Method for producing optical element

Abstract

The purpose of an embodiment of the present invention is to provide a method for producing an optical element for improving display quality.　According to one embodiment, this method for producing an optical element comprises: disposing a photocurable resin between a first plane of a plano-convex lens and a second plane of a plano-concave lens; splitting the emitted light from a light source into object light and reference light; and curing the photocurable resin by irradiating the resin with the object light from the convex side of the plano-convex lens and the reference light from the concave side of the plano-concave lens.

Description

Optical element manufacturing method

[0001] SUMMARY OF THE INVENTION An embodiment of the present invention relates to a method for manufacturing an optical element.

[0002] In recent years, attention has been focused on technology that provides, for example, virtual reality (VR) using a head-mounted display worn on a user's head. A head-mounted display is configured to display images on a display provided in front of the user's eyes. This allows a user wearing the head-mounted display to experience a realistic virtual reality space. As an optical system for such a head-mounted display, technology that applies an optical system including a holographic optical element is known.

[0003] Special Publication No. 2023-510478

[0004] An object of the embodiment is to provide a method for manufacturing an optical element for improving display quality.

[0005] According to one embodiment, a method for manufacturing an optical element includes disposing a photocurable resin between a first plane of a plano-convex lens and a second plane of a plano-concave lens, splitting light emitted from a light source into object light and reference light, irradiating the object light from the convex side of the plano-convex lens and irradiating the reference light from the concave side of the plano-concave lens, and curing the photocurable resin.

[0006] FIG. 1 is a perspective view showing an example of the appearance of a head-mounted display 1. FIG. 2 is a cross-sectional view showing an example of the configuration of a display device DSP. FIG. 3 is a diagram for explaining the optical action of the display device DSP shown in FIG. 2. FIG. 4 is a diagram for explaining the first reflecting surface RS1 and the curved surface shape. FIG. 5 is a diagram showing simulation results. FIG. 6 is a cross-sectional view showing another example of the configuration of the display device DSP. FIG. 7 is a diagram showing an example of a manufacturing apparatus 100 for manufacturing a holographic optical element HE. FIG. 8 is an enlarged view of the exposure optical system EX shown in FIG. 7. FIG. 9 is a diagram for explaining the state of the object beam OB passing through the plano-convex lens L1 and the reference beam RB passing through the plano-concave lens L2.

[0007] The present embodiment will be described below with reference to the drawings. The disclosure is merely an example, and appropriate modifications that a person skilled in the art can easily make while maintaining the gist of the invention are naturally included within the scope of the present invention. Furthermore, the drawings may be schematic in terms of the width, thickness, shape, etc. of each part compared to the actual embodiment for clarity of explanation, but these are merely examples and are not intended to limit the interpretation of the present invention. Furthermore, in this specification and each drawing, components that perform the same or similar functions as those described above with reference to the previous drawings are designated by the same reference numerals, and redundant detailed descriptions may be omitted as appropriate.

[0008] In addition, to facilitate understanding, the drawings depict, as necessary, mutually orthogonal X, Y, and Z axes. The direction along the X axis is referred to as the first direction X, the direction along the Y axis is referred to as the second direction Y, and the direction along the Z axis is referred to as the third direction Z. The first direction X and the second direction Y are directions parallel to the substrates that constitute the display device DSP, and the third direction Z corresponds to the thickness direction of the display device DSP. The plane defined by the X and Y axes is referred to as the X-Y plane, and viewing the X-Y plane is referred to as planar view.

[0009] 1 is a perspective view showing an example of the appearance of a head-mounted display 1. The head-mounted display 1 includes, for example, a display device DSPR for the right eye and a display device DSPL for the left eye. When a user wears the head-mounted display 1 on his or her head, the display device DSPR is disposed so as to be located in front of the user's right eye, and the display device DSPL is disposed so as to be located in front of the user's left eye. The display device DSPR has substantially the same configuration as the display device DSPL.

[0010] 2 is a cross-sectional view showing an example of the configuration of the display device DSP. The display device DSP described here can be applied to each of the above-mentioned display devices DSPR and DSPL.

[0011] The display device DSP includes a display module DM and an optical system 4. The display module DM is configured to emit linearly polarized display light DL. The optical system 4 is configured to guide the display light DL from the display module DM to the user's eyes.

[0012] In one example, the display module DM comprises a display panel 2 and an illumination device 3. The display panel 2 is arranged between the illumination device 3 and an optical system 4. The illumination device 3 is arranged on the rear side of the display panel 2 and is configured to illuminate the display panel 2.

[0013] The configuration of the display module DM is not limited to the illustrated example. For example, the display module DM may be a display panel equipped with self-luminous light-emitting elements such as organic electroluminescence (EL) elements, micro LEDs, and mini LEDs. When the display module DM is a display panel equipped with light-emitting elements, the illumination device is omitted.

[0014] The display panel 2 is a transmissive liquid crystal panel formed in a flat plate shape. The display panel 2 includes a first substrate SUB1, a second substrate SUB2, a liquid crystal layer LC, a first polarizer PL1, and a second polarizer PL2. The liquid crystal layer LC is held between the first substrate SUB1 and the second substrate SUB2 in the third direction Z and sealed with a seal SE. The first polarizer PL1 is disposed between the illumination device 3 and the first substrate SUB1 in the third direction Z. The second polarizer PL2 is disposed between the second substrate SUB2 and the optical system 4 in the third direction Z. The surface of the second polarizer PL2 is referred to as a display surface DS. The display surface DS is, for example, parallel to the X-Y plane.

[0015] In the display panel 2, illumination light from the illumination device 3 is selectively modulated by the liquid crystal layer LC, transmitted through the second polarizer PL2, and converted into linearly polarized display light DL.

[0016] The optical system 4 includes a first structure 4A and a second structure 4B. The first structure 4A is spaced apart from the second structure 4B in the third direction Z. An air layer 4C is interposed between the first structure 4A and the second structure 4B. The display panel 2 is disposed between the lighting device 3 and the first structure 4A in the third direction Z. The first structure 4A is disposed between the display panel 2 and the second structure 4B (or between the display panel 2 and the air layer 4C) in the third direction Z.

[0017] The first structure 4A includes a first retardation plate R1 facing the display module DM, a holographic optical element HE facing the first retardation plate R1, and a second retardation plate R2 facing the holographic optical element HE. In one example, the first retardation plate R1, the holographic optical element HE, and the second retardation plate R2 are stacked in the third direction Z and bonded to one another.

[0018] The first retardation plate R1 and the second retardation plate R2 are quarter-wave plates that impart a quarter-wave phase difference to the light passing through them. The holographic optical element HE has an interference fringe pattern and a refractive index component with a period corresponding to the wavelength in the thickness direction. Such a holographic optical element HE is configured to reflect and diffract a portion of the incident light in a predetermined direction. The holographic optical element HE has a virtual first reflecting surface (Bragg surface) RS1.

[0019] The second structure 4B includes a reflective polarizer PR facing the second retardation plate R2. The reflective polarizer PR is spaced apart from the second retardation plate R2. An air layer 4C is interposed between the second retardation plate R2 and the reflective polarizer PR.

[0020] The reflective polarizer PR is curved convexly toward the holographic optical element HE and is configured to reflect a first linearly polarized light component of the incident light and transmit a second linearly polarized light component that is orthogonal to the first linearly polarized light component.

[0021] FIG. 3 is a diagram for explaining the optical action of the display device DSP shown in FIG.

[0022] First, the display module DM emits display light DL, which is first linearly polarized light LP1, from the display surface DS. Here, the first linearly polarized light LP1 is, for example, linearly polarized light that vibrates in a direction perpendicular to the paper surface. The display light DL passes through the first retardation plate R1 and is converted into first circularly polarized light CP1. Here, the first circularly polarized light CP1 is, for example, left-handed circularly polarized light.

[0023] Of the first circularly polarized light CP1 that has passed through the first retardation plate R1, a portion of the first circularly polarized light CP1 passes through the holographic optical element HE. The first circularly polarized light CP1 that has passed through the holographic optical element HE passes through the second retardation plate R2 and is converted into first linearly polarized light LP1.

[0024] The first linearly polarized light LP1 that has passed through the second retardation plate R2 is reflected by the reflective polarizer PR. The first linearly polarized light LP1 that has been reflected by the reflective polarizer PR is then passed through the second retardation plate R2 and converted into the first circularly polarized light CP1.

[0025] Of the first circularly polarized light CP1 that has passed through the second retardation plate R2, a portion of the first circularly polarized light CP1 is reflected by the holographic optical element HE. When the first circularly polarized light CP1 is reflected by the holographic optical element HE, the first circularly polarized light CP1 is converted into second circularly polarized light CP2. The second circularly polarized light CP2 is circularly polarized in the opposite direction to the first circularly polarized light CP1, and in this case, for example, is clockwise circularly polarized light.

[0026] The second circularly polarized light CP2 reflected by the holographic optical element HE is transmitted through the second retardation plate R2 and converted into second linearly polarized light LP2, which is, for example, linearly polarized light LP2 that vibrates in a direction parallel to the paper surface.

[0027] The second linearly polarized light LP2 transmitted through the second retardation plate R2 is transmitted through the reflective polarizer PR and is focused on the pupil E of the user through the lens action of the holographic optical element HE and the curved reflective polarizer PR.

[0028] Note that a portion of the light reflected by the holographic optical element HE and a portion of the light transmitted through the holographic optical element HE are absorbed in the display module DM, and almost none of them reach the pupil E.

[0029] Furthermore, the first linearly polarized light LP1 described with reference to FIG. 3 may be replaced with the second linearly polarized light LP2, and the first circularly polarized light CP1 may be replaced with the second circularly polarized light CP2.

[0030] In such a display device DSP, the optical system 4 has an optical path that passes three times between the holographic optical element HE and the reflective polarizer PR. That is, in the optical system 4, the optical distance between the holographic optical element HE and the reflective polarizer PR is approximately three times the actual distance between the holographic optical element HE and the reflective polarizer PR. As a result, when the display surface DS of the display module DM is treated as an object, the user can observe a magnified virtual image of an object formed at a distance via the optical system 4.

[0031] Next, the curved surface shapes of the first reflecting surface RS1 of the holographic optical element HE and the reflective polarizing plate PR will be described in more detail.

[0032] FIG. 4 is a diagram for explaining the first reflecting surface RS1 and the curved surface shape.

[0033] In Fig. 4, of the normal lines to the display surface DS, the normal line passing through the center Eo of the pupil is defined as the optical axis Op. The optical axis Op is parallel to the third direction Z shown in Fig. 2 and other figures. The point at which the display surface DS intersects with the optical axis Op is referred to as the reference point Rf. The point at which the holographic optical element HE intersects with the optical axis Op is referred to as the center Ho. The point at which the reflective polarizing plate PR intersects with the optical axis Op is referred to as the center Po.

[0034] The inclination angle and curved surface shape of the first reflecting surface RS1 will now be described. Note that the inclination angle in this specification is defined as the angle (acute angle) between the reflecting surface and a plane parallel to the display surface DS (the XY plane).

[0035] In the holographic optical element HE, the first reflecting surface RS1 is parallel to the display surface DS at the position where it intersects with the optical axis Op, and the tilt angle α1 is zero. The tilt angle α1 increases as it moves away from the center Ho. The tilt angles α1 of the first reflecting surfaces RS1 located at equal distances from the center Ho are equal. In this embodiment, the tilt angle α1 is defined as a fifth-order odd function of the radius r from the center Ho. In other words, the following relational expression (1) holds: α1=A1*r+A3*r ３ +A5*r ５ ...(1) Here, examples of A1, A3, and A5 are shown in the drawing.

[0036] In the reflective polarizing plate PR, the inclination angle of the curved surface shape is defined as the angle (acute angle) between the tangent of the curved reflective polarizing plate PR and the plane (X-Y plane) parallel to the display surface DS. The inclination angle of the curved surface shape increases as it moves away from the center Po. The inclination angle is the same at positions equidistant from the center Po. In this embodiment, the curved surface shape S is defined as a sixth-order even function of the radius r from the center Po. In other words, the following relational expression (2) holds: S=T+C2*r ２ +C4*r ４ +C6*r ６ ...(2) where T is the distance along the optical axis Op from the reference point rf to the center Po, and examples of C2, C4, and C6 are shown in the drawing.

[0037] The figure shows one of the principal rays PB that reach the center Eo of the pupil out of the light emitted from the display surface DS of the display module DM. The angle between the optical axis Op and the principal ray PB is defined as θ.

[0038] Here, a plane (for example, the XZ plane) that includes the optical axis Op and the principal ray PB is called a meridian plane, and a plane that is perpendicular to the meridian plane and that includes the principal ray PB is called a sagittal plane.

[0039] Next, the inventors performed a simulation using a ray tracing method to calculate the transverse aberration Δφx in the meridional plane and the transverse aberration Δφy in the sagittal plane.

[0040] FIG. 5 is a diagram showing the simulation results.

[0041] Simulations were performed for angles θ between the optical axis Op and the chief ray PB of 0°, 10°, 20°, 30°, 40°, and 50°, and the results are shown in graphs. In each graph, the horizontal axis represents the distances xp (mm) and yp (mm) from the center of the pupil to the point where each ray passes through the pupil plane, and the vertical axis represents the transverse aberrations Δφx and Δφy (arc-min).

[0042] In this simulation, the inclination angle α1 of the first reflecting surface RS1 is defined by the above relational expression (1), and the values ​​applied to A1, A3, and A5 are the values ​​shown in Fig. 4. The curved surface shape S is defined by the above relational expression (2), and the values ​​applied to C2, C4, and C6 are the values ​​shown in Fig. 4, and T is 9 mm.

[0043] According to the simulation results shown in the figure, assuming a pupil diameter of 3 mm, it was confirmed that all lateral aberrations were within ±1 when the distances xp and yp were in the range of −1.5 mm to +1.5 mm.

[0044] As described above, according to this embodiment, in the optical system 4 of the display device DSP, the tilt angle of the first reflecting surface RS1 included in the holographic optical element HE and the curved surface shape of the curved reflective polarizing plate PR are optimized, thereby mitigating the effects of aberration and improving the display quality.

[0045] The inventors also conducted a separate simulation for a comparative example. In this comparative example, the holographic optical element HE has a retroreflective surface, and an optical system equipped with a flat reflective polarizing plate is used. Simulations of this comparative example confirmed that the transverse aberration Δφx in the meridional plane increases as the angle θ increases. In particular, when the angle θ exceeds 10°, the transverse aberration Δφx exceeds 2 when the distance xp exceeds ±1 mm. On the other hand, the transverse aberration Δφy in the sagittal plane was approximately within ±1 regardless of the angle θ. Thus, in the comparative example, it was confirmed that the transverse aberration Δφx increases as the angle θ increases.

[0046] Next, another configuration example will be described.

[0047] 6 is a cross-sectional view showing another example of the configuration of the display device DSP. The display device DSP described here can be applied to each of the display devices DSPR and DSPL shown in FIG.

[0048] The configuration example shown in Fig. 6 differs from the configuration example shown in Fig. 2 in the optical system 4. The main differences will be described below. Note that the display module DM is the same as the configuration example shown in Fig. 2 and detailed description will be omitted, but it is configured to emit linearly polarized display light DL.

[0049] The optical system 4 includes a first structure 4A and a second structure 4B. The first structure 4A is spaced apart from the second structure 4B in the third direction Z. An air layer 4C is interposed between the first structure 4A and the second structure 4B.

[0050] The first structure 4A includes a first retardation plate R1 facing the display module DM, a holographic optical element HE facing the first retardation plate R1, and a second retardation plate R2 facing the holographic optical element HE.

[0051] The second structure 4B includes a reflective polarizer PR facing the second retarder R2 and a lens element LS facing the reflective polarizer PR. The lens element LS is a plano-convex lens having a convex surface LSA in contact with the reflective polarizer PR and a flat surface LSB on the opposite side of the convex surface LSA. In one example, the reflective polarizer PR and the lens element LS are stacked in the third direction Z and bonded to each other. The reflective polarizer PR arranged on the convex surface LSA is curved convexly toward the holographic optical element HE. By being bonded to the convex surface LSA, the reflective polarizer PR is more likely to maintain its shape.

[0052] The optical action of the display device DSP having such a configuration example is substantially the same as that of the example shown in FIG. 2, and therefore a description thereof will be omitted.

[0053] In each of the above configuration examples, various anti-reflection layers may be applied in order to suppress undesired reflection on the surface of the optical element.

[0054] Next, a method for manufacturing the above-mentioned holographic optical element HE will be described.

[0055] FIG. 7 is a diagram showing an example of a manufacturing apparatus 100 for manufacturing the holographic optical element HE.

[0056] The manufacturing apparatus 100 includes a light source 101, a magnifying optical system 102, a beam splitter 103, a plurality of mirrors 104, 105, and 106, and an exposure optical system EX.

[0057] The light source 101 is a monochromatic light source and is configured to emit, for example, a laser beam of a specific wavelength. The light source 101 may be, for example, a red laser light source, a green laser light source, or a blue laser light source. Furthermore, the light source 101 may include all of the red laser light source, the green laser light source, and the blue laser light source as multiple light sources. It is desirable that the wavelength of the light source applied here matches the wavelength of the light source applied to the above-mentioned lighting device 3.

[0058] The magnifying optical system 102 includes a plurality of lenses and is configured to expand the beam diameter of the laser beam emitted from the light source 101 and collimate it.

[0059] The beam splitter 103 splits the laser beam transmitted through the magnifying optical system 102 into a reference beam and an object beam, and may be a half mirror or a polarizing beam splitter. For example, the object beam is guided to the exposure optical system EX, and the reference beam is guided to the exposure optical system EX via multiple mirrors 104, 105, and 106.

[0060] FIG. 8 is an enlarged view of the exposure optical system EX shown in FIG.

[0061] The exposure optical system EX includes a plano-convex lens L1 and a plano-concave lens L2. The plano-convex lens L1 has a first flat surface LF1 and a convex surface LC1 facing the first flat surface LF1. The plano-concave lens L2 has a second flat surface LF2 and a concave surface LC2 facing the second flat surface LF2. The plano-convex lens L1 and the plano-concave lens L2 are arranged such that the first flat surface LF1 and the second flat surface LF2 face each other.

[0062] In this exposure optical system EX, the photocurable resin PM coated on the support SP is positioned between the first plane LF1 and the second plane LF2. Meanwhile, as described with reference to FIG. 7 , the reference beam RB and the object beam OB split by the beam splitter 103 are each guided to the exposure optical system EX. The object beam OB is irradiated from the convex surface LC1 of the plano-convex lens L1, and the reference beam RB is irradiated from the concave surface LC2 of the plano-concave lens L2. This records an interference fringe pattern between the object beam OB and the reference beam RB in the photocurable resin PM. The photocurable resin PM then hardens as it is irradiated with these beams. In this manner, a holographic optical element HE can be obtained.

[0063] FIG. 9 is a diagram for explaining the state of the object beam OB passing through the plano-convex lens L1 and the state of the reference beam RB passing through the plano-concave lens L2.

[0064] In the plano-convex lens L1, the intersection of the optical axis Op and the convex surface LC1 is called the first center O1. The shape of the convex surface LC1 is an aspheric surface defined by a 12th-order even function of the radius r from the first center O1.

[0065] In the plano-concave lens L2, the intersection of the optical axis Op and the concave surface LC2 is referred to as the second center O2. The shape of the concave surface LC2 is an aspheric surface defined by a 12th-order even function of the radius r from the second center O2.

[0066] As shown in the figure, the object beam OB is refracted by the convex surface LC1, and the reference beam RB is refracted by the concave surface LC2. The trajectory of the reference beam RB refracted by the concave surface LC2 approximately coincides with the trajectory of the light that is reflected by the reflective polarizing plate PR shown in Figure 3 and then enters the holographic optical element HE. Also, the trajectory of the object beam OB refracted by the convex surface LC1 approximately coincides with the trajectory of the light that is reflected by the holographic optical element HE shown in Figure 3. In other words, by recording the interference fringes of the reference beam RB and the object beam OB in the photocurable resin PM, a holographic optical element HE having a first reflecting surface RS1 inclined at the above-mentioned inclination angle α1 can be obtained.

[0067] As described above, according to this embodiment, it is possible to provide a method for manufacturing an optical element for improving display quality.

[0068] Although several embodiments of the present invention have been described, these embodiments are presented as examples and are not intended to limit the scope of the invention. These novel embodiments can be embodied in various other forms, and various omissions, substitutions, and modifications can be made without departing from the spirit of the invention. These embodiments and their modifications are included within the scope and spirit of the invention, and are also included in the inventions and their equivalents as defined in the claims.

[0069] DM...display module 4...optical system HE...holographic optical element RS1...first reflecting surface PR...reflective polarizing plate LS...lens element R1...first retardation plate R2...second retardation plate 100...manufacturing apparatus EX...exposure optical system L1...plano-convex lens LC1...convex surface LF1...first plane L2...plano-concave lens LC2...concave surface LF2...second plane

Claims

1. A method for manufacturing an optical element, comprising: placing a photocurable resin between a first flat surface of a plano-convex lens and a second flat surface of a plano-concave lens; splitting light emitted from a light source into object light and reference light; irradiating the convex surface of the plano-convex lens with the object light and the concave surface of the plano-concave lens with the reference light, thereby curing the photocurable resin.

2. The method for manufacturing an optical element according to claim 1, wherein the object light is refracted at the convex surface, which is an aspherical surface, when the object light is irradiated.

3. The method for manufacturing an optical element according to claim 2, wherein the reference light is refracted on an aspherical surface when irradiating the reference light.

Images