阅读说明：本技术 全息光学元件及其制造方法 (Holographic optical element and method for manufacturing the same ) 是由 金成妍 宋民守 秋素英 黄惠垣 于 2020-09-24 设计创作，主要内容包括：本公开内容的一个实施方案提供了全息光学元件和包括全息光栅的全息光学元件的制造方法,所述制造方法包括：通过用光敏树脂涂覆基底的一个表面来形成光敏基底的步骤(a)；以及通过用激光照射光敏基底的一个表面和另一个表面中的每一者来记录全息光栅的步骤(b),其中在步骤(a)中,施加光敏树脂使得光敏树脂涂层的高度沿预定方向变化。(One embodiment of the present disclosure provides a holographic optical element and a method of manufacturing a holographic optical element including a holographic grating, the method of manufacturing including: a step (a) of forming a photosensitive substrate by coating one surface of a substrate with a photosensitive resin; and a step (b) of recording a holographic grating by irradiating each of one surface and the other surface of the photosensitive substrate with laser light, wherein in the step (a), the photosensitive resin is applied such that a height of the photosensitive resin coating layer varies in a predetermined direction.)

1. A method of manufacturing a holographic optical element comprising a holographic grating, the method of manufacturing comprising:

a step (a) of forming a photosensitive substrate by coating one surface of a substrate with a photosensitive resin; and

a step (b) of recording the holographic grating by irradiating each of one surface and the other surface of the photosensitive substrate with laser light,

wherein in the step (a), the photosensitive resin is applied such that the height of the photosensitive resin coating layer is varied in a predetermined direction.

2. The manufacturing method according to claim 1, wherein a height of the photosensitive resin coating layer gradually increases in the predetermined direction.

3. The manufacturing method according to claim 1, wherein in the step (a), the photosensitive resin is sprayed to a plurality of positions on one surface of the substrate, and an amount of the photosensitive resin sprayed varies depending on the positions.

4. The manufacturing method according to claim 1, wherein the step (a) includes:

a step (a-1) of immersing the substrate in a container containing the photosensitive resin; and

a step (a-2) of separating the substrate from the container by moving the substrate in one direction, and

in the step (a-2), the substrate is separated from the container while varying the moving speed of the substrate.

5. The manufacturing method according to claim 1, wherein the step (a) includes:

a step (a-1) of providing the photosensitive resin between the substrate and an auxiliary substrate; and

a step (a-2) of moving at least one of the substrate and the auxiliary substrate, and

in the step (a-2), at least one of the substrate and the auxiliary substrate is moved while changing a relative moving speed of one of the substrate and the auxiliary substrate with respect to the other.

6. The manufacturing method according to claim 1, wherein in the step (a), the photosensitive resin is provided in a state where one surface of the substrate is inclined with respect to a base surface, and the photosensitive resin is dried.

7. A holographic optical element includes 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,

wherein a height of the photosensitive resin coating varies along a predetermined direction, and a height of the holographic grating varies along the predetermined direction.

8. The holographic optical element of claim 7, wherein a height of the photosensitive resin coating gradually increases along the predetermined direction, and a height of the holographic grating gradually increases along the predetermined direction.

9. The holographic optical element of claim 7, wherein the holographic grating is recorded over an entire height of the photosensitive resin coating, and the holographic gratings have the same width.

Technical Field

The present disclosure claims priority and benefit of korean patent application No. 10-2019-0121206, filed on 30.9.2019 to the korean intellectual property office, the entire contents of which are incorporated herein by reference. The present disclosure relates to a holographic optical element and a method of manufacturing the same.

Background

Recently, as interest in a display device implementing Augmented Reality (AR), Mixed Reality (MR), or Virtual Reality (VR) has increased, research on such a display device has been actively conducted. Display units implementing AR, MR, or VR include diffractive light guide plates that utilize diffraction phenomena based on wave-like properties of light.

As such a diffractive light guide plate, a type including a plurality of diffractive optical elements having a plurality of embossed grating patterns and a type including a transmissive hologram optical element in which a hologram grating pattern is recorded in a photosensitive material may be mainly used.

Fig. 1 is a diagram schematically illustrating one embodiment of a diffractive light guide plate including a transmissive holographic optical element.

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 hologram optical element 3 which is provided on one surface 2a of the light guide plate 2 and which orients a part La of the light guided in the light guide plate 2 toward another direction by diffraction.

The holographic optical element 3 may be provided by recording a plurality of holographic gratings 3a by laser interference on the opposite surface of a photosensitive substrate coated with a photosensitive material.

The plurality of hologram gratings 3a in the diffraction light guide 1 having the form shown in fig. 1 are all configured to have the same width. In general, the efficiency of light diffraction by the holographic grating 3a tends to be proportional to the width of the grating pattern 3 a. Here, the diffraction efficiency may be defined as a ratio of the diffracted light La to the light L reaching the hologram optical element 3.

Meanwhile, the amount of light guided in the light guide plate 2 decreases from one side a to the other side B due to diffracted light La that is oriented and lost in the other direction by diffraction via the hologram element 3. Here, when the efficiency of light diffraction by the hologram grating 3a is the same for all the corresponding hologram gratings 3a, the amount of light reaching the hologram grating 3a decreases from one side a to the other side B, but the diffraction efficiency is the same. Therefore, the amount of diffracted light La also necessarily decreases from one side a to the other side B. That is, uniformity of the diffracted light La diffracted by the hologram grating 3a for the display is deteriorated, which is problematic.

Fig. 2 is a diagram schematically illustrating another embodiment of a diffractive light guide plate including a transmissive holographic optical element.

In order to solve the problem of the deterioration of uniformity of the diffracted light La in the diffractive light guide plate 1 in the above-described embodiment, the diffractive light guide plate 1 'in another embodiment may be configured such that the width of each of the plurality of holographic gratings 3 a' increases from one side a to the other side B. By doing so, the diffraction efficiency of the holographic grating 3 a' increases from one side a to the other side B. In this case, since the diffraction efficiency increases even when the amount of light reaching the hologram grating 3a 'decreases from one side a to the other side B, the amount of diffracted light La' may be substantially uniform from one side a to the other side B.

Meanwhile, the following recording process using a laser may be generally used to form the hologram optical element 3 in which the width of the grating pattern 3 a' increases from one side a to the other side B as shown in fig. 2.

Fig. 3 is a diagram schematically showing one example of a recording process using a laser for manufacturing a transmissive holographic optical element.

First, a photosensitive substrate 30 in which one surface of a substrate 31 is coated with a photosensitive resin 32 is prepared. As an example, the substrate 30 may be a film type that may be later attached to a light guide plate. As another example, the substrate 30 may also be provided as a light guide plate itself that can guide light.

Then, one surface 30a and the other surface 30b of the photosensitive substrate 30 are irradiated with laser rays L1 and L2, respectively, to record a holographic grating. Here, in order to increase the width of the hologram grating from one side a to the other side B, it is necessary to increase the amount of light and/or the irradiation time of the laser lights L1 and L2 from one side a to the other side B of the photosensitive substrate 30. However, the process of increasing the amount of light and/or the irradiation time of the laser lights L1 and L2 for each position is complicated, and it is difficult to continuously change the amount of light and/or the irradiation time according to the position.

Since the above-described background art is technical information grasped by the present inventors for the purpose of obtaining the embodiments of the present disclosure or acquired in the course of obtaining the embodiments of the present disclosure, it may not necessarily be said that the background art is a well-known art disclosed to the general public before filing applications of the embodiments of the present disclosure.

Disclosure of Invention

Technical problem

Embodiments of the present disclosure are directed to providing a holographic optical element including a holographic grating having different heights according to positions, and a manufacturing method capable of easily forming the holographic optical element.

The technical problems of the present disclosure are not limited to the foregoing problems, and other problems not mentioned will be clearly understood from the following description by those skilled in the art.

Technical scheme

One embodiment of the present disclosure provides a method of manufacturing a holographic optical element including a holographic grating, the method of manufacturing including: a step (a) of forming a photosensitive substrate by coating one surface of a substrate with a photosensitive resin; and a step (b) of recording a holographic grating by irradiating each of one surface and the other surface of the photosensitive substrate with laser light, wherein in the step (a), the photosensitive resin is applied such that a height of the photosensitive resin coating layer varies in a predetermined direction.

In the present embodiment, the height of the photosensitive resin coating layer may gradually increase in a predetermined direction.

In the present embodiment, in the step (a), the photosensitive resin may be sprayed to a plurality of locations on one surface of the substrate, and the amount of the sprayed photosensitive resin may vary depending on the locations.

In this embodiment, step (a) may comprise: a step (a-1) of immersing the substrate in a container containing a photosensitive resin; and a step (a-2) of separating the substrate from the container by moving the substrate in one direction, and in the step (a-2), the substrate may be separated from the container while changing a moving speed of the substrate.

In this embodiment, step (a) may comprise: a step (a-1) of providing a photosensitive resin between a substrate and an auxiliary substrate; and a step (a-2) of moving at least one of the substrate and the auxiliary substrate, and in the step (a-2), at least one of the substrate and the auxiliary substrate may be moved while changing a relative moving speed of one of the substrate and the auxiliary substrate with respect to the other.

In the present embodiment, in the step (a), the photosensitive resin may be provided in a state where one surface of the substrate is inclined with respect to the base surface (ground), and the photosensitive resin may be dried.

Another embodiment provides a holographic optical element including a photosensitive resin coating formed on one surface of a substrate and a plurality of holographic gratings recorded in the photosensitive resin coating, wherein a height of the photosensitive resin coating varies in a predetermined direction, and a height of the holographic gratings varies in the predetermined direction.

In another embodiment, the height of the photosensitive resin coating may gradually increase in a predetermined direction, and the height of the holographic grating may gradually increase in the predetermined direction.

In another embodiment, the holographic grating may be recorded over the entire height of the photosensitive resin coating, and the holographic grating may have the same width.

Advantageous effects

According to one embodiment of the present disclosure, a holographic grating having different heights according to positions may be easily formed.

According to one embodiment of the present disclosure, the height of the photosensitive resin coating may vary in a predetermined direction, and the holographic grating may be recorded in the photosensitive resin coating, so that the diffraction efficiency of the holographic optical element may be adjusted.

Further, when the hologram optical element according to one embodiment of the present disclosure is applied to a diffractive light guide plate, in the case where the diffraction efficiency of the hologram optical element increases even when the amount of light reaching the hologram grating decreases from one side of the diffractive light guide plate to the other side, the amount of diffracted light at the diffractive light guide plate may be substantially uniform.

Effects of the present disclosure are not limited to those described above, and those not mentioned can be clearly understood from the present specification and the drawings by those skilled in the art.

Drawings

Fig. 1 is a diagram schematically illustrating one embodiment of a diffractive light guide plate including a transmissive holographic optical element.

Fig. 2 is a diagram schematically illustrating another embodiment of a diffractive light guide plate including a transmissive holographic optical element.

Fig. 3 is a diagram schematically showing one example of a recording process using a laser for manufacturing a transmissive holographic optical element.

Fig. 4 is a diagram schematically illustrating a diffractive light guide plate including a transmissive holographic optical element according to one embodiment of the present disclosure.

Fig. 5 to 7 are diagrams for describing a method of manufacturing a holographic optical element according to an embodiment of the present disclosure.

Fig. 8 is a view schematically showing a method of forming a photosensitive resin coating layer on one surface of a substrate according to a first embodiment.

Fig. 9 is a view schematically showing a method of forming a photosensitive resin coating layer on one surface of a substrate according to a second embodiment.

Fig. 10 is a view schematically showing a method of forming a photosensitive resin coating layer on one surface of a substrate according to a third embodiment.

Fig. 11 is a view schematically showing a method of forming a photosensitive resin coating layer on one surface of a substrate according to a fourth embodiment.

Fig. 12 is a graph illustrating a comparison of diffraction efficiencies between an embodiment and a comparative example according to the present disclosure.

Fig. 13 is a graph illustrating a comparison of the amount of light between an embodiment and a comparative example according to the present disclosure.

Detailed Description

The present disclosure will become apparent from the detailed description of embodiments and the accompanying drawings. However, the present disclosure is not limited to the embodiments described below, but may be implemented in various different forms, which are provided only for completeness of the present disclosure and for comprehension of the scope of the present disclosure to those skilled in the art, and the present disclosure will be defined by the scope of the claims.

Meanwhile, the terms used in the present specification are used to illustrate the embodiments, not to limit the present disclosure. In this specification, the singular forms include the plural forms unless the context clearly dictates otherwise. The components, steps, operations and/or elements referred to by the terms "comprising" and/or "including" as used in this specification do not preclude the presence or addition of one or more other components, steps, operations and/or elements. The terms "first," "second," and the like may be used to describe various components, but the components should not be construed as limited by these terms. These terms are only used to distinguish one component from another component.

Fig. 4 is a diagram schematically illustrating a diffractive light guide plate including a transmissive holographic optical element according to one embodiment of the present disclosure.

The diffractive light guide plate 10 according to one embodiment of the present disclosure may include a light guide plate 11 and a holographic optical element 12 disposed on one surface 11a of the light guide plate 11.

The hologram optical element 12 may be provided by recording a plurality of hologram gratings 12a on the opposite surface of the photosensitive resin coating 12b by laser interference.

As shown in fig. 4, the height of the photosensitive resin coating 12B of the hologram optical element 12 increases from one side a to the other side B, and the hologram grating 12a is recorded over the entire height of the photosensitive resin coating 12B. Therefore, similarly to the photosensitive resin coating 12B, the height of the holographic grating 12a may also increase from one side a to the other side B.

The heights of the plurality of holographic gratings 12a in the diffractive light guide plate 10 shown in fig. 4 increase from one side a to the other side B, and the efficiency of light diffraction by the holographic gratings 12a may increase as the heights of the holographic gratings 12a increase. Accordingly, since the diffraction efficiency gradually increases even when the amount of light reaching the hologram grating 12a decreases from one side a to the other side B, the amount of diffracted light La ″ may be substantially uniform from one side a to the other side B.

A manufacturing method of a holographic optical element according to one embodiment of the present disclosure is a method for manufacturing a holographic optical element in which a plurality of holographic gratings having different heights according to positions are formed. For example, in the holographic optical element manufactured in the present embodiment, as shown in fig. 4, the heights of the plurality of holographic gratings 12a may increase from one side a to the other side B.

Fig. 5 to 7 are diagrams for describing a method of manufacturing a holographic optical element according to an embodiment of the present disclosure.

A method of manufacturing a holographic optical element according to one embodiment of the present disclosure may include: a step (a) of forming a photosensitive substrate by coating one surface of a substrate with a photosensitive resin; and a step (b) of recording the holographic grating by irradiating each of the one surface and the other surface of the photosensitive substrate with laser light.

The step (a) may be a step of forming the photosensitive resin coating 52 by coating one surface of the substrate 51 with a photosensitive resin to form the photosensitive substrate 50 including the photosensitive resin coating 52. As an example, the substrate 51 may be a film type that may be attached to a light guide plate later. As another example, the substrate 51 may also be provided as a light guide plate itself that can guide light. In the case where the substrate 51 is a light guide plate, a glass substrate or a plastic substrate having a high refractive index characteristic may be used. Examples of the photosensitive resin may include a photopolymer, a photoresist, a silver halide emulsion, dichromated gelatin, a photographic emulsion, a photo-plastic material, and a photo-refractive material.

Here, in step (a), the photosensitive resin 52' may be applied such that the height of the photosensitive resin coating 52 varies in a predetermined direction. As shown in fig. 5, the photosensitive resin coating 52 may be formed such that the height h' of the continuously formed photosensitive resin coating 52 increases from one side C to the other side D.

Referring to fig. 6 and 7, the step (b) may be a step of irradiating one surface 50a and the other surface 50b of the photosensitive substrate 50 with laser rays L1 and L2, respectively, to record the holographic grating 61 a. Referring to fig. 6, one surface 50a and the other surface 50b of the photosensitive substrate 50 in which the height h' of the resin coating 52 increases from one side C to the other side D as shown in fig. 5 are irradiated with laser rays L1 and L2, respectively. Here, for the first laser light L1 and the second laser light L2 with which the one surface 50a and the other surface 50b of the photosensitive substrate 50 are irradiated, the amount of light and/or irradiation time according to the position may be the same for each type of laser light, thereby making the holographic grating 61a have substantially the same width as shown in fig. 10. Meanwhile, since the height of the photosensitive resin coating 52 increases from the one side C to the other side D, the hologram optical element 61 in which the height of the hologram grating 61a recorded in the photosensitive resin coating 51 increases from the one side C to the other side D can be manufactured. Here, the height of the holographic gratings 61a may mean a height from a bottom surface between the holographic gratings 61a to an upper surface of each holographic grating 61 a. Further, the bottom surface between the holographic gratings 61a may be flush with one surface of the substrate 51. Accordingly, the holographic grating 61a may be formed to have different heights from one surface of the substrate 51.

Fig. 8 is a view schematically showing a method of forming a photosensitive resin coating layer on one surface of a substrate according to a first embodiment.

Referring to fig. 8, in step (a), the photosensitive resin 52 'may be sprayed at a plurality of positions on one surface of the substrate 51, and the amount of the sprayed photosensitive resin 52' may vary according to the positions. In this case, a plurality of the spray devices 80 may be arranged and the amount of the photosensitive resin sprayed by each spray device 80 may be controlled to be different. Alternatively, when only one spray device 80 is used, the amount of the photosensitive resin sprayed by the spray device 80 may be controlled to be different according to the position by moving the spray device 80 or the substrate 51.

Fig. 9 is a view schematically showing a method of forming a photosensitive resin coating layer on one surface of a substrate according to a second embodiment.

Referring to fig. 9, step (a) may include: a step (a-1) of immersing the substrate 51 in a container 90 containing the photosensitive resin 52' (see (a) and (b) of fig. 9); and a step (a-2) of separating the substrate 51 from the container 90 by moving the substrate 51 in one direction (see (c) of fig. 9). Here, the photosensitive resin 52' in the container 90 may be in a liquid state. Here, in the step (a-2), the substrate 51 may be separated from the container 90 while changing the moving speed of the substrate 51. For example, in the case of gradually increasing the moving speed of the substrate 51 while separating the substrate 51 from the container 90, the height of the photosensitive resin coating 52 may be decreased from the upper portion 80u to the lower portion 80d of the substrate 51. As another example, in the case of gradually reducing the moving speed of the substrate 51 when separating the substrate 51 from the container 90, the height of the photosensitive resin coating 52 may increase from the upper portion 51u to the lower portion 51d of the substrate 51.

Fig. 10 is a view schematically showing a method of forming a photosensitive resin coating layer on one surface of a substrate according to a third embodiment.

Referring to fig. 10, step (a) may include: a step (a-1) of providing a photosensitive resin between the substrate 51 and the auxiliary substrate 100; and a step (a-2) of moving at least one of the substrate 51 or the auxiliary substrate 100. Here, the photosensitive resin 52' may be in a liquid state between the substrate 51 and the auxiliary substrate 100. Here, in the step (a-2), at least one of the substrate 51 and the auxiliary substrate 100 may be moved while changing a relative moving speed of one of the substrate 51 and the auxiliary substrate 100 with respect to the other. For example, in the case of increasing the relative moving speed between the substrate 51 and the auxiliary substrate 100, the height of the photosensitive resin coating 52 on the substrate 51 may be gradually decreased in the moving direction of the auxiliary substrate 100. As another example, in the case of reducing the relative moving speed between the substrate 51 and the auxiliary substrate 100, the height of the photosensitive resin coating 52 on the substrate 51 may be gradually increased in the moving direction of the auxiliary substrate 100.

The method of forming the photosensitive resin coating 52 on one surface of the substrate 51 according to the third embodiment as described above may be applicable to a mass-production process because of the mechanism of easily organizing and controlling the relative movement of the auxiliary substrate 100 with respect to the substrate 51.

Fig. 11 is a view schematically showing a method of forming a photosensitive resin coating layer on one surface of a substrate according to a fourth embodiment.

Referring to fig. 11, in step (a), the photosensitive resin 52' may be provided in a state where one surface 51a of the substrate 51 is inclined with respect to the base surface E, and may be dried while varying the slope of the one surface of the substrate 51 with respect to the base surface E. First, as shown in (a) of fig. 11, when the liquid photosensitive resin 52 'is cast in a state where one surface 51a of the substrate 51 is inclined with respect to the base surface E, the upper surface of the photosensitive resin 52' may be kept in a state parallel to the base surface E. Here, since the one surface 51a of the substrate 51 is inclined with respect to the base surface 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 the one side C to the other side D. In this state, when the photosensitive resin 52 'is dried, the photosensitive resin coating 52 may be formed such that the distance between the one surface 51a of the substrate 51 and the upper surface of the photosensitive resin 52' gradually increases from the one side C to the other side D. As shown in fig. 11 (b), when one surface 51a of the substrate 51 is arranged in parallel with the base surface E, the height of the photosensitive resin coating 52 increases from one side C to the other side D of the substrate 51.

According to one embodiment of the present disclosure, a holographic grating having different heights according to positions may be easily formed.

EMBODIMENTS FOR CARRYING OUT THE INVENTION

Fig. 12 is a graph illustrating a comparison of diffraction efficiencies between an embodiment and a comparative example according to the present disclosure.

For comparison, a holographic grating was recorded by irradiating the opposite surface of the photosensitive resin coating with laser light. A laser having a wavelength of 532nm and an output power of 250mW was used, and the reference beam and the object beam with which the photosensitive resin coating was irradiated had the same power of 2mW, so that a Beam Ratio (BR) became 1. The hologram grating was recorded by irradiating the photosensitive resin coating with laser light at each of angles of 0 degrees and 60 degrees, and the recording time thereof was the same, 10 seconds.

Here, in example 1, the photosensitive substrate in which the height of the photosensitive resin coating layer is increased according to the embodiment of the present disclosure is used, whereas in comparative example 1, the photosensitive substrate in which the height of the photosensitive resin coating layer is uniform is used.

With the holographic optical elements of embodiment 1 and comparative example 1, four measurement positions (#1 to #4) are set at predetermined intervals from one side to the other side so as to measure the intensities of diffracted light and transmitted light at each point. The intensities of the diffracted light and the transmitted light were obtained by measuring the amount of light corresponding to 532nm by using a power meter.

As in the following equation, the relative diffraction efficiency according to the height of the photosensitive resin coating (i.e., the height of the holographic grating) is obtained using the intensities of the diffracted light and the transmitted light.

< equation >

In the following table 1 for comparing the values of the comparative example and the example, it can be understood that, in the example 1 in which the height of the photosensitive resin coating layer is changed according to the measurement position, the diffraction efficiency is changed according to the height. More specifically, it can be understood that the diffraction efficiency increases in proportion to the height. In contrast, in comparative example 1 in which the height of the photosensitive resin coating layer was uniform, the value of the diffraction efficiency was maintained at the same level without significant variation according to the height.

[ Table 1]

The diffraction efficiency of the optical element can be adjusted according to the height of the photosensitive resin coating (i.e., the height of the recorded holographic grating), which enables adjustment of the diffraction efficiency according to the area of the holographic optical element.

Therefore, in the case where the diffraction efficiency of the hologram optical element 12 gradually increases as the height of the plurality of hologram gratings 12a increases from one side a to the other side B as in the diffraction light guide plate 10 shown in fig. 4, the amount of diffracted light at the diffraction light guide plate 10 may be substantially the same even when the amount of light reaching the hologram optical element 12 decreases.

Fig. 13 is a graph illustrating a difference in the amount of light emitted in the above-described diffractive light guide plate between the embodiment according to the present disclosure and the comparative example.

In example 2, a diffractive light guide plate was formed by recording a holographic grating in a photosensitive substrate in which the height of a photosensitive resin coating layer was increased according to an embodiment of the present disclosure, and a plurality of holographic gratings having heights increasing from one side to the other side were recorded in the light guide plate as shown in fig. 4. In comparative example 2, as shown in fig. 1, a diffraction light guide plate was formed by recording a plurality of hologram gratings in a photosensitive resin coating having a uniform height on a light guide plate. In example 2 and comparative example 2, a hologram grating was recorded by the same method as in example 1 and comparative example 1, and as shown in the following table, the height of the photosensitive resin coating was varied according to the measurement position.

For the diffractive light guide plates of example 2 and comparative example 2, six measurement positions (#1 to #6) were set at predetermined intervals from one side to the other side so as to measure the height of the photosensitive resin coating and the amount of emitted light at each point. The amount of emitted light was obtained by measuring the amount of light emitted by the holographic optical element at each measurement position while making 100uW of 532nm light incident on the light guide plate and propagating 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 in example 2 and comparative example 2 are shown in table 2 below.

[ Table 2]

As a comparison of example 2 and comparative example 2 is made in fig. 13, it can be understood that in example 2 in which the height of the photosensitive resin coating is gradually increased, the amount of emitted light is substantially uniform regardless of the measurement position. In contrast, it can be understood that in the case where the height of the photosensitive resin coating is uniform, the amount of emitted light sharply decreases from one side to the other side.

Although the present disclosure has been described with respect to the above preferred embodiments, various modifications or adaptations may be made without departing from the subject and scope of the present disclosure. Therefore, the appended claims are to encompass such modifications or changes as long as they pertain to the subject matter of this disclosure.