Screen-free true holographic display device and method based on off-axis super lens array

Abstract

The invention relates to the technical field of screen-free true holographic display, and particularly discloses a screen-free true holographic display device and method based on an off-axis super lens array. Comprising a light source module, a polarization regulation and control module, a spatial light modulator, an off-axis super-lens array piece, noise light and a controller electrically connected with the spatial light modulator, which are sequentially arranged on a light path. According to the screen-free true holographic display device and method based on the off-axis super lens array, the off-axis super lens is used for perfectly regulating and controlling the phase of a light beam, so that light rays are subjected to off-axis focusing in space to form space pixel points, meanwhile, light (noise light) which is not effectively regulated and controlled by the super lens is physically separated in space to prevent the noise light from entering a visual field, and the display effect of the screen-free true holographic display device is improved. Meanwhile, a spatial light modulator is used, and dynamic display of a screen-free true hologram is achieved by controlling on-off of an incident light beam.

Description

Technical Field

[0001] This invention relates to the field of holographic display technology, specifically to a screenless true holographic display device and method based on an off-axis superlens array. Background Technology

[0002] True holographic display technology is an advanced display technology that achieves true three-dimensional imaging of objects based on the core principles of light interference and diffraction. Unlike pseudo-holographic technology, which relies on optical techniques to simulate a three-dimensional effect, this technology uses beam splitting to divide a highly coherent light source into an object light wave carrying the three-dimensional information of the object and a reference light wave as a phase reference. The two beams form interference fringes on the recording medium that contain all the information of the light wave amplitude and phase. During reconstruction, the hologram is illuminated by the reference light wave, and the original object light wavefront is accurately reconstructed using diffraction. This presents viewers with a three-dimensional virtual image with complete parallax, motion parallax, and true depth cues. Furthermore, the hologram has the characteristic of information redundancy, and any part of it can reproduce the complete image of the original object.

[0003] True holographic display technology can reconstruct the complete three-dimensional wavefront of an object, providing users with an ultimate three-dimensional display experience with natural depth, parallax, and focusing effects. Traditional true holographic display systems typically rely on spatial light modulators (SLMs) to load computational holograms (CGHs) and use complex optical lens groups to achieve light wave diffraction and imaging. However, existing technologies face numerous challenges: The system is large and complex. Traditional Fourier lens groups are large and heavy, which is not conducive to the miniaturization and integration of the system. The imaging quality is limited. Traditional lenses have aberrations, which reduce the resolution and fidelity of the reconstructed image. They must rely on a physical medium. Whether it is the SLM itself, the holographic plate, or water mist, rotating screen, etc., the existing technology requires a physical surface or medium to carry the image, which cannot achieve a true "screenless" floating display in the air. Inefficiency and background light pollution: These are the core technical bottlenecks. Even with the use of new superlenses, their diffraction efficiency is difficult to reach 100%. Unmodulated or ineffectively controlled light will superimpose with the useful light carrying image information, resulting in severe background light pollution, extremely low image signal-to-noise ratio, and the image being submerged in a halo, making it impossible to observe directly with the naked eye. Therefore, there is an urgent need in this field for a screenless true holographic display technology that can overcome the above-mentioned defects, especially the problem of background light pollution, so as to achieve miniaturization, high image quality, and high signal-to-noise ratio. Summary of the Invention

[0004] To solve the above technical problems, the present invention is achieved through the following technical solution: a screenless true holographic display device and method based on an off-axis superlens array, comprising: a light source module, a polarization control module, a spatial light modulator, an off-axis superlens array, noise light, and a controller electrically connected to the spatial light modulator, arranged sequentially in the optical path; and further comprising a light absorption element arranged in the propagation path of the noise light. The light source module is used to provide a coherent and partially coherent incident light beam; The polarization control module is used to convert the incident light into circularly polarized light. The polarization control module includes a linear polarizer and a waveplate arranged in sequence. The linear polarizer is used to filter the polarization of the incident light, and the waveplate is used to convert the linearly polarized light into circularly polarized light. The spatial light modulator is set in the outgoing light path of the polarization control module and is configured to load pattern data generated by the controller. The pattern data is generated based on the spatial coordinates of the three-dimensional object to be displayed, and is used to allow circularly polarized light in the corresponding area to pass through and block light in other areas, thereby achieving light selection. The off-axis superlens array is set in the output light path of the spatial light modulator and includes multiple micro off-axis superlens units. Each superlens unit precisely corresponds to one or more pixel regions on the spatial light modulator. It is used to efficiently focus circularly polarized light passing through the corresponding region of the spatial light modulator off-axis and converge it to a preset three-dimensional coordinate point in free space to form a spatial pixel. At the same time, it allows the noise light that is not effectively controlled to propagate along the original propagation path, thereby realizing the spatial physical separation of signal light and noise light. The controller is used for collaborative calculation and control, including generating the pattern data based on the spatial coordinates of the three-dimensional object to be displayed, and loading the pattern data onto the spatial light modulator; The light-absorbing element is positioned along the main propagation path of the noise light, typically in the direction of the optical axis, to absorb the noise light, improve the image signal-to-noise ratio, and ensure clear observation by the naked eye within the observation area. The circularly polarized light is either left-handed or right-handed circularly polarized light. The incident polarization state of the off-axis superlens array is designed to match the polarization state of the circularly polarized light. The spatial light modulator is either LCOS-SLM, LCD-SLM, or DMD, with a resolution of not less than x and a pixel pitch of not more than μm. The pattern data is either binary pattern data or grayscale pattern data. The position of the spatial pixel to be lit in the pattern data is in a "transparent" state, and other positions are in a "blocked" state. The light source module is either a laser, an LED, or a superluminescent diode. The wavelength of the incident light matches the operating wavelength of the off-axis superlens array. Preferably, the off-axis superlens array is a planar optical element based on a metasurface. Each micro-off-axis superlens unit is composed of a subwavelength-scale nanostructure array. The nanostructure array is designed based on the PB phase principle to accurately compensate for the phase difference generated when light propagates at different positions of the lens. This achieves precise control of the isophase surface of the light wave, allowing the light to converge at the spatial pixel focus and form a perfect outgoing spherical wave. The number of micro-off-axis superlens units in the off-axis superlens array is no less than ten thousand. The preset three-dimensional coordinate points corresponding to each micro-off-axis superlens unit are mutually non-overlapping, collectively forming a spatial pixel matrix of the three-dimensional image. The matrix corresponds to the spatial shape of the reconstructed three-dimensional object in free space, ensuring multi-angle observation within the observation area. The controller is a high-performance computer and a dedicated embedded control chip, running any one of the customized display control software, capable of updating pattern data in real time to achieve dynamic three-dimensional image display. Preferably, an adjusting rod is threadedly connected to the side of the adjusting seat, and a light-absorbing housing is rotatably connected to the inner side of the adjusting seat. One end of the adjusting rod is fixedly connected to the middle of the side of the light-absorbing housing. A heat sink is fixedly connected to the inner side of the light-absorbing housing, and a light-absorbing plate is fixedly connected to the side of the heat sink. The main propagation path of the noise light is along the optical axis. The light-absorbing plate is either a black absorbing plate or a light-absorbing coating. The light-absorbing housing and the light-absorbing plate are arranged on the extension line of the optical axis and located on the emission side of the off-axis superlens array. A liquid cooling component is used to dissipate heat from a heat sink, and the side of the liquid cooling component is fixedly connected to the inside of the heat sink. A cleaning component is used to clean the side of the light-absorbing plate, and the side of the cleaning component is fixedly connected to the inner side of the light-absorbing shell. Preferably, the liquid cooling component includes heat dissipation pipes and a water storage pipe. The heat dissipation pipes adopt a spiral layout, which significantly increases the contact area and heat exchange time between the coolant and the heat sink. This effectively removes the heat transferred from the light-absorbing plate to the heat sink, preventing the light-absorbing coating from aging and reducing the absorption rate due to prolonged high temperatures, thus extending the service life of the light-absorbing plate. The filter cartridge intercepts impurities in the coolant, preventing blockage of the heat dissipation pipes. The water filling pipe design allows for convenient replenishment of coolant loss, ensuring uninterrupted cooling circulation. The side of the heat dissipation pipe is fixedly connected to the inner side of the heat sink. A water outlet pipe is fixedly connected to the top of the water storage pipe, and the other end of the water outlet pipe is fixedly connected to the heat dissipation pipe. A filter cartridge is fixedly connected to the top of the inner cavity of the water storage pipe. A water pump is fixedly connected to the bottom of the inner cavity of the water pipe, and an inlet pipe is fixedly connected to the output end of the water pump. The sides of the inlet pipe and the outlet pipe are fixedly connected to the inner side of the light-absorbing shell. The other end of the inlet pipe is fixedly connected to the end of the heat dissipation pipe away from the outlet pipe. A water filling pipe is fixedly connected to the side of the water storage pipe. During the light absorption operation, since the main propagation path of the noise light is along the optical axis, the light-absorbing shell and the light-absorbing plate can be set on the extension line of the optical axis and deployed on the emission side of the off-axis superlens array to absorb the noise light. By turning on the liquid cooling component to cool the heat dissipation plate, the heat generated by the light-absorbing plate after absorbing the noise light can be removed in time, and the light absorption performance of the light-absorbing plate is not affected by the excessive surface temperature. Preferably, the cleaning component includes a cleaning housing, the side of which is fixedly connected to a light-absorbing housing. Sliding grooves are provided on both sides of the cleaning housing. A mounting frame is fixedly connected to the inner side of the cleaning housing, and a clearance groove is provided in the middle of the mounting frame. Air suction units are fixedly connected to both sides of the inner cavity of the cleaning housing. A driving component is fixedly connected to the middle of the inner side of the cleaning housing. A connecting shaft is fixedly connected to the output end of the driving component. An electrostatic dust removal rod is fixedly connected to the other end of the connecting shaft via an mounting sleeve. Collection grooves are provided on both sides of the cleaning housing. An air groove is provided on the side of the collection groove away from the mesh opening. [The last sentence appears to be incomplete and possibly refers to a different component.] The device features a mesh design, and a moving component is slidably connected to the inner side of the collection tank. With the assistance of a driving component and a clearance groove, the movement path and distance of the electrostatic dust removal rod can be controlled, ensuring thorough cleaning of the light-absorbing panel's side without any blind spots. Electrostatic adsorption is a non-contact cleaning method, avoiding scratches on the light-absorbing panel's surface coating caused by traditional wiping, thus preserving the panel's light-absorbing performance. Through the negative pressure adsorption of the suction machine combined with the guidance of the mesh in the mounting frame, dust on the dust removal rod can be quickly transferred to the collection tank, preventing dust from scattering back into the light-absorbing panel or the device's interior during cleaning. The cleanable design of the collection tank facilitates regular centralized dust removal, eliminating the interference of dust accumulation on light absorption at the source. Preferably, the moving component includes two moving rods, both ends of which are fixedly connected to the inner side of the collection trough. A moving frame is slidably connected to the moving rods, and both sides of the moving frame are slidably connected to the inner side of the collection trough. A circular groove is formed on the side of the moving frame, and a feeding groove is formed on the side of the moving frame away from the circular groove. A guide block is fixedly connected to the side of the moving frame through a circular rod, and the side of the circular rod is slidably connected to the inner side of the sliding groove. Through the linkage and extrusion structure of the guide block, the circular rod and the moving frame, a directional thrust can be formed on the dust in the collection trough, which can quickly gather the dispersed dust to the designated square groove position, avoid dust remaining in the dead corner of the collection trough and ensure the cleaning effect. A screenless true holographic display method based on an off-axis superlens array includes the following steps: S1: Generate pattern data: The controller generates pattern data defining the light-transmitting area on the spatial light modulator based on the spatial coordinates of the three-dimensional object to be displayed; when the pattern data is binary pattern data, the difference in light transmittance between the "light-transmitting" area and the "light-blocking" area is not less than 90%; when it is grayscale pattern data, the light transmittance is graded at least 256 levels; the controller updates the pattern data in real time according to the dynamic changes of the three-dimensional object to be displayed, with an update frequency of not less than 10Hz, to achieve dynamic screenless true holographic display; S2: Modulated polarization state: The incident light emitted by the light source module is converted into circularly polarized light through the polarization control module; the polarization control module realizes the polarization state conversion through a combination of linear polarizers and waveplates, and the polarization direction of the circularly polarized light is consistent with the designed incident polarization direction of the off-axis superlens array; the wavelength range of the incident light is 400nm-760nm, and the deviation between the operating wavelength of the off-axis superlens array and the wavelength of the incident light does not exceed ±10nm; S3: Selecting the light beam: Load the pattern data generated in step S1 onto the spatial light modulator, and illuminate the spatial light modulator with circularly polarized light, so that only the light energy of the "transparent" area in the pattern data can pass through; S4: Spatial Separation and Focusing: Light from the spatial light modulator is irradiated onto the off-axis superlens array. The corresponding superlens unit in the array focuses a portion of the light off-axis onto a preset three-dimensional coordinate point in free space to form a spatial pixel. Noise light not effectively controlled by the superlens propagates along its original path, achieving spatial physical separation from the signal light. The diffraction efficiency of the off-axis superlens array for the signal light is not less than 20%, and the angle between the propagation direction of the noise light and the off-axis focusing direction of the signal light is not less than 15°. The superlens unit precisely controls the phase of the incident circularly polarized light through a subwavelength nanostructure array, ensuring that all light rays passing through the superlens unit are completely phase-synchronized at the preset spatial pixel focal point, forming a perfect spherical wave. Each superlens unit focuses to form a spatial pixel, and the luminous intensity of the spatial pixel is not less than 100 cd / m², which can be directly observed by the naked eye within the observation area without significant halo interference. S5: Reconstructing the screenless image: All the illuminated spatial pixels together constitute an aerial three-dimensional image that is not attached to any physical carrier and is spatially separated from noise light, ensuring clear observation within the observation area; the brightness uniformity error of the spatial pixels in the aerial three-dimensional image does not exceed 15%, and the center distance between adjacent spatial pixels is not greater than 1mm. S6: Noise light absorption, which absorbs noise light by setting a light absorption element in the noise light propagation path to prevent noise light from entering the observation area.

[0005] This invention provides a screenless true holographic display device and method based on an off-axis superlens array. It has the following beneficial effects: 1. This screenless true holographic display device and method based on an off-axis superlens array utilizes the perfect control of the beam phase by an off-axis superlens to enable off-axis focusing of light in space to form spatial pixels. At the same time, light that is not effectively controlled by the superlens (noise light) is physically separated in space to prevent noise light from entering the field of view and affecting the image quality. Simultaneously, a spatial light modulator is used to control the on / off state of the incident beam to achieve dynamic display of the screenless true hologram. The off-axis superlens array can truly "reshape" the passing light into a spatial pixel with the characteristics of a real light emitter that is visible to the naked eye, while traditional lenses cannot achieve this effect.

[0006] 2. This screenless true holographic display device and method based on off-axis superlens array achieves high signal-to-noise ratio screenless aerial imaging, fundamentally solving the problem of background light pollution. By using off-axis superlens array, the signal light and the noise light generated by insufficient superlens efficiency can be spatially and physically separated, avoiding the interference of background light on imaging quality. Practical screenless true holographic display visible to the naked eye can be achieved without relying on high-power laser.

[0007] 3. The screenless true holographic display device and method based on off-axis superlens array significantly improves beam utilization efficiency, far exceeding that of traditional holographic technology. Compared with the holographic reticle used in traditional holographic technology, the beam utilization efficiency of the superlens used in this solution is improved by at least one order of magnitude. The beam utilization rate of traditional holographic technology is extremely low, and there is no relevant quantitative testing standard. The efficiency advantage of this technology directly promotes the development of holographic display technology towards low power consumption and practical application.

[0008] 4. The screenless true holographic display device and method based on off-axis superlens array has strong environmental adaptability and can meet the clear imaging requirements in natural light and indoor lighting environments. Combined with the natural sensitivity of the human eye to light, this technology can still ensure that the hologram is clearly visible even in natural light environments. In a lit laboratory environment with the lights on, the human eye can still clearly observe the controlled light at a distance of 1m from the superlens array, which improves the applicability of the technology in various scenarios.

[0009] 5. The screenless true holographic display device and method based on off-axis superlens array focuses on the field of holographic display rather than the field of lenses. It has more precise positioning, beam control accuracy compared with traditional lenses, and beam utilization efficiency and holographic image position compared with traditional holographic technology. It can fully highlight the technological advancement and uniqueness of this solution in the field of holographic display.

[0010] 6. This screenless true holographic display device and method based on off-axis superlens array provides an unprecedented sense of immersion and interactivity. Since the image is in real space, users can freely observe within the field of view and achieve natural occlusion and spatial superposition of virtual images and real objects, providing a perfect display solution for applications such as augmented reality (AR).

[0011] 7. The screenless true holographic display device and method based on off-axis superlens array has an extremely simple and stable system structure. It uses an ultra-thin superlens array to replace the traditional lens group and complex medium generation device. The "simplicity" of this solution focuses on the imaging medium level. Compared with traditional holographic technology, it does not require a dedicated imaging screen, directly eliminating a whole "screen" subsystem. Based on this improvement, the overall system structure is greatly simplified, which not only has extremely high stability and reliability, but is also easier to integrate into various miniaturized devices.

[0012] 8. The screenless true holographic display device and method based on off-axis superlens array has high imaging quality. The inherent aberration correction capability and phase modulation capability of the superlens ensure that each reconstructed spatial pixel has high brightness and high fidelity. Attached Figure Description

[0013] Figure 1 This is a schematic diagram of the screenless true holographic display device based on an off-axis superlens array according to the present invention; Figure 2 This is a schematic diagram illustrating the traditional lens focusing principle and the causes of aberrations in this invention. Figure 3 This is a schematic diagram illustrating the focusing principle of the superlens and the generation of perfect spherical waves in this invention. Figure 4 This is a schematic diagram showing the correspondence between the superlens array, spatial light modulator, and spatial pixels of the present invention; Figure 5 This is a schematic diagram of the structure of the light-absorbing element of the present invention; Figure 6 This is a schematic diagram of the structure of the adjusting seat of the present invention; Figure 7 This is a schematic diagram of the heat sink of the present invention; Figure 8 This is a schematic diagram of the liquid cooling component of the present invention; Figure 9This is a schematic diagram of the cleaning component of the present invention; Figure 10 This is a schematic diagram of the structure of the cleaning shell of the present invention; Figure 11 This is a schematic diagram of the structure of the moving component of the present invention; Figure 12 This is a schematic flowchart of the screenless true holographic display method based on off-axis superlens array of the present invention.

[0014] In the diagram: 101, Light source module; 102, Linear polarizer; 103, Waveplate; 104, Spatial light modulator; 105, Off-axis superlens array; 106, Three-dimensional object; 107, Observation area; 108, Controller; 109, Noise light; 110, Light absorption element; 111, Adjustment seat; 112, Adjustment rod; 113, Light-absorbing housing; 114, Light-absorbing plate; 115, Liquid cooling component; 1151, Heat sink; 1152, Water outlet pipe; 1153, Water storage pipe; 1154, Water inlet pipe; 1155, Filter cartridge; 1156, Water filling pipe; 1157, Water pump; 11 6. Cleaning components; 1161. Cleaning housing; 1162. Slide groove; 1163. Mounting frame; 1164. Suction unit; 1165. Drive unit; 1166. Connecting shaft; 1167. Electrostatic dust removal rod; 1168. Collection tank; 1169. Moving assembly; 11691. Moving rod; 11692. Moving frame; 11693. Feed chute; 11694. Guide block; 11695. Circular groove; 1170. Mesh; 117. Heat sink; 301. Superlens unit; 302. Nanostructure array; 303. Spatial pixel; 304. Spherical wave; 305. Phase plane. Detailed Implementation

[0015] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0016] Example 1, please refer to Figure 1 The present invention provides a technical solution: a screenless true holographic display device based on an off-axis superlens array, comprising: a light source module 101, a polarization control module, a spatial light modulator 104, an off-axis superlens array 105, a noise light 109, and a controller 108 electrically connected to the spatial light modulator 104, and further comprising a light absorption element 110 disposed on the propagation path of the noise light 109. Please see Figure 2This is used to illustrate the shortcomings of the conventional lens 201, demonstrating the process by which incident light 202 is focused by the conventional lens to the focal point 203 and forms a distorted outgoing wavefront 204. The focusing principle of the conventional lens 201 is based on geometric optics. It guides light 202 to converge at the focal point 203 through its curved surface shape. However, due to the dispersion of the lens material and the limitations of its surface shape, light rays from different paths do not have completely equal optical paths when they reach the focal point, resulting in inconsistent phases of the light rays at the focal point. Therefore, the light rays emitted from the focal point do not constitute a perfect spherical wave 304, but rather a distorted wavefront 204. Physically, this convergence point is merely a region with high energy density, rather than a "light source" with clear boundaries and a sense of solidity, and cannot be reliably recognized by the brain as an independent spatial pixel; The light source module 101 is used to provide a coherent and partially coherent incident light; The polarization control module is used to convert incident light into circularly polarized light. The polarization control module includes a linear polarizer 102 and a waveplate 103 arranged in sequence. The linear polarizer 102 is used to polarize the incident light, and the waveplate 103 is used to convert the linearly polarized light into circularly polarized light. The size of the waveplate 103 is one-quarter. Mainstream superlens designs usually operate under specific circularly polarized light incident conditions to achieve the highest diffraction efficiency and the best imaging quality. The spatial light modulator 104 is set in the outgoing light path of the polarization control module and is configured to load pattern data generated by the controller 108. The pattern data is generated based on the spatial coordinates of the three-dimensional object 106 to be displayed and is used to allow circularly polarized light in the corresponding area to pass through and block light in other areas, thereby achieving light gating. Please see Figures 3-4 This is used to explain the working mechanism of the superlens unit 301, and to demonstrate the principle that the nanostructure array 302 controls the incident light to form an equiphase surface 305, which is finally converged at the focal point of the spatial pixel 303 and generates a perfect outgoing spherical wave 304. The off-axis superlens array 105 is set in the outgoing light path of the spatial light modulator 104 and contains multiple micro off-axis superlens units 301. Each superlens unit 301 corresponds precisely to one or more pixel regions on the spatial light modulator 104. It is used to efficiently focus the circularly polarized light passing through the corresponding region of the spatial light modulator 104 off-axis, and converge it to a preset three-dimensional coordinate point in free space to form a spatial pixel 303. At the same time, it allows the noise light 109 that is not effectively controlled to propagate along the original propagation path, so as to achieve spatial physical separation of signal light and noise light 109. The controller 108 is used for collaborative computing and control, including generating pattern data based on the spatial coordinates of the three-dimensional object 106 to be displayed, and loading the pattern data onto the spatial light modulator 104; The light-absorbing element 110 is positioned on the main propagation path of the noise light 109, usually in the direction of the optical axis, to absorb the noise light 109, improve the image signal-to-noise ratio, and ensure clear observation by the naked eye within the observation area 107. The circularly polarized light is either left-handed or right-handed circularly polarized light. The off-axis superlens array 105 is designed to match the polarization state of the incident light. The spatial light modulator 104 is either LCOS-SLM, LCD-SLM, or DMD, with a resolution of not less than 1080x and a pixel pitch of not more than 10μm. The pattern data is either binary pattern data or grayscale pattern data. The position corresponding to the spatial pixel 303 to be lit in the pattern data is in a "transparent" state, while other positions are in a "blocked" state. The light source module 101 is either a laser, an LED, or a superluminescent diode. The wavelength of the incident light matches the operating wavelength of the off-axis superlens array 105. The off-axis superlens array 105 is a planar optical element based on a metasurface. Each micro off-axis superlens unit 301 is composed of a subwavelength-scale nanostructure array 302. The nanostructure array 302 is designed based on the PB phase principle and is used to accurately compensate for the phase difference generated when light propagates at different positions of the lens. The off-axis superlens array 105 is a planar optical element based on a metasurface. Each micro off-axis superlens unit 301 is composed of a subwavelength-scale nanostructure array 302. The nanostructure array 302 is designed based on the PB phase principle and is used to accurately compensate for the phase difference generated when light propagates at different positions of the lens, so as to achieve precise control of the equiphase surface 305 of the light wave, so that the light converges at the focal point of the spatial pixel 303 and forms a perfect outgoing spherical wave 304. This ensures that all the light rays passing through the superlens not only coincide in position when they reach the focal point of the preset spatial pixel 303, but more importantly, their phase planes 305 are completely synchronized. When these light waves that are perfectly synchronized on phase surfaces 305 are superimposed at the focal point, they will form a perfect, outwardly uniformly expanding spherical wave 304 starting from that point. This spherical wave 304 emitted from the focal point is similar to the light wave emitted by a real point light source at that location; The spherical wave 304 emitted from the focal point is physically indistinguishable from the light wave emitted from the same location by a real point source. The principle of holography is to use a holographic reticle to precisely control the reference light, so that the controlled light enters the human eye and "tricks" the brain into believing that the light is traveling in a straight line, and finally presents a virtual image at the corresponding position. From this perspective, the concept of holography and the concept of virtual image are consistent. The improvement lies in replacing the traditional holographic reticle with a metasurface, and resetting the position of the image so that it is no longer limited to the back of the reticle; When an observer's eye receives this perfect spherical wave 304, their visual system automatically interprets it as: "There is a luminous object at the center of this spherical wave 304". Therefore, the observer will clearly "see" a bright, clear, and substantial point of light suspended at the focal point, namely "visible spatial pixel 303"; The number of micro off-axis superlens units 301 in the off-axis superlens array 105 is no less than 1 million. The preset three-dimensional coordinate points corresponding to each micro off-axis superlens unit 301 do not overlap with each other, and together they form a spatial pixel matrix 303 of the three-dimensional image. The matrix corresponds to the spatial shape of the reconstructed three-dimensional object 106 in free space, ensuring the multi-angle observation effect within the observation area 107. The controller 108 is a high-performance computer and a dedicated embedded control chip, running any one of the customized display control software, which can update the pattern data in real time to achieve dynamic three-dimensional image display. Since the diffraction efficiency of current superlenses cannot reach 100%, when circularly polarized light shines on an off-axis superlens array, the duty cycle of the nanostructures on the superlenses is limited, and the polarization conversion efficiency of the nanostructures is not 100%. Therefore, only a portion of the light (e.g., about 30%) will be effectively modulated by its nanostructure and deflected and focused at the designed off-axis angle to form the signal light we need; The remaining light (e.g., about 70%) will not be effectively modulated by the nanostructure; its polarization state may change or remain unchanged, and it will continue to travel along the original propagation path (usually the optical axis). This uncontrolled portion of light constitutes the main noise light 109. Since the signal light is focused off-axis, while the noise light 109 propagates along the optical axis, the two are physically separated in space, thus avoiding background light pollution and greatly improving the signal-to-noise ratio of the image; Generate pattern data: The controller 108 generates a pattern data based on the spatial coordinates of the three-dimensional object 106 to be displayed. This data defines which areas on the SLM need to be transparent.

[0017] Modulated polarization state: The incident light emitted by the light source is converted into circularly polarized light after passing through the polarization modulation module.

[0018] Gating the light: The pattern data is loaded onto the SLM, and circularly polarized light is shone onto the SLM. Only the light from the "transparent" area defined in the pattern data can pass through the SLM. Spatial Separation and Focusing: The light from the SLM shines onto the off-axis superlens array, and the corresponding superlens unit 301 in the array focuses this light off-axis onto a preset three-dimensional coordinate point in free space, forming a spatial pixel 303. At the same time, the noise light 109, which is not effectively controlled by the superlens, propagates along its original path and is spatially separated from the signal light. Reconstructing a screenless image: All the illuminated spatial pixels 303 together constitute an aerial three-dimensional image that is not attached to any physical carrier and is spatially separated from the noise light 109; Example 2, please refer to Figures 5-7 Based on Embodiment 1, the present invention provides a technical solution: the light absorption element 110 includes an adjustment seat 111: An adjusting rod 112 is threadedly connected to the side of the adjusting seat 111. A light-absorbing housing 113 is rotatably connected to the inner side of the adjusting seat 111. One end of the adjusting rod 112 is fixedly connected to the middle of the side of the light-absorbing housing 113. A heat sink 117 is fixedly connected to the inner side of the light-absorbing housing 113. A light-absorbing plate 114 is fixedly connected to the side of the heat sink 117. The main propagation path of the noise light 109 is the optical axis direction. The light-absorbing plate 114 is either a black absorbing plate or a light-absorbing coating. The light-absorbing housing 113 and the light-absorbing plate 114 are arranged on the extension line of the optical axis and located on the emission side of the off-axis superlens array 105. Liquid cooling component 115 is used to dissipate heat from heat sink 117. The side of liquid cooling component 115 is fixedly connected to the inside of heat sink 117. Cleaning component 116 is used to clean the side of light-absorbing plate 114. The side of cleaning component 116 is fixedly connected to the inside of light-absorbing housing 113. During the light absorption process, since the main propagation path of the noise light 109 is along the optical axis, the light-absorbing housing 113 and the light-absorbing plate 114 can be placed on the extension line of the optical axis and deployed on the emission side of the off-axis superlens array to achieve the absorption of the noise light 109. By adjusting the angle of the light-absorbing housing 113 inside the adjusting seat 111 with the adjusting rod 112, it is possible to ensure alignment with the propagation path of the noise light 109 and ensure stable and reliable light absorption effect. By turning on the liquid cooling component 115 to cool down the heat sink 117, the heat generated by the light absorbing plate 114 after absorbing the noise light 109 can be removed in time, thus preventing the light absorbing plate 114 from affecting its light absorption performance due to excessive surface temperature. When the device is left idle for a long time, the dust on the surface of the light-absorbing plate 114 can be cleaned by the cleaning component 116 to prevent dust from accumulating and covering the light-absorbing surface, thereby interfering with the absorption efficiency of the light-absorbing plate 114 for noise light 109. Please see Figure 8The liquid cooling component 115 includes a heat dissipation pipe 1151 and a water storage pipe 1153. The side of the heat dissipation pipe 1151 is fixedly connected to the inside of the heat dissipation plate 117. The top of the water storage pipe 1153 is fixedly connected to a water outlet pipe 1152. The other end of the water outlet pipe 1152 is fixedly connected to the heat dissipation pipe 1151. The top of the inner cavity of the water storage pipe 1153 is fixedly connected to a filter cylinder 1155. The bottom of the inner cavity of the water storage pipe 1153 is fixedly connected to a water pump 1157. The output end of the water pump 1157 is fixedly connected to an inlet pipe 1154. The sides of both the inlet pipe 1154 and the outlet pipe 1152 are fixedly connected to the inside of the light-absorbing housing 113. The other end of the inlet pipe 1154 is fixedly connected to the end of the heat dissipation pipe 1151 away from the outlet pipe 1152. The side of the water storage pipe 1153 is fixedly connected to a water filling pipe 1156. Please see Figures 9-10 The cleaning component 116 includes a cleaning housing 1161, the side of which is fixedly connected to a light-absorbing housing 113. Sliding grooves 1162 are provided on both sides of the cleaning housing 1161. A mounting frame 1163 is fixedly connected to the inner side of the cleaning housing 1161. A clearance groove is provided in the middle of the mounting frame 1163. Air suction units 1164 are fixedly connected to both sides of the inner cavity of the cleaning housing 1161. A driving component 1165 is fixedly connected to the middle of the inner side of the cleaning housing 1161. A connecting shaft 1166 is fixedly connected to the output end of the driving component 1165. An electrostatic dust removal rod 1167 is fixedly connected to the other end of the connecting shaft 1166 via an installation sleeve. Collection grooves 1168 are provided on both sides of the cleaning housing 1161. An air groove is provided on the side of the collection groove 1168 away from the mesh 1170. Mesh 1170 is provided on both sides of the collection groove 1168. A moving component 1169 is slidably connected to the inner side of the collection groove 1168. When it is necessary to clean the dust attached to the side of the light-absorbing plate 114, the drive unit 1165 can be activated. The output end of the drive unit 1165 drives the electrostatic dust removal rod 1167 to move upward along the clearance groove inside the mounting frame 1163 until it approaches the side of the light-absorbing plate 114 through the connecting shaft 1166 and the mounting sleeve on the shaft. Then, high-voltage direct current is applied to the electrostatic dust removal rod 1167 to generate corona discharge at its electrodes, ionizing the surrounding air to form positive and negative ions. After the ions collide with the dust particles, they become charged and are adsorbed onto the surface of the dust removal rod. After the dust is adsorbed, the drive component 1165 rotates in reverse, and through the connecting shaft 1166 and the mounting sleeve, it drives the electrostatic dust removal rod 1167 to move downward along the relief groove and be stored in the mounting frame 1163. At this time, the suction machine 1164 is turned on to clean both sides of the inner cavity of the outer shell 1161. The suction generated by the suction machine 1164, through the air groove of the collection groove 1168, sucks the dust adsorbed on the surface of the rod into the collection groove 1168 through the mesh 1170. When dust accumulates to a certain amount in the collection tank 1168, the movable component 1169 can be slid to push the dust and impurities in the tank out through the square groove at the slide 1162, making it convenient for staff to collect and process them in a unified manner. Please see Figure 11 The moving component 1169 includes two moving rods 11691. Both ends of the moving rods 11691 are fixedly connected to the inner side of the collection trough 1168. A moving frame 11692 is slidably connected to the moving rods 11691. Both sides of the moving frame 11692 are slidably connected to the inner side of the collection trough 1168. A circular groove 11695 is opened on the side of the moving frame 11692. A feeding groove 11693 is opened on the side of the moving frame 11692 away from the circular groove 11695. A guide block 11694 is fixedly connected to the side of the moving frame 11692 through a circular rod, and the side of the circular rod is slidably connected to the inner side of the groove 1162. When cleaning the dust accumulated in the collection tank 1168, the staff can push the guide block 11694, which drives the movable frame 11692 to slide along the movable rod 11691 via the round rod; During this process, the guide block 11694 pushes and squeezes the dust in the collection tank 1168 through the feed chute 11693 opened on the side, while the moving frame 11692 simultaneously squeezes the dust upwards, and finally gathers and pushes the dust into the square groove at the slide chute 1162, which is convenient for staff to clean and dispose of it in a unified manner. Example 3, please refer to Figure 12 Based on Embodiment 1, the present invention provides a technical solution: A screenless true holographic display method based on an off-axis superlens array includes the following steps: S1: Generate pattern data: The controller 108 generates pattern data defining the light-transmitting area on the spatial light modulator 104 based on the spatial coordinates of the three-dimensional object 106 to be displayed; when the pattern data is binary pattern data, the difference in light transmittance between the "light-transmitting" area and the "light-blocking" area is not less than 90%; when it is grayscale pattern data, the light transmittance is graded at least 256 levels; the controller 108 updates the pattern data in real time according to the dynamic changes of the three-dimensional object 106 to be displayed, with an update frequency of not less than 10Hz, to achieve dynamic screenless true holographic display; S2: Modulated polarization state: The incident light emitted by the light source module 101 is converted into circularly polarized light through the polarization control module; the polarization control module realizes the polarization state conversion through the combination of linear polarizer 102 and waveplate 103, and the polarization direction of the circularly polarized light is consistent with the designed incident polarization direction of the off-axis superlens array 105; the wavelength range of the incident light is 400nm-760nm, and the deviation between the working wavelength of the off-axis superlens array 105 and the wavelength of the incident light does not exceed ±10nm; S3: Selecting the light beam: Load the pattern data generated in step S1 onto the spatial light modulator 104, and illuminate the spatial light modulator 104 with circularly polarized light, so that only the light energy of the "transparent" area in the pattern data can pass through; S4: Spatial Separation and Focusing: Light from the spatial light modulator 104 is irradiated onto the off-axis superlens array 105. The corresponding superlens unit 301 in the array focuses part of the light off-axis onto a preset three-dimensional coordinate point in free space to form a spatial pixel 303. Noise light 109, which is not effectively controlled by the superlens, propagates along its original path, achieving spatial physical separation from the signal light. The diffraction efficiency of the off-axis superlens array 105 for the signal light is not less than 20%, and the angle between the propagation direction of the noise light 109 and the off-axis focusing direction of the signal light is not less than 15°. The superlens unit 301 precisely controls the phase of the incident circularly polarized light through the subwavelength nanostructure array 302, so that the light passing through the superlens unit 301 is completely synchronized at the focal point of the preset spatial pixel 303, forming a perfect spherical wave 304. Each superlens unit 301 is focused to form a spatial pixel 303. The luminous intensity of the spatial pixel 303 is not less than 100 cd / m², which can be directly observed by the naked eye in the observation area 107 without obvious halo interference. S5: Reconstructing a screenless image: The illuminated spatial pixels 303 together constitute an aerial three-dimensional image that is not attached to any physical carrier and is spatially separated from the noise light 109, ensuring clear observation within the observation area 107; the brightness uniformity error of the spatial pixels 303 in the aerial three-dimensional image does not exceed 15%, and the center distance between adjacent spatial pixels 303 is not greater than 1mm. S6: Noise light 109 absorption: The noise light 109 is absorbed by the light absorption element 110 set in the propagation path of the noise light 109, so as to prevent the noise light 109 from entering the observation area 107.

[0019] Specific workflow: The light source module 101 uses a red helium-neon laser with a wavelength of 632.8nm to provide a high-quality collimated coherent light beam; Polarization control module: includes a linear polarizer 102 and a waveplate 103, used to convert the linearly polarized light output by the laser into left-hand circularly polarized light; Spatial light modulator 104: Employs an LCOS-SLM with a resolution of 1920x1080 and a pixel pitch of 8μm; Off-axis superlens array: Design and fabricate an off-axis superlens array with an operating wavelength of 632.8 nm for incident left-handed circularly polarized light. The array consists of millions of micro-superlens units 301, each designed to focus the incident left-handed circularly polarized light off-axis to a specific three-dimensional coordinate point in free space. Controller 108: A high-performance computer running customized display control software; Light-absorbing element 110: A black light-absorbing plate 114 placed on the extension line of the optical axis; The controller 108 loads a 3D model, such as a virtual cube model, and generates a binary pattern data based on its geometry. For example, the SLM pixels corresponding to points on the surface of a cube are set to "transparent"; like Figure 4 As shown; in the light-transmitting part, the spatial light modulator 104 allows the light beam on it to pass through and illuminate the corresponding superlens unit 301, so that the corresponding spatial pixel 303 is lit up, while other areas are "light-blocked". Figure 4 The schematic diagram shows that in the superlens array here, each superlens unit 301 corresponds to a spatial pixel 303, and they are independent of each other without crosstalk. One superlens unit 301 corresponds to one or more light on / off control units of the spatial light modulator 104, and one light on / off control unit of the spatial light modulator 104 corresponds to only one superlens unit 301. This correspondence is determined by the size of the superlens unit 301 and the light on / off control unit of the spatial light modulator 104. The red collimated laser emitted by the light source module 101 passes sequentially through the linear polarizer 102 and the waveplate 103, and is converted into left-hand circularly polarized light. When the left-handed circularly polarized light is shone onto the LCOS-SLM loaded with pattern data, only the corresponding area on the surface of the cube is allowed to pass through; The light shines onto the off-axis superlens array, and the corresponding superlens unit 301 in the array focuses the light off-axis onto a preset three-dimensional coordinate point in free space. Millions of such points together constitute a three-dimensional cube holographic image suspended in the air. Meanwhile, since the efficiency of the superlens is not 100%, about 70% of the light is not effectively controlled and propagates along the optical axis as noise light 109. The noise light 109 is absorbed by the light-absorbing element 110 and will not enter the observation area 107 at all. Within the observation area 107, users can clearly observe this high-contrast, high-brightness red 3D cube image from different angles, experiencing a true sense of suspension and 3D. It is worth noting that although polarizing elements are used in the optical path, the human eye is not sensitive to the polarization state of light, so the human eye will not experience any discomfort or visual difference when observing.

[0020] Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of them. All other embodiments obtained by those skilled in the art and related fields based on the embodiments of the present invention without inventive effort should fall within the scope of protection of the present invention. Structures, devices, and operating methods not specifically described and explained in the present invention, unless otherwise specified or limited, shall be implemented according to conventional means in the art.

Claims

1. A screenless true holographic display device based on an off-axis superlens array, characterized in that, include: The light source module (101), polarization control module, spatial light modulator (104), off-axis superlens array (105), noise light (109) and controller (108) electrically connected to the spatial light modulator (104) are arranged sequentially on the optical path, and also include a light absorption element (110) arranged on the propagation path of the noise light (109). The light source module (101) is used to provide a coherent and partially coherent incident light; The polarization control module is used to convert incident light into circularly polarized light. The polarization control module includes a linear polarizer (102) and a waveplate (103) arranged in sequence. The linear polarizer (102) is used to perform polarization filtering on the incident light, and the waveplate (103) is used to convert the linearly polarized light into circularly polarized light. The spatial light modulator (104) is set in the outgoing light path of the polarization control module and is configured to load pattern data generated by the controller (108). The pattern data is generated based on the spatial coordinates of the three-dimensional object (106) to be displayed, and is used to allow circularly polarized light in the corresponding area to pass through and block light in other areas, thereby achieving light selection. The off-axis superlens array (105) is set on the outgoing light path of the spatial light modulator (104) and includes multiple micro off-axis superlens units (301). Each superlens unit (301) corresponds precisely to one or more pixel regions on the spatial light modulator (104) and is used to focus the circularly polarized light passing through the corresponding region of the spatial light modulator (104) off-axis and converge it to a preset three-dimensional coordinate point in free space to form a spatial pixel (303). At the same time, the noise light (109) that is not effectively controlled propagates along the original propagation path, thereby realizing the spatial physical separation of the signal light and the noise light (109). The controller (108) is used for collaborative calculation and control, including generating the pattern data based on the spatial coordinates of the three-dimensional object (106) to be displayed, and loading the pattern data onto the spatial light modulator (104); The light-absorbing element (110) is positioned on the main propagation path of the noise light (109), usually in the direction of the optical axis, to absorb the noise light (109), improve the image signal-to-noise ratio, and ensure clear observation by the naked eye within the observation area (107).

2. The screenless true holographic display device based on an off-axis superlens array according to claim 1, characterized in that: The off-axis superlens array (105) is designed to match the polarization state of the incident light with that of the circularly polarized light. The pattern data is either binary pattern data or grayscale pattern data. The position corresponding to the spatial pixel (303) to be lit in the pattern data is in the "transparent" state, and the other positions are in the "blocked" state.

3. A screenless true holographic display device based on an off-axis superlens array according to claim 2, characterized in that, Also includes: The system comprises a superlens unit (301), a nanostructure array (302), a spatial pixel (303), a spherical wave (304), and a phase surface (305). The off-axis superlens array (105) is a planar optical element based on a metasurface. Each micro-off-axis superlens unit (301) is composed of a subwavelength-scale nanostructure array (302). The nanostructure array (302) is designed based on the PB phase principle and is used to accurately compensate for the phase difference generated when light propagates at different positions of the lens. The off-axis superlens array (105) is a planar optical element based on a metasurface. Each micro-off-axis superlens unit (301) is composed of a subwavelength-scale nanostructure array (302). The nanostructure array (302) is designed based on the PB phase principle and is used to accurately compensate for the phase difference generated when light propagates at different positions of the lens, thereby achieving precise control of the light wave phase surface (305) so that the light converges at the focal point of the spatial pixel (303) and forms a perfect outgoing spherical wave (304).

4. A screenless true holographic display device based on an off-axis superlens array according to claim 3, characterized in that, The number of micro off-axis superlens units (301) in the off-axis superlens array (105) is no less than 1 million. The preset three-dimensional coordinate points corresponding to each micro off-axis superlens unit (301) do not overlap with each other, and together they form a spatial pixel (303) matrix of the three-dimensional image. The matrix corresponds to the spatial shape of the reconstructed three-dimensional object (106) in free space, ensuring the multi-angle observation effect in the observation area (107).

5. A screenless true holographic display device based on an off-axis superlens array according to claim 4, characterized in that, The light-absorbing element (110) includes an adjustment base (111): An adjusting rod (112) is threadedly connected to the side of the adjusting seat (111), and a light-absorbing shell (113) is rotatably connected to the inner side of the adjusting seat (111). One end of the adjusting rod (112) is fixedly connected to the middle of the side of the light-absorbing shell (113). A heat sink (117) is fixedly connected to the inner side of the light-absorbing shell (113), and a light-absorbing plate (114) is fixedly connected to the side of the heat sink (117). A liquid cooling component (115) is used to dissipate heat from the heat sink (117), and the side of the liquid cooling component (115) is fixedly connected to the inside of the heat sink (117). A cleaning component (116) is used to clean the side of the light-absorbing plate (114), and the side of the cleaning component (116) is fixedly connected to the inside of the light-absorbing shell (113). The liquid cooling component (115) includes a heat dissipation pipe (1151) and a water storage pipe (1153). The side of the heat dissipation pipe (1151) is fixedly connected to the inside of the heat dissipation plate (117). The top of the water storage pipe (1153) is fixedly connected to a water outlet pipe (1152). The other end of the water outlet pipe (1152) is fixedly connected to the heat dissipation pipe (1151). The top of the inner cavity of the water storage pipe (1153) is fixedly connected to a filter cylinder (1155). The bottom of the inner cavity of the water storage pipe (1153) is fixedly connected to a water pump (1157). The output end of the water pump (1157) is fixedly connected to a water inlet pipe (1154). The other end of the water inlet pipe (1154) is fixedly connected to the end of the heat dissipation pipe (1151) away from the water outlet pipe (1152). The side of the water storage pipe (1153) is fixedly connected to a water filling pipe (1156).

6. A screenless true holographic display device based on an off-axis superlens array according to claim 5, characterized in that: The sides of the inlet pipe (1154) and the outlet pipe (1152) are fixedly connected to the inner side of the light-absorbing shell (113). The main propagation path of the noise light (109) is the optical axis direction. The light-absorbing plate (114) is either a black absorption plate or a light-absorbing coating. The light-absorbing shell (113) and the light-absorbing plate (114) are arranged on the optical axis extension line and located on the emission side of the off-axis superlens array (105).

7. A screenless true holographic display device based on an off-axis superlens array according to claim 6, characterized in that: The cleaning component (116) includes a cleaning housing (1161), with sliding grooves (1162) on both sides of the cleaning housing (1161), a mounting frame (1163) fixedly connected to the inner side of the cleaning housing (1161), a suction machine (1164) fixedly connected to both sides of the inner cavity of the cleaning housing (1161), a driving component (1165) fixedly connected to the middle of the inner side of the cleaning housing (1161), a connecting shaft (1166) fixedly connected to the output end of the driving component (1165), an electrostatic dust removal rod (1167) fixedly connected to the other end of the connecting shaft (1166) by means of an installation sleeve, a collection groove (1168) on both sides of the cleaning housing (1161), a mesh (1170) on both sides of the collection groove (1168), and a moving component (1169) slidably connected to the inner side of the collection groove (1168).

8. A screenless true holographic display device based on an off-axis superlens array according to claim 7, characterized in that: The side of the cleaning shell (1161) is fixedly connected to the light-absorbing shell (113), the middle of the mounting frame (1163) is provided with a clearance groove, and the side of the collecting groove (1168) away from the mesh (1170) is provided with an air groove.

9. A screenless true holographic display device based on an off-axis superlens array according to claim 8, characterized in that: The moving component (1169) includes two moving rods (11691). Both ends of the moving rods (11691) are fixedly connected to the inner side of the collection trough (1168). A moving frame (11692) is slidably connected to the moving rods (11691). Both sides of the moving frame (11692) are slidably connected to the inner side of the collection trough (1168). A circular groove (11695) is provided on the side of the moving frame (11692). A feeding groove (11693) is provided on the side of the moving frame (11692) away from the circular groove (11695). A guide block (11694) is fixedly connected to the side of the moving frame (11692) by a circular rod. The side of the circular rod is slidably connected to the inner side of the sliding groove (1162).

10. A screenless true holographic display method based on an off-axis superlens array, wherein the screenless true holographic display device based on an off-axis superlens array according to claim 1 is characterized in that, Includes the following steps: S1: Generate pattern data: The controller (108) generates pattern data defining the light-transmitting area on the spatial light modulator (104) based on the spatial coordinates of the three-dimensional object (106) to be displayed. S2: Modulated polarization state: The incident light emitted by the light source module (101) is converted into circularly polarized light after passing through the polarization control module; S3: Selecting the light beam: Load the pattern data generated in step S1 onto the spatial light modulator (104), and illuminate the spatial light modulator (104) with circularly polarized light, so that only the light energy of the "transparent" area in the pattern data can pass through; S4: Spatial separation and focusing: The light from the spatial light modulator (104) is irradiated onto the off-axis superlens array (105). The corresponding superlens unit (301) in the array focuses part of the light off-axis onto a preset three-dimensional coordinate point in free space to form a spatial pixel (303). The noise light (109) that is not effectively controlled by the superlens propagates along the original path and achieves spatial physical separation from the signal light. S5: Reconstructing the screenless image: All the illuminated spatial pixels (303) together constitute an aerial three-dimensional image that is not attached to any physical carrier and is spatially separated from the noise light (109), ensuring clear observation within the observation area (107); S6: Noise light (109) absorption. The noise light (109) is absorbed by the light absorption element (110) set on the propagation path of the noise light (109), so as to prevent the noise light (109) from entering the observation area (107).

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