Exposure device for manufacturing volume holographic grating
By introducing calibration and adjustment components into the exposure device of the bulk holographic grating, the problem of difficulty in controlling the incident angle accuracy in the dual-beam interference method is solved, and high-precision exposure beam incident angle control is achieved, and the imaging quality of the bulk holographic grating is improved.
Patent Information
- Application Number
- CN202421955017.8
- Authority / Receiving Office
- CN · China
- Patent Type
- Utility models(China)
- Current Assignee / Owner
- Filing Date
- 2024-08-13
- Publication Date
- 2025-05-09
- Estimated Expiration
- 2034-08-13
AI Technical Summary
In the prior art, when producing a bulk holographic grating with a dual-beam interference method, it is difficult to control the accuracy of the incident angle to the level of 0.001°, resulting in the impact of imaging quality.
An exposure device including an exposure system, an adjustment assembly and a calibration assembly is designed. The adjustment assembly adjusts the incident angle through a rotatable mirror, and the calibration assembly calibrates the initial angle of the mirror through a aperture, beam splitter and detector to ensure precise control of the incident angle.
By improving the accuracy of the initial angle of the reflector, high-precision control of the incident angle of the exposure beam is achieved, and the imaging quality of the bulk holographic grating is significantly improved.
Smart Images
Figure CN222850764U_ABST
Abstract
Description
Technical Field
[0001] The present invention belongs to the technical field of optical waveguides, and in particular relates to an exposure device for making a volume holographic grating. Background Art
[0002] With the rapid development of science and technology, augmented reality (AR) technology is gradually penetrating into every corner of our lives with its unique charm, and is widely used in education, entertainment, medical treatment, industrial manufacturing and other fields. As the core carrier of this technology, the performance of the optical display system of AR devices is directly related to user experience and market acceptance. At present, AR display systems on the market generally use micro-display screens and optical combiners to realize the integration of virtual information and the real world. Among them, the optical combiner is a combination of various optical elements such as prisms, free-form surfaces, BirdBath, optical waveguides, etc. Its design is particularly critical and is also a key part to distinguish AR display systems. Among the many optical combination solutions, the optical waveguide solution is regarded as the most promising technical path due to its excellent optical effects, compact appearance and good mass production prospects.
[0003] Optical waveguides can generally be divided into two categories: geometric optical waveguides and diffractive optical waveguides. Geometric optical waveguides are so-called array optical waveguides, which achieve image output and eye box expansion by stacking array reflectors. Although this technology can provide clear image quality, its complex manufacturing process and high cost limit its wide application in the consumer market. Diffractive optical waveguides mainly include surface relief optical waveguides and volume holographic optical waveguides. Surface relief optical waveguides can be mass-produced using nanoimprinting technology, which has aroused great interest from AR optical module manufacturers. It has the advantages of a large field of view and a large eye movement range, but it also brings problems of light leakage and ambient light rainbow patterns. At the same time, related micro-nano processing technology is also a huge challenge. The volume holographic grating in the volume holographic optical waveguide is a Bragg grating. When the wavelength and angle of the incident light meet the Bragg matching conditions, it will be diffracted with extremely high diffraction efficiency, so it has good angle selectivity and wavelength selectivity. These two characteristics can greatly suppress light leakage and ambient light rainbow patterns. In addition, volume holographic gratings also have the advantages of high diffraction efficiency, fast development iteration, large-area preparation, and low cost.
[0004] Volume holographic gratings are manufactured based on holographic interferometry technology, usually using a double-beam interferometry method for exposure. Figure 1 As shown in the figure, the double-beam interferometry method mainly uses two coherent light beams to illuminate the photosensitive material at a certain angle. Due to the interference of the two beams of light, an interference pattern is formed inside the material, that is, a periodic intensity change, thereby forming a grating in the photosensitive material. In the double-beam interferometry method, the surface period Λ of the grating is related to multiple factors, the most important of which are the wavelength of the laser and the angle between the two coherent light beams. The relationship between the surface period Λ of the grating and these factors can be expressed by the following formula:
[0005]
[0006] Where Λ is the surface period of the grating, λ is the wavelength of the laser in the photosensitive material, and 0 is the wavelength of the laser in a vacuum environment, n is the refractive index of the photosensitive material, θ 1 and θ 2 are the incident angles of the two coherent light beams.
[0007] Assume that the target surface period (i.e., design period) of the grating is Λ 0 ,but
[0008]
[0009] Assume θ 1 and θ 2 There are slight deviations from the design values, namely Δθ 1 and Δθ 2 , then the surface period deviation ΔΛ of the grating is
[0010]
[0011] Take Λ 0 =0.410μm,λ 0 =0.532μm, n=1.51, θ 1 =15 degrees, θ 2 =50.548 degrees, then
[0012] (1)
[0013] When using the double-beam interference method to expose and make a volume holographic grating, the deviation between the surface period of the obtained volume holographic grating and the designed period has a great influence on the imaging quality. This deviation value must be less than 4 e -5μm (0.04nm), that is
[0014]
[0015] Substituting into formula (1) we can get:
[0016]
[0017]
[0018] It can be seen that in the process of making a volume holographic grating by a double-beam exposure process, the precision of the incident angle of the two coherent light beams must reach 0.001° level to ensure the imaging quality of the obtained volume holographic grating. Therefore, it is necessary to propose an exposure scheme to improve the angle precision of the exposure beam. Utility Model Content
[0019] The present invention aims to overcome at least one defect in the prior art, and provides an exposure device for making a volume holographic grating, thereby improving the angular accuracy of the exposure beam.
[0020] The exposure device comprises an exposure system, an adjustment component and a calibration component. The exposure system is used to emit signal light and reference light to a volume holographic grating to be exposed. The adjustment component and the calibration component are arranged on the optical path of the signal light and / or the reference light. The adjustment component comprises a rotatable reflector located on the optical path, and is used to adjust the incident angle of the signal light or the reference light on the volume holographic grating to be exposed. The calibration component comprises an aperture, a beam splitter and a detector. The aperture and the beam splitter are sequentially arranged on the optical path between the exposure system and the reflector. The detector is arranged on one side of the beam splitter, and detects the spot position of the light reflected by the beam splitter, so as to calibrate the initial angle of the reflector.
[0021] This scheme adds a calibration component to the optical path between the exposure system and the reflector. The light emitted by the exposure system passes through the aperture and the beam splitter in turn and is incident on the reflector. After being reflected by the reflector, it is incident on the surface of the volume holographic grating to be exposed. At least part of the light will be reflected by the volume holographic grating surface. When this part of the light returns to the beam splitter along the incident path, it will be reflected by the beam splitter to the detector. The detector can detect the spot position of the light from the beam splitter, and based on this, it can be determined whether the light is vertically incident on the volume holographic grating surface, so as to achieve the purpose of calibrating the initial angle of the reflector. The relative angle of the reflector will be adjusted based on the initial angle to achieve the purpose of adjusting the incident angle of the exposure beam. Therefore, the improvement of the initial angle accuracy of the reflector is conducive to improving the angle accuracy of the exposure beam.
[0022] The beam splitter can be a polarizing beam splitter, for which the calibration component also includes a wave plate group, which is arranged on the optical path between the beam splitter and the reflector, including a quarter wave plate and a half wave plate that can be switched with each other, the quarter wave plate is used for calibration, and the half wave plate is used for exposure. In addition, the beam splitter can also be a non-polarizing beam splitter.
[0023] The detector may be an image sensor or a photoelectric detector. The photoelectric detector may be a two-quadrant detector or a four-quadrant detector.
[0024] The adjustment component preferably includes a rotating mechanism, which is connected to the reflector and drives the reflector to rotate around the rotation center to adjust the incident angle of the signal light or the reference light on the volume holographic grating. The rotation of the reflector is controlled by the rotating mechanism, which is conducive to improving the rotation accuracy of the reflector, thereby improving the incident angle θ 1 and θ 2Specifically, the rotating mechanism can adopt an electric rotating mechanism such as an electric rotating table and an electric angle table, so as to electrically control the rotation of the reflector, which can not only avoid manual adjustment and further improve the efficiency of making volume holographic gratings, but also enable the exposure angle to be accurately controlled, greatly improving the production accuracy of volume holographic gratings.
[0025] The adjustment component can be configured with a first lens and a second lens, the first lens and the second lens are sequentially arranged on the optical path between the reflector and the volume holographic grating to be exposed, the optical axis of the first lens coincides with the optical axis of the second lens, the first lens has a first focus, the second lens has a second focus, the first focus and the second focus coincide and are located between the first lens and the second lens, the first lens and the second lens have a first base point and a second base point, the first base point and the second base point are conjugate and are both located on the optical axis, the first base point is located on the side of the first lens facing away from the second lens and coincides with the rotation center of the reflector, the rotation center is located on the reflection surface of the reflector, and the second base point is located on the side of the second lens facing away from the first lens and coincides with the volume holographic grating to be exposed. The coordinated action of the first lens and the second lens ensures that the incident angle of the signal light or the reference light on the volume holographic grating changes while the irradiated area remains basically unchanged, so that the incident angle of the signal light or the reference light on the volume holographic grating can be changed by rotating the reflector by a certain angle without moving the position, and at the same time, it can ensure that the adjusted signal light or the reference light can always be incident on the volume holographic grating and interfere, and even the center of the irradiated area of the volume holographic grating always coincides with the second focus of the second lens, thereby greatly improving the efficiency of making the volume holographic grating.
[0026] Adjustment components are provided on the optical paths of the signal light and the reference light, and the second base point of the adjustment component located on the optical path of the signal light coincides with the second base point of the adjustment component located on the optical path of the reference light, ensuring that the irradiation area of the signal light on the volume holographic grating and the irradiation area of the reference light on the volume holographic grating overlap each other as much as possible.
[0027] The adjustment component can also be equipped with a moving mechanism, which is connected to the reflector through transmission, and drives the reflector to move so that the signal light in the irradiation area of the volume holographic grating to be exposed and the reference light in the irradiation area of the volume holographic grating to be exposed basically overlap. Controlling the movement of the reflector by the moving mechanism is conducive to improving the movement accuracy of the reflector. Specifically, the moving mechanism can adopt an electric moving mechanism such as an electric translation stage and an electric lifting stage to electrically control the rotation and movement of the reflector, which can not only avoid manual adjustment, but also enable the exposure position to be accurately controlled, thereby improving the production efficiency and production accuracy of the volume holographic grating.
[0028] The adjustment component preferably includes a rotating and moving mechanism, which is a rotating mechanism and a moving mechanism combined into one, and is connected to the reflector through transmission, driving the reflector to rotate around its rotation center to adjust the incident angle of the signal light or the reference light on the volume holographic grating to be exposed, and driving the reflector to move so that the signal light in the irradiation area of the volume holographic grating to be exposed and the reference light in the irradiation area of the volume holographic grating to be exposed basically overlap. Specifically, the rotating and moving mechanism can adopt an electric displacement mechanism such as an electric multi-dimensional combination stage to electrically control the rotation and movement of the reflector, which can not only avoid manual adjustment, but also enable the exposure angle and exposure position to be accurately controlled, thereby improving the production efficiency and production accuracy of the volume holographic grating.
[0029] Compared with the prior art, this solution has the following beneficial effects: this solution adds a calibration component to the optical path between the exposure system and the reflector, and the light emitted by the exposure system passes through the aperture and the beam splitter in turn and is incident on the reflector, and is reflected by the reflector and incident on the surface of the volume holographic grating to be exposed, wherein at least part of the light will be reflected by the volume holographic grating surface, and when the part of the light returns to the beam splitter along the incident path, it will be reflected by the beam splitter to the detector, and the detector can detect the spot position of the light from the beam splitter, and it can be determined whether the light is vertically incident on the volume holographic grating surface, thereby achieving the purpose of calibrating the initial angle of the reflector. Subsequently, the relative angle of the reflector will be adjusted based on the initial angle to achieve the purpose of adjusting the incident angle of the exposure beam, therefore, the improvement of the initial angle accuracy of the reflector is conducive to improving the angle accuracy of the exposure beam. BRIEF DESCRIPTION OF THE DRAWINGS
[0030] The drawings are for illustrative purposes only and should not be construed as limitations on the present invention. In order to better illustrate the present invention, some parts of the drawings may be omitted, enlarged, or reduced, and do not represent the size of actual products. For those skilled in the art, it is understandable that some well-known structures and their descriptions in the drawings may be omitted.
[0031] Figure 1 It is a schematic diagram of two-beam interference.
[0032] Figure 2 This is a schematic diagram of the exposure light path of the volume holographic grating.
[0033] Figure 3 This is a schematic diagram of the reconstruction optical path of the volume holographic grating.
[0034] Figure 4 It is a schematic diagram of the structure of an exposure device in which a signal light path is equipped with an adjustment component and a calibration component.
[0035] Figure 5 It is a schematic diagram of the structure of an exposure device in which a reference light path is equipped with an adjustment component and a calibration component.
[0036] Figure 6 It is a schematic diagram of the structure of an exposure device in which both the signal light and reference light optical paths are equipped with adjustment components and calibration components.
[0037] Figure 7 It is a schematic diagram of the structure of an exposure device in which the adjustment component adopts a third lens group.
[0038] Figure 8 It is a schematic diagram of the structure of an exposure device in which the adjustment components on the optical paths of signal light and reference light both adopt the third lens group.
[0039] Fig. 9 It is a schematic diagram of the structure of an exposure device in which the adjustment component adopts a moving mechanism.
[0040] Fig.10 It is a schematic diagram of the calibration light path when the light is vertically incident on the surface of the volume holographic grating to be exposed.
[0041] Fig.11 It is a schematic diagram of the calibration light path when the light is incident obliquely on the surface of the volume holographic grating to be exposed.
[0042] Fig.12 It is a schematic diagram of the structure of an exposure device using a polarization beam splitter.
[0043] Fig.13 It is a schematic diagram of the pixel distribution of the image sensor.
[0044] Fig.14 This is a schematic diagram of the quadrant distribution of a two-quadrant detector. Among them, the output voltage of quadrant 1 is V 1 , the output voltage of quadrant 2 is V 2 .
[0045] Fig.15 This is a schematic diagram of the quadrant distribution of the four-quadrant detector. Among them, the output voltage of quadrant 1 is V 1 , the output voltage of quadrant 2 is V 2 , the output voltage of quadrant 3 is V 3 , the output voltage of quadrant 4 is V 4 .
[0046] Explanation of the figure marks: exposure system 100, signal light generator 110, reference light generator 120, adjustment system 200, adjustment components 210, 220, reflector 201, rotating mechanism 202, first lens 203, second lens 204, moving mechanism 205, calibration system 300, calibration components 310, 320, aperture 301, beam splitter 302, detector 303, wave plate group 304, stage 410, second moving mechanism 420, volume holographic grating 001. DETAILED DESCRIPTION
[0047] In order to enable those skilled in the art to better understand the present solution, the present solution is further described in detail below in conjunction with specific embodiments.
[0048] Figures 4 to 6 The exposure device for making a volume holographic grating is illustrated. The exposure device is equipped with an exposure system 100, and the exposure system 100 includes a signal light generator 110 and a reference light generator 120, which are used to emit signal light and reference light to the volume holographic grating to be exposed. The signal light generator 110 and the reference light generator 120 can share a light source, and the light source is divided into two beams by a beam splitter, etc., and respectively emitted as signal light and reference light through the signal light generator 110 and the reference light generator 120, or each can have an independent light source, which is a signal light source and a reference light source. In addition to the light source, the signal light generator 110 can also be equipped with a first lens group to shape the light beam emitted by the light source and emit signal light. The first lens group can shape the light beam emitted by the light source into a parallel light beam, or it can shape it into a divergent light beam. The reference light generator 120 can also be equipped with a second lens group to shape the light beam emitted by the light source and emit reference light. The second lens group can also shape the light beam emitted by the light source into a parallel light beam or a divergent light beam.
[0049] The volume holographic grating is made of holographic photosensitive material. The signal light and the reference light are irradiated onto the holographic photosensitive material to form double-beam interference, such as Figure 2 The holographic photosensitive material records the interference fringe distribution in the form of a refractive index change distribution, and the fringe corresponds to the desired grating structure, namely, a volume holographic grating. Figure 3 The reproduction optical path of the obtained volume holographic grating is shown in the figure. The reproduction process is the use process. When the light is incident on the volume holographic grating along the direction of the reference light, it is extended to generate the straight light L 0 (0th order light) and diffracted light L +1 (+1 level light), the direction of the direct light is consistent with the direction of the reference light, and the direction of the diffracted light is consistent with the direction of the signal light. Therefore, after the signal light is recorded on the holographic photosensitive material using the reference light and a volume holographic grating is formed, the signal light can be reproduced by light whose direction is consistent with the direction of the reference light.
[0050] The grating period d of the diffraction grating can be decomposed into the surface period and the vertical period. In actual design, the surface period of the grating is generally designed to be a fixed value first, and then the vertical period of the grating is adjusted to obtain a holographic volume grating with different Bragg matching angles or wavelengths, thereby optimizing the performance of the volume holographic grating waveguide. From the grating formula: nλ=d(sinα-sinβ), it can be seen that when the wavelength λ and the diffraction order are constant, the incident angle α and the diffraction angle β need to be adjusted to produce a holographic volume grating waveguide with different grating periods d. The incident angle α and the diffraction angle β correspond to the incident angle θ of the signal light on the volume holographic grating to be exposed in the exposure process. 1and the incident angle θ of the reference light on the volume holographic grating to be exposed 2 , it is necessary to artificially change these two angles to produce a holographic grating waveguide with different grating periods d.
[0051] In order to facilitate the adjustment of the incident angle of the light beam, the exposure device is also equipped with an adjustment system 200, which includes adjustment components 210 and 220. The adjustment components can be arranged on the optical path of the signal light (such as Figure 4 ), can also be configured in the optical path of the reference light (such as Figure 5 ), and an adjustment component (such as Figure 6 ).like Figures 7 to 12 As shown, the adjustment component 210 / 220 is configured with a rotatable mirror 201 located on the optical path. The signal light or reference light emitted by the exposure system 100 is reflected by the mirror 201 and then incident on the volume holographic grating to be exposed. By rotating the mirror 201 to adjust the angle of the mirror 201, the incident angle of the signal light or the reference light on the volume holographic grating can be adjusted.
[0052] like Figures 7-9 As shown, the adjustment component 210 / 220 can also be equipped with a rotating mechanism 202, which is connected to the reflector 201 in a transmission manner, and drives the reflector 201 to rotate around the rotation center to adjust the incident angle of the signal light or the reference light on the volume holographic grating. The rotation of the reflector 201 is controlled by the rotating mechanism 202, which is conducive to improving the rotation accuracy of the reflector 201, thereby improving the incident angle θ 1 and θ 2 Accuracy. Specifically, the rotating mechanism 202 can adopt an electric rotating mechanism 202 such as an electric rotating table and an electric angle table, so as to electrically control the rotation of the reflector 201, which can not only avoid manual adjustment and further improve the efficiency of making volume holographic gratings, but also enable the exposure angle to be accurately controlled, greatly improving the production accuracy of volume holographic gratings. An electric rotating table is an electric mechanical device that can rotate around a fixed axis, usually composed of one or more motors, reducers, bearings, turntables and control systems, etc., which can realize continuous or intermittent rotation of objects, and has the characteristics of high precision, high speed, high torque and good stability. An electric angle table (sometimes also called an electric tilt table or angle adjustment table) is a device that can accurately rotate an object within a small angle range, usually including a rotatable platform, a motor, a reducer, an angle sensor and a control system, etc., which can realize precise angle adjustment of objects, and has the characteristics of high precision, high resolution and fast response.
[0053] like Figure 7-8As shown, the adjustment component 210 / 220 can be configured with a third lens group to allow the light in the optical path to be irradiated onto the volume holographic grating to be exposed before and after the reflector 201 rotates, and to interfere with the light in another optical path. The third lens group includes a first lens 203 and a second lens 204, which are located between the reflector 201 and the volume holographic grating to be exposed, and are sequentially arranged on the optical path along the propagation direction of the light (signal light or reference light). The optical axis of the first lens 203 coincides with the optical axis of the second lens 204, and the first lens 203 has a first focal point F 1 , the second lens 204 has a second focal point F 2 , the first focus F 1 and the second focus F 2 The first lens 203 and the second lens 204 overlap and are located between the first lens 203 and the second lens 204. The first lens 203 and the second lens 204 form a whole having a pair of conjugate points, which are the first base point A 1 and the second base point A 2 , the first base point A 1 and the second base point A 2 Both are located on the optical axes of the first lens 203 and the second lens 204. The first base point A 1 The second base point A is located on the side of the first lens 203 facing away from the second lens 204 and coincides with the rotation center O of the reflector 201. The rotation center is located on the reflection surface of the reflector 201. 2 The second lens 204 is located on the side facing away from the first lens 203 and overlaps with the volume holographic grating to be exposed.
[0054] Therefore, as long as the reflector 201 is rotated around the rotation center O by a certain angle, the incident angle of the signal light or the reference light on the volume holographic grating can be changed without adjusting the position of the reflector 201, and at the same time, it can be ensured that the adjusted signal light or the reference light can always be incident on the volume holographic grating and interfere, and even the center of the illuminated area of the volume holographic grating always coincides with the second focus of the second lens 204, which greatly improves the efficiency of making the volume holographic grating. Through a large number of experiments, a relationship table between the grating period and the exposure angle (the angle of the reflector 201) can be obtained, as shown in Table 1 (the values in the table are virtual values, which need to be obtained according to the specific exposure device experiment during the equipment debugging stage). During production, it is only necessary to rotate the reflector 201 according to the target grating period and the relationship table.
[0055] Table 1 Relationship between grating period and exposure angle of exposure device using the third lens group
[0056]
[0057] like Figure 8As shown, for the case where an adjustment component is provided on each of the optical paths of the signal light and the reference light, and both adjustment components use the third lens group, the second base point of the adjustment component 210 located on the optical path of the signal light and the second base point of the adjustment component 220 located on the optical path of the reference light are preferably coincident, to ensure that the irradiation area of the signal light on the volume holographic grating and the irradiation area of the reference light on the volume holographic grating overlap each other as much as possible.
[0058] like Fig. 9 As shown, the adjustment component 210 / 220 can also be equipped with a moving mechanism 205 to make the light in the optical path be irradiated on the volume holographic grating to be exposed before and after the reflector 201 rotates, and interfere with the light in the other optical path. The moving mechanism 205 is connected to the reflector 201 in a transmission manner, and drives the reflector 201 to move so that the signal light in the irradiation area of the volume holographic grating to be exposed and the reference light in the irradiation area of the volume holographic grating to be exposed basically overlap. The movement of the reflector 201 is controlled by the moving mechanism 205, which is conducive to improving the movement accuracy of the reflector 201. Through a large number of experiments, a relationship table between the grating period and the exposure angle (the angle of the reflector 201) and the exposure position (the position of the reflector 201) can be obtained, as shown in Table 2 (the values in the table are all virtual values, which need to be obtained according to the specific exposure device experiment during the equipment debugging stage). When making, it is only necessary to rotate and move the reflector 201 according to the target grating period and the relationship table.
[0059] Table 2 Relationship between the grating period, exposure angle and exposure position of the exposure device using a moving mechanism
[0060]
[0061] Specifically, the moving mechanism 205 can adopt an electric moving mechanism 205 such as an electric translation table and an electric lifting table, so as to electrically control the rotation and movement of the reflector 201, which can not only avoid manual adjustment, but also enable the exposure position to be accurately controlled, thereby improving the production efficiency and production accuracy of the volume holographic grating. The electric translation table is a mechanical device that realizes linear displacement through electric drive, usually composed of a motor, a reducer, a transmission mechanism, a guide rail and a platform, etc., which can accurately move the load in a specified direction, and has the characteristics of high precision, high stability and large load-bearing capacity. The electric lifting table is an electric mechanical device that can realize lifting and lowering in the vertical direction, usually composed of a motor, a reducer, a lifting mechanism, a support structure and a control system, etc., which can carry objects of a certain weight and realize smooth lifting and lowering movement, and has the characteristics of large load-bearing capacity, high stability and easy operation.
[0062] In the case where the adjustment component 210 / 220 controls the rotation of the reflector 201 through the rotating mechanism 202 and controls the movement of the reflector 201 through the moving mechanism 205, the rotating mechanism 202 and the moving mechanism 205 can be combined into one, and an electric displacement mechanism such as an electric multi-dimensional combination stage that integrates the functions of rotation and movement can be used to electrically control the rotation and movement of the reflector 201, which can not only avoid manual adjustment, but also enable the exposure angle and exposure position to be accurately controlled, thereby improving the production efficiency and production accuracy of the volume holographic grating. The electric multi-dimensional combination stage is a precision device that integrates electric drive technology and multi-dimensional motion capabilities, and is mainly used to achieve precise displacement and positioning of multiple axes (such as X, Y, Z axes and possible rotation axes), and has the characteristics of high precision, multi-axis linkage, and good stability.
[0063] In contrast, the adjustment component 210 / 220 using the third lens group does not need to adjust the position of the reflector 201 to ensure that the irradiation area of the light in its optical path remains basically unchanged before and after the adjustment, and the adjustment efficiency is higher, and the efficiency of making the volume holographic grating is correspondingly higher; and although the adjustment component 210 / 220 using the moving mechanism 205 needs to adjust the position of the reflector 201 to ensure that the light in its optical path and the light in another optical path basically overlap in the irradiation area on the volume holographic grating to be exposed, for a large area volume holographic grating to be exposed with different design periods in each area, the moving mechanism 205 can flexibly adjust the irradiation area of the signal light and the reference light, and the exposure process does not need to move the position of the volume holographic grating to be exposed, and a volume holographic grating with different grating periods in different areas can be obtained.
[0064] Combined with the background technology, it can be known that the incident angle θ 1 and θ 2 The adjustment accuracy needs to be controlled to 0.001° level to ensure the imaging quality of the obtained volume holographic grating. This requires that the initial angle of the reflector 201 must be accurate. Otherwise, no matter how accurate the rotation of the reflector 201 is, it is difficult to ensure that the incident angle θ 1 and θ 2 To this end, the exposure device is also equipped with a calibration system 300, which includes calibration components 310 and 320. The calibration components are arranged on the optical path equipped with the adjustment components, such as Figures 4 and 5 If both the signal light path and the reference light path are equipped with adjustment components, a calibration component can be configured for each, such as Figure 6 .like Figures 10-12 As shown, the calibration component 310 / 320 includes an aperture 301, a beam splitter 302 and a detector 303, and is located as a whole between the exposure system 100 and the reflector 201, wherein the aperture 301 and the beam splitter 302 are sequentially arranged on the optical path along the propagation direction of the light (signal light or reference light), and the detector 303 is arranged on one side of the beam splitter 302.
[0065] When in use, the signal light or reference light emitted by the exposure system 100 passes through the aperture 301 and the beam splitter 302 in sequence and is incident on the reflector 201. After being reflected by the reflector 201, it is incident on the surface of the volume holographic grating to be exposed. After being incident on the surface of the volume holographic grating, at least part of the light will be reflected by the surface of the volume holographic grating. If the signal light or the reference light is incident on the surface of the volume holographic grating vertically or nearly vertically (such as Fig.10 ), the light reflected from the volume holographic grating surface will return along the incident path, be reflected by the reflector 201 and the beam splitter 302 in turn, and finally be incident on the detector 303. The detector 303 can detect the spot position of the light reflected by the beam splitter 302. If the signal light or the reference light is obviously not perpendicular to the volume holographic grating surface when it is incident on the volume holographic grating surface (such as Fig.11 ), the light reflected by the volume holographic grating surface will not be incident on the detector 303, and the detector 303 will not detect the light spot. According to whether the light spot is detected and the position of the light spot, it can be determined whether the signal light or the reference light is vertically incident on the volume holographic grating surface, thereby determining whether the initial angle of the reflector 201 is accurate. If the initial angle of the reflector 201 is not accurate enough, the angle of the reflector 201 can be adjusted and the above operation can be repeated until the position of the light spot detected by the detector 303 is accurate, thereby completing the calibration of the initial angle of the reflector 201, so as to improve the angle accuracy of the exposure beam.
[0066] The beam splitter 302 can be a polarizing beam splitter (PBS) or a non-polarizing beam splitter. If the beam splitter 302 is a polarizing beam splitter, the calibration assembly 310 / 320 is further configured with a wave plate group 304, which is arranged on the optical path between the beam splitter 302 and the reflector 201, such as Fig.12 The wave plate group 304 includes a quarter wave plate and a half wave plate that can be switched with each other, wherein the quarter wave plate is used for calibration and the half wave plate is used for exposure. During the calibration process, the wave plate group 304 needs to be switched to a quarter wave plate; after the calibration is completed or before exposure, the wave plate group 304 needs to be switched to a half wave plate.
[0067] The detector 303 may be an image sensor or a photoelectric detector. The photoelectric detector may be a two-quadrant detector or a four-quadrant detector.
[0068] For image sensors (such as Fig.13 ), assuming that the coordinates of each pixel on the image sensor are ( i , j ), the light intensity detected by each pixel is I ij , then the center of the weighted average of the spot ( i 0 , j0 )for
[0069]
[0070] like( i 0 , j 0 ) = ( I 0 , J 0 ),in( I 0 , J 0 ) is a pre-calibrated pixel coordinate value, it is determined that the light is vertically incident on the surface of the volume holographic grating to be exposed.
[0071] For a two-quadrant detector (such as Fig.14 ), assuming that the output voltages of the two quadrants are V 1 、V 2 , the voltage difference between the two output voltages ΔV=V 1 -V 2 If ΔV=0, it is determined that the light is vertically incident on the surface of the volume holographic grating to be exposed.
[0072] For a four-quadrant detector (such as Fig.15 ), assuming that the output voltages of the four quadrants are V 1 、V 2 、V 3 、V 4 , can be found in ΔV=(V 1 +V 3 )-(V 2 +V 4 ) = 0, it is determined that the light is vertically incident on the surface of the volume holographic grating to be exposed, or it can be determined that ΔV a =(V 1 +V 3 )-(V 2 +V 4 )=0 and ΔV b =(V 1 +V 2 )-(V 3 +V 4 )=0, it is determined that the light is vertically incident on the surface of the volume holographic grating to be exposed.
[0073] The exposure device can also be equipped with a stage 410, which is used to load the volume holographic grating to be exposed, and plays a role in positioning and fixing the volume holographic grating. Different volume holographic gratings may have different thicknesses, and the volume holographic grating to be exposed is generally loaded on a plane carrier or directly formed in an optical structure such as an optical waveguide. For a device using a third lens group, in order to ensure that the second focus of the second lens is exactly located on the volume holographic grating, the stage 410 can be connected to a second moving mechanism 420, and the second moving mechanism 420 can drive the stage 410 to move, and then drive the volume holographic grating loaded on the stage 410 to move until the volume holographic grating coincides with the second focus of the second lens. Specifically, the second moving mechanism 420 can adopt an electric moving mechanism such as an electric translation table, an electric lifting table, etc., so as to electrically control the movement of the stage 410, which can not only avoid manual adjustment, but also enable the position of the volume holographic grating loaded on the stage 410 to be precisely controlled, thereby further improving the production efficiency and production accuracy of the volume holographic grating.
[0074] Obviously, the above embodiments of the present invention are merely examples for clearly illustrating the present invention, and are not intended to limit the implementation methods of the present invention. For those skilled in the art, other different forms of changes or modifications can be made based on the above description. It is not necessary and impossible to list all implementation methods here. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention shall be included in the protection scope of the claims of the present invention.
Claims
1. An exposure device for making a volume holographic grating, characterized in that: The exposure device comprises an exposure system, an adjustment component and a calibration component. The exposure system is used to emit signal light and reference light to a volume holographic grating to be exposed, and the adjustment component and the calibration component are arranged on the optical path of the signal light and / or the reference light; the adjustment component comprises a rotatable reflector located on the optical path, and is used to adjust the incident angle of the signal light or the reference light on the volume holographic grating to be exposed; the calibration component comprises an aperture, a beam splitter and a detector, and the aperture and the beam splitter are sequentially arranged on the optical path between the exposure system and the reflector, and the detector is arranged on one side of the beam splitter to detect the spot position of the light reflected by the beam splitter, so as to calibrate the initial angle of the reflector.
2. The exposure device for making a volume holographic grating according to claim 1, characterized in that: The beam splitter is a polarizing beam splitter, and the calibration component further includes a wave plate group, which is arranged on the optical path between the beam splitter and the reflector and includes a quarter wave plate and a half wave plate that can be switched with each other, the quarter wave plate is used for calibration, and the half wave plate is used for exposure; or The beam splitter is a non-polarizing beam splitter.
3. The exposure device for making a volume holographic grating according to claim 1, characterized in that: The detector is an image sensor or a photoelectric detector, and the photoelectric detector is a two-quadrant detector or a four-quadrant detector.
4. The exposure device for producing a volume holographic grating according to any one of claims 1 to 3, characterized in that: The adjustment component also includes a rotating mechanism, which is connected to the reflector in a transmission manner and drives the reflector to rotate around a rotation center to adjust the incident angle of the signal light or the reference light on the volume holographic grating.
5. The exposure device for making a volume holographic grating according to claim 4, characterized in that: The adjustment component also includes a first lens and a second lens, which are sequentially arranged on an optical path between the reflector and the volume holographic grating to be exposed, the optical axis of the first lens coincides with the optical axis of the second lens, the first lens has a first focus, the second lens has a second focus, the first focus and the second focus coincide and are located between the first lens and the second lens, the first lens and the second lens have a first base point and a second base point, the first base point and the second base point are conjugate and are both located on the optical axis, the first base point is located on the side of the first lens facing away from the second lens and coincides with the rotation center of the reflector, the rotation center is located on the reflection surface of the reflector, and the second base point is located on the side of the second lens facing away from the first lens and coincides with the volume holographic grating to be exposed.
6. The exposure device for making a volume holographic grating according to claim 5, characterized in that: The adjustment component is disposed on the optical paths of the signal light and the reference light, and the second base point of the adjustment component on the optical path of the signal light coincides with the second base point of the adjustment component on the optical path of the reference light.
7. The exposure device for making a volume holographic grating according to claim 4, characterized in that: The adjustment component also includes a moving mechanism, which is transmission-connected to the reflector to drive the reflector to move so that the signal light in the irradiation area of the to-be-exposed volume holographic grating and the reference light in the irradiation area of the to-be-exposed volume holographic grating substantially overlap.
8. The exposure device for making a volume holographic grating according to claim 7, characterized in that: The rotating mechanism is an electric rotating table or an electric angular table; and / or The moving mechanism is an electric translation platform or an electric lifting platform.
9. The exposure device for producing a volume holographic grating according to any one of claims 1 to 3, characterized in that: The adjustment component also includes a rotating movement mechanism, which is connected to the reflector in a transmission manner, drives the reflector to rotate around its rotation center to adjust the incident angle of the signal light or the reference light on the volume holographic grating to be exposed, and drives the reflector to move so that the signal light in the irradiation area of the volume holographic grating to be exposed and the reference light in the irradiation area of the volume holographic grating to be exposed basically overlap.
10. The exposure device for making a volume holographic grating according to claim 9, characterized in that: The rotating movement mechanism is an electric multi-dimensional combination table.