Holographic optical element and method of manufacturing the same

Abstract

An embodiment of the present invention provides a method for manufacturing a holographic optical element including a holographic grating, comprising the steps of: (a) applying a photosensitive resin to one side of a substrate to form a photosensitive substrate; and (b) irradiating laser light onto each of the one side and the other side of the photosensitive substrate to record a holographic grating, wherein the step (a) applies the photosensitive resin so that the height of the applied layer of the photosensitive resin varies along a predetermined direction.

Description

[Technical Field]

[0001] This invention claims the benefit of the filing date of Korean Patent Application No. 10-2019-0121206, filed with the Korean Intellectual Property Office on September 30, 2019, the entire contents of which are incorporated herein by reference. The present invention relates to a holographic optical element and a method for manufacturing the same. [Background technology]

[0002] Recently, as interest in display devices that realize augmented reality (AR), mixed reality (MR), or virtual reality (VR) has grown, research into such display devices has become active. Display units that realize augmented reality, mixed reality, or virtual reality include diffractive light guide plates that utilize the diffraction phenomenon based on the wave properties of light.

[0003] Such diffractive light guide plates are mainly of the type that includes a plurality of diffractive optical elements having a plurality of concave-convex grating patterns, and of the type that includes a transmission holographic optical element in which a holographic grating pattern is recorded in a photosensitive material.

[0004] FIG. 1 is a diagram schematically illustrating one embodiment of a diffractive light guide plate including a transmission type holographic optical element.

[0005] The diffractive light guide plate 1 includes a light guide plate 2 that guides light L provided from an external light source (not shown) or another region of the light guide plate 2 from one side A to the other side B by internal reflection, and a holographic optical element 3 that is provided on one surface 2a of the light guide plate 2 and directs a portion La of the light guided inside the light guide plate 2 in different directions by diffraction.

[0006] The holographic optical element 3 is provided by recording a plurality of holographic gratings 3a on both sides of a photosensitive substrate coated with a photosensitive material by irradiating laser light on both sides of the substrate.

[0007] 1, the multiple holographic gratings 3a in the diffractive light guide plate 1 are all configured to have the same width, but generally, the diffraction efficiency of light by the holographic gratings 3a tends to be proportional to the width of the grating patterns 3a. Here, the diffraction efficiency is defined as the ratio of diffracted light La to light L that reaches the holographic optical element 3.

[0008] Meanwhile, the amount of light guided inside the light guide plate 2 decreases from one side A to the other side B due to diffracted light La being directed in different directions and lost due to diffraction through the holographic optical element 3. If the light diffraction efficiency of each holographic grating 3a were the same, the amount of light reaching the holographic grating 3a would decrease from one side A to the other side B, but because the diffraction efficiencies are all the same, the amount of diffracted light La also inevitably decreases from one side A to the other side B. In other words, there is a problem in that the uniformity of diffracted light La diffracted by the holographic grating 3a decreases due to the display.

[0009] FIG. 2 is a diagram schematically illustrating another form of a diffractive light guide plate including a transmission type holographic optical element.

[0010] To address the problem of reduced uniformity of diffracted light La in the diffraction light guide plate 1 of one embodiment described above, a diffraction light guide plate 1' of another embodiment is configured such that the width of the plurality of holographic gratings 3a' increases from one side A to the other side B. As a result, the diffraction efficiency of the holographic gratings 3a' increases from one side A to the other side B. Although the amount of light reaching the holographic gratings 3a' decreases from one side A to the other side B, the diffraction efficiency gradually improves, so that the amount of diffracted light La' can be substantially the same from one side A to the other side B.

[0011] Meanwhile, in order to form a holographic optical element 3' in which the width of the grating pattern 3a' increases from one side A to the other side B as shown in FIG. 2, the following laser beam recording process is generally used.

[0012] FIG. 3 is a diagram simply illustrating an example of a laser light recording process for producing a transmission type holographic optical element.

[0013] First, a photosensitive substrate 30 is prepared, with a photosensitive resin 32 applied to one surface of the substrate 31. For example, the substrate 31 is provided as a film type that can be attached to a light guide plate later. In another example, the substrate 31 may be provided directly as a light guide plate that can guide light.

[0014] A holographic grating is recorded by irradiating one surface 30a and the other surface 30b of the photosensitive substrate 30 with laser beams L1 and L2, respectively. In order to increase the width of the holographic grating from one side A to the other side B of the photosensitive substrate 30, it is necessary to increase the light intensity and / or irradiation time of the laser beams L1 and L2 from one side A to the other side B. However, this process of increasing the light intensity and / or irradiation time of the laser beams L1 and L2 for each position is complicated, and it is difficult to continuously modulate the light intensity and / or irradiation time according to the position.

[0015] The above-mentioned background art is technical information that the inventor possesses for the purpose of deriving the embodiments of the present invention or that he / she acquired in the process of deriving the embodiments of the present invention, and is not necessarily publicly known art that was disclosed to the general public prior to the filing of the embodiments of the present invention. Summary of the Invention [Problem to be solved by the invention]

[0016] SUMMARY OF THE INVENTION An object of the present invention is to provide a holographic optical element having a holographic grating whose height varies depending on the position, and a method for easily manufacturing the same.

[0017] However, the problems to be solved by the present invention are not limited to those described above, and other problems not described will be clearly understood by those skilled in the art from the following description. [Means for solving the problem]

[0018] An embodiment of the present invention provides a method for manufacturing a holographic optical element including a holographic grating, comprising the steps of: (a) applying a photosensitive resin to one side of a substrate to form a photosensitive substrate; and (b) irradiating laser light onto each of the one side and the other side of the photosensitive substrate to record a holographic grating, wherein the step (a) applies the photosensitive resin so that the height of the applied layer of the photosensitive resin varies along a predetermined direction.

[0019] In this embodiment, the photosensitive resin coating layer is formed so that its height gradually increases along a predetermined direction.

[0020] In this embodiment, the step (a) can spray the photosensitive resin onto one surface of the substrate at a plurality of positions, and the amount of the photosensitive resin sprayed can be different for each position.

[0021] In this embodiment, the step (a) includes: (a-1) immersing the substrate in a container containing the photosensitive resin; and (a-2) moving the substrate in one direction to remove (take out) the substrate from the container, and the step (a-2) can remove the substrate from the container by changing the moving speed of the substrate.

[0022] In this embodiment, the step (a) includes: (a-1) providing the photosensitive resin between the substrate and the auxiliary substrate; and (a-2) moving at least one of the substrate and the auxiliary substrate, and the step (a-2) can move at least one of the substrate and the auxiliary substrate by changing the relative moving speed of the other with respect to the substrate or the auxiliary substrate.

[0023] In this embodiment, the step (a) may be performed by providing the photosensitive resin in a state where one surface of the substrate is tilted relative to the ground, and then drying the photosensitive resin.

[0024] In another embodiment, there is provided a holographic optical element including a photosensitive resin coating layer formed on one side of a substrate and a plurality of holographic gratings recorded in the photosensitive resin coating layer, wherein the photosensitive resin coating layer is formed to have different heights along a predetermined direction, and the holographic gratings are formed to have different heights along the predetermined direction.

[0025] In another embodiment, the photosensitive resin coating layer is formed to have a height that gradually increases along a predetermined direction, and the holographic grating is formed to have a height that gradually increases along the predetermined direction.

[0026] In another embodiment, the holographic gratings are recorded over the entire height of the photosensitive resin coating, and the widths of the holographic gratings may be identical to each other. [Effects of the Invention]

[0027] According to the embodiment of the present invention, it is possible to easily form a holographic grating having different heights depending on the position.

[0028] Furthermore, according to an embodiment of the present invention, the photosensitive resin coating layer is made to have different heights along a predetermined direction, and a holographic grating is recorded in this photosensitive resin coating layer, thereby adjusting the diffraction efficiency of the holographic optical element.

[0029] Furthermore, when a holographic optical element according to an embodiment of the present invention is applied to a diffraction light guide plate, even if the amount of light reaching the holographic grating decreases from one side of the diffraction light guide plate to the other, if the diffraction efficiency of the holographic optical element is configured to gradually increase, the amount of diffracted light in the diffraction light guide plate can be substantially the same.

[0030] The effects of the present invention are not limited to those described above, and other effects not described will be clearly understood by those skilled in the art from the present specification and the accompanying drawings. [Brief explanation of the drawings]

[0031] [Figure 1] FIG. 1 is a diagram illustrating a configuration of a diffractive light guide plate including a transmissive holographic optical element. [Figure 2] 10A and 10B are diagrams illustrating another form of a diffractive light guide plate including a transmission type holographic optical element. [Figure 3] FIG. 1 is a diagram simply illustrating an example of a laser light recording process for manufacturing a transmission type holographic optical element. [Figure 4] 1 is a diagram illustrating an example of a diffractive light guide plate including a transmissive holographic optical element according to an embodiment of the present invention; [Figure 5] 1A to 1C are diagrams illustrating a method for manufacturing a holographic optical element according to an embodiment of the present invention. [Figure 6] 1A to 1C are diagrams illustrating a method for manufacturing a holographic optical element according to an embodiment of the present invention. [Figure 7] 1A to 1C are diagrams illustrating a method for manufacturing a holographic optical element according to an embodiment of the present invention. [Figure 8] 3A to 3C are diagrams schematically illustrating a method for forming a photosensitive resin coating layer on one surface of a substrate according to a first embodiment. [Figure 9] 5A to 5C are diagrams schematically illustrating a method for forming a photosensitive resin coating layer on one surface of a substrate according to a second embodiment. [Figure 10] 10A to 10C are diagrams schematically illustrating a method for forming a photosensitive resin coating layer on one surface of a substrate according to a third embodiment. [Figure 11] 10A to 10C are diagrams schematically illustrating a method for forming a photosensitive resin coating layer on one surface of a substrate according to a fourth embodiment. [Figure 12] 1 is a graph comparing the diffraction efficiencies of an example of the present invention and a comparative example. [Figure 13] 1 is a graph comparing the light amounts of an example of the present invention and a comparative example. DETAILED DESCRIPTION OF THE INVENTION

[0032] The present invention will become clearer with reference to the following detailed embodiments in conjunction with the accompanying drawings. However, the present invention is not limited to the embodiments disclosed below, and may be embodied in various different forms. These embodiments are provided solely to complete the disclosure of the present invention and to fully convey the scope of the invention to those skilled in the art. The present invention is defined solely by the scope of the claims.

[0033] Meanwhile, the terms used in this specification are intended to describe the embodiments and are not intended to limit the present invention. In this specification, the singular form includes the plural form unless otherwise specified in the text. When used in this specification, the terms "comprises" and / or "comprising" mean that a referenced component, step, operation, and / or element does not exclude the presence or addition of one or more other components, steps, operations, and / or elements. Terms such as "first," "second," etc. are used to describe various components, but the components should not be limited by the terms. Terms are used only to distinguish one component from another.

[0034] FIG. 4 is a diagram schematically illustrating one form of a diffractive light guide plate including a transmission type holographic optical element according to an embodiment of the present invention.

[0035] A diffractive light guide plate 10 according to an embodiment of the present invention may include a light guide plate 11 and a holographic optical element 12 provided on one surface 11 a of the light guide plate 11 .

[0036] The holographic optical element 12 is provided by recording a plurality of holographic gratings 12a on both sides of a photosensitive resin coating layer 12b by irradiating laser light onto the both sides of the layer.

[0037] The photosensitive resin coating layer 12b of the holographic optical element 12 is configured so that its height increases from one side A to the other side B. As shown in FIG. 4, the holographic grating 12a is recorded over the entire height of the photosensitive resin coating layer 12b, so that the holographic grating 12a, like the photosensitive resin coating layer 12b, also increases in height from one side A to the other side B.

[0038] 4 is configured so that the height of the plurality of holographic gratings 12a increases from one side A to the other side B, and the diffraction efficiency of light diffracted by the holographic gratings 12a can increase as the height of the holographic gratings 12a increases. Therefore, even though the amount of light reaching the holographic gratings 12a decreases from one side A to the other side B, the diffraction efficiency gradually increases, so that the amount of diffracted light La'' can be substantially the same whether it is from one side A to the other side B.

[0039] A method for manufacturing a holographic optical element according to an embodiment of the present invention is a method for manufacturing a holographic optical element having a plurality of holographic gratings with different heights depending on the position. For example, the holographic optical element manufactured according to this embodiment is configured such that the heights of the plurality of holographic gratings 12a increase from one side A to the other side B, as shown in FIG.

[0040] 5 to 7 are diagrams illustrating a method for manufacturing a holographic optical element according to an embodiment of the present invention.

[0041] A method for manufacturing a holographic optical element according to one embodiment of the present invention may include the steps of: (a) forming a photosensitive substrate by applying a photosensitive resin to one side of a substrate; and (b) irradiating laser light onto one side and the other side of the photosensitive substrate, respectively, to record a holographic grating.

[0042] Step (a) is a step of forming a photosensitive substrate 50 including a photosensitive resin coating layer 52 by coating one surface of a substrate 51 with a photosensitive resin to form a photosensitive resin coating layer 52. For example, the substrate 51 is provided as a film type that can be later attached to a light guide plate. Alternatively, the substrate 51 may be directly provided as a light guide plate capable of guiding light. When the substrate 51 is a light guide plate, a glass substrate or a plastic substrate having high refractive index is used. Examples of the photosensitive resin include photopolymer, photoresist, silver halide emulsion, dichromated gelatin, photographic emulsion, photothermoplastic, and photorefractive materials.

[0043] Here, in step (a), the photosensitive resin 52' may be applied so that the height of the photosensitive resin coating layer 52 varies along a predetermined direction. As shown in Fig. 5, the photosensitive resin coating layer 52 may be formed so that the height h' of the continuously formed photosensitive resin coating layer 52 gradually increases from one side C to the other side D.

[0044] 6 and 7, step (b) is a step of irradiating laser beams L1 and L2 onto one surface 50a and the other surface 50b of the photosensitive substrate 50, respectively, to record a holographic grating 61a. Referring to Fig. 6, laser beams L1 and L2 are irradiated onto one surface 50a and the other surface 50b of the photosensitive substrate 50, which has a configuration in which the height h' of the resin coating layer 52 increases from one side C to the other side D of the configuration shown in Fig. 5. Here, the first laser beam L1 and the second laser beam L2 irradiated onto the one surface 50a and the other surface 50b of the photosensitive substrate 50 have the same light intensity and / or irradiation time depending on the position for each type of laser beam, thereby forming holographic gratings 61a with substantially the same width, as shown in Fig. 7. Meanwhile, since the height of the photosensitive resin coating layer 52 is configured to increase from one side C to the other side D, it is possible to manufacture a holographic optical element 61 in which the height of the holographic grating 61a recorded in the photosensitive resin coating layer 52 also increases from one side C to the other side D. Here, the height of the holographic grating 61a may refer to the height from the bottom surface of the gap between the holographic gratings 61a to the top surface of the holographic grating 61a. The bottom surface between the holographic gratings 61a may be at the same height as one surface of the substrate 51. Therefore, the holographic gratings 61a are formed to have different heights from one surface of the substrate 51.

[0045] FIG. 8 is a diagram schematically illustrating a method for forming a photosensitive resin coating layer on one surface of a substrate according to the first embodiment.

[0046] 8, in step (a), photosensitive resin 52' is sprayed onto one surface of substrate 51 at a plurality of positions, and the amount of photosensitive resin 52' sprayed can be varied for each position. In this case, a plurality of spraying devices 80 can be arranged, and the amount of photosensitive resin sprayed by each spraying device 80 can be controlled to be different. Even if only one spraying device 80 is used, the amount of photosensitive resin sprayed by each spraying device 80 can be controlled to be different for each position while moving spraying device 80 or substrate 51.

[0047] FIG. 9 is a diagram schematically illustrating a method for forming a photosensitive resin coating layer on one surface of a substrate according to the second embodiment.

[0048] Referring to FIG. 9, step (a) may include: (a-1) immersing the substrate 51 in a container 90 containing a photosensitive resin 52′ (see FIGS. 9(a) and 9(b)); and (a-2) moving the substrate 51 in one direction to remove it from the container 90 (see FIG. 9(c)). The photosensitive resin 52′ is provided in a solution state in the container 90. In step (a-2), the substrate 51 may be removed from the container 90 by changing the moving speed of the substrate 51. For example, if the moving speed of the substrate 51 is gradually increased while removing the substrate 51 from the container 90, the height of the photosensitive resin coating layer 52 gradually decreases from the upper portion 51u to the lower portion 51d of the substrate 51. Alternatively, if the moving speed of the substrate 51 is gradually decreased while removing the substrate 51 from the container 90, the height of the photosensitive resin coating layer 52 gradually increases from the upper portion 51u to the lower portion 51d of the substrate 51.

[0049] FIG. 10 is a diagram schematically showing a method for forming a photosensitive resin coating layer on one surface of a substrate according to the third embodiment.

[0050] 10, step (a) may include (a-1) providing a photosensitive resin between the substrate 51 and the auxiliary substrate 100, and (a-2) moving at least one of the substrate 51 and the auxiliary substrate 100. Here, the photosensitive resin 52' is provided in a solution state between the substrate 51 and the auxiliary substrate 100. Here, step (a-2) may move at least one of the substrate 51 and the auxiliary substrate 100 by changing the relative movement speed of one of the substrate 51 and the auxiliary substrate 100 with respect to the other. For example, by increasing the relative movement speed of the substrate 51 and the auxiliary substrate 100, the height of the photosensitive resin coating layer 52 on the substrate 51 gradually decreases along the movement direction of the auxiliary substrate 100. As another example, by decreasing the relative movement speed of the substrate 51 and the auxiliary substrate 100, the height of the photosensitive resin coating layer 52 on the substrate 51 gradually increases along the movement direction of the auxiliary substrate 100.

[0051] The method of forming the photosensitive resin coating layer 52 on one surface of the substrate 51 according to the third embodiment as described above is easy to organize and control the auxiliary substrate 100 and the mechanism for moving the auxiliary substrate 100 relative to the substrate 51, and may be suitable as a process for mass production.

[0052] FIG. 11 is a diagram schematically showing a method for forming a photosensitive resin coating layer on one surface of a substrate according to the fourth embodiment.

[0053] 11, in step (a), a photosensitive resin 52' is provided with one surface 51a of the substrate 51 tilted relative to the ground E, and the photosensitive resin can be dried by changing the tilt of the one surface 51a of the substrate 51 relative to the ground E. First, when the solution of the photosensitive resin 52' is cast with the one surface 51a of the substrate 51 tilted relative to the ground E, the upper surface of the photosensitive resin 52' can be maintained parallel to the ground E, as shown in FIG. 11(a). At this time, because the one surface 51a of the substrate 51 is tilted relative to the ground E, the distance between the one surface 51a of the substrate 51 and the upper surface of the photosensitive resin 52' may gradually increase from one side C to the other side D. When the photosensitive resin 52' is dried in this state, a photosensitive resin coating layer 52 is formed in which the distance between the one surface 51a of the substrate 51 and the upper surface of the photosensitive resin 52' gradually increases from one side C to the other side D. As shown in FIG. 11(b), when one surface 51a of the substrate 51 is aligned parallel to the ground surface E, the photosensitive resin coating layer 52 assumes a shape in which its height increases from one side C of the substrate 51 to the other side D.

[0054] According to the embodiment of the present invention, it is possible to easily form a holographic grating having different heights depending on the position. [Example]

[0055] FIG. 12 is a graph comparing the diffraction efficiency of an example of the present invention and a comparative example.

[0056] To achieve this, a holographic grating was recorded by irradiating both sides of the photosensitive resin coating layer with laser light. A laser beam with a wavelength of 532 nm and an output of 250 mW was used, and the reference light and object light irradiated onto the photosensitive resin coating layer had the same power of 2 mW so that the beam ratio (BR) was 1. The laser beam was incident on the photosensitive resin coating layer at angles of 0 degrees and 60 degrees, respectively, to record the holographic grating, and the recording time was the same, 10 seconds.

[0057] In this case, in Example 1, a photosensitive substrate configured so that the height of the photosensitive resin coating layer increases according to an embodiment of the present invention was used, and in Comparative Example 1, a photosensitive substrate in which the height of the photosensitive resin coating layer is constant was used.

[0058] For the holographic optical elements of Example 1 and Comparative Example 1, the intensities of diffracted light and transmitted light were measured at four measurement positions (#1 to #4) at regular intervals from one side to the other. The intensities of diffracted light and transmitted light were obtained by measuring the amount of light equivalent to 532 nm using a power meter.

[0059] Using the intensities of the diffracted light and the transmitted light, the relative diffraction efficiency according to the height of the photosensitive resin coating layer, that is, the height of the holographic grating, was determined using the following formula.

[0060] <expression>

[0061] Relative diffraction efficiency = {diffracted light intensity / (diffracted light intensity + transmitted light intensity)} x 100

[0062] Looking at Table 1 below, which compares the values ​​of the comparative example and the working example, it can be seen that in Working Example 1, where the height of the photosensitive resin coating layer changes depending on the measurement position, the diffraction efficiency changes depending on the height, and more specifically, it can be seen that the diffraction efficiency increases in proportion to the height. In contrast, in Comparative Example 1, where the height of the photosensitive resin coating layer is constant, the diffraction efficiency value remains at the same level with no substantial change depending on the height.

[0063] [Table 1]

[0064] The diffraction efficiency of the optical element can be adjusted according to the height of the photosensitive resin coating layer, in other words, the height of the recorded holographic grating, and this can be used to adjust the diffraction efficiency according to the area of ​​the holographic optical element.

[0065] Therefore, as in the diffraction light guide plate 10 shown in FIG. 4, by configuring the plurality of holographic gratings 12a so that their heights increase from one side A to the other side B, the diffraction efficiency of the holographic optical element 12 can be gradually increased. Even if the amount of light reaching the holographic optical element 12 decreases, the amount of diffracted light in the diffraction light guide plate 10 can be kept substantially the same.

[0066] FIG. 13 is a graph showing the difference in the amount of emitted light between the example of the present invention and the comparative example in the diffractive light guide plate described above.

[0067] In Example 2, a diffraction light guide plate was fabricated by recording a holographic grating on a photosensitive substrate configured with an increasing height of the photosensitive resin coating layer according to an embodiment of the present invention, and as shown in Figure 4, the light guide plate had a shape in which multiple holographic gratings were recorded, with the height increasing from one side to the other. In Comparative Example 2, a diffraction light guide plate was fabricated by recording multiple holographic gratings on a photosensitive resin coating layer of a constant height on the light guide plate, as shown in Figure 1. The method of recording the holographic gratings in Example 2 and Comparative Example 2 was the same as in Example 1 and Comparative Example 1, and the height of the photosensitive resin coating layer was configured to vary depending on the measurement position, as shown in the table below.

[0068] For the diffractive light guide plates of Example 2 and Comparative Example 2, six measurement positions (#1 to #6) were determined at regular intervals from one side to the other, and the height of the photosensitive resin coating layer and the amount of emitted light at each position were measured. The amount of emitted light was obtained by irradiating 532 nm light with an amount of 100 uW into the light guide plate and measuring the amount of emitted light that passed through the holographic optical element at each measurement position as the light traveled from one side of the light guide plate to the other. The height of the photosensitive resin coating layer and the amount of emitted light at each measurement position for Example 2 and Comparative Example 2 are shown in Table 2 below.

[0069] [Table 2]

[0070] 13, comparing Example 2 and Comparative Example 2, it can be seen that in Example 2, where the height of the photosensitive resin coating layer is gradually increased, the amount of emitted light remains substantially the same regardless of the measurement position. In contrast, when the height of the photosensitive resin coating layer is maintained constant, it can be seen that the amount of emitted light decreases rapidly from one side to the other.

[0071] Although the present invention has been described with reference to the preferred embodiment above, various modifications and variations can be made without departing from the spirit and scope of the invention, and therefore, the appended claims are intended to cover all such modifications and variations as fall within the spirit and scope of the invention. [Explanation of symbols]

[0072] 2a one side 3, 3a, 3a' Holographic optical element 11a One side 12 Holographic Optical Elements 12a Holographic grating 12b Photosensitive resin coating layer 30 Base material 30a one side 30b Other side 31 Base material 32 Photosensitive resin 50 Photosensitive substrate 50a One side 50b other side 51 Base material 51a one side 52 Resin coating layer 52' Photosensitive resin 61 Holographic Optical Elements 61a Holographic grating 90 containers 100 Auxiliary base material E Ground L light L1 laser light L2 laser light La Hikari

Claims

1. (a) applying a photosensitive resin to one side of a substrate to form a photosensitive substrate; (b) irradiating one surface and the other surface of the photosensitive substrate with laser light to record a holographic grating; The step (a) includes: applying the photosensitive resin in a predetermined direction so that the height of the applied layer of the photosensitive resin gradually increases; the holographic grating is recorded over the entire height from the bottom surface to the top surface of the photosensitive resin coating layer, and the widths of the holographic gratings are the same; the substrate is a film type that can be attached to the light guide plate, The step (a) includes: A method for manufacturing a transmission holographic optical element, in which photosensitive resin is supplied while one surface of the substrate is tilted with respect to the ground, and the upper surface of the photosensitive resin is held parallel to the ground, so that the height of the applied layer of photosensitive resin gradually increases along a predetermined direction due to gravity, and the photosensitive resin is dried in this state.

2. 2. The method for producing a transmission holographic optical element according to claim 1, wherein the photosensitive resin coating layer is formed so that its height gradually increases along a predetermined direction.

3. A transmission holographic optical element including a photosensitive resin coating layer formed on one surface of a substrate and a plurality of holographic gratings recorded in the photosensitive resin coating layer, the photosensitive resin coating layer is formed so as to gradually increase in height along a predetermined direction, the holographic grating is formed so as to gradually increase in height along the predetermined direction, the holographic gratings are recorded over the entire height from the bottom surface to the top surface of the photosensitive resin coating layer, and the widths of the holographic gratings are the same; The minimum height of the photosensitive resin coating layer is 5 um and the maximum height is 15 um; A transmission type holographic optical element, wherein the substrate is a film type that can be attached to a light guide plate.

4. the photosensitive resin coating layer is formed so as to gradually increase in height along the predetermined direction, 4. The transmission type holographic optical element according to claim 3, wherein the holographic grating is formed so as to gradually increase in height along the predetermined direction.

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