Multi-spectral imaging system of heat-adjustable reflective plane lens

Abstract

The invention relates to a multispectral imaging system of a heat-adjustable reflective plane lens. The multispectral imaging system comprises a thermosensitive cholesteric liquid crystal plane lens, a temperature control device and an image acquisition device, the thermosensitive cholesteric liquid crystal plane lens comprises a substrate, a light-operated orientation layer and a cholesteric liquid crystal layer, the light-operated orientation layer is arranged on the upper surface of the substrate, the cholesteric liquid crystal layer is arranged on the upper surface of the light-operated orientation layer, and the cholesteric liquid crystal layer is provided with an adjustable reflection band; the temperature control device is used for adjusting the temperature of the thermosensitive cholesteric liquid crystal plane lens so as to adjust the wavelength range of a reflection band; and the image acquisition device is used for capturing an image reflected by the thermosensitive cholesteric liquid crystal plane lens. The system overcomes the defects that a traditional system is limited in adjusting range, complex in structure, low in response speed, poor in stability and the like, accurate and rapid adjustment of the wavelength range of a reflection band is achieved by integrating the thermosensitive cholesteric liquid crystal plane lens and the temperature control device, and the flexibility and practicability of the system are improved.

Description

Technical Field

[0001] The present application relates to the technical field of optical imaging, and in particular to a multi-spectral imaging system of a thermally adjustable reflective plane lens. Background Art

[0002] Multispectral imaging (MSI) technology plays a vital role in many fields such as agriculture, environmental monitoring and biomedicine. By capturing images of multiple specific electromagnetic spectrum bands, the technology can simultaneously detect spectral features and spatial information, thereby achieving a comprehensive analysis of material composition and real-time conditions.

[0003] In the field of multispectral imaging technology, traditional imaging systems often use filters with fixed wavelengths or limited wavelength ranges to achieve image capture in different spectral bands. However, these systems have certain limitations in practical applications. In particular, in situations where the spectral range needs to be dynamically adjusted or continuous spectral imaging is required, the flexibility of traditional technologies is insufficient.

[0004] In order to overcome this limitation, people began to explore the use of tunable optical elements to build multispectral imaging systems. Among them, liquid crystal materials have attracted much attention due to their unique electro-optical properties. Cholesteric liquid crystal is a liquid crystal phase with a periodic spiral structure. Its reflection band wavelength can be adjusted with the change of the pitch. This property makes it possible to build tunable optical elements.

[0005] However, existing multispectral imaging systems based on cholesteric liquid crystals often have some defects. On the one hand, some systems use complex external devices or methods to adjust the pitch of the liquid crystal, which not only increases the complexity and cost of the system, but also limits the portability and practicality of the system; on the other hand, some systems have a limited adjustment range and cannot meet the needs of wide spectral range imaging; in addition, some systems may have problems such as slow response speed and poor stability during the adjustment process, which affects the quality and effect of imaging. Summary of the invention

[0006] In order to solve the above-mentioned defects, the present application provides a multi-spectral imaging system of a thermally tunable reflective plane lens.

[0007] The above-mentioned invention objective of the present application is achieved through the following technical solutions:

[0008] A multi-spectral imaging system of a heat-adjustable reflective plane lens, comprising a heat-sensitive cholesteric liquid crystal plane lens, a temperature control device and an image acquisition device;

[0009] The thermosensitive cholesteric liquid crystal flat lens comprises a substrate, a light-controlled alignment layer and a cholesteric liquid crystal layer, wherein the light-controlled alignment layer is disposed on the upper surface of the substrate, the cholesteric liquid crystal layer is disposed on the upper surface of the light-controlled alignment layer, and the cholesteric liquid crystal layer has an adjustable reflection band;

[0010] The temperature control device is used to adjust the temperature of the thermosensitive cholesteric liquid crystal plane lens, thereby changing its pitch, and further adjusting the wavelength range of the reflection band;

[0011] The image acquisition device is used to capture the image reflected by the thermosensitive cholesteric liquid crystal plane lens.

[0012] By adopting the above technical solution, the thermosensitive cholesteric liquid crystal plane lens includes a substrate, a light-controlled orientation layer and a cholesteric liquid crystal layer. The cholesteric liquid crystal layer has a unique periodic spiral structure, so that the wavelength of its reflection band can be adjusted according to the change of the pitch. The light-controlled orientation layer is arranged on the upper surface of the substrate, providing a stable orientation environment for the cholesteric liquid crystal layer, ensuring the stability and consistency of the reflection band; the temperature control device changes the arrangement of liquid crystal molecules by controlling the temperature of the thermosensitive cholesteric liquid crystal plane lens, and then adjusts the pitch, so that the wavelength range of the reflection band can be flexibly adjusted, which not only simplifies the complex external adjustment equipment in the traditional system, but also improves the response speed and stability of the system; the image acquisition device is responsible for capturing the image reflected by the thermosensitive cholesteric liquid crystal plane lens, Since the wavelength range of the reflection band of the lens can be flexibly adjusted, the image acquisition device can capture images of different spectral bands, meeting the needs of multi-spectral imaging. Compared with the traditional multi-spectral imaging system, the present application overcomes the defects of the traditional system such as limited adjustment range, complex structure, slow response speed and poor stability. By integrating the thermosensitive cholesteric liquid crystal plane lens and the temperature control device, the wavelength range of the reflection band can be accurately and quickly adjusted, thereby improving the flexibility and practicality of the system. At the same time, the simplified system structure makes the system more portable and easy to operate, providing strong support for continuous imaging in a wide spectral range. In addition, the stable reflection band and fast response speed ensure the quality and effect of imaging, which makes the present application have broad application prospects in the field of multi-spectral imaging.

[0013] In a preferred example, the present application can be further configured as follows: the substrate is made of a transparent material selected from one or more combinations of glass, polymer or quartz, and is used to support the light-controlled alignment layer and the cholesteric liquid crystal layer.

[0014] By adopting the above technical solution, the substrate is made of a transparent material, and the transparent material is selected from one or more combinations of glass, polymer or quartz. Since the main function of the substrate is to support the light-controlled orientation layer and the cholesteric liquid crystal layer, and glass, polymer and quartz are all materials with good transparency and stability, they can effectively transmit light and ensure that the reflective characteristics of the cholesteric liquid crystal layer are not affected by the substrate material; at the same time, these materials also have good mechanical strength and weather resistance, can withstand temperature changes and the test of the external environment, and maintain the stability and durability of the lens system.

[0015] In a preferred example, the present application can be further configured as follows: the photo-controlled alignment layer is prepared by photo-alignment technology to imprint a preset phase distribution onto the liquid crystal molecules of the cholesteric liquid crystal layer, thereby controlling the helical structure of the cholesteric liquid crystal layer.

[0016] By adopting the above technical solution, the light-controlled orientation layer is prepared by the photo-alignment technology, and its core function is to accurately imprint the preset phase distribution on the liquid crystal molecules of the cholesteric liquid crystal layer, thereby effectively controlling the spiral structure of the cholesteric liquid crystal layer; the photo-alignment technology is an optical processing method, which uses light of a specific wavelength and polarization state to irradiate the light-controlled orientation layer, triggering a chemical reaction or physical change inside the material, thereby forming a specific orientation pattern, which can guide the liquid crystal molecules of the cholesteric liquid crystal layer to arrange in a preset manner to form a desired spiral structure, which is the basis for the cholesteric liquid crystal layer to have an adjustable reflection band characteristic, which determines the wavelength and bandwidth of the reflected light; through the control of the light-controlled orientation layer, the spiral structure of the cholesteric liquid crystal layer can be stably and repeatably prepared, thereby improving the reliability and consistency of the lens system; at the same time, the light-controlled orientation layer can also flexibly adjust the phase distribution according to actual needs, thereby achieving fine regulation of the spiral structure of the cholesteric liquid crystal layer.

[0017] In a preferred example, the present application can be further configured as follows: the cholesteric liquid crystal layer is formed by mixing a cholesteric liquid crystal material and a chiral dopant, the cholesteric liquid crystal material is selected from a nematic liquid crystal material, and the chiral dopant is used to adjust the spiral pitch of the cholesteric liquid crystal layer.

[0018] By adopting the above technical solution, the cholesteric liquid crystal layer is formed by mixing a cholesteric liquid crystal material and a chiral dopant, wherein the cholesteric liquid crystal material is selected from a nematic liquid crystal material, and the chiral dopant is used to finely adjust the spiral pitch of the cholesteric liquid crystal layer; the nematic liquid crystal material itself has a certain orientation, but in the absence of a chiral dopant, it cannot form a stable spiral structure, and the addition of the chiral dopant breaks the symmetry of the liquid crystal molecules and induces them to form a spiral structure with a specific pitch, and the spiral structure makes the cholesteric liquid crystal layer have a reflective property within a specific wavelength range, that is, it can reflect light of a specific wavelength and let light of other wavelengths pass through; by adjusting the type and concentration of the chiral dopant, the cholesteric liquid crystal layer can be controlled. The spiral pitch of the liquid crystal layer can be adjusted to adjust the wavelength range of its reflection band. This feature is crucial for multi-spectral imaging systems because it allows the system to flexibly capture images in different spectral bands as needed. Compared with traditional filter systems with fixed wavelengths or limited wavelength ranges, this tunability greatly improves the flexibility and practicality of the system. In addition, since the reflective properties of the cholesteric liquid crystal layer are based on its spiral structure, this structure is self-stable and reversible. When external conditions (such as temperature) change, the spiral structure will change accordingly, but this change is reversible, that is, when the external conditions are restored, the spiral structure will also return to its original state. This feature ensures the stability and reliability of the system in different environments.

[0019] In a preferred example, the present application can be further configured as follows: the wavelength range of the reflection band is controlled by adjusting the concentration of the chiral dopant and / or the temperature of the temperature control device, thereby achieving multi-spectral imaging.

[0020] By adopting the above technical solution, the chiral dopant plays a vital role in the cholesteric liquid crystal layer, and its concentration directly determines the pitch of the helical structure of the liquid crystal molecules, thereby affecting the wavelength range of the reflection band; by adjusting the concentration of the chiral dopant, the tightness of the helical structure can be changed, so that the reflection band can cover different wavelength regions. This adjustment method provides the possibility of customizing specific wavelength reflection bands during the manufacturing process, meeting diverse application needs; in addition to adjusting the concentration of the chiral dopant, the system also adjusts the temperature of the cholesteric liquid crystal layer through a temperature control device; changes in temperature will affect the arrangement and motion state of the liquid crystal molecules, thereby changing the pitch of the helical structure and realizing dynamic adjustment of the wavelength range of the reflection band. This thermal tuning mechanism enables the system to adjust the wavelength of the reflection band in real time according to actual needs during operation, providing great convenience for multi-spectral imaging.

[0021] In a preferred example, the present application may be further configured as follows: the temperature control device includes a heating element and / or a cooling element;

[0022] The heating element is selected from one or more combinations of a resistance heater, a laser heater or a microwave heater, and the cooling element is selected from one or more combinations of a liquid nitrogen cooler, a semiconductor refrigeration sheet or an air cooling device.

[0023] By adopting the above technical scheme, the temperature control device adopts a heating element and / or a cooling element to achieve the regulation of the temperature of the cholesteric liquid crystal layer; the heating element is selected from one or more combinations of a resistance heater, a laser heater or a microwave heater, and provides a corresponding heating effect according to the system requirements: the resistance heater generates heat by passing an electric current through a resistor, and the heating is rapid and stable; the laser heater uses the high energy density of the laser to achieve local rapid heating with high precision; the microwave heater generates heat inside the material through the interaction between microwaves and the material, and the heating efficiency is high; at the same time, the cooling element is selected from one or more combinations of a liquid nitrogen cooler, a semiconductor refrigeration sheet or an air cooling device, providing the system with a variety of cooling methods: the liquid nitrogen cooler uses the extremely low temperature of liquid nitrogen to achieve rapid cooling, and the effect is significant; the semiconductor refrigeration sheet realizes electric cooling through the Peltier effect, which is small in size, light in weight, and easy to integrate; the air cooling device takes away heat through air flow, which is simple and reliable; compared with the traditional temperature control method using a single heating or cooling means, the present application uses a combination of multiple heating and cooling elements, which not only improves the range and accuracy of temperature control, but also enhances the adaptability and stability of the system.

[0024] In a preferred example, the present application can be further configured as follows: the image acquisition device is a charge coupled device, a complementary metal oxide semiconductor sensor, or other types of image sensors.

[0025] By adopting the above technical solution, the image acquisition device adopts a charge coupled device (CCD), a complementary metal oxide semiconductor sensor (CMOS) or other types of image sensors; the charge coupled device (CCD) is a highly sensitive photoelectric conversion device with the advantages of low noise, high resolution and wide dynamic range. It can accurately convert light signals into electrical signals and retain the details and color information of the image; the complementary metal oxide semiconductor sensor (CMOS) is an image sensor with high integration, low power consumption and fast response speed. It integrates the photoelectric conversion element and the signal processing circuit on the same chip to realize the direct digital output of the image, which is convenient for subsequent image processing and transmission; in addition, it also supports the use of other types of image sensors to meet different application scenarios and needs.

[0026] In a preferred example, the present application can be further configured as follows: it also includes a light source, the light source is used to emit polychromatic light to the thermosensitive cholesteric liquid crystal plane lens, and the polychromatic light is captured by the image acquisition device after being reflected by the thermosensitive cholesteric liquid crystal plane lens.

[0027] By adopting the above technical scheme, in the multi-spectral imaging system of the thermally adjustable reflective plane lens, the addition of the light source provides the necessary lighting conditions for the system, and the light source is designed to emit polychromatic light to the thermosensitive cholesteric liquid crystal plane lens. The polychromatic light contains multiple spectral components and can cover different wavelength ranges required by the system, thereby meeting the needs of multi-spectral imaging; when the polychromatic light is irradiated onto the thermosensitive cholesteric liquid crystal plane lens, the lens reflects light of a specific wavelength according to its current temperature state, because the spiral structure of the cholesteric liquid crystal layer changes with temperature, thereby affecting the wavelength range of its reflection band; therefore, by adjusting the temperature of the lens, light of different wavelengths can be selectively reflected to achieve spectral screening and regulation; the reflected light is captured by an image acquisition device.

[0028] In a preferred example, the present application can be further configured as follows: it also includes a data processing unit, and the data processing unit is used to receive the digital signal acquired by the image acquisition device and perform corresponding processing.

[0029] By adopting the above technical solution, the data processing unit is used to receive the digital signals collected by the image acquisition device. After receiving these digital signals, the data processing unit will perform corresponding processing, including pre-processing operations such as denoising, enhancement, and correction on the signals to improve the quality of the image, and perform spectral analysis on the image to extract image information at different wavelengths to achieve separation and reconstruction of multi-spectral images; in addition, the data processing unit can also perform image recognition, feature extraction, target detection and other processing to provide support for subsequent image applications.

[0030] In a preferred example, the present application may be further configured as follows: the initial liquid crystal molecule orientation of the cholesteric liquid crystal layer is preset to be a parabolic shape that focuses the thermosensitive cholesteric liquid crystal plane lens.

[0031] By adopting the above technical solution, the initial liquid crystal molecular orientation of the cholesteric liquid crystal layer is preset to the parabolic shape of the focusing lens. In the initial state of the cholesteric liquid crystal layer, the liquid crystal molecules are arranged in a parabolic shape, so that when light passes through the liquid crystal layer, it can be focused like passing through a parabolic mirror; due to the spiral structure of the cholesteric liquid crystal, this focusing effect is not limited to a single wavelength, but can be achieved within a certain wavelength range, which not only improves the focusing performance of the lens, but also enhances the flexibility and practicality of the system.

[0032] In summary, the present application includes at least one of the following beneficial technical effects:

[0033] 1. The present application overcomes the defects of the traditional system such as limited adjustment range, complex structure, slow response speed and poor stability. By integrating a thermosensitive cholesteric liquid crystal plane lens and a temperature control device, accurate and rapid adjustment of the wavelength range of the reflection band is achieved, thereby improving the flexibility and practicality of the system. At the same time, the simplified system structure makes the system more portable and easy to operate, providing strong support for continuous imaging in a wide spectral range. In addition, the stable reflection band and fast response speed ensure the quality and effect of imaging, making the present application have broad application prospects in the field of multispectral imaging. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Figure 1 is a dynamic reflection MSI conceptual diagram of an embodiment of a multi-spectral imaging system of a thermally tunable reflective flat lens of the present application;

[0035] Figure 2 It is a diagram showing the manufacture and performance characterization of a device of a multi-spectral imaging system embodiment of a thermally tunable reflective flat lens of the present application;

[0036] Figure 3 This is a multi-spectral imaging diagram of a thermally tunable plane lens of an embodiment of a multi-spectral imaging system of a thermally tunable reflective plane lens of the present application;

[0037] Figure 4 This is a device imaging performance characterization diagram of an embodiment of a multi-spectral imaging system of a thermally tunable reflective plane lens of the present application. DETAILED DESCRIPTION

[0038] The following is combined with Figure 1-4 This application is described in further detail.

[0039] In one embodiment, the present application discloses a multi-spectral imaging system of a thermally adjustable reflective plane lens, which specifically includes a thermosensitive cholesteric liquid crystal plane lens, a temperature control device and an image acquisition device. The thermosensitive cholesteric liquid crystal plane lens includes a substrate, a photo-controlled orientation layer and a cholesteric liquid crystal layer. The photo-controlled orientation layer is arranged on the upper surface of the substrate, the cholesteric liquid crystal layer is arranged on the upper surface of the photo-controlled orientation layer, and the cholesteric liquid crystal layer has an adjustable reflection band; the temperature control device is used to adjust the temperature of the thermosensitive cholesteric liquid crystal plane lens, thereby changing its pitch, and then adjusting the wavelength range of the reflection band; the image acquisition device is used to capture an image reflected by the thermosensitive cholesteric liquid crystal plane lens.

[0040] In this embodiment, specifically, the substrate is made of a transparent material, selected from one or more combinations of glass, polymer or quartz, and is used to support the light-controlled orientation layer and the cholesteric liquid crystal layer. Glass, polymer and quartz are all materials with good transparency and stability, which can effectively transmit light and ensure that the reflective properties of the cholesteric liquid crystal layer are not affected by the substrate material; at the same time, these materials also have good mechanical strength and weather resistance, can withstand temperature changes and the test of the external environment, and maintain the stability and durability of the lens system.

[0041] In the present embodiment, specifically, the photo-controlled orientation layer is prepared by photo-alignment technology, and is used to imprint a preset phase distribution onto the liquid crystal molecules of the cholesteric liquid crystal layer, thereby controlling the spiral structure of the cholesteric liquid crystal layer, including key parameters such as pitch and spiral direction, so as to achieve fine regulation of the optical properties of the liquid crystal layer. The initial liquid crystal molecular orientation of the cholesteric liquid crystal layer is preset to a parabolic shape that focuses on a thermosensitive cholesteric liquid crystal plane lens. Based on the focusing principle of a parabolic reflector, by simulating a parabolic shape, when light passes through the lens, it will be guided and focused on a specific point or line, thereby achieving precise control of the light. In addition, since the cholesteric liquid crystal layer has a thermosensitive property, its spiral structure will change with changes in temperature, which means that by adjusting the temperature, the optical properties of the liquid crystal layer, including reflection wavelength, transmittance, etc., can be further adjusted.

[0042] In this embodiment, specifically, the cholesteric liquid crystal layer is formed by mixing a cholesteric liquid crystal material and a chiral dopant, the cholesteric liquid crystal material is selected from a nematic liquid crystal material, and the chiral dopant is used to adjust the helical pitch of the cholesteric liquid crystal layer.

[0043] In this embodiment, specifically, the wavelength range of the reflection band is controlled by adjusting the concentration of the chiral dopant and / or the temperature of the temperature control device, thereby achieving multi-spectral imaging.

[0044] In this embodiment, specifically, the temperature control device includes a heating element and / or a cooling element; the heating element is selected from one or more combinations of a resistance heater, a laser heater or a microwave heater, and the cooling element is selected from one or more combinations of a liquid nitrogen cooler, a semiconductor refrigeration sheet or an air cooling device.

[0045] In this embodiment, specifically, the image acquisition device is a charge coupled device, a complementary metal oxide semiconductor sensor, or other types of image sensors.

[0046] In this embodiment, specifically, a light source is included, and the light source is used to emit polychromatic light to the thermosensitive cholesteric liquid crystal plane lens. The polychromatic light is captured by the image acquisition device after being reflected by the thermosensitive cholesteric liquid crystal plane lens.

[0047] In this embodiment, specifically, a data processing unit is included, and the data processing unit is used to receive the digital signal collected by the image collection device and perform corresponding processing.

[0048] In this embodiment, specifically, the initial liquid crystal molecule orientation of the cholesteric liquid crystal layer is preset to be a parabolic shape of a focusing thermosensitive cholesteric liquid crystal plane lens.

[0049] In this embodiment, specifically, through the induction of the chiral dopant, the arrangement and helical structure of the cholesteric liquid crystal molecules inside the cholesteric liquid crystal (CLC) form a one-dimensional self-assembled chiral superstructure, which gives the CLC a spin-selective photonic band gap (PBG) with a span from n o p to n e p;

[0050] Where p represents the helical pitch, n o and n e represent the ordinary refractive index and the special refractive index respectively; when the light conforms to the chirality of the small crystal inside the CLC and is within the PBG incidence range, it will be reflected and carry a geometric phase φ, which is twice the initial surface liquid crystal (LC) orientation α of the small crystal, expressed as φ = ±2α, where the sign depends on the chirality of the small crystal; in contrast, the remaining components transmit the CLC with a uniform phase delay; this phenomenon allows reflective imaging to be achieved by presetting the initial direction of the LC to the parabolic profile of the focusing lens, which can be calculated based on the optical path difference between the center and edge of the lens, as described by the following formula:

[0051]

[0052] where λ, r and f are the incident wavelength, radius and focal length of the lens, respectively; therefore, incident light with the same chirality as the CLC is reflected, aggregated and forms an image.

[0053] Furthermore, the rich field responsiveness of CLC enables its helical configuration to be flexibly manipulated by light, heat, electric / magnetic fields, etc., which provides a powerful platform for active photonic devices; in particular, the introduction of thermosensitive CLC promotes the dynamic tunability of the operating wavelength; by adjusting the temperature, the helical pitch can be well controlled to adjust the wavelength range of the reflected light; this temperature modulation advantageously expands the operational versatility of CLC-based devices, enabling them to be responsively adjusted to environmental conditions.

[0054] like Figure 1 As shown, Figure 1(a) shows a vertical view of the designed CLC planar lens with a chiral upper structure, where the LC is periodically rotated along the helical axis, and the helical pitch p is defined as the distance that the LC guide completes a full 360° rotation; the pink curve represents the parabolic equiphase surface, when red (R), green (G), and blue (B) light from an object is incident on the lens simultaneously, only the wavelengths within the PBG can be reflected and imaged; Figure 1 In (b), when the device is subjected to thermal changes (heating or cooling), the helical pitch is adjusted accordingly, resulting in a wavelength shift of the PBG; this adjustment changes the operating band of the system, thereby achieving adaptive functionality for specific imaging requirements; therefore, by controlling the temperature of the thermal stage, the present system can selectively image the RGB optical components, thereby facilitating the realization of advanced MSI functions (such as Figure 1 (c)).

[0055] In this embodiment, specifically, the thermosensitive cholesteric liquid crystal material is mixed with a nematic LC host E7 (NCLCP, China) and a left-handed chiral dopant S811 (NCLCP, China) in a mass ratio of 68:32; wherein, in order to facilitate positioning, a UV photosensitive positioning agent SD1 is dissolved in dimethylformamide at a concentration of 0.3wt%, and then spin-coated on an indium tin oxide (ITO) glass substrate, and annealed on a 100°C high temperature stage for 10 minutes to form a uniform photo-alignment layer; an empty 30°C / min pass Linkam LTS120 thermal stage leads to the formation of a uniform planar texture, and under the effective guidance of the SD1 layer, the spiral structure develops into a planar lens with a size of about 2mm×2mm.

[0056] In this embodiment, specifically, the device is observed under a polarizing optical microscope (POM) using a pair of crossed polarizers. Figure 2 The fabrication and performance characterization of the device are shown in Figure 1. Figure 2 (a) is the pre-designed distribution of the liquid crystal heat guide, and the color bar indicates the transition from 0° to 180°; see Figure 2 (b), the POM image shows a clear pattern with minimal defects and impurities that reduce the optical efficiency, and the light and dark variations of the microstructure are consistent with the designed lens phase; where the helical pitch p of the CLC is determined by the following formula:

[0057] Where c is the weight ratio, HTP is the helical twisting force of the chiral dopant;

[0058] The central wavelength λc and bandwidth Δλ of PBG are calculated as:

[0059] λ c =(n e +n o ) / 2×p, and

[0060] Δλ=(n e -n o )×p,

[0061] Therefore, the following formula can be derived:

[0062] λ c =(n e +n o ) / (2×c×HTP)

[0063] See Figure 2 (c) When the device is heated from 29.9°C to 35.2°C, a significant blue shift of 250 nm in the central wavelength λc of the photonic band gap (PBG) is observed, and the rate of change gradually decreases; the aforementioned content provides a record of the reflectance spectrum measured at the normal angle using a fiber spectrometer, indicating that the wide-shifted PBG covers almost the entire visible spectrum range of 450 to 750 nm; this is attributed to the temperature-dependent solubility of the chiral dopant and the ordinary refractive index n o , extraordinary refractive index n e Due to the decrease in the helical pitch, the bandwidth of the PBG becomes narrower, while the reflectivity remains above 40% and is close to the theoretical maximum value of 50%; the color of the brightly textured structure also changes accordingly, changing to red, orange, yellow, green, cyan and blue in sequence;

[0064] Notably, the structure remains well maintained after temperature stabilization, the whole process is reversible, and the developed device exhibits excellent tunable optical properties and high reflectivity, making it of great significance in multispectral imaging applications.

[0065] like Figure 3 The figure shows the multispectral imaging of the thermally tunable flat lens. The thermally tunable flat lens with wavelength selectivity in the visible spectrum makes active multispectral imaging (MSI) possible. Figure 3 (a) Shows the optical setup used for the focusing and imaging properties of the device; a supercontinuum laser (SuperK EVO, NKT Photonics, Denmark) is combined with an acousto-optic filter (SuperK SELECT, NKT, Denmark) to output various monochromatic lasers; a polarizer is combined with a broadband quarter-wave plate to convert the incident light into circularly polarized light that conforms to the chiral superstructure; since the lens operates in axial reflection mode, a charge-coupled device (CCD) is strategically placed in front of the beam splitter (BS) to capture the generated image;

[0066] For further information, see Figure 3(b) By incrementally adjusting the position of the CCD near the focus, the focal length f of the lens at 533 nm is detected, and the longitudinal propagation path of the xz plane is constructed by collecting and processing multiple sets of cross-sectional intensity data; at 533 nm, the peak light intensity shows that the focal length f = 72 mm, which matches the design of the present application, and the corresponding point spread function (PSF) is characterized and displayed, see Figure 3 (c), the full width at half maximum (FWHM) of this wavelength is 30 μm;

[0067] In order to verify the MSI capacity of the lens, a hollow mask with the letter "E" is inserted in front of the BS as an object, see Figure 3 (d) By adjusting the temperature of the hot section, the letter "E" of different wavelengths can be clearly imaged. It can be seen that f is negatively correlated with λ, based on the Gaussian imaging formula: Where v and u represent the image distance and object distance respectively. It can be seen that when u is constant, v is positively correlated with f. Therefore, the size of the image increases with the decrease of wavelength. In this embodiment, u=10cm is fixed, and the measured distances v are 15cm (633nm), 17.5cm (600nm), 19.5cm (580nm), 24cm (533nm) and 36cm (480nm). It is worth noting that when the incident angle remains unchanged, the edge of the image becomes more visible at shorter wavelengths due to the improvement of resolution. The focusing efficiencies of the lenses are 89.2% (633nm), 87.4% (600nm), 88.6% (580nm), 84.6% (533nm) and 77.8% (480nm) respectively. The above results demonstrate the effective performance of the lens over a wide bandwidth. MSI exploits the potential of this tunable lens, and its working wavelength selectivity in the visible spectrum is particularly striking. The captured color information can be easily recognized by the human eye, and has broad application prospects in environmental monitoring, biomedical imaging, agricultural assessment, etc.

[0068] In this embodiment, specifically, Figure 4 The figure shows the device imaging performance characterization. In order to evaluate the imaging quality of the thermal CLC lens, a white light LED is used as the light source and a 1951USAF resolution target is used as the object. The measurement settings are shown in Figure 4 (a), where the target is strategically positioned at less than one focal length to ensure optimal clarity during observation, Figure 4(b) and 4(c) are the 1951 USAF resolution target and its local magnified microscopic images; due to its unique polarization selectivity, only left-handed circularly polarized light (LCP) is reflected and focused, while right-handed circularly polarized light (RCP) passes through the lens, which minimizes crosstalk in imaging compared to traditional geometric phase lenses; in addition, the thermally tunable PBG of the CLC lens allows rich color changes in images observed at different temperatures; see Figure 4 (d) Figure 4 (e) and Figure 4 (f), RGB resolution target images captured at 30.1℃, 31.7℃, and 34.0℃ vividly demonstrate this capability; it is noteworthy that the entire 4th group of the resolution target can be clearly seen in these images, verifying the excellent imaging performance and color selectivity of the lens proposed in this application; the slightly rounded edges of the image can be attributed to the simultaneous imaging of multiple wavelengths within the PBG, and this thermal tunability enhances the versatility of the lens and enables the extraction of corresponding information of various colors from complex and colorful objects.

[0069] Compared with conventional MSI, the CLC planar lens-based MSI proposed in this application has significant advantages such as low cost, light weight, and compact structure. In addition, it has a dynamic and controllable operating bandwidth in the visible light range, which exceeds the capabilities of conventional lenses. The operating bandwidth can be extended to the infrared region by adjusting the concentration of chiral dopants. In addition, the spectral resolution can be improved by adopting nematic LC with reduced birefringence or spiral LC with narrower PBGs. In addition, to further improve the imaging quality, various strategies can be adopted, including applying anti-reflection coatings on the substrate and expanding the size of the lens area by using low-magnification objectives during the photopatterning process. In addition to imaging applications, this innovative technology is also expected to realize various dynamic functions such as tunable beam deflectors, vortex beam generators, and holographic displays, all of which can be achieved by carefully pre-designing the exposure pattern.

[0070] This application proposes a thermally tunable reflective CLC planar lens for MSI. It allows reversible and repeatable adjustment of the operating wavelength range from 450 nm to 750 nm through temperature control. The planar lens has a focal length of 72 mm at 533 nm and a FWHM of the corresponding PSF of 30 um. Due to the tunable bandpass PBG of the CLC, the MSI has good image quality and high efficiency in the visible spectrum. The device is compatible with lasers and incoherent LEDs, and its polarization selectivity and reflection mode can reduce optical components, thereby minimizing the volume of the optical device. The device is suitable for capturing rich color information from the target and paves the way for innovations in various fields such as telecommunications, medical diagnosis, and environmental monitoring.

[0071] It should be understood that the size of the serial numbers of the steps in the above embodiments does not mean the order of execution. The execution order of each process should be determined by its function and internal logic, and should not constitute any limitation on the implementation process of the embodiments of the present application.

[0072] The embodiments described above are only used to illustrate the technical solutions of the present application, rather than to limit them. Although the present application has been described in detail with reference to the aforementioned embodiments, a person skilled in the art should understand that the technical solutions described in the aforementioned embodiments may still be modified, or some of the technical features may be replaced by equivalents. Such modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the embodiments of the present application, and should all be included in the protection scope of the present application.

Claims

1. A multi-spectral imaging system with a thermally tunable reflective plane lens, characterized in that: It includes a thermosensitive cholesteric liquid crystal plane lens, a temperature control device and an image acquisition device; The thermosensitive cholesteric liquid crystal flat lens comprises a substrate, a light-controlled alignment layer and a cholesteric liquid crystal layer, wherein the light-controlled alignment layer is disposed on the upper surface of the substrate, the cholesteric liquid crystal layer is disposed on the upper surface of the light-controlled alignment layer, and the cholesteric liquid crystal layer has an adjustable reflection band; The temperature control device is used to adjust the temperature of the thermosensitive cholesteric liquid crystal plane lens, thereby changing its pitch, and further adjusting the wavelength range of the reflection band; The image acquisition device is used to capture the image reflected by the thermosensitive cholesteric liquid crystal plane lens.

2. The multi-spectral imaging system of a thermally tunable reflective plane lens according to claim 1, characterized in that: The substrate is made of a transparent material selected from one or more combinations of glass, polymer or quartz, and is used to support the light-controlled alignment layer and the cholesteric liquid crystal layer.

3. The multi-spectral imaging system of the thermally tunable reflective plane lens according to claim 1, characterized in that: The photo-controlled alignment layer is prepared by photo-alignment technology and is used to imprint a preset phase distribution onto the liquid crystal molecules of the cholesteric liquid crystal layer, thereby controlling the helical structure of the cholesteric liquid crystal layer.

4. The multi-spectral imaging system of a thermally tunable reflective plane lens according to claim 1, characterized in that: The cholesteric liquid crystal layer is formed by mixing a cholesteric liquid crystal material and a chiral dopant, the cholesteric liquid crystal material is selected from a nematic liquid crystal material, and the chiral dopant is used to adjust the helical pitch of the cholesteric liquid crystal layer.

5. The multi-spectral imaging system of the thermally tunable reflective plane lens according to claim 4, characterized in that: The wavelength range of the reflection band is controlled by adjusting the concentration of the chiral dopant and / or the temperature of the temperature control device, thereby achieving multi-spectral imaging.

6. The multi-spectral imaging system of a thermally tunable reflective plane lens according to claim 1, characterized in that: The temperature control device comprises a heating element and / or a cooling element; The heating element is selected from one or more combinations of a resistance heater, a laser heater or a microwave heater, and the cooling element is selected from one or more combinations of a liquid nitrogen cooler, a semiconductor refrigeration sheet or an air cooling device.

7. The multi-spectral imaging system of a thermally tunable reflective plane lens according to claim 1, characterized in that: The image acquisition device is a charge coupled device, a complementary metal oxide semiconductor sensor or other types of image sensors.

8. The multi-spectral imaging system of a thermally tunable reflective plane lens according to claim 1, characterized in that: It also includes a light source, which is used to emit polychromatic light to the thermosensitive cholesteric liquid crystal plane lens. The polychromatic light is captured by the image acquisition device after being reflected by the thermosensitive cholesteric liquid crystal plane lens.

9. The multi-spectral imaging system of a thermally tunable reflective plane lens according to claim 1, characterized in that: It also includes a data processing unit, which is used to receive the digital signal collected by the image collection device and perform corresponding processing.

10. The multi-spectral imaging system of a thermally tunable reflective plane lens according to claim 3, characterized in that: The initial liquid crystal molecule orientation of the cholesteric liquid crystal layer is preset to be a parabola shape that focuses the thermosensitive cholesteric liquid crystal plane lens.

Images