Grating detection device

Abstract

The application belongs to the technical field of optics, and particularly relates to a grating detection device, which has a calibration state, an exposure state and a detection state. The grating detection device comprises a light source assembly, a shutter, a placement area and an image sensor which are sequentially arranged in the light path of the light source assembly. The light source assembly generates first interference light and second interference light. In the exposure state, the first interference light and the second interference light are incident on the volume holographic material along a first direction and a second direction respectively. In the detection state, the first interference light is incident on the volume holographic material along the first direction and is emitted from the volume holographic material along a third direction, and the second interference light is blocked by the shutter. In the calibration state, the second interference light passes through the placement area and irradiates the image sensor along the second direction. The image sensor acquires the positions of the light spots formed by the first interference light and the second interference light on the image sensor. The grating detection device can quantify the angle offset of light, thereby providing calculation data for the shrinkage deformation of the volume holographic material.

Description

Technical Field

[0001] This application belongs to the field of optical technology, and more specifically, relates to a grating detection device. Background Technology

[0002] Shrinkage deformation during the exposure of volume holographic materials can cause a shift in the Bragg condition, affecting optical performance. The sensitivity of volume holographic materials is bidirectionally coupled with shrinkage deformation. While related technologies can use sensitivity testing to aid in assessing optical performance, these methods cannot precisely calibrate the degree of shrinkage deformation. This lack of quantitative guidance for subsequent material formulation optimization and process improvement makes it difficult to reduce the impact of shrinkage deformation on the overall performance of optical devices. Utility Model Content

[0003] The purpose of this application is to provide a grating detection device to solve the technical problem in the prior art that it is difficult to accurately detect the shrinkage and deformation degree of volumetric holographic materials.

[0004] To achieve the above objectives, the technical solution adopted in this application is as follows:

[0005] A grating detection device is provided, having a calibration state, an exposure state, and a detection state. The grating detection device includes a light source assembly and a shutter, a placement area, and an image sensor sequentially arranged in the optical path of the light source assembly, wherein:

[0006] The placement area is used to place the volumetric holographic material to be detected in both the exposure state and the detection state.

[0007] The light source assembly generates a first interference light and a second interference light. During the exposure state, the first interference light and the second interference light are incident on the volume holographic material along a first direction and a second direction, respectively.

[0008] In the detection state, the first interference light is incident on the volume holographic material along the first direction and exits from the volume holographic material along a third direction, the third direction being set at an angle to the second direction, and the second interference light is blocked by the shutter.

[0009] In the calibration state, the second interference light passes through the placement area along the second direction and illuminates the image sensor;

[0010] The image sensor acquires the position of the first spot formed by the second interference light on the image sensor in the calibration state, and acquires the position of the second spot formed by the first interference light on the image sensor in the detection state.

[0011] In some embodiments, the grating detection device further includes an angle amplifier disposed in the optical path of the light source assembly. The angle amplifier is located between the placement area and the image sensor. The angle amplifier is used to deflect the propagation directions of the first interference light and the second interference light emitted after diffraction from the volume holographic material, so as to increase the angular offset of the first interference light emitted after diffraction from the volume holographic material relative to the second direction, and / or increase the angular offset of the second interference light emitted after diffraction from the volume holographic material relative to the first direction.

[0012] In some embodiments, the angle amplifier includes a first mirror group and a second mirror group disposed in the optical path of the light source assembly, the first mirror group being disposed on the side of the second mirror group away from the image sensor, and the focal length f1 of the first mirror group being greater than the focal length f2 of the second mirror group.

[0013] In some embodiments, the optical axes of the first lens group and the second lens group are coaxially arranged, and the distance between the first lens group and the second lens group is d, where d = f1 + f2.

[0014] In some embodiments, the light source assembly includes a light emitter and a beam splitter, wherein the light emitted by the light emitter is split into a first interference light and a second interference light by the beam splitter;

[0015] The optical path of the first interference light is provided with a first reflecting mirror. The first interference light emitted from the beam splitter is reflected by the first reflecting mirror and then incident on the volume holographic material along the first direction; and / or,

[0016] The optical path of the second interference light is provided with a second reflector. The second interference light emitted from the beam splitter is reflected by the second reflector and then enters the volume holographic material along the second direction.

[0017] In some embodiments, the emitter is a single-mode laser.

[0018] In some embodiments, the grating detection device includes a first beam expander, which is disposed in the optical path of the first interference light and located on the side of the placement area opposite to the image sensor. The cross-sectional width of the first interference light emitted from the first beam expander is greater than the cross-sectional width of the first interference light incident on the first beam expander; and / or,

[0019] The grating detection device includes a second beam expander, which is disposed in the optical path of the second interference light and located on the side of the placement area away from the image sensor. The cross-sectional width of the second interference light emitted from the second beam expander is greater than the cross-sectional width of the second interference light incident on the second beam expander.

[0020] In some embodiments, the grating detection device further includes a first optical filter, which is disposed in the optical path of the first interference light and located on the side of the placement area opposite to the image sensor; and / or,

[0021] The grating detection device further includes a second optical filter, which is disposed in the optical path of the second interference light and located on the side of the placement area away from the image sensor.

[0022] In some embodiments, the second direction is perpendicular to the surface of the volume holographic material.

[0023] In some embodiments, the first interfering light is a parallel beam; and / or,

[0024] The second interference beam is a parallel beam.

[0025] The beneficial effect of the grating detection device provided in this application is that the image sensor can record the irradiation positions of the first interference light and the second interference light, providing measurement data for the shrinkage deformation of the volume holographic material. Ideally, if the first interference light is used alone to irradiate the volume holographic material, the propagation direction of the first interference light emitted after diffraction is parallel to the second direction. If the second interference light is used alone to irradiate the volume holographic material, the propagation direction of the second interference light emitted after diffraction is parallel to the first direction. In the calibration state, by not placing the volume holographic material in the placement area, the second interference light generated by the light source assembly can directly pass through the placement area and irradiate the image sensor. The image sensor can record the position of the first light spot S1 formed by the second interference light irradiation, that is, it can record the position where the ideal first interference light, after diffraction by the volume holographic material, irradiates the image sensor when there is no shrinkage. Then, the volume holographic material to be detected is placed in the placement area, and the detection state is switched to the exposure state to measure the volume holographic material. After the material undergoes exposure processing, the shutter can be used to block the second interference light to switch the grating detection device to the detection state. At this time, the first interference light is incident on the volume holographic material from the first direction. The first interference light emitted along the third direction after being diffracted by the volume holographic material illuminates the image sensor to form the second spot S2. The image sensor can record the position of the second spot S2, that is, it can record the position of the first interference light emitted after being diffracted by the volume holographic material and illuminating the image sensor under actual shrinkage conditions. The image sensor can also measure the distance X between the first spot S1 and the second spot S2. Combined with the distance between the image sensor and the placement area, the angular offset of the light can be quantified, thereby providing calculation data for the shrinkage deformation of the volume holographic material to reduce the impact of shrinkage deformation on the overall performance of the optical equipment. Attached Figure Description

[0026] To more clearly illustrate the technical solutions in the embodiments of this application, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0027] Figure 1 A schematic diagram of the grating detection device provided in the embodiments of this application in the calibration state;

[0028] Figure 2 for Figure 1 A schematic diagram of the grating detection device in the exposure state (angle amplifier and image sensor not shown);

[0029] Figure 3 for Figure 1 A schematic diagram of the grating detection device in the detection state (angle amplifier and image sensor not shown);

[0030] Figure 4 for Figure 1 A schematic diagram of the grating detection device in the detection state;

[0031] Figure 5 A schematic diagram of the volume holographic material, angle amplifier, and image sensor provided in the embodiments of this application;

[0032] Figure 6 A schematic diagram of the angle amplifier and image sensor provided in the embodiments of this application;

[0033] Figure 7 This is a schematic diagram of the first beam expander provided in an embodiment of this application.

[0034] The following are the labeling elements in the figure:

[0035] 100. Holographic materials;

[0036] 10. Placement area;

[0037] 1. Light source assembly; 11. Light emitter; 12. Beam splitter; 2. Shutter; 3. Image sensor; 4. Angle amplifier; 41. First lens group; 42. Second lens group; 5. First beam expander; 51. First optical filter; 52. First lens; 6. Second beam expander; 61. Second optical filter; 62. Second lens; 7. First reflector. Detailed Implementation

[0038] To make the technical problems, technical solutions, and beneficial effects to be solved by this application clearer, the following detailed description is provided in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and are not intended to limit the scope of this application.

[0039] It should be noted that when a component is referred to as being "fixed to" or "set on" another component, it can be directly on or indirectly on that other component. When a component is referred to as being "connected to" another component, it can be directly connected to or indirectly connected to that other component.

[0040] It should be understood that the terms "length", "cross-sectional width", "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", and "outer" indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing this application and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on this application.

[0041] Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include one or more of that feature. In the description of this application, "multiple" means two or more, "multiple sets" means two or more sets, "multiple pieces" means two or more pieces, and "several" means one or more, unless otherwise explicitly specified.

[0042] Volume holographic materials, as an advanced optical medium capable of constructing three-dimensional nanoscale periodic grating structures internally, have become core supporting materials in modern photonics, information storage, and display technologies due to their ability to precisely control light waves based on the Bragg diffraction effect, especially demonstrating irreplaceable application value in the field of near-eye displays. In the field of near-eye displays, volume holographic waveguides are considered key optical components for realizing optical devices such as "glasses-style" augmented reality (AR) technology, and their performance directly determines the display field of view, image clarity, and the thinness and lightness of the device.

[0043] However, volume holographic materials generally face the technical challenge of shrinkage during actual preparation and application. Shrinkage refers to the non-uniform volume shrinkage that occurs during exposure curing or subsequent processing. When photosensitive polymers are exposed under a coherent laser interference field, monomer molecules undergo cross-linking polymerization, shortening the intermolecular distance and increasing the material density. Simultaneously, the release of thermal stress and solvent evaporation during curing further exacerbate the volume change, thus causing shrinkage.

[0044] The sensitivity of volume holographic materials (referring to the material's response efficiency to incident light, i.e., the ability to form a stable holographic grating under the light energy received per unit area) and shrinkage deformation have a significant bidirectional coupling effect, which further exacerbates the difficulty of performance control: On the one hand, high-sensitivity materials respond rapidly to light signals and can complete the polymerization reaction within tens of seconds, but rapid polymerization leads to the rapid stacking of molecular chain segments and the rapid shortening of the distance between molecules, causing stress concentration inside the material and directly aggravating the degree of shrinkage deformation; on the other hand, the non-uniform stress generated by shrinkage deformation will change the local refractive index distribution of the material, destroy the periodic structure of the three-dimensional grating, and cause the material's response capability to incident light to decrease.

[0045] The effects of shrinkage deformation on the optical properties of volume holographic materials are mainly reflected in three aspects:

[0046] 1. Bragg wavelength shift: Changes in the grating period cause the diffraction wavelength to deviate from the design value, which manifests as color distortion in display applications; for example, a hologram designed for red light (632nm) may only be able to diffract efficiently at a shorter wavelength (such as 610nm) after being shrunk and deformed.

[0047] 2. Angle-selective drift: Grating surface distortion causes the actual diffraction angle to deviate from the theoretical value, resulting in image misalignment or a reduced field of view.

[0048] 3. Decreased diffraction efficiency: Uneven grating modulation depth leads to reduced diffraction efficiency, resulting in impaired image brightness and contrast.

[0049] Therefore, a grating detection device is needed to accurately calibrate the shrinkage of volume holographic materials.

[0050] Based on this, embodiments of this application provide a grating detection device to solve the above-mentioned problems.

[0051] Reference Figures 1 to 4This application provides a grating detection device with a calibration state, an exposure state, and a detection state. The grating detection device includes a light source assembly 1 and a shutter 2, a placement area 10, and an image sensor 3 sequentially arranged in the optical path of the light source assembly 1. The placement area 10 is used to place the volume holographic material 100 to be detected in the exposure state and the detection state. The light source assembly 1 generates a first interference light and a second interference light. In the exposure state, the first interference light and the second interference light are incident on the volume holographic material 100 along a first direction and a second direction, respectively. In the detection state, the first interference light is incident on the volume holographic material 100 along the first direction and exits from the volume holographic material 100 along a third direction. The third direction is set at an angle to the first direction and the second direction, respectively. The second interference light is blocked by the shutter 2. In the calibration state, the second interference light passes through the placement area along the second direction and illuminates the image sensor 3. The image sensor 3 acquires the position of the first light spot S1 formed by the second interference light in the image sensor 3 in the calibration state and the position of the second light spot S2 formed by the first interference light in the image sensor 3 in the detection state.

[0052] It should be noted that by measuring the angular offset of the diffracted light from the finished volume holographic material 100 in batches, the shrinkage rate of this volume holographic material 100 can be inferred. This can help material engineers improve the formulation of photosensitive materials (such as the ratio of monomers, polymers, and photoinitiators) or help process engineers optimize parameters such as exposure energy, time, and post-processing (such as UV curing and baking) to reduce shrinkage from the source.

[0053] Furthermore, in many optical systems, the propagation angle of the light beam is precisely designed. After calibrating the angle offset, this angle can be pre-compensated either in the mechanical design or introduced as a calibration parameter in the software control to ensure that the outgoing light path is consistent with the theoretical design. In specific AR glasses, a volume holographic grating is used as a coupler (input coupler and output coupler) to couple light from a microdisplay into a waveguide and finally into the human eye. This places extremely high demands on the angle and wavelength selectivity of the grating, directly affecting the field of view (FOV), brightness, image uniformity, and the "rainbow effect." By precisely calibrating the reduction and clarifying the angle offset of the light outgoing angle, the accurate realization of the designed field of view can be ensured while improving the rainbow effect.

[0054] It should be noted that in this embodiment, the first and second interference lights have the same frequency, the same vibration direction, and a constant phase difference. When the grating detection device is in the exposure state, the volume holographic material 100 can be exposed. The exposure process here refers to interference recording. Interference recording means that when two interference lights (corresponding to the first and second interference lights) with the same frequency, the same vibration direction, and a constant phase difference meet, they will superimpose on each other to form alternating bright and dark interference fringes (i.e., interference images). Exposure processing of the volume holographic material 100 is the process of recording an interference image onto the volume holographic material 100. (When the chemical photosensitive material on the volume holographic material 100 is irradiated by the bright and dark fringes of light interference, the chemical photosensitive material changes and forms a striped distribution of micro-nano structures (i.e., gratings). This process causes the volume holographic material 100 to shrink and deform. The interference recording allows the volume holographic material 100 to record all the information of the two interference beams (including both the amplitude information of the light intensity and the depth information of the phase). After the exposure processing of the volume holographic material 100 is completed, the interference image can be permanently recorded. In some embodiments, the first direction and the second direction are set at an angle.

[0055] It should be noted that, referring to Figure 2 When the first interference light and the second interference light are simultaneously incident on the volume holographic material 100 to expose it, the first interference light and the second interference light can each exit from the volume holographic material 100. After exposure, in subsequent use, ideally, the volume holographic material 100 does not shrink or deform. When the first interference light and the second interference light, identical to those used in the exposure state, are incident on the volume holographic material 100, their exit directions are parallel to the first and second directions, satisfying the Bragg condition. Ideally, if the volume holographic material 100 is irradiated only with the first interference light, the propagation direction of the first interference light emitted after diffraction is parallel to the second direction; if the volume holographic material 100 is irradiated only with the second interference light, the propagation direction of the second interference light emitted after diffraction is parallel to the first direction. However, due to the shrinkage and deformation of the volume holographic material 100 after exposure, if the first interference light is used alone to illuminate the volume holographic material 100, the first interference light emitted after diffraction will deviate from the first direction. If the second interference light is used alone to illuminate the volume holographic material 100, the emission direction of the second interference light emitted after diffraction will deviate from the second direction, resulting in Bragg condition mismatch. In this case, the propagation direction of the first interference light emitted after diffraction from the volume holographic material 100 can be denoted as the third direction, and the propagation direction of the second interference light emitted after diffraction from the volume holographic material 100 can be denoted as the fourth direction. After the volume holographic material 100 has undergone exposure processing, due to the characteristics of the volume holographic material 100, referring to... Figure 3The second interference light is blocked, and only the first interference light is incident on the volume holographic material 100 along the first direction. Under the optical action of the volume holographic material 100, the first interference light can diffract out light rays emitted from the volume holographic material 100 along the third direction.

[0056] It should be noted that the volume holographic material 100 can be processed into a film shape to facilitate the calculation of the shrinkage and deformation of the volume holographic material 100.

[0057] It should be noted that the image sensor 3 is a core electronic component that converts light signals (photons) into electrical signals, which are then processed into digital images by subsequent circuitry, essentially acting as the "electronic retina" of a digital device. Its core function is to replace the photosensitivity of traditional film, realizing the conversion from "light" to "electricity" to "digital signal," making it a core component of all digital imaging devices. The image sensor 3 is used to detect the intensity and position information of the incident light beam, converting this information into the shrinkage deformation of the volume holographic material 100 and characterizing it. Specifically, the image sensor 3 can be a charge-coupled device (CCD) or a complementary metal-oxide-semiconductor (CMOS).

[0058] The grating detection device provided in this application embodiment has an image sensor 3 that can record the irradiation positions of the first interference light and the second interference light, providing measurement data for the shrinkage deformation of the volume holographic material 100. Ideally, if the first interference light is used alone to irradiate the volume holographic material 100, the propagation direction of the first interference light emitted after diffraction by the volume holographic material 100 is parallel to the second direction; if the second interference light is used alone to irradiate the volume holographic material 100, the propagation direction of the second interference light emitted after diffraction by the volume holographic material 100 is parallel to the first direction. (Referring to...) Figure 1 In the calibration state, by not placing the volume holographic material 100 in the placement area 10, the second interference light generated by the light source assembly 1 can directly pass through the placement area 10 and illuminate the image sensor 3. The image sensor 3 can record the position of the first light spot S1 formed by the illumination of the second interference light, that is, it can record the position of the ideal first interference light that is diffracted by the volume holographic material 100 and illuminates the image sensor when there is no shrinkage. Then, the volume holographic material 100 to be detected is placed in the placement area 10, and the detection state is switched to the exposure state to expose the volume holographic material 100. After the exposure process is completed, the shutter 2 can be used to block the second interference light to switch the grating detection device to the detection state, referring to... Figure 4 and Figure 5At this time, the first interference light is incident on the volume holographic material from the first direction. The first interference light emitted from the third direction after being diffracted by the volume holographic material 100 illuminates the image sensor 3 to form the second spot S2. The image sensor 3 can record the position of the second spot S2, that is, it can record the position of the first interference light emitted after being diffracted by the volume holographic material 100 and illuminating the image sensor under the actual shrinkage condition. The image sensor can also measure the distance X between the first spot S1 and the second spot S2. Combined with the distance between the image sensor 3 and the placement area 10, the angular offset of the light can be quantified, thereby providing calculation data for the shrinkage deformation of the volume holographic material 100, so as to reduce the impact of shrinkage deformation on the overall performance of the optical device.

[0059] In some embodiments, the grating detection device further includes an angle amplifier 4 disposed in the optical path of the light source assembly 1. The angle amplifier 4 is located between the placement area 10 and the image sensor 3. The angle amplifier 4 is used to deflect the propagation direction of the first interference light and the second interference light emitted after diffraction from the volume holographic material 100, so as to increase the angular offset of the first interference light emitted after diffraction from the volume holographic material 100 relative to the second direction, and / or increase the angular offset of the second interference light emitted after diffraction from the volume holographic material 100 relative to the first direction.

[0060] Reference Figure 5 Under the optical action of the volume holographic material 100, the first interference light emitted from the volume holographic material 100 and propagating along a third direction forms an angle θ1 with the second direction. In some cases, for volume holographic materials 100 with small shrinkage deformation, the value of θ1 is relatively small, and the distance X between the first light spot S1 and the second light spot S2 formed on the image sensor 3 is small, requiring high measurement accuracy and making the measurement difficult. An angle amplifier 4 is set up, which can refract the propagation direction of the first interference light emitted after diffraction by the volume holographic material 100, thereby increasing the angle between the first interference light and the second direction to θ2, that is, increasing the angular offset of the propagation direction of the first interference light from θ1 to θ2. In this way, the distance X between the first light spot S1 and the second light spot S2 formed on the image sensor 3 can be increased, thus reducing the measurement accuracy requirement and the measurement difficulty. Furthermore, during the recording of the first light spot S1, the angle amplifier 4 can also increase the angular offset of the propagation direction of the second interference light. Since the same angle amplifier 4 is used in both processes and the increase factor of the angular offset of the propagation direction is the same, the angular offset of the light can be directly calculated to quantify the angular offset of the light, thereby providing measurement data for the shrinkage deformation of the volume holographic material 100.

[0061] In this embodiment, the image sensor 3 can calculate θ2 = arctan(X / L) based on the position information of the first light spot S1 and the second light spot S2 and the distance L between the image sensor 3 and the angle amplifier 4. The first interference light has been deflected by the angle amplifier 4 by a factor of K before entering the image sensor 3, so the actual angle deflection of the first interference light can be calculated as θ1 = θ2 / K.

[0062] Reference Figure 6 In some embodiments, the angle amplifier 4 includes a first mirror group 41 and a second mirror group 42 disposed in the optical path of the light source assembly 1. The first mirror group 41 is disposed on the side of the second mirror group 42 away from the image sensor 3, and the focal length f1 of the first mirror group 41 is greater than the focal length f2 of the second mirror group 42.

[0063] It should be noted that the first lens group may include one or more lenses. When the first lens group includes only one lens, the focal length of this lens is the focal length of the first lens group. When the first lens group includes multiple lenses, the combined focal length of these multiple lenses is the focal length of the first lens group. The second lens group is similar, and will not be described in detail in the embodiments of this application.

[0064] By making the focal length f1 of the first lens group 41 greater than the focal length f2 of the second lens group 42, the exit angle of the angle amplifier 4 can be made greater than the incident angle, thereby amplifying the angular offset of the light.

[0065] In this embodiment, the amplification factor of the angle amplifier 4 on the angular offset of the light can be denoted as K, where K = f1 / f2. Since f1 is greater than f2, K > 1, thus amplifying the angular offset of the light.

[0066] In this embodiment of the application, the optical axis of the first lens group 41 and the optical axis of the second lens group 42 are coaxially arranged, and the distance between the first lens group 41 and the second lens group 42 is d, where d = f1 + f2.

[0067] The optical axes of the first mirror group 41 and the second mirror group 42 are set coaxially, with d = f1 + f2. This makes the two mirror groups form a focusless system (the output is also a parallel beam when the input is a parallel beam). In this way, when the interference light emitted from the volume holographic material 100 passes through the angle amplifier 4, the interference light can propagate stably along the axis, reducing the light deflection and scattering caused by problems such as mirror group eccentricity, reducing the detection error caused by optical path instability, and improving the accuracy and consistency of angle amplification.

[0068] In this embodiment, the focal length f1 of the first lens group 41 is greater than the focal length f2 of the second lens group 42. The optical axes of the first lens group 41 and the second lens group 42 are coaxial, and the distance d between the first lens group 41 and the second lens group 42 is d = f1 + f2. The angle amplifier 4 is equivalent to an inverted telescope (a telescope system with the eyepiece in front and the objective lens behind). Of course, in other embodiments, the angle amplifier 4 can also be a double-wedge system, a multi-reflection cavity, or other structures.

[0069] Reference Figures 1 to 4 The light source assembly 1 includes a light emitter 11 and a beam splitter 12. The light emitted by the light emitter 11 is split into a first interference beam and a second interference beam by the beam splitter 12. In some embodiments, a first reflector 7 is provided in the optical path of the first interference beam, and the first interference beam emitted from the beam splitter 12 is reflected by the first reflector 7 and then incident on the holographic material 100 along a first direction. In other embodiments, a second reflector is provided in the optical path of the second interference beam, and the second interference beam emitted from the beam splitter 12 is reflected by the second reflector and then incident on the holographic material 100 along a second direction. In the embodiments of this application, a first reflector 7 is provided in the optical path of the first interference beam.

[0070] Beam splitter 12 splits the light emitted by emitter 11 into a first interference beam and a second interference beam. The first and second interference beams originate from the same source, ensuring that they have the same frequency, vibration direction, and constant phase difference, thus guaranteeing the effectiveness of the exposure processing on the volume holographic material 100. It is understood that the first and second interference beams emitted from beam splitter 12 will propagate in different directions. Without a reflector, these two reflected beams will not intersect. The reflector can change the propagation direction of the first and / or second interference beams, allowing them to simultaneously illuminate the volume holographic material 100 and form interference fringes.

[0071] In some embodiments, beam splitter 12 may be a beam splitter prism.

[0072] In some embodiments, the emitter 11 is a single-mode laser.

[0073] It should be noted that a single-mode laser refers to a laser that generates and maintains only a single transverse mode and a single longitudinal mode during laser output.

[0074] Single-mode lasers output only a single longitudinal mode, resulting in an extremely narrow spectral cross-section. This signifies highly stable and singular laser frequency / wavelength, leading to exceptionally strong coherence (including temporal and spatial coherence). For temporal coherence, the same beam exhibits strong phase correlation at different time points; for spatial coherence, the beam shows strong phase correlation at different positions. This improves the exposure processing accuracy of volume holographic materials 100. Furthermore, because single-mode lasers maintain only a single mode, the fluctuation in laser output power is minimal, significantly reducing detection errors.

[0075] In other embodiments, the light emitter 11 can also be other forms of light source, such as a monochromatic light-emitting diode (LED), a multimode laser, a continuous spectrum laser, etc.

[0076] Reference Figure 7 In some embodiments, the grating detection device includes a first beam expander 5, which is disposed in the optical path of the first interference light and located on the side of the placement area 10 away from the image sensor 3. The cross-sectional width of the first interference light emitted from the first beam expander 5 is greater than the cross-sectional width of the first interference light incident on the first beam expander 5. The grating detection device also includes a second beam expander 6, which is disposed in the optical path of the second interference light and located on the side of the placement area 10 away from the image sensor 3. The cross-sectional width of the second interference light emitted from the second beam expander 6 is greater than the cross-sectional width of the second interference light incident on the second beam expander 6.

[0077] It should be noted that when the cross-sectional shape of the first interfering light is circular, the diameter of the cross-section is the same as the width of the cross-section; when the cross-sectional shape is elliptical, the major axis of the cross-section is the same as the width; when the cross-sectional shape is rectangular, the width of the rectangular cross-section is the same as the width; and when the cross-section is of other shapes, the maximum size of the cross-section is the same as the width. The same principle applies to the second interfering light, and will not be elaborated further in this embodiment.

[0078] The first beam expander 5 and the second beam expander 6 can respectively increase the cross-sectional width of the first interference light and the second interference light, thereby expanding the beam and turning the "point" light source into a "surface" light source. The expanded first interference light and the second interference light can expose the volume holographic material 100 over a large area, thereby forming a large-area holographic grating on the volume holographic material 100.

[0079] In some embodiments, the grating detection device further includes a first optical filter 51, which is disposed in the optical path of the first interference light and located on the side of the placement area 10 away from the image sensor 3; the grating detection device further includes a second optical filter 61, which is disposed in the optical path of the second interference light and located on the side of the placement area 10 away from the image sensor 3.

[0080] It should be noted that in the embodiments of this application, both the first optical filter 51 and the second optical filter 61 are spatial optical filters. A spatial optical filter is an optical element or device that selectively transmits specific optical signals. Its core function is to "filter" out the target optical signal from complex incident light (light containing multiple wavelengths, frequencies, or polarization states) and allow it to pass through, while suppressing or blocking unwanted stray light signals. Its working principle is based on differences in optical properties, such as the wavelength, frequency, polarization direction, and phase of light, and achieves signal filtering through physical mechanisms such as material absorption, thin-film interference, grating diffraction, and polarization selection.

[0081] The first optical filter 51 and the second optical filter 61 can respectively filter out high-frequency noise signals in the first interference light and the second interference light to improve the accuracy of exposure and detection.

[0082] In this embodiment, the first beam expander 5 includes a first optical filter 51, which can also expand the beam of the first interference light; the second beam expander 6 includes a second optical filter 61, which can also expand the beam of the second interference light.

[0083] In some embodiments, the first interference beam is a parallel beam; the second interference beam is a parallel beam.

[0084] It should be noted that a parallel beam refers to a type of beam in which the light rays propagate in completely parallel directions. Its core characteristics are: all the light rays in the beam do not converge or diverge during propagation, and any two light rays always remain parallel (ideally); during propagation, the beam diameter remains basically unchanged (ideally completely unchanged), and does not expand with increasing distance like a beam emitted from a point source; due to the parallel propagation directions, the energy density distribution of the beam cross-section is relatively uniform.

[0085] By setting the first and second interference beams as parallel beams, the beam diameter remains essentially unchanged (ideally completely unchanged), unlike the beam emitted by a point source which expands with increasing distance. This allows for convenient arrangement of various devices and reduces the impact of distance errors between devices on the detection results. The energy density distribution of the parallel beam cross-section is relatively uniform, which helps to improve the processing effect on the volume holographic material 100.

[0086] In this embodiment, the first beam expander 5 includes a first lens 52, which can focus the divergent first interference light after beam expansion to form a parallel beam; the second beam expander 6 includes a second lens 62, which can focus the divergent second interference light after beam expansion to form a parallel beam.

[0087] In some embodiments, the first lens 52 and the second lens 62 may be Fourier lenses.

[0088] In this embodiment of the application, the second direction is perpendicular to the surface of the volume holographic material 100, that is, the second interference light can be incident perpendicularly on the volume holographic material 100.

[0089] With the second direction perpendicular to the surface of the volume holographic material 100, the second interference light can be incident perpendicularly on the volume holographic material 100. It is understood that aligning the light path in the perpendicular direction is more intuitive and can be determined visually or with the aid of simple tooling, eliminating the need for high-precision angle measuring instruments (such as goniometers) to calibrate the incident angle. This simplifies the structure and reduces the complexity of the device. The perpendicularly incident second interference light reduces optical path interference and is less prone to dispersion, thus helping to optimize the exposure processing quality.

[0090] In this embodiment, the degree of shrinkage deformation of the volume holographic material 100 can be inferred by using a grating detection device to quantify the diffraction angle shift after shrinkage deformation of the volume holographic material 100, and then the periodic change of the volume holographic material 100 can be calculated:

[0091] Switch the grating detection device to the calibration state so that the holographic material 100 is not placed in the placement area 10. The second interference light generated by the light source assembly 1 can directly pass through the placement area 10 and the angle magnification device to illuminate the image sensor 3. The image sensor 3 records the position of the first light spot S1 formed by the illumination of the second interference light.

[0092] Turn off light source component 1;

[0093] The volume holographic material 100 to be tested is placed in the placement area 10, and the grating detection device is switched to the exposure state so that the first interference light and the second interference light are simultaneously incident on the volume holographic material 100 to expose the volume holographic material 100.

[0094] Switch the grating detection device to the detection state, use shutter 2 to block the second interference light, the first interference light generated by the diffraction of the volume holographic material 100 and emitted in the third direction passes through the angle magnification device to illuminate the image sensor 3 to form the second light spot S2, the image sensor 3 records the position of the second light spot S2, and measures the distance X between the first light spot S1 and the second light spot S2.

[0095] The image sensor 3 can calculate θ2 = arctan(X / L) based on the position information of the first light spot S1 and the second light spot S2 received and the distance L between the image sensor 3 and the angle amplifier 4. Before the first interference light enters the image sensor 3, it has been deflected by the angle amplifier 4 by a factor of K. Therefore, the actual angle deflection of the first interference light can be calculated as θ1 = θ2 / K.

[0096] The principle of the reduction in intensity detection due to the angular shift of the diffraction spot can be described by the Bragg angle shift expression (1):

[0097]

[0098] Where Λ0 is the designed grating period, n0 is the average refractive index of the film layer; λ is the wavelength of the first interference light (the wavelengths of the first and second interference lights are the same); Θ B Θ is the Bragg angle of the first interfering light; B It is a known and definite value, 2ΛsinΘ at exposure time. B =λ, where Δn is the refractive index modulation of the volume holographic material 100. Using equation (1), the periodic variation ΔΛ of the volume holographic material 100 can be calculated from the actual angle θ1 of the first interference light.

[0099] The above description is merely a preferred embodiment of this application and is not intended to limit this application. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of this application should be included within the protection scope of this application.

Claims

1. A grating detection device, characterized in that, The grating detection device has calibration, exposure, and detection states. It includes a light source assembly and a shutter, a placement area, and an image sensor sequentially arranged in the optical path of the light source assembly, wherein: The placement area is used to place the volumetric holographic material to be detected in both the exposure state and the detection state. The light source assembly generates a first interference light and a second interference light. During the exposure state, the first interference light and the second interference light are incident on the volume holographic material along a first direction and a second direction, respectively. In the detection state, the first interference light is incident on the volume holographic material along the first direction and exits from the volume holographic material along a third direction, the third direction being set at an angle to the second direction, and the second interference light is blocked by the shutter. In the calibration state, the second interference light passes through the placement area along the second direction and illuminates the image sensor; The image sensor acquires the position of the first spot formed by the second interference light on the image sensor in the calibration state, and acquires the position of the second spot formed by the first interference light on the image sensor in the detection state.

2. The grating detection device as described in claim 1, characterized in that, The grating detection device further includes an angle amplifier disposed in the optical path of the light source assembly. The angle amplifier is located between the placement area and the image sensor. The angle amplifier is used to deflect the propagation directions of the first interference light and the second interference light emitted after diffraction from the volume holographic material, so as to increase the angular offset of the first interference light emitted after diffraction from the volume holographic material relative to the second direction, and / or increase the angular offset of the second interference light emitted after diffraction from the volume holographic material relative to the first direction.

3. The grating detection device as described in claim 2, characterized in that, The angle amplifier includes a first mirror group and a second mirror group disposed in the optical path of the light source assembly. The first mirror group is disposed on the side of the second mirror group away from the image sensor, and the focal length f1 of the first mirror group is greater than the focal length f2 of the second mirror group.

4. The grating detection device as described in claim 3, characterized in that, The optical axes of the first mirror group and the second mirror group are coaxially arranged, and the distance between the first mirror group and the second mirror group is d, where d = f1 + f2.

5. The grating detection device according to any one of claims 1-4, characterized in that, The light source assembly includes a light emitter and a beam splitter, wherein the light emitted by the light emitter is split into a first interference light and a second interference light by the beam splitter; The optical path of the first interference light is provided with a first reflecting mirror. The first interference light emitted from the beam splitter is reflected by the first reflecting mirror and then enters the volume holographic material along the first direction. And / or, The optical path of the second interference light is provided with a second reflector. The second interference light emitted from the beam splitter is reflected by the second reflector and then enters the volume holographic material along the second direction.

6. The grating detection device as described in claim 5, characterized in that, The emitter is a single-mode laser.

7. The grating detection device according to any one of claims 1-4, characterized in that, The grating detection device includes a first beam expander, which is disposed in the optical path of the first interference light and located on the side of the placement area opposite to the image sensor. The cross-sectional width of the first interference light emitted from the first beam expander is greater than the cross-sectional width of the first interference light incident on the first beam expander; and / or, The grating detection device includes a second beam expander, which is disposed in the optical path of the second interference light and located on the side of the placement area away from the image sensor. The cross-sectional width of the second interference light emitted from the second beam expander is greater than the cross-sectional width of the second interference light incident on the second beam expander.

8. The grating detection device according to any one of claims 1-4, characterized in that, The grating detection device further includes a first optical filter, which is disposed in the optical path of the first interference light and located on the side of the placement area opposite to the image sensor; and / or, The grating detection device further includes a second optical filter, which is disposed in the optical path of the second interference light and located on the side of the placement area away from the image sensor.

9. The grating detection device according to any one of claims 1-4, characterized in that, The second direction is perpendicular to the surface of the volumetric holographic material.

10. The grating detection device according to any one of claims 1-4, characterized in that, The first interference beam is a parallel beam; and / or, The second interference beam is a parallel beam.

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