An exposure apparatus for preparing a volume holographic optical waveguide

Abstract

The utility model provides an exposure device for preparation volume holographic optical waveguide, first reflector translation and / or rotation are driven to reflector adjusting assembly, mask plate adjusting assembly drives mask plate assembly translation and / or rotation, the output beam of light source, after the polarization state is adjusted to polarization adjusting assembly, the beam expander component expansion and first reflector reflection are inducted to surface relief grating mask plate, zero order diffraction light and first order diffraction light of surface relief grating mask plate are inducted to the waveguide that is exposed to light and carry out exposure, form volume holographic optical waveguide. Utilize surface relief grating mask plate exposure formation volume holographic optical waveguide's light path structure, use single beam to induct surface relief grating and produce zero order light and first order diffraction light, system is stable, and error is little, utilize the diffraction light of surface relief grating mask plate and carry out exposure, can make the period of exposure volume holographic grating and the period of surface relief grating, duty factor are completely identical, thereby low -cost fast exposure volume holographic grating.

Description

Technical Field

[0001] This utility model relates to the field of optical technology, and in particular to an exposure device for fabricating bulk holographic waveguides. Background Technology

[0002] Augmented reality (AR) head-mounted near-eye display technology is considered the next generation of interactive display technology. Currently, the most typical technical solutions include three main categories: catadioptric prisms, freeform surface elements, and diffractive waveguides. Among them, diffractive waveguides are further divided into three types: surface relief gratings (SRG), volume holographic gratings (VHG), and polarizing volume gratings (PVG).

[0003] The principle behind the formation of volume holographic gratings is that two beams of light interfere in a photosensitive medium, producing alternating bright and dark fringes, which form a grating structure within the medium after exposure. However, forming a volume holographic grating using a dual-beam interference optical path requires building two optical paths, necessitating a large number of components. Furthermore, the angle between the two beams needs to be precisely adjusted during exposure. Therefore, existing exposure methods for volume holographic gratings are highly susceptible to environmental changes, leading to exposure defects and affecting the final optical effect of the grating. Utility Model Content

[0004] This invention provides an exposure apparatus for fabricating volume holographic waveguides. The apparatus provides an optical path structure for forming volume holographic waveguides using a surface relief grating mask. By using a pre-fabricated surface relief grating mask, a single beam is incident on the surface relief grating to generate zero-order and first-order diffracted light. Compared with the existing dual-beam optical path, this method eliminates one optical path, reducing optical components, system complexity, system stability, and error. By using the diffracted light generated by the surface relief grating mask for exposure, the period and duty cycle of the exposed volume holographic grating are completely consistent with the period and duty cycle of the surface relief grating, thus enabling low-cost and rapid exposure of volume holographic gratings.

[0005] This invention provides an exposure apparatus for fabricating a bulk holographic waveguide, comprising a light source, a polarization adjustment component, a beam expander component, a first reflector, a reflector adjustment component, a mask assembly, and a mask adjustment component. The first reflector is disposed on the reflector adjustment component, which drives the first reflector to translate and / or rotate. The mask assembly is disposed on the mask adjustment component, which drives the mask assembly to translate and / or rotate. The mask assembly includes a surface relief grating mask, the surface of which carries the waveguide to be exposed.

[0006] The output beam of the light source is polarized by the polarization adjustment component, expanded by the beam expander component, and reflected by the first reflector before being incident on the surface relief grating mask. The zero-order diffracted light and the first-order diffracted light of the surface relief grating mask are incident on the waveguide to be exposed for exposure, forming a volume holographic waveguide.

[0007] Optionally, it also includes an optical platform, wherein the light source, the polarization adjustment component, the beam expander component, the mirror adjustment component, and the mask adjustment component are all disposed on the same side of the optical platform.

[0008] Optionally, the light source is located on the surface of the optical platform, and both the polarization adjustment component and the beam expander component are at a preset distance from the surface of the optical platform where the light source is placed. The exposure device further includes a second reflector and a third reflector. The second reflector reflects the output beam of the light source to be transmitted along a first direction, and the third reflector reflects the beam transmitted in the first direction to be transmitted along a second direction. The first direction is perpendicular to the surface of the optical platform, and the second direction is parallel to the surface of the optical platform.

[0009] Optionally, the optical platform has a guide rail on its surface, and the reflector adjustment assembly includes a sliding base and a rotatable base. The sliding base is located on the guide rail, and the sliding base drives the first reflector to translate along the guide rail, while the rotatable base drives the first reflector to rotate.

[0010] Optionally, the beam expanding assembly includes a first beam expanding lens group and a second beam expanding lens group. The first beam expanding lens group is located on the side of the second beam expanding lens group closer to the polarization adjustment assembly. The first beam expanding lens group includes a first lens and a second lens arranged along the beam transmission direction. The second beam expanding lens group includes a third lens, a filter, and a fourth lens arranged along the beam transmission direction. The filter is located on the focal plane between the third lens and the fourth lens.

[0011] Optionally, it also includes an adjustable aperture located between the second lens and the third lens. When the adjustable aperture is opened to its maximum, the output beam of the second lens is fully transmitted, and when the adjustable aperture is closed, the output beam of the second lens is blocked by the adjustable aperture.

[0012] Optionally, the reflective surface of the first reflector is provided with an anti-reflection coating.

[0013] Optionally, the mask adjustment assembly includes an embedded base and a base moving slide rail. The mask assembly is disposed on the embedded base. The embedded base drives the mask assembly to translate on the base moving slide rail. The embedded base drives the mask assembly to rotate in the plane where the embedded base is located, about the normal at the geometric center of the embedded base as the axis.

[0014] Optionally, the mask assembly further includes a light-absorbing plate located on the side of the surface relief grating mask away from the first reflector, and during exposure, the waveguide to be exposed is located between the light-absorbing plate and the surface relief grating mask.

[0015] Optionally, the surface relief grating mask may further include a half-wave plate on the side near the first reflector. The fast axis direction of the half-wave plate is parallel to a third direction, which is the bisector of the angle between the grating line direction of the surface relief grating mask and the polarization direction of the incident light.

[0016] The exposure apparatus of this invention provides an optical path structure for forming a volume holographic waveguide by exposing a surface relief grating mask. By using a pre-prepared surface relief grating mask, a single beam is incident on the surface relief grating to generate zero-order light and first-order diffracted light. Compared with the existing dual-beam optical path, one less optical path is required, which can reduce optical components, reduce system complexity, make the system more stable, and reduce errors. By using the diffracted light generated by the surface relief grating mask for exposure, the period of the exposed volume holographic grating can be made to be completely consistent with the period and duty cycle of the surface relief grating, thereby enabling low-cost and rapid exposure of volume holographic gratings.

[0017] It should be understood that the description in this section is not intended to identify key or essential features of the embodiments of this utility model, nor is it intended to limit the scope of this utility model. Other features of this utility model will become readily apparent from the following description. Attached Figure Description

[0018] To more clearly illustrate the technical solutions in the embodiments of this utility model, the drawings used in the description of the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this utility model. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0019] Figure 1 A schematic diagram of the structure of an exposure device for fabricating a bulk holographic waveguide, provided for an embodiment of this utility model;

[0020] Figure 2 A schematic diagram of the structure of a mask assembly provided in an embodiment of this utility model;

[0021] Figure 3 A side view schematic diagram of an exposure device for fabricating a bulk holographic waveguide, provided for an embodiment of this utility model;

[0022] Figure 4 A side view schematic diagram of a reflector adjustment assembly provided in an embodiment of this utility model;

[0023] Figure 5 A top view schematic diagram of a mask adjustment assembly provided in an embodiment of this utility model;

[0024] Figure 6 A top view schematic diagram of a mask assembly provided in an embodiment of this utility model;

[0025] Figure 7 A schematic diagram of the structure of a surface relief grating mask provided in an embodiment of this utility model;

[0026] Figure 8 A schematic diagram of the structure of a waveguide to be exposed provided in an embodiment of this utility model;

[0027] Figure 9 A top view of a surface relief grating mask provided for an embodiment of this utility model;

[0028] Figure 10 A top view schematic diagram of another surface relief grating mask provided for an embodiment of this utility model;

[0029] Figure 11 This is a schematic diagram of the structure of a half-wave plate assembly provided in an embodiment of the present utility model. Detailed Implementation

[0030] To enable those skilled in the art to better understand the present invention, the technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings of the embodiments. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort should fall within the protection scope of the present invention.

[0031] It should be noted that the terminology used in the embodiments of this utility model is for the purpose of describing specific embodiments only and is not intended to limit the utility model. It should be noted that directional terms such as "upper," "lower," "left," and "right" described in the embodiments of this utility model are used to describe the angles shown in the accompanying drawings and should not be construed as limiting the embodiments of this utility model. Furthermore, in the context, it should be understood that when referring to an element being formed "on" or "below" another element, it can be formed not only directly on or below the other element, but also indirectly on or below it through intermediate elements. The terms "first," "second," etc., are used for descriptive purposes only and do not indicate any order, quantity, or importance, but are merely used to distinguish different components. It should be understood that such terms can be interchanged where appropriate so that the embodiments of this utility model described herein can be implemented in orders other than those illustrated or described herein. Furthermore, the terms “comprising” and “having”, and any variations thereof, are intended to cover non-exclusive inclusion, such that a process, method, system, product, or apparatus that includes a series of steps or units is not necessarily limited to those steps or units that are explicitly listed, but may include other steps or units that are not explicitly listed or that are inherent to such process, method, product, or apparatus.

[0032] Traditional surface relief gratings are limited in size due to etching and imprinting techniques. Fabricating large-area diffractive waveguides requires assembling multiple surface relief gratings using a piece-and-paste method, increasing the complexity and cost significantly. Volume holographic gratings, on the other hand, offer the advantage of low-cost, rapid exposure for large-area volume holographic waveguides. This invention utilizes a surface relief grating mask to form the optical path structure of a volume holographic waveguide, as detailed below:

[0033] Figure 1 This is a schematic diagram of the structure of an exposure device for fabricating a bulk holographic waveguide, provided by an embodiment of the present invention. Figure 2 This is a schematic diagram of the structure of a mask assembly provided in an embodiment of the present invention, with reference to... Figure 1 The exposure apparatus includes a light source 100, a polarization adjustment assembly 200, a beam expander 300, a first reflector 400, a reflector adjustment assembly 500, a mask assembly 600, and a mask adjustment assembly 700. The first reflector 400 is mounted on the reflector adjustment assembly 500, and the reflector adjustment assembly 500 drives the first reflector 400 to translate and / or rotate. The mask assembly 600 is mounted on the mask adjustment assembly 700, and the mask adjustment assembly 700 drives the mask assembly 600 to translate and / or rotate. (Reference) Figure 2The mask assembly 600 includes a surface relief grating mask 610, the surface of which carries the waveguide 620 to be exposed. The output beam of the light source 100 is polarized by the polarization adjustment assembly 200, expanded by the beam expansion assembly 300, and reflected by the first reflector 400 before being incident on the surface relief grating mask 610. The zero-order diffracted light and the first-order diffracted light of the surface relief grating mask 610 are incident on the waveguide 620 to be exposed for exposure, forming a volume holographic waveguide.

[0034] It is understandable that the polarization adjustment component 200 can be a half-wave plate, which can change the output beam of the light source 100 from the s-polarization state (vertical polarization) to the p-polarization state (horizontal polarization). The beam expander component 300 can be equipped with at least one lens group, which can expand the spot diameter of the output beam and collimate the beam. The angle of the first reflector 400 can be changed by using the reflector adjustment component 500, so that the angle between the output beam and the incident mask component 600 can be adjusted, thereby enabling the creation of volume holographic gratings of various structures.

[0035] Specifically, the light source 100 can be a single-mode, 532nm narrowband laser with a power greater than 5W, and the spot diameter of the output beam of the light source 100 can be 1mm~5mm.

[0036] The exposure apparatus of this invention provides an optical path structure for forming a volume holographic waveguide by exposing a surface relief grating mask 610. By using a pre-prepared surface relief grating mask 610, a single beam is incident on the surface relief grating to generate zero-order light and first-order diffracted light. Compared with the existing dual-beam optical path, one less optical path is required, which can reduce optical components, reduce system complexity, make the system more stable, and reduce errors. By using the diffracted light generated by the surface relief grating mask 610 for exposure, the period of the exposed volume holographic grating can be made to be completely consistent with the period and duty cycle of the surface relief grating, thereby enabling low-cost and rapid exposure of volume holographic gratings.

[0037] Optionally, based on the above embodiments, the exposure apparatus further includes an optical platform 800, and the light source 100, polarization adjustment component 200, beam expander component 300, mirror adjustment component 500 and mask adjustment component 700 are all disposed on the same side of the optical platform 800.

[0038] Optionally, based on the above embodiments, continue to refer to... Figure 1The light source 100 is located on the surface of the optical platform 800. The polarization adjustment component 200 and the beam expander component 300 are both at a preset distance from the surface of the optical platform 800 where the light source 100 is placed. The exposure device also includes a second reflector 900 and a third reflector 1000. The second reflector 900 reflects the output beam of the light source 100 and transmits it along the first direction z. The third reflector 1000 reflects the beam transmitted along the first direction z and transmits it along the second direction x. The first direction z is perpendicular to the surface of the optical platform 800, and the second direction x is parallel to the surface of the optical platform 800.

[0039] Figure 3 This is a side view schematic diagram of an exposure apparatus for fabricating a bulk holographic waveguide, provided as an embodiment of the present invention. (Refer to...) Figure 3 The optical platform 800 is equipped with a guide rail 810, a support rod 820, and a support base 830. The guide rail 810 has a dovetail-shaped cross-section. The support base 830 is slidably connected to the guide rail 810 and can slide on the guide rail 810. The support rod 820 is mounted on the support base 830, and an optical element 840 is mounted on the support rod 820. The optical element 840 can be a third reflector 1000, a polarization adjustment component 200, a beam expander 300, etc. It is understood that the polarization adjustment component 200 and the beam expander 300 are both mounted on the support rod 820, thus maintaining a preset distance from the surface of the optical platform 800 where the light source 100 is placed. In specific implementation, a target can be set on the guide rail 810 to collimate and adjust the second reflector 900 and the third reflector 1000, so that the output beam of the third reflector 1000 is completely parallel to the surface of the optical platform 800.

[0040] Figure 4 This is a side view schematic diagram of a reflector adjustment assembly provided in an embodiment of the present invention. Optionally, based on the above embodiment, refer to... Figure 1 and Figure 4 The optical platform 800 is provided with a guide rail 810. The reflector adjustment assembly 500 includes a sliding base 510 and a rotatable base 520. The sliding base 510 is located on the guide rail 810. The sliding base 510 drives the first reflector 400 to translate along the guide rail 810. The rotatable base 520 drives the first reflector 400 to rotate.

[0041] Understandably, the first reflector 400 is fixed in the reflector adjustment assembly 500, wherein the sliding base 510 can slide along the second direction x following the guide rail 810 with a sliding accuracy of 0.1mm; the rotatable base 520 is used to fix the first reflector 400 and can allow the first reflector 400 to rotate around the rotation axis 521, that is, around the fourth direction y, with a rotation angle range of 0-180° and a rotation angle accuracy of 0.1°. When the angle of the first reflector 400 is rotated to 45°, the parallel light propagating along the second direction x is reflected and then propagates in the first direction z, that is, vertically upward.

[0042] Optionally, based on the above embodiments, continue to refer to... Figure 1 The beam expander assembly 300 includes a first beam expander lens group 310 and a second beam expander lens group 320. The first beam expander lens group 310 is located on the side of the second beam expander lens group 320 closer to the polarization adjustment assembly 200. The first beam expander lens group 310 includes a first lens 311 and a second lens 312 arranged along the beam transmission direction. The second beam expander lens group 320 includes a third lens 321, a filter 322 and a fourth lens 323 arranged along the beam transmission direction. The filter 322 is located on the focal plane between the third lens 321 and the fourth lens 323.

[0043] The first beam expander group 310 can be a commercially available small magnifying lens group, and the second beam expander group 320 can be an independently designed large-size lens group. The sizes of the first lens 311, the second lens 312, the third lens 321, and the fourth lens 323 can be increased sequentially. The combination of the first beam expander group 310 and the second beam expander group 320 can produce parallel light with a beam diameter magnified by 15 to 100 times.

[0044] For example, the magnification β1 of the first beam expander group 310 is β1 = -f2 / f1, where f1 is the focal length of the first lens 311 and f2 is the focal length of the second lens 312. The magnification β1 of the first beam expander group 310 is approximately 5 to 10 times. After the first beam expander group 310 is installed and aligned with the target, the beam spot diameter Φ1 after one beam expansion is approximately 10 mm to 50 mm. The second beam expander group 320 can be composed of two cemented doublet lenses. The focal length of the third lens 321 is f3 = 40mm~100mm. (If the focal length of the third lens 321 is too small, it will result in large aberrations; if it is too large, it will result in an excessively long optical path.) Therefore, the diameter D3 of the third lens 321 needs to be greater than the diameter of the light spot after the first beam expansion, i.e., D3 > Φ1. The second beam expander group 320 needs to satisfy a magnification of 3~10 times. According to the geometric optics formula, the magnification β2 of the second beam expander group 320 is β2 = -f4 / f3, where f3 is the focal length of the third lens 321 and f4 is the focal length of the fourth lens 323. The focal length of the fourth lens 323 is f4 = 3f2~10f2, f4 = 120mm~1000mm. The diameter of the light spot after the second beam expansion is approximately 100mm~500mm. The diameter D4 of the fourth lens 323 needs to be greater than Φ2. After collimation adjustment, the second beam expander group 320 forms a 4F system, which can obtain parallel light with a larger spot diameter, thereby enabling low-cost and rapid exposure of large-area volume holographic gratings.

[0045] Understandably, filter 322 can be a small aperture with a diameter of approximately 0.5mm to 1mm, used to filter out high-frequency information in the optical path system; in this case, the aperture acts as a low-pass filter. Optionally, an even smaller aperture, approximately 1μm to 30μm in diameter, can be added to the focal plane between the first lens 311 and the second lens 312, serving as a low-pass filter for the first beam expander group 310. This results in a smaller phase difference between points on the wavefront of the resulting parallel light, leading to better exposure. After beam expansion by the first beam expander group 310 and the second beam expander group 320, parallel light with a diameter of 100mm to 200mm can be obtained.

[0046] Optionally, based on the above embodiments, continue to refer to... Figure 1 The exposure apparatus also includes an adjustable aperture 330 located between the second lens 312 and the third lens 321. When the adjustable aperture 330 is opened to its maximum, the output beam of the second lens 312 is fully transmitted. When the adjustable aperture 330 is closed, the output beam of the second lens 312 is blocked by the adjustable aperture 330.

[0047] Understandably, to achieve rapid exposure, an adjustable aperture 330 is inserted between the second lens 312 and the third lens 321. In this case, the adjustable aperture 330 can act as a light-blocking plate. When the adjustable aperture 330 is opened to its maximum, the entire output beam of the light source 100 can pass through. When the adjustable aperture 330 is closed, the output beam cannot pass through, which can prevent damage caused by repeated switching of the light source 100.

[0048] Optionally, based on the above embodiments, the reflective surface of the first reflector 400 is provided with an anti-reflection coating.

[0049] It should be noted that the size of the first reflecting mirror 400 needs to be larger than the diameter of the parallel light spot after the beam expander 300 expands the spot diameter. The side length of the first reflecting mirror 400 can be 200mm~300mm, and the anti-reflection coating can be selected from high-reflection coatings such as dielectric film, silver film, and aluminum film.

[0050] Figure 5 This is a top view schematic diagram of a mask adjustment assembly provided in an embodiment of the present invention. Optionally, based on the above embodiment, refer to... Figure 5 The mask template adjustment assembly 700 includes an embedded base 710 and a base moving slide rail 720. The mask template assembly 600 is disposed on the embedded base 710. The embedded base 710 drives the mask template assembly 600 to translate on the base moving slide rail 720. The embedded base 710 drives the mask template assembly 600 to rotate in the plane where the embedded base 710 is located, about the normal at the geometric center of the embedded base 710 as the axis.

[0051] Understandably, a bracket can be mounted on the optical platform 800, with one end fixed to the surface of the optical platform 800 and the other end positioned above the first reflector 400. An embedded base 710 is mounted on the second end of the bracket, and a mask assembly 600 is placed within the first slot 711 of the embedded base 710, thereby fixing the mask assembly 600. The embedded base 710 can translate freely in the horizontal plane along either the second direction (x) or the fourth direction (y), with a range of movement from 0 to 500 mm and a translation accuracy of 0.1 mm. The embedded base 710 can rotate freely 360° in the horizontal plane along its central normal axis, with a rotation angle accuracy of 0.1°. The base sliding rail 720 is detachably connected to the embedded base 710, allowing the size of the embedded base 710 to be changed to accommodate waveguides 620 of different sizes and areas to be exposed.

[0052] Optionally, based on the above embodiments, continue to refer to... Figure 2The mask assembly 600 also includes a light-absorbing plate 630, which is located on the side of the surface relief grating mask 610 away from the first reflector 400, and the waveguide 620 to be exposed is located between the light-absorbing plate 630 and the surface relief grating mask 610 during exposure.

[0053] By setting up the light-absorbing plate 630, some of the illumination light can be prevented from being reflected back into the waveguide 620 to be exposed during exposure, thus affecting the exposure effect.

[0054] Figure 6 This is a top view schematic diagram of a mask assembly provided in an embodiment of the present invention. Figure 7 This is a schematic diagram of the structure of a surface relief grating mask provided in an embodiment of the present invention. Figure 8 This is a schematic diagram of the structure of a waveguide to be exposed provided in an embodiment of the present utility model. It can be understood that, with reference to Figure 2 as well as Figures 6-8 During exposure, a light-absorbing plate 630 is placed above the waveguide 620 to be exposed, which can prevent some of the illumination light from being reflected back into the waveguide 620. (Referencing...) Figure 6 The mask assembly 600 also includes a base plate 640, on which a second slot 641 is provided. The surface-embossed grating mask 610 is embedded in and installed in the second slot 641 of the base plate 640 for easy fixation. (Reference) Figure 7 The surface relief grating mask 610 is provided with a surface relief grating ( Figure 7 (As shown in the shaded area), an incident light beam passes through the surface relief grating mask 610, generating two beams. The shape and size of the surface relief grating mask 610 can be customized according to the actual shape and size of the waveguide 620 to be exposed. It contains one or more grating structures, and the period, duty cycle, height, orientation, and shape of the grating structures can be different. Reference Figure 8 Two beams of light are incident on the waveguide 620 to be exposed, achieving exposure and producing a volume holographic grating. For example, Figure 9This is a top view schematic diagram of a surface relief grating mask provided in an embodiment of the present invention. The surface relief grating mask includes three one-dimensional grating regions, specifically a first grating region 611, a second grating region 612, and a third grating region 613. During exposure of the first and third regions of the waveguide 620 to be exposed, the first and third regions of the waveguide 620 correspond to the first grating regions 611 and 613 of the surface relief grating mask. The first reflector 400 is adjusted to reflect the waveguide 620 at an angle of 35° to 55°. During exposure of the second region of the waveguide 620 to be exposed, the second region of the waveguide 620 corresponds to the second grating region 612 of the surface relief grating mask. The first reflector 400 is adjusted to reflect the waveguide 620 at an angle of 10° to 35°. Figure 9 It also shows the horizontal rotation angle of the surface relief grating mask 610 when exposing different areas of the waveguide 620 to be exposed, that is, the direction of the grating lines in different areas of the surface relief grating mask 610. Figure 10 A top view schematic diagram of another surface relief grating mask provided in an embodiment of this utility model, with reference to... Figure 10 The surface relief grating mask includes a two-dimensional grating region 614.

[0055] Specifically, considering that multiple grating structures with different orientations need to be exposed in a waveguide to be exposed, since the grating line directions of each grating structure to be exposed may be different, while the polarization direction of the incident light is fixed, it is necessary to frequently adjust the angle of the mask assembly 600° and expose each grating region one by one in order to expose multiple grating structures with different grating line directions. To significantly shorten the exposure time, this embodiment of the invention also designs a half-wave plate assembly. Figure 11 This is a schematic diagram of a half-wave plate assembly provided in an embodiment of the present invention. Optionally, based on the above embodiment, the surface relief grating mask 610 further includes a half-wave plate 650 on the side near the first reflecting mirror 400. (See reference...) Figure 11 The fast axis direction of the half-wave plate 650 is parallel to the third direction, which is the bisector of the angle between the grating line direction of the surface relief grating mask 610 and the polarization direction of the incident light.

[0056] It is understood that the half-wave plate 650 is mounted on the side of the surface relief grating mask 610 near the first reflector 400, and the component morphology and size of the half-wave plate 650 correspond to the grating area on the surface relief grating mask 610. For example, assuming the surface relief grating mask 610 is as follows... Figure 9 As shown, the half-wave plate assembly formed by the half-wave plate 650 designed with reference to the surface relief grating mask 610 is as follows: Figure 11This includes a first half-wave plate 651, a second half-wave plate 652, and a third half-wave plate 653. The fast axis direction of the half-wave plate 650 is parallel to the third direction. Since the component shape and size of the half-wave plate 650 correspond to the grating area on the surface relief grating mask 610, and the fast axis direction of the half-wave plate 650 is parallel to the third direction, after installing the half-wave plate 650, as... Figure 9 The surface relief grating mask 610 can expose multiple grating areas simultaneously, instead of adjusting the position and angle of the mask assembly 600 each time to expose grating areas with different grating line directions, which greatly shortens the time for mass exposure production.

[0057] It should be noted that the half-wave plate 650 is positioned on the side of the surface relief grating mask 610 near the first reflector 400, but does not contact the surface relief grating mask 610. The closer the half-wave plate 650 is to the surface relief grating mask 610, the smaller its size can be. The minimum size of the half-wave plate 650 can be the same as the size of the surface relief grating mask 610. When the distance between the half-wave plate 650 and the surface relief grating mask 610 is large, the area of ​​the half-wave plate 650 needs to be increased.

[0058] The exposure process of the exposure apparatus for fabricating bulk holographic waveguides provided in this embodiment of the invention includes the following steps:

[0059] 1. Turn on the light source to 100.

[0060] The power output of the light source 100 is within 1W.

[0061] 2. Adjust the polarization adjustment component 200 to change the output beam of the light source 100 to p-polarized light.

[0062] 3. Open the adjustable aperture 330, and adjust the sliding base 510 and rotatable base 520 of the first reflector 400 so that parallel light is reflected by the first reflector 400 at a preset angle into the mask assembly 600 above. The preset angle is within the range of 10° to 80°.

[0063] 4. Place only the surface relief grating mask 610 inside the mask assembly 600, adjust the horizontal position of the embedded base 710 so that the laser is incident on the surface relief grating mask 610, and after the parallel light passes through the surface relief grating mask 610, two or more parallel beams appear above it. Rotate the embedded base 710 so that the parallel beams above reach the designated position.

[0064] The embedded base 710 has a rotation angle range of 0~360° in the plane containing the second direction x and the fourth direction y.

[0065] 5. Fix the position and angle of the sliding base 510 and the rotatable base 520, and close the adjustable aperture 330.

[0066] 6. Remove the mask assembly 600, and install and fix the waveguide 620 to be exposed and the light-absorbing plate 630 above the surface relief grating mask 610.

[0067] This process involves filling the space between the surface-embossed grating mask 610, the waveguide 620 to be exposed, and the light-absorbing plate 630 with refractive index matching liquids of different refractive indices. The refractive index of the matching liquid needs to be approximately the same as that of the material beneath it. The material of the volume holographic grating in the waveguide 620 to be exposed is mainly composed of photopolymers and various doped particles.

[0068] 7. Place the mask assembly 600 back into the embedded base 710, open the adjustable aperture 330, and expose the waveguide 620 to be exposed according to the specified time.

[0069] 8. After exposure, a volume holographic grating structure is formed in the grating material of the waveguide 620 to be exposed. The light source 100 is turned off, and the exposed waveguide is taken out for other processing to finally obtain a volume holographic waveguide that can realize AR imaging.

[0070] Specifically, in one embodiment, a design such as Figure 9 The waveguide sheet shown has three one-dimensional gratings with periods ranging from 300nm to 450nm. The positions and orientations of the gratings in each region are different. The specific steps are as follows:

[0071] 1. Turn on light source 100 and adjust its power output to 1W.

[0072] 2. Adjust the polarization adjustment component 200 to change the output beam of the light source 100 to p-polarized light.

[0073] 3. Open the adjustable aperture 330, and adjust the sliding base 510 and the rotatable base 520 of the first reflector 400 so that the parallel light passes through the first reflector 400 and is reflected at a preset angle into the mask assembly 600 above.

[0074] The preset angle ranges from 35° to 55°.

[0075] 4. Place the surface relief grating mask 610 inside the mask assembly 600, adjust the horizontal position of the embedded base 710 so that the laser is incident on the first grating area 611 in the surface relief grating mask 610. After the parallel light passes through the surface relief grating mask 610, two parallel beams appear above. Rotate the embedded base 710 so that the straight line connecting the two beams is parallel to the guide rail 810.

[0076] 5. Record the position and angle of the sliding base 510 and the rotatable base 520, and close the adjustable aperture 330.

[0077] 6. Repeat steps 3 to 5 to successively change the first grating region 611 into the second grating region 612 and the third grating region 613.

[0078] The angle range of the second grating region 612 in step 3 is 10° to 35° from the first reflector 400.

[0079] 7. Remove the mask assembly 600, and install and fix the waveguide 620 to be exposed and the light-absorbing plate 630 above the surface relief grating mask 610;

[0080] The waveguide 620 to be exposed includes a grating material, a waveguide substrate, and a release film. The grating material is located between the waveguide substrate and the release film. The waveguide substrate is placed on one side close to the surface relief grating mask 610. A matching liquid with a refractive index of 1.7, which is adapted to the refractive index of the waveguide substrate, is applied between the waveguide substrate and the surface relief grating mask 610. The release film is placed on one side close to the light-absorbing glass. A matching liquid with a refractive index of 1.5, which is adapted to the refractive index of the grating material, is applied between the release film and the light-absorbing glass.

[0081] 8. Place the mask assembly 600 back into the embedded base 710, adjust it to the recorded position and angle, fix it, open the adjustable aperture 330, and expose the areas in the waveguide to be exposed that correspond to the first grating area 611, the second grating area 612, and the third grating area 613 in turn.

[0082] The exposure time varies from 30 seconds to 10 minutes. After the exposure is complete, the adjustable aperture of 330 is turned off.

[0083] 9. Turn off the light source 100, remove the mask assembly 600, take out the exposed optical waveguide, and perform post-processing to obtain a volume holographic optical waveguide that can realize AR imaging.

[0084] For example, in another embodiment, a design such as Figure 10 The 70mm×70mm waveguide sheet with a two-dimensional grating shown has a grating period in the range of 300nm~450nm. The specific steps are as follows:

[0085] 1. Turn on light source 100 and adjust its power output to 1W.

[0086] 2. Adjust the polarization adjustment component 200 to change the output beam of the light source 100 to p-polarized light.

[0087] 3. Open the adjustable aperture 330, and adjust the sliding base 510 and the rotatable base 520 of the first reflector 400 so that the parallel light passes through the first reflector 400 and is reflected at a preset angle into the mask assembly 600 above.

[0088] The preset angle range is 40° to 50°.

[0089] 4. Place only the surface relief grating mask 610 inside the mask assembly 600, adjust the horizontal position of the embedded base 710 so that the laser is incident on the grating area in the surface relief grating mask 610, and after the parallel light passes through the surface relief grating mask 610, multiple beams of parallel light appear above. Rotate the embedded base 710 to the specified angle.

[0090] 5. Record the position and angle of the sliding base 510 and the rotatable base 520, and close the adjustable aperture 330.

[0091] 6. Remove the mask assembly 600, and install and fix the waveguide 620 to be exposed and the light-absorbing plate 630 above the surface relief grating mask 610. The waveguide 620 to be exposed includes a grating material, a waveguide substrate, and a release film. The grating material is located between the waveguide substrate and the release film. The waveguide substrate is placed on the side close to the surface relief grating mask 610. A matching liquid with a refractive index of 1.7, which is compatible with the refractive index of the waveguide substrate, is applied between the waveguide substrate and the surface relief grating mask 610. The release film is placed on the side close to the light-absorbing glass. A matching liquid with a refractive index of 1.5, which is compatible with the refractive index of the grating material, is applied between the release film and the light-absorbing glass.

[0092] 7. Place the mask assembly 600 back into the embedded base 710, adjust it to the recorded position and angle, and then open the adjustable aperture 330 for exposure. The exposure time varies from 30 seconds to 10 minutes. After the exposure is complete, close the adjustable aperture 330.

[0093] 8. Turn off the light source 100, remove the mask assembly 600, take out the exposed optical waveguide, perform post-processing, and obtain a complete two-dimensional volumetric holographic optical waveguide.

[0094] In summary, the exposure apparatus of this invention provides an optical path structure for forming a volume holographic waveguide using a surface relief grating mask 610. By using the pre-prepared surface relief grating mask 610, a single beam incident on the surface relief grating generates zero-order and first-order diffracted light. Compared to the existing dual-beam optical path, this eliminates one optical path, reducing optical components, system complexity, system stability, and error. Exposure using the diffracted light generated by the surface relief grating mask 610 ensures that the period and duty cycle of the exposed volume holographic grating are perfectly consistent with the period and duty cycle of the surface relief grating, thus enabling low-cost and rapid exposure of the volume holographic grating. Furthermore, the beam expander 300 allows for the exposure of a large-area volume holographic waveguide. The filter 322 minimizes the phase difference between points on the obtained parallel light wavefront, resulting in better exposure. The adjustable aperture 330 prevents damage caused by repeated switching of the light source 100. The base sliding rail 720 and the embedded base 710 are detachably connected, allowing the size of the embedded base 710 to be changed to accommodate waveguides 620 of different sizes and areas to be exposed. A light-absorbing plate 630 is placed above the waveguide 620 to prevent some of the illumination light from being reflected back into the waveguide 620. A half-wave plate 650 is mounted on the side of the surface-embossed grating mask 610 near the first reflector 400. The component morphology and size of the half-wave plate 650 are consistent with the grating area on the surface-embossed grating mask 610, allowing for simultaneous exposure of multiple grating areas without needing to adjust the position and angle of the mask assembly 600 each time, significantly shortening the time for mass production.

[0095] The specific embodiments described above do not constitute a limitation on the scope of protection of this utility model. Those skilled in the art should understand that various modifications, combinations, sub-combinations, and substitutions can be made according to design requirements and other factors. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of this utility model should be included within the scope of protection of this utility model.

Claims

1. An exposure apparatus for fabricating a bulk holographic waveguide, characterized in that, The device includes a light source, a polarization adjustment component, a beam expander component, a first reflector, a reflector adjustment component, a mask assembly, and a mask adjustment component. The first reflector is disposed on the reflector adjustment component, and the reflector adjustment component drives the first reflector to translate and / or rotate. The mask assembly is disposed on the mask adjustment component, and the mask adjustment component drives the mask assembly to translate and / or rotate. The mask assembly includes a surface relief grating mask, and the surface of the surface relief grating mask carries the waveguide to be exposed. The output beam of the light source is polarized by the polarization adjustment component, expanded by the beam expander component, and reflected by the first reflector before being incident on the surface relief grating mask. The zero-order diffracted light and the first-order diffracted light of the surface relief grating mask are incident on the waveguide to be exposed for exposure, forming a volume holographic waveguide.

2. The exposure apparatus for fabricating a bulk holographic waveguide according to claim 1, characterized in that, It also includes an optical platform, wherein the light source, the polarization adjustment component, the beam expander component, the mirror adjustment component, and the mask adjustment component are all disposed on the same side of the optical platform.

3. The exposure apparatus for fabricating a bulk holographic waveguide according to claim 2, characterized in that, The light source is located on the surface of the optical platform. The polarization adjustment component and the beam expander component are both at a preset distance from the surface of the optical platform where the light source is placed. The exposure device also includes a second mirror and a third mirror. The second mirror reflects the output beam of the light source and transmits it along a first direction. The third mirror reflects the beam transmitted in the first direction and transmits it along a second direction. The first direction is perpendicular to the surface of the optical platform, and the second direction is parallel to the surface of the optical platform.

4. The exposure apparatus for fabricating a bulk holographic waveguide according to claim 2, characterized in that, The optical platform has a guide rail on its surface. The mirror adjustment assembly includes a sliding base and a rotatable base. The sliding base is located on the guide rail. The sliding base moves the first mirror along the guide rail and the rotatable base rotates the first mirror.

5. The exposure apparatus for fabricating a bulk holographic waveguide according to claim 1, characterized in that, The beam expanding assembly includes a first beam expanding lens group and a second beam expanding lens group. The first beam expanding lens group is located on the side of the second beam expanding lens group closer to the polarization adjustment assembly. The first beam expanding lens group includes a first lens and a second lens arranged along the beam transmission direction. The second beam expanding lens group includes a third lens, a filter, and a fourth lens arranged along the beam transmission direction. The filter is located on the focal plane between the third lens and the fourth lens.

6. The exposure apparatus for fabricating a bulk holographic waveguide according to claim 5, characterized in that, It also includes an adjustable aperture located between the second lens and the third lens. When the adjustable aperture is opened to its maximum, the output beam of the second lens is fully transmitted, and when the adjustable aperture is closed, the output beam of the second lens is blocked by the adjustable aperture.

7. The exposure apparatus for fabricating a bulk holographic waveguide according to claim 1, characterized in that, The reflective surface of the first reflector is provided with an anti-reflection coating.

8. The exposure apparatus for fabricating a bulk holographic waveguide according to claim 1, characterized in that, The mask adjustment assembly includes an embedded base and a base moving slide rail. The mask assembly is disposed on the embedded base. The embedded base drives the mask assembly to translate on the base moving slide rail. The embedded base drives the mask assembly to rotate in the plane where the embedded base is located, about the normal at the geometric center of the embedded base as the axis.

9. The exposure apparatus for fabricating a bulk holographic waveguide according to claim 1, characterized in that, The mask assembly further includes a light-absorbing plate located on the side of the surface relief grating mask away from the first reflector, and during exposure, the waveguide to be exposed is located between the light-absorbing plate and the surface relief grating mask.

10. The exposure apparatus for fabricating a bulk holographic waveguide according to claim 1, characterized in that, The surface relief grating mask also includes a half-wave plate on the side near the first reflector. The fast axis direction of the half-wave plate is parallel to a third direction, which is the bisector of the angle between the grating line direction of the surface relief grating mask and the polarization direction of the incident light.

Images