A holographic exposure system

Abstract

The scheme belongs to the technical field of volume holographic grating, and discloses a holographic exposure system. The system comprises a mask plate which is arranged in parallel to and apart from a sample to be exposed, and the mask plate comprises a first mask grating and a second mask grating which are parallel to the sample to be exposed. When the mask plate is irradiated by a collimated light beam with a constant incident angle with respect to the spatial position, the first mask grating generates first diffracted light with an angle varying with the spatial position, and the second mask grating generates second diffracted light with an angle varying with the spatial position. The first diffracted light and the second diffracted light interfere on the sample to be exposed, the sample to be exposed records interference fringes, and a volume holographic grating with a Bragg surface tilt angle varying with the spatial position is formed. The system can not only avoid the introduction of installation alignment accuracy, stray light control and other problems, but also realize the preparation of the volume holographic grating with the Bragg surface tilt angle varying with the spatial position.

Description

Technical Field

[0001] This solution belongs to the field of volume holographic grating technology, specifically involving a holographic exposure system. Background Technology

[0002] The method of fabricating volume holographic gratings using mask exposure involves a collimated beam incident on a mask. Two predetermined mask gratings generate 0th-order and 1st-order diffraction, respectively. The two diffracted beams interfere and expose the photosensitive material to form the volume holographic grating. This method eliminates the errors of conventional dual-beam optical paths through the high-precision fabricated mask master and is conducive to building integrated holographic exposure equipment. It is the most feasible technical path for mass production of volume holographic waveguides.

[0003] Volume holographic waveguides need to ensure that the surface period of their coupling, turning, and coupling gratings meets the zero dispersion condition, and the surface period within each volume holographic grating region must remain constant with spatial position (variation error <0.05nm), otherwise it will lead to image quality degradation or even ghosting.

[0004] The display effect of volume holographic waveguides, especially the field-of-view uniformity, depends on the angular bandwidth of the volume holographic grating, i.e., the range of incident angles within which the volume holographic grating can achieve a certain diffraction efficiency. This is typically measured by the Bragg angle of incidence (the angle of incidence that satisfies the Bragg condition, theoretically corresponding to the peak diffraction efficiency) and the full width at half maximum (FWHM). These values ​​must match the field-of-view of the waveguide design to ensure high field-of-view uniformity. The Bragg angle of incidence depends on the tilt angle of the Bragg surface of the volume holographic grating, while the FWHM depends on the grating thickness. If the tilt angle of the Bragg surface of the volume holographic grating remains constant with position, then its Bragg angle of incidence also remains constant, only responding to a small range of incident angles near that angle, which may not meet the field-of-view requirements of the waveguide design. Therefore, to improve the field-of-view uniformity of volume holographic waveguides, it is necessary to use volume holographic gratings with a Bragg surface tilt angle that varies with spatial position.

[0005] Current mask exposure methods can achieve a constant surface period with spatial position, but cannot achieve the fabrication of volume holographic gratings with varying Bragg surface tilt angles with spatial position. Alternatively, curved lenses or mirrors are required, which introduces challenges such as installation alignment accuracy and stray light control. Utility Model Content

[0006] This solution aims to overcome at least one of the defects in the existing technology and provide a holographic exposure system for fabricating volume holographic gratings with Bragg plane tilt angle varying with spatial position, while avoiding problems such as installation alignment accuracy and stray light control.

[0007] To solve the above-mentioned technical problems, the following technical solution is adopted: A holographic exposure system includes a mask disposed parallel to and at a distance from a sample to be exposed. The mask includes a first mask grating and a second mask grating parallel to the sample. When the mask is illuminated by a collimated beam with a constant incident angle depending on the spatial position, the first mask grating generates first diffracted light with an angle varying with the spatial position, and the second mask grating generates second diffracted light with an angle varying with the spatial position. The first and second diffracted lights interfere on the sample to be exposed, and the sample records interference fringes, forming a volume holographic grating with a Bragg plane tilt angle varying with the spatial position.

[0008] This system utilizes a first mask grating and a second mask grating whose diffraction angle varies with spatial position to deflect a collimated beam with a constant incident angle. It eliminates the need for other optical components such as curved mirrors, has low requirements for installation and alignment accuracy, and allows for relatively controllable stray light. This avoids the problems of installation and alignment accuracy and stray light control, and enables the fabrication of volume holographic gratings with Bragg surface tilt angle varying with spatial position.

[0009] The second diffracted light is a first-order diffracted light, and the surface period of the second mask grating is constant with the spatial position. This makes the volume holographic grating formed by exposure not only change the Bragg plane tilt angle with the spatial position, but also have a constant surface period with the spatial position. It can be applied to volume holographic waveguides as a coupling grating, turning grating or coupling grating of the volume holographic waveguide.

[0010] The second mask grating preferably generates a chirped grating with first-order diffraction. Different positions of the chirped grating can diffract the incident collimated beam into first-order diffracted light at different angles, so that different positions of the sample to be exposed receive second diffracted light at different angles.

[0011] The first mask grating is preferably a metasurface grating or a chirped grating that produces -1st order diffraction. The metasurface grating can convert the incident collimated beam into a divergent beam, that is, diffract at different angles at different positions, thus ensuring that different positions on the sample to be exposed receive first diffracted light at different angles. Similarly, different positions of the chirped grating can diffract the incident collimated beam into -1st order diffracted light at different angles, thus ensuring that different positions on the sample to be exposed receive first diffracted light at different angles.

[0012] The photomask also includes a light-transmitting substrate, and a first photomask grating and a second photomask grating are fixed on the surface or inside the light-transmitting substrate to fix the relative positions of the first photomask grating and the second photomask grating, so as to ensure that the first diffracted light and the second diffracted light can interfere on the sample to be exposed.

[0013] The system also includes a light-transmitting cover plate located between the sample to be exposed and the photomask. The cover plate has a first surface and a second surface that are parallel and opposite to each other. The photomask is attached to the first surface, and the sample to be exposed is attached to the second surface, so as to strictly control the distance and parallelism between the sample to be exposed and the photomask. The thickness of the cover plate can be adjusted according to the area of ​​the two photomask gratings and the angle of the two diffracted beams to avoid the overlap of the two photomask gratings.

[0014] A refractive index matching liquid is filled between the mask and the first surface so that the first and second diffracted lights are coupled from the mask to the light-transmitting cover plate.

[0015] A refractive index matching liquid is filled between the sample to be exposed and the second surface so that the first and second diffracted lights are coupled out from the light-transmitting cover plate to the sample to be exposed.

[0016] The system also includes a light-absorbing glass located on the side of the sample to be exposed away from the mask, in order to absorb the light reaching the side of the sample to be exposed away from the mask, including first diffracted light and second diffracted light emitted from the sample to be exposed onto the light-absorbing glass, so as to prevent it from interfering with the exposure.

[0017] The system also includes a light source assembly that emits a collimated beam with a constant incident angle as the spatial position toward the mask.

[0018] Compared with existing technologies, this solution has the following advantages: by using a first mask grating and a second mask grating whose diffraction angle varies with spatial position, the collimated beam with a constant incident angle can be deflected. This eliminates the need for other optical components such as curved mirrors, reduces the requirements for installation and alignment accuracy, and makes stray light relatively controllable. It avoids the problems of installation and alignment accuracy and stray light control, and enables the fabrication of a volume holographic grating with a Bragg surface tilt angle that varies with spatial position. Attached Figure Description

[0019] The accompanying drawings are for illustrative purposes only and should not be construed as limiting the scope of this solution. To better illustrate the solution, some components in the drawings may be omitted, enlarged, or reduced, and do not represent the actual dimensions of the product. It is understandable to those skilled in the art that some well-known structures and their descriptions may be omitted in the drawings.

[0020] Figure 1 This is a schematic diagram of the structure and optical path of a holographic exposure system.

[0021] Figure 2 This is a schematic diagram of the structure and optical path of another holographic exposure system.

[0022] Explanation of reference numerals in the attached drawings: Sample to be exposed 100, volume holographic grating 110, mask 210, first mask grating 211, second mask grating 212, light-transmitting substrate 213, light-transmitting cover plate 220. Detailed Implementation

[0023] To enable those skilled in the art to better understand this solution, the following detailed description is provided in conjunction with specific embodiments.

[0024] Figures 1-2 A possible holographic exposure system is illustrated for exposing a sample 100 to be exposed, forming a volume holographic grating 110 in the sample 100. For example... Figures 1-2 As shown, the holographic exposure system includes a mask 210, which is equipped with a first mask grating 211 and a second mask grating 212. The mask 210, the first mask grating 211, the second mask grating 212, and the sample 100 to be exposed are all plate-shaped structures. The mask 210 is parallel to and spaced apart from the sample 100, and the first mask grating 211 and the second mask grating 212 are also parallel to the sample 100. When the mask 210 is illuminated by a collimated beam with an incident angle that remains constant with spatial position, the first mask grating 211 generates first diffracted light, and the second mask grating 212 generates second diffracted light. The first and second diffracted lights interfere on the sample 100, and the photosensitive material in the sample 100 records interference fringes, forming a volume holographic grating 110. The angle of the first diffracted light changes with the spatial position, and the angle of the second diffracted light also changes with the spatial position, causing the Bragg plane tilt angle of the formed holographic grating 110 to change with the spatial position. Since the exposure process utilizes the grating structure processed with high precision on the mask 210 to deflect the incident collimated beam, there is no need to introduce other optical components such as curved mirrors. The installation and alignment accuracy requirements are low, and stray light is relatively controllable. Thus, a three-dimensional holographic grating 110 is formed while avoiding the problems of installation and alignment accuracy and stray light control.

[0025] The relationship between the vector of the volume holographic grating 110 and the wave vectors of the two diffracted beams is as follows: ,in It is a volume holographic grating 110 vector. and These are the wave vectors of the first and second diffracted beams, respectively, and their amplitudes are the reciprocals of the wavelength of the light in the grating medium. The volume period of the volume holographic grating 110... Surface period P s = P / cos( α ),in α It is the Bragg surface tilt angle of the volume holographic grating 110. Therefore, according to the design requirements of the volume holographic grating 110, including the surface period and the Bragg surface tilt angle that varies with spatial position, the angle of the two diffracted beams that varies with spatial position can be calculated.

[0026] The first mask grating 211 and the second mask grating can be collectively referred to as mask gratings, and the first diffracted light and the second diffracted light can be collectively referred to as diffracted light. One of the mask gratings produces first-order diffraction under collimated beam illumination, and the corresponding diffracted light is the first-order diffracted light. The surface period of this mask grating is constant with spatial position, so that the resulting volume holographic grating 110 not only has its Bragg surface tilt angle varying with spatial position, but also its surface period remaining constant with spatial position. This allows it to be applied to volume holographic waveguides as a coupling grating, transition grating, or coupling grating. The mask grating that produces first-order diffraction can be a chirped grating or other grating capable of producing first-order diffraction, while the other mask grating can be a metasurface grating, a chirped grating, or other grating.

[0027] exist Figure 1 In the holographic exposure system shown, the first mask grating 211 is a metasurface grating, and the second mask grating is a chirped grating that generates first-order diffraction. The metasurface grating can convert the incident collimated beam into a divergent beam, that is, diffract at different angles at different positions, so that different positions of the sample 100 to be exposed receive first diffracted light at different angles. Different positions of the chirped grating can diffract the incident collimated beam into diffracted light at different angles, so that different positions of the sample 100 to be exposed receive second diffracted light at different angles. For the first diffracted light diffracted by the metasurface grating, this diffraction angle that varies with spatial position can be achieved at a given incident angle of the collimated beam through a specific metasurface grating design. For the second diffracted light diffracted by the first-order chirped grating, the grating period that varies with spatial position can be calculated through the grating equation to generate this first-order diffraction angle that varies with spatial position.

[0028] exist Figure 2 In the holographic exposure system shown, the first mask grating 211 is a chirped grating that generates -1st order diffraction, and the second mask grating 212 is a chirped grating that generates 1st order diffraction. Different positions of the chirped grating can diffract the incident collimated beam into diffracted light at different angles, thus allowing different positions of the sample 100 to receive first and second diffracted light at different angles. For the first diffracted light generated by the -1st order diffraction of the chirped grating, a grating period that varies with spatial position can be calculated using the grating equation for a given incident angle of the collimated beam to generate this -1st order diffraction angle that varies with spatial position. For the second diffracted light generated by the 1st order diffraction of the chirped grating, another grating period that varies with spatial position can be calculated using the grating equation to generate this 1st order diffraction angle that varies with spatial position.

[0029] In addition to the first mask grating 211 and the second mask grating 212, the mask plate 210 may also be configured with a light-transmitting substrate 213. The first mask grating 211 and the second mask grating 212 may be fixedly configured on the surface of the light-transmitting substrate 213 or fixedly configured inside the light-transmitting substrate 213, so as to fix the relative position of the first mask grating 211 and the second mask grating 212, and ensure that the first diffracted light and the second diffracted light can interfere on the sample 100 to be exposed.

[0030] The holographic exposure system can be configured with a light-transmitting cover plate 220, which is located between the sample 100 to be exposed and the mask 210. The light-transmitting cover plate 220 has parallel and opposite first and second surfaces. The mask 210 is attached to the first surface, and the sample 100 to be exposed is attached to the second surface, in order to strictly control the distance and parallelism between the sample 100 and the mask 210. The thickness of the light-transmitting cover plate 220 can be adjusted according to the area of ​​the two mask gratings and the angle of the two diffracted beams to avoid overlap of the two mask gratings. A refractive index matching liquid can be filled between the mask 210 and the first surface to couple the first and second diffracted beams from the mask 210 to the light-transmitting cover plate 220. A refractive index matching liquid is also filled between the sample 100 to be exposed and the second surface to couple the first and second diffracted beams from the light-transmitting cover plate 220 to the sample 100 to be exposed.

[0031] The holographic exposure system can be configured with light-absorbing glass located on the side of the sample 100 to be exposed that faces away from the mask 210, so as to absorb the light reaching the side of the sample 100 to be exposed that faces away from the mask 210, including the first diffracted light and the second diffracted light emitted from the sample 100 to the light-absorbing glass, so as to prevent it from interfering with the exposure.

[0032] The holographic exposure system can be configured with a light source assembly. A collimated beam with a constant incident angle depending on the spatial position can be provided by the light source assembly. That is, the light source assembly emits a collimated beam with a constant incident angle onto the mask 210. The light source assembly includes a light source and a beam shaping element. The beam shaping element shapes the beam generated by the light source into a collimated beam and emits it onto the mask 210. The incident angle of the collimated beam on the mask 210 is constant depending on the spatial position.

[0033] Obviously, the above embodiments of this solution are merely examples for clearly illustrating this solution, and are not intended to limit the implementation of this solution. Those skilled in the art can make other variations or modifications based on the above description. It is neither necessary nor possible to exhaustively list all possible implementations here. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of this solution should be included within the scope of protection of the claims of this solution.

Claims

1. A holographic exposure system, characterized in that, The system includes a mask plate parallel to and spaced apart from the sample to be exposed. The mask plate includes a first mask grating and a second mask grating parallel to the sample to be exposed. When the mask plate is illuminated by a collimated beam with a constant incident angle depending on the spatial position, the first mask grating generates a first diffracted light with an angle varying with the spatial position, and the second mask grating generates a second diffracted light with an angle varying with the spatial position. The first diffracted light and the second diffracted light interfere on the sample to be exposed, and the sample to be exposed records interference fringes, forming a volume holographic grating with a Bragg surface tilt angle varying with the spatial position.

2. The holographic exposure system according to claim 1, characterized in that, The second diffracted light is a first-order diffracted light, the surface period of the second mask grating is constant with spatial position, and the surface period of the volume holographic grating is constant with spatial position.

3. The holographic exposure system according to claim 2, characterized in that, The second mask grating is a chirped grating that produces first-order diffraction.

4. The holographic exposure system according to claim 2, characterized in that, The first mask grating is a metasurface grating or a chirped grating that produces -1st order diffraction.

5. The holographic exposure system according to any one of claims 1 to 4, characterized in that, The mask also includes a light-transmitting substrate, and the first mask grating and the second mask grating are fixed to the surface or interior of the light-transmitting substrate.

6. The holographic exposure system according to any one of claims 1 to 4, characterized in that, The system also includes a light-transmitting cover plate located between the sample to be exposed and the photomask. The light-transmitting cover plate has a first surface and a second surface that are parallel and opposite to each other. The photomask is attached to the first surface, and the sample to be exposed is attached to the second surface.

7. The holographic exposure system according to claim 6, characterized in that, The space between the mask and the first surface is filled with a refractive index matching liquid.

8. The holographic exposure system according to claim 6, characterized in that, The space between the sample to be exposed and the second surface is filled with a refractive index matching liquid.

9. The holographic exposure system according to any one of claims 1 to 4, characterized in that, The system also includes a light-absorbing glass located on the side of the sample to be exposed that faces away from the mask.

10. The holographic exposure system according to any one of claims 1 to 4, characterized in that, The system also includes a light source assembly that emits a collimated beam with a constant incident angle as the spatial position toward the mask.

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