, wherein "0" indicates that the micromirror is flipped in the reverse direction by -12°, and "1" indicates that the micromirror is flipped in the forward direction, thereby realizing spatial light ON:OFF encoding; after the ultraviolet light carrying the detection object information passes through the ultraviolet conversion module, the object information is recorded on the light wave of the excited fluorescence band, and is collimated by a lens and then shot into the digital micromirror array to realize the spatial encoding of the visible fluorescence band light beam, and the spatial encoding module matrix is ​​obtained to encode and modulate the target information, and finally the encoded target information is obtained.

4. The optical imaging system according to claim 3, characterized in that: In the single pixel imaging module, a two-dimensional image of the target object is firstly set The two-dimensional image contains N = n1 × n2 pixels, and a modulation mask pattern with spatial resolution is set. The two are encoded by the spatial light coding module and transmitted. The modulation mask sequence of the spatial light coding module is expressed as M represents the number of codes implemented by the spatial light coding module. The modulation mask of the i-th frame is used; the corresponding M total light intensity values ​​are obtained after the modulation mask interacts with the two-dimensional image of the target object. The total light intensity is expressed as The above light intensity is captured by the photodiode; the quantized two-dimensional image of the target object is represented as The modulation mask of the spatial light coding module is expressed as get: HI = p, (1) The single-pixel imaging module uses the modulation mask sequence H of the known spatial light encoding module and the signal sequence p captured by the photodetector to reversely solve the two-dimensional image of the target object; specifically, both ends of formula (1) are multiplied by the inverse matrix of H, that is, I is obtained to achieve image reconstruction: I = H -1 p, (2)。 5. The optical imaging system according to claim 1, characterized in that: The workflow is: (i) The ultraviolet emission module provides the light source conditions required for imaging and realizes ultraviolet irradiation of the target image; through the lead wire and external power supply control, the voltage is limited to below 12V and the current is 60mA, and the ultraviolet light-emitting diode is lit. The wavelength range is 260nm-370nm, and 265nm, 305nm and 365nm ultraviolet light-emitting diodes are selected to irradiate the target to obtain the target space information of the target under ultraviolet light; (ii) an ultraviolet down-conversion module, which down-converts the target space information carried by the invisible ultraviolet light into visible light and keeps carrying the target space information; cadmium selenide powder is dissolved in toluene, swirls and spreads evenly and waits for volatilization, and then condenses into a quantum dot film on one side of the transparent glass. The ultraviolet light carrying the target space information irradiates the quantum dot film to excite fluorescence and carry the detected target space information and transmit it; (iii) a spatial light encoding module, which combines a modulated mask pattern with spatial resolution with a fluorescent target image; a digital micromirror array performs matrix encoding, and realizes whether light is reflected or not by flipping the micromirrors at different angles, thereby realizing spatial light encoding; the target spatial information converted into fluorescence after the ultraviolet irradiation of the quantum dot film is collimated by a lens and then incident on the digital micromirror array, so as to realize spatial encoding of the visible fluorescent band light beam, and finally obtain the encoded target information; (iv) A single-pixel imaging module receives light signals through a photodetector to reconstruct the invisible ultraviolet target image; uses a photodiode (PD) to detect the light intensity of the encoded target signal, and combines the total light intensity detection with the known spatial encoding of the digital micromirror array to inversely decode the target information.

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