Light guide device

Abstract

This device has a light guide substrate that propagates light through internal reflection. The light guide substrate includes: a light incident portion having a first portion and a second portion serving as a 1D diffraction grating, the first portion causing received light to propagate as a first beam along a first path within the light guide substrate, and the second portion causing received light to propagate as a second beam along a second path within the light guide substrate; a first reflection portion, which is a 1D diffraction grating, changing the direction of the first path of the first beam; a second reflection portion, which is a 1D diffraction grating, changing the direction of the second path of the second beam; and a light emitting portion, which is a 2D diffraction grating, receiving the first beam and the second beam from the first reflection portion and the second reflection portion, combining the first beam and the second beam, and emitting them to the outside of the light guide substrate. The device is configured such that, in the surface of the light guide substrate, the center of the smallest circle including the first portion is farther away from the light emitting portion than the center of the smallest circle including the second portion, and the first path passes through the region of the light guide substrate containing the second portion.

Description

Technical Field

[0001] This invention relates to a light guide device for augmented reality systems. Background Technology

[0002] An augmented reality system is being used that displays images of virtual objects as part of or overlaid with the surrounding environment, thereby generating a virtual image of the augmented reality environment. As an example, the augmented reality system is implemented as a head-mounted display or other wearable device.

[0003] An augmented reality system includes: a light source that generates a virtual image; a light incident section that acquires the generated virtual image; a light guide section that propagates the image acquired by the light incident section as light rays; and a light emitting section that receives light rays from the light guide section, reconstructs an image based on the light rays, and provides it to the user. The light incident section, the light emitting section, and the light guide section are collectively referred to as a light guiding device.

[0004] Various light guiding devices have been developed to date (Patent Documents 1-3). However, a light guiding device with sufficiently high utilization efficiency of light from a light source has not yet been developed. Therefore, there is a need for a light guiding device with sufficiently high utilization efficiency of light from a light source.

[0005] Existing technical documents

[0006] Patent documents

[0007] Patent Document 1: US9791703B1

[0008] Patent Document 2: US2020 / 0225498A1

[0009] Patent Document 3: US2021 / 0109273A1 Summary of the Invention

[0010] The problem that the invention aims to solve

[0011] The objective of this invention is to provide a light guiding device with sufficiently high light utilization efficiency from a light source.

[0012] Methods for solving problems

[0013] The light guiding device of the present invention includes: a light guiding substrate that propagates light through internal reflection; a light incident portion having a first portion and a second portion that are respectively configured as a 1D diffraction grating provided on the light guiding substrate, the first portion being configured to propagate received light as a first beam along a first path within the light guiding substrate, and the second portion being configured to propagate received light as a second beam along a second path within the light guiding substrate; and a first reflection portion that is a 1D diffraction grating provided on the light guiding substrate. The light guide device comprises a diffraction grating configured to change the direction of the first path of the first light beam; a second reversal portion, which is a 1D diffraction grating provided on the light guide substrate, configured to change the direction of the second path of the second light beam; and a light emission portion, which is a 2D diffraction grating provided on the light guide substrate, configured to receive the first light beam from the first reversal portion and the second light beam from the second reversal portion, combine the first light beam and the second light beam, and emit them outward from the light guide substrate. In this invention, the center of the smallest circle including the first portion in the surface of the light guide substrate is farther from the light emission portion than the center of the smallest circle including the second portion, and the first path passes through the region of the light guide substrate containing the second portion.

[0014] The light guide device of the present invention is configured such that, in the surface of the light guide substrate, the center of the smallest circle including the first portion is farther away from the light emission portion than the center of the smallest circle including the second portion. The first path passes through the region of the light guide substrate containing the second portion. Therefore, compared to conventional light guide devices configured such that the path of light rays from one of the first and second portions toward the light emission portion does not pass through the region of the light guide substrate containing the other of the first and second portions, the diffraction efficiency when receiving light in the light incident portion can be improved. Furthermore, since the path of light rays from the first portion toward the light emission portion passes through the region of the light guide substrate containing the second portion, the degree of freedom in dividing the light incident portion into the first and second portions is much greater than that of conventional light guide devices configured such that the path of light rays from one of the first and second portions toward the light emission portion does not pass through the region of the light guide substrate containing the other of the first and second portions. Therefore, it is possible to improve the utilization efficiency of light from the light source by changing the method of dividing the incident light into part 1 and part 2.

[0015] The light guide device of the first embodiment of the present invention is configured such that, in the surface of the light guide substrate, with reference to a straight line passing through the center of the smallest circle including the light incident portion and the direction of the groove of the first portion of the diffraction grating, the area occupied by the second portion in the region on the side of the light incident portion away from the light emitting portion is 2% or more.

[0016] In this embodiment, in the surface of the light guide substrate, taking a straight line passing through the center of the smallest circle containing the light incident portion and the direction of the groove of the first part of the diffraction grating as a reference, the area occupied by the second part in the region on the side of the light incident portion away from the light emitting portion is made to be more than 2%. As a result, compared with the case where the straight line passing through the center of the smallest circle containing the light incident portion and the direction of the groove of the first part of the diffraction grating is used as the boundary line between the first part and the second part, the utilization efficiency of the light from the light source can be improved.

[0017] The light guide device of the second embodiment of the present invention is configured such that, in the surface of the light guide substrate, with reference to a straight line passing through the center of the smallest circle containing the light incident portion and the direction of the groove of the first portion of the diffraction grating, the area occupied by the first portion is 10% or more in the region closer to the light emitting portion of the light incident portion.

[0018] In this embodiment, in the surface of the light guide substrate, taking a straight line passing through the center of the smallest circle containing the light incident portion and the direction of the groove of the first part of the diffraction grating as a reference, the area occupied by the first part in the region closer to the light emission portion of the light incident portion is made to be more than 10%. As a result, compared with the case where the straight line passing through the center of the smallest circle containing the light incident portion and the direction of the groove of the first part of the diffraction grating is used as the boundary line between the first part and the second part, the utilization efficiency of the light from the light source can be improved.

[0019] In the light guiding device of the third embodiment of the present invention, in the surface of the light guiding substrate, the boundary line between the first part and the second part in the light incident portion is configured such that there is a straight line that intersects the boundary line at two or more points, and the straight line is a straight line parallel to the direction of the groove of the diffraction grating of the first part.

[0020] The light guiding device of the fourth embodiment of the present invention is configured such that, in the surface of the light guiding substrate, the direction of the boundary line between the first part and the second part in the light incident portion is not uniform, and the maximum value of the difference between the angle of the line segment or tangent of the boundary line and the reference direction is 75 degrees or more.

[0021] In this embodiment, the absolute value of the difference between the angle of the line segment or the tangent of the boundary line of the first part and the second part in the light incident part relative to the reference direction in the surface of the light guide substrate is 75 degrees or more. As a result, compared with the case where the boundary line of the first part and the second part is a straight line passing through the center of the smallest circle containing the light incident part, the utilization efficiency of the light from the light source can be improved.

[0022] The light guiding device of the fifth embodiment of the present invention is configured such that, in the surface of the light guiding substrate, at least one of the first portion and the second portion has at least two portions that are separated from each other by the other of the first portion and the second portion.

[0023] In this embodiment, in the surface of the light guide substrate, at least one of the first part and the second part has at least two parts that are separated from each other by the other of the first part and the second part. This improves the utilization efficiency of light from the light source compared to the case where a straight line passing through the center of the smallest circle containing the light incident part is used as the boundary line between the first part and the second part.

[0024] The light guiding device of the sixth embodiment of the present invention is configured such that the imaginary horizontal direction and the vertical direction when using the light guiding device are respectively defined as the x-axis and the y-axis, the inclination of the groove direction of the 1D diffraction grating of the first part relative to the y-axis is within 5 degrees, and the inclination of the groove direction of the 1D diffraction grating of the second part relative to the x-axis is within 15 degrees.

[0025] The light guiding device of the seventh embodiment of the present invention is configured such that the period of the 1D diffraction grating of the first part is less than or equal to the period of the 1D diffraction grating of the second part.

[0026] The light guide device of the eighth embodiment of the present invention is configured such that, in the surface of the light guide substrate, with a straight line passing through the center of the smallest circle including the light incident portion and an imaginary vertical direction when using the light guide device, the area occupied by the second portion in the region on the side of the light incident portion away from the light emitting portion is 2% or more.

[0027] In this embodiment, in the surface of the light guide substrate, a straight line passing through the center of the smallest circle containing the light incident portion and an imaginary vertical direction when using the light guide device is used as a reference. In the area on the side of the light incident portion away from the light emitting portion, the area occupied by the second part is 2% or more. As a result, compared with the case where the straight line passing through the center of the smallest circle containing the light incident portion is used as the boundary line between the first part and the second part, the utilization efficiency of the light from the light source can be improved.

[0028] The light guide device of the ninth embodiment of the present invention is configured such that, in the surface of the light guide substrate, based on a straight line passing through the center of the smallest circle including the light incident portion and an imaginary vertical direction when using the light guide device, the area occupied by the first portion in the region closer to the light emitting portion of the light incident portion is 10% or more.

[0029] In this embodiment, on the surface of the light guide substrate, a straight line passing through the center of the smallest circle containing the light incident portion and assumed to be a vertical line when using the light guide device is used as a reference. In the area closer to the light emitting portion of the light incident portion, the area occupied by the first part is 10% or more. As a result, compared with the case where the straight line passing through the center of the smallest circle containing the light incident portion is used as the boundary line between the first part and the second part, the utilization efficiency of the light from the light source can be improved. Attached Figure Description

[0030] Figure 1 This is a perspective view of the light guiding device of the present invention.

[0031] Figure 2 This is a cross-sectional view of the light guide device of the present invention.

[0032] Figure 3 This is a flowchart illustrating the design method of the light guide device of the present invention.

[0033] Figure 4 This is a diagram used to illustrate the coordinates used in this specification.

[0034] Figure 5 This diagram shows the light rays emitted from the center of the light-emitting surface of the light source and incident on the light-receiving surface of the light-incident part in the xz section, traveling within the light guide substrate.

[0035] Figure 6 This is a diagram showing the incident angle θax of the light rays incident on the light guide substrate and the incident angle θgx of the inner surface of the light guide substrate in the xz section.

[0036] Figure 7 This is a diagram showing the incident angle θay of the light rays incident on the light guide substrate and the incident angle θgy of the inner surface of the light guide substrate in the yz section.

[0037] Figure 8 This is a diagram showing the relationship between the incident angle of the light-receiving surface of the light-incident portion and the incident angle of the inner surface of the light guide substrate in the xz section.

[0038] Figure 9 This diagram shows the region of the light incident section in which light can propagate at an incident angle of at least the critical angle at the inner surface of the light guide substrate and with a spacing smaller than the pupil size.

[0039] Figure 10 This is a top view of the light guide device of Embodiment 1.

[0040] Figure 11 This is a diagram showing the xz cross-section of the light guide device of Embodiment 1.

[0041] Figure 12 This is a top view of the light guide device of the comparative example.

[0042] Figure 13 This is a diagram showing the xz cross-section of the light guide device of the comparative example.

[0043] Figure 14 This is a top view of the light guide device in Embodiment 2.

[0044] Figure 15 This is a top view of the light incident section in Embodiment 2.

[0045] Figure 16 This is a top view of the light guide device in Embodiment 3.

[0046] Figure 17 This is a top view of the light incident section in Embodiment 3.

[0047] Figure 18 This is a top view of the light guide device in Embodiment 4.

[0048] Figure 19 This is a top view of the light incident section in Embodiment 4.

[0049] Figure 20 This is a top view of the light guide device in Embodiment 5.

[0050] Figure 21 This is a top view of the light incident section in Embodiment 5. Detailed Implementation

[0051] Figure 1 This is a perspective view of the light guiding device 100 of the present invention.

[0052] Figure 2 This is a cross-sectional view of the light guide device 100 of the present invention.

[0053] The light guiding device 100 includes a light guiding substrate 150, a light incident section 110, a first light reflecting section 121, a second light reflecting section 122, and a light emitting section 130. The light incident section 110 has a first portion 111 and a second portion 112, which are respectively 1D surface-structured diffraction gratings. The first light reflecting section 121 and the second light reflecting section 122 are both 1D surface-structured diffraction gratings. The light emitting section 130 is a 2D surface-structured diffraction grating.

[0054] The light source 50 is configured to form an image on the light incident section 110. The light source 50 may also be a laser light source that forms an image on the light incident section 110 by scanning a laser beam. Figure 2 In this diagram, the distance between the light source 50 and the light guide substrate 150 is denoted by D. Light received by the first portion 111 of the light incident section 110 is captured as diffracted light within the light guide substrate 150 and transmitted to the first light reflection section 121 via total internal reflection within the light guide substrate 150. Figure 2 In this diagram, the thickness of the light guide substrate 150 is represented by d. Light arriving at the first light reflection section 121 has its direction of travel changed by the first light reflection section 121 and is then transmitted to the light emission section 130. Light received by the second portion 112 of the light incident section 110 is captured as diffracted light within the light guide substrate 150 and transmitted to the second light reflection section 122 via total internal reflection within the light guide substrate 150. Light arriving at the second light reflection section 122 has its direction of travel changed by the second light reflection section 122 and is transmitted to the light emission section 130. The light emission section 130 combines the light received from the first light reflection section 121 and the second light reflection section 122, forming an image within the eye chamber 200. The eye chamber 200 refers to the area where the image will not be lost even if the observer's pupil moves. Figure 2 In the diagram, the distance between the eye box 200 and the light guide substrate 150 is represented by D'. Figure 2 The light path within the light guide substrate 150 is used to illustrate the path of total internal reflection within the light guide substrate 150 and does not represent the actual path.

[0055] Figure 3 This is a flowchart illustrating the design method of the light guide device 100 of the present invention.

[0056] exist Figure 3 In step S1010, the size of the light incident section 110 is determined.

[0057] Figure 4 This is a diagram used to illustrate the coordinates used in this specification. The direction corresponding to the horizontal direction when using the light guide device 100 is defined as the x-axis, and the direction corresponding to the vertical direction is defined as the y-axis. The coordinates of the x-axis are determined such that the coordinates of the light emitting section 130 are greater than the coordinates of the light incident section 110, and the coordinates of the y-axis are determined such that the coordinates of the light emitting section 130 are less than the coordinates of the light incident section 110. The z-axis is defined with the intersection of the x-axis and y-axis as the origin and perpendicular to both axes.

[0058] For example, the x-axis and y-axis are defined on the light-receiving surface of the light-incident section 110, with the center of the light-receiving surface as the origin. The center of the light source 50 is located at a distance D from the origin on the z-axis. The coordinates of the z-axis are determined such that the coordinates of the center of the light source 50 are less than the coordinates of the origin. The angle of incidence of the light ray emitted from the center of the light source 50 and reaching point P on the light-receiving surface of the light-incident section 110 is denoted by θ. The x-axis component and y-axis component of θ are denoted by θx and θy, respectively. θx and θy are positive when the light ray travels with increasing coordinates before incident. Figure 4 In this case, θx is negative and θy is positive.

[0059] The length L1x in the X-axis direction and the length L1y in the Y-axis direction of the light incident section 110 are determined according to the following formulas.

[0060] L1 x =2·D·tanθ xmax +L10 x / 2

[0061] L1 y =2·D·tanθ ymax +L10 y / 2

[0062] Here,

[0063] D is the distance from the center of the light source to the origin.

[0064] L10x is the length of the light source along the X-axis.

[0065] L10y is the length of the light source along the Y-axis.

[0066] θxmax is the maximum absolute value of θx.

[0067] θymax is the maximum absolute value of θy.

[0068] exist Figure 3 In step S1020, the grating period Λ1 of the first part 111 of the light incident section 110 is determined. The groove of the diffraction grating of the first part 111 is set in the Y-axis direction.

[0069] Figure 5 This diagram shows the light rays emitted from the center of the emitting surface of the light source 50 and incident on the light-receiving surface of the light incident section 110, traveling within the light guide substrate 150 in the xz section. Figure 5 In this light guide substrate 150, the x-axis coordinate is determined such that the coordinate of the light emitting section 130 is larger than the coordinate of the light incident section 110. Therefore, the direction of light travel within the light guide substrate 150 is along the x-axis in a direction where the coordinate increases. Furthermore, θx is negative.

[0070] Figure 6 This is a diagram showing the incident angle θax of the light rays incident on the light guide substrate 150 and the incident angle θgx of the inner surface of the light guide substrate 150 in the xz section. For simplicity, in Figure 6 The light incident section 110 is not shown in the diagram. The grooves of the diffraction grating are perpendicular to the plane of the paper. The diffraction formula is as follows. Figure 6 In this case, the light travels in the direction of decreasing x-coordinate and then enters the light incident part 110, so the value of θax is negative.

[0071]

[0072] Here,

[0073] na is the refractive index of air.

[0074] ng is the refractive index of the light guide substrate.

[0075] θax is the angle of incidence in the xz section of the light-receiving surface of the incident part.

[0076] θgx is the angle of incidence in the xz section of the inner surface of the light guide substrate.

[0077] m is the diffraction number, m=1

[0078] λ is the wavelength of light.

[0079] Λ is the grating period

[0080] exist Figure 6 In the case where the incident angle θgx on the inner surface of the light guide substrate 150 is above the critical angle, the light entering the light guide substrate 150 from the light receiving surface of the light incident section 110 can be as... Figure 2 As shown, it travels within the light guide substrate 150 while undergoing total internal reflection. Therefore, the incident angle θax of the light-receiving surface of the light incident section 110 needs to be determined such that the incident angle θgx of the inner surface of the light guide substrate 150 is above the critical angle.

[0081] Substituting the critical angle into θgx in equation (1) yields the following equation.

[0082]

[0083] In equation (2), the maximum incident angle -θxmax in the xz section is substituted into θax to calculate Λ, and this value is set as Λ1. As mentioned above, θxmax is an absolute value. According to equation (2), when the grating period is Λ1, as θax increases (the absolute value of θax decreases), θgx increases. Therefore, as long as θax is above -θxmax, θgx becomes above the critical angle, so that the light can travel within the light guide substrate 150 while undergoing total internal reflection.

[0084] Typically, by reducing the grating period, θgx increases the absolute value of the incident angle above the critical angle.

[0085] exist Figure 3 In step S1030, the grating period Λ2 of the second part 112 of the light incident section 110 is determined. The groove of the diffraction grating in the second part 112 is set in the X-axis direction. The coordinate of the y-axis is determined in such a way that the coordinate of the light emitting section 130 is smaller than the coordinate of the light incident section 110. Therefore, the direction of light traveling in the light guide substrate 150 is along the y-axis in a direction where the coordinate decreases.

[0086] Figure 7This is a diagram showing the incident angle θay of the light rays incident on the light guide substrate 150 and the incident angle θgy of the inner surface of the light guide substrate 150 in the yz section. Figure 7 The spacing p represents the distance between the two points. Figure 7 The yz section shown represents the interval between points where light undergoes total internal reflection on the inner surface of the light guide substrate 150. For simplicity, in... Figure 7 The light incident section 110 is not shown. The grooves of the diffraction grating are perpendicular to the plane of the paper. The diffraction formula is as follows. Figure 7 In this case, the light travels along the direction of decreasing y-coordinate and then enters the light incident part 110, so the value of θay is negative.

[0087]

[0088] Here,

[0089] θay is the angle of incidence in the yz section of the light-receiving surface of the incident part.

[0090] θgy is the angle of incidence in the yz section of the inner surface of the light guide substrate.

[0091] To provide a stable image to the observer, the spacing p needs to be set below the size of the pupil. The incident angle θgy of the inner surface of the light guide substrate corresponding to the spacing p of the pupil size is called the spacing angle θp. The spacing angle θp is calculated based on the spacing p of the pupil size using the following formula.

[0092]

[0093] Substituting θp into θgy in equation (1)', we get the following equation.

[0094]

[0095] In equation (3)', the grating period Λ is appropriately determined, and the incident angle θay in the yz section of the light-receiving surface of the light-incident part is calculated. If the absolute value of θay is greater than the maximum incident angle in the yz section, then this value is set as Λ2. If the absolute value of θay is smaller than the maximum incident angle in the yz section, then the grating period Λ is reduced and Λ2 is calculated.

[0096] Generally, increasing the grating period reduces the spacing length, making the image easier to observe. Therefore, increasing the grating period is preferable as long as the maximum incident angle condition is met. The relationship between the grating period and the spacing length will be explained in detail in Example 1.

[0097] Figure 8 This is a diagram showing the relationship between the incident angle of the light-receiving surface of the light-incident portion and the incident angle of the inner surface of the light guide substrate in the xz section. Figure 8The above relationship is indicated in Embodiment 1, which will be described later. Figure 8 The horizontal axis represents the angle of incidence in the xz section of the light incident section 110. Figure 8 The vertical axis represents the total internal reflection angle in the xz section of the inner surface of the light guide substrate. If the angle of incidence in the xz section of the light-receiving surface of the light-incident portion is θacx or higher, then the angle of incidence in the xz section of the inner surface of the light guide substrate is above the critical angle. If the angle of incidence in the xz section of the light-receiving surface of the light-incident portion is θapx or lower, then the spacing is smaller than the pupil size. θapx is the angle of incidence in the xz section corresponding to the spacing angle. Thus, the angle of incidence in the xz section of the light-receiving surface of the light-incident portion needs to be within the range where the angle of incidence in the xz section of the inner surface of the light guide substrate is above the critical angle and the spacing is smaller than the pupil size.

[0098] exist Figure 3 In step S1040, the region in the light incident section 110 that allows light to propagate with an incident angle of at least the critical angle at the inner surface of the light guide substrate and a spacing smaller than the pupil size is determined.

[0099] The critical angle of light in the xz section is examined. In the xz section, when the incident angle of the inner surface of the light guide substrate is the critical angle, the incident angle θacx of the light-receiving surface is a negative value. θacx is obtained by substituting Λ1 into Λ in equation (2).

[0100] In the xz section, the condition for the incident angle of the inner surface of the light guide substrate to be above the critical angle can be expressed by the following formula.

[0101]

[0102] Here,

[0103] θax is the angle of incidence of the light-receiving surface of the incident portion in the xz section.

[0104] θay is the angle of incidence of the light-receiving surface of the incident portion in the yz section.

[0105] α is the tilt angle (counterclockwise) of the grating groove with its direction approximately along the y-axis relative to the y-axis.

[0106] The critical angle of light in the yz section is examined. When the incident angle of the inner surface of the light guide substrate is the critical angle, the incident angle θacy of the light receiving surface is a positive value. θacy is obtained by substituting Λ2 into Λ in the following formula obtained from equation (1)'.

[0107]

[0108] In the yz section, the condition for the incident angle of the inner surface of the light guide substrate to be above the critical angle can be expressed by the following formula.

[0109]

[0110] Here,

[0111] θax is the angle of incidence of the light-receiving surface of the incident portion in the xz section.

[0112] θay is the angle of incidence of the light-receiving surface of the incident portion in the yz section.

[0113] β is the tilt angle (counterclockwise) of the grating groove, whose direction is approximately along the X-axis, relative to the X-axis.

[0114] The spacing of the light rays in the xz section is examined. The incident angle θapx of the light-receiving surface corresponding to the spacing of the pupil size in the light guide substrate is a positive value. θapx is obtained by substituting Λ1 into θgx in equation (1) and then substituting θp into Λ.

[0115]

[0116] In the xz section, the condition for setting the spacing in the light guide substrate to an incident angle below the pupil size can be expressed by the following formula.

[0117]

[0118] Here,

[0119] θax is the angle of incidence of the light-receiving surface of the incident portion in the xz section.

[0120] θay is the angle of incidence of the light-receiving surface of the incident portion in the yz section.

[0121] α is the tilt angle (counterclockwise) of the grating groove with its direction approximately along the Y-axis relative to the Y-axis.

[0122] The spacing of the light rays in the yz section is examined. The incident angle θapy of the light-receiving surface corresponding to the spacing of the pupil size in the light guide substrate is negative. θapy is obtained by substituting Λ2 into Λ in equation (3)'.

[0123] In the yz section, the condition for setting the spacing in the light guide substrate to an incident angle below the pupil size can be expressed by the following formula.

[0124]

[0125] Here,

[0126] θax is the angle of incidence of the light-receiving surface of the incident portion in the xz section.

[0127] θay is the angle of incidence of the light-receiving surface of the incident portion in the yz section.

[0128] β is the tilt angle (counterclockwise) of the grating groove, whose direction is approximately along the X-axis, relative to the X-axis.

[0129] In addition, the light emitted from the first and second parts of the light incident section changes direction by approximately 90 degrees at the first and second light reflection sections. Therefore, when considering the wavenumber space, in order for the light to propagate with the incident angle of the inner surface of the light guide substrate being above the critical angle and the spacing being less than the pupil size, the following additional conditions need to be met.

[0130] The additional condition for the ray incident from Part 111 can be expressed by the following formula.

[0131]

[0132] In the xz section, the incident angle θacx' of the light-receiving surface corresponding to the critical angle when the grating period is Λ2 is obtained by substituting Λ2 into Λ in equation (2).

[0133] The condition for the angle of incidence of the ray incident from Part 2, 112 can be expressed by the following formula.

[0134]

[0135] In the yz section, the incident angle θapy' of the light-receiving surface corresponding to the distance between the grating period and the pupil size is obtained by substituting Λ1 into Λ in equation (3).

[0136] Figure 9 This diagram shows the region of the light incident section 110, which allows light to propagate at an incident angle of at least the critical angle to the inner surface of the light guide substrate and with a spacing smaller than the pupil size. Figure 9 The x-axis represents tan(θax). Figure 9 The y-axis is represented by tan(θay). Figure 9 The straight lines L1, L2, L3, and L4 represent equations (4), (5), (6), and (7), respectively. Furthermore, L1' and L4' represent equations (4)' and (7)', respectively. The region enclosed by the straight lines L1', L2, L3, and L4' is the region where light can propagate at an incident angle greater than or equal to the critical angle of the inner surface of the light guide substrate and with a spacing smaller than the pupil size. This region is referred to as the repeating region.

[0137] exist Figure 3 In step S1050, the dimensions of the light emitting section 130 are determined.

[0138] make Figure 4The origin of the coordinate system shown is aligned with the center of the surface of the light emitting section 130, and the surface containing the x-axis and y-axis is aligned with the surface of the light emitting section 130. Furthermore, the center of the eyebox 200 is determined on the z-axis, and the eyebox 200 is parallel to the surface containing the x-axis and y-axis. The angle of incidence of a ray emitted from point P' on the surface of the light emitting section 130 and incident on the center of the eyebox 200 is denoted by θ. The x-axis component and y-axis component of θ are denoted by θx and θy, respectively.

[0139] The lengths L2x in the X-axis direction and L2y in the Y-axis direction of the light emitting section 130 are determined according to the following formulas.

[0140] L2 x =2·D′·tanθ xmax +L20 x / 2

[0141] L2 y =2·D′·tanθ ymax +L20 y / 2

[0142] Here,

[0143] D' is the distance from the center of the eyebox surface to the origin (the center of the light-emitting surface).

[0144] L20x is the length of the eyebox along the X-axis.

[0145] L20y is the length of the eyebox along the Y-axis.

[0146] θxmax is the maximum absolute value of θx.

[0147] θymax is the maximum absolute value of θy.

[0148] In addition, the light emitting part 130 is a two-dimensional surface structure diffraction grating on the light guide substrate, and the grating period of each of the two diffraction gratings is the same as the grating period of the one-dimensional diffraction grating of the first part 111 or the second part 112 of the corresponding light incident part 110.

[0149] exist Figure 3 In step S1060, the relative positions of the light incident part 110 and the light emitting part 130 are determined based on the interpupillary distance and the positional relationship between the eyes and ears.

[0150] exist Figure 3In step S1070, while considering the overlapping region, the method of dividing the light incident section 110 into the first part 111 and the second part 112 is changed, and the brightness of the image observed by the pupil is evaluated using optical simulation (e.g., optical simulation using VirtualLab), thereby optimizing the segmentation method. Moreover, corresponding to the light incident section 110 thus segmented, the shapes of the first light reflection section 121 and the second light reflection section 122 are optimized.

[0151] In conventional devices, the path of light rays from one of the first and second portions toward the light emission portion does not pass through the region of the light guide substrate containing the other of the first and second portions. On the other hand, the light guide device of the present invention is configured such that, in the surface of the light guide substrate, the center of the smallest circle including the first portion is farther from the light emission portion than the center of the smallest circle including the second portion, and the path of light rays from the first portion toward the light emission portion passes through the region of the light guide substrate containing the second portion. Therefore, compared to conventional light guide devices, the method of dividing the light incident portion 110 into the first portion 111 and the second portion 112 in the light guide device of the present invention offers much greater freedom.

[0152] The embodiments and comparative examples of the present invention will be described below.

[0153] The light guide substrate 150, which includes a light incident section 110, a first light reflecting section 121, a second light reflecting section 122, and a light emitting section 130, is made of polycarbonate and has a refractive index of 1.6748 for light with a wavelength of 520 nanometers. The thickness of the light guide substrate 150 is 1.25 millimeters. Corresponding components in each embodiment are indicated by the same reference numerals.

[0154] The light incident section 110 is rectangular, with a length of 3.343 mm in the X-axis direction and a length of 2.49 mm in the Y-axis direction. The groove of the first part 111 of the light incident section 110 is approximately in the Y-axis direction, and the grating period is 410 nm. The groove of the second part 112 of the light incident section 110 is approximately in the X-axis direction, and the grating period is 460 nm.

[0155] The light emitting section 130 is rectangular, with a length of 21.207 mm in the X-axis direction and a length of 11.929 mm in the Y-axis direction. The grating period of the light emitting section 130 in the X-axis direction is 460 nm, and the grating period in the Y-axis direction is 460 nm.

[0156] The direction of the grooves in a grating is represented by a clockwise angle with respect to the y-axis. The direction of the grooves in a grating is also called the grating direction.

[0157] The distance D between the light source 50 and the light incident part 110 is 6.3 mm, and the distance D' between the light emitting part 130 and the eyebox 200 is 18 mm. The diagonal field of view of the light incident part 110 is 30 degrees.

[0158] Light source 50 is a laser light source with a spot size of 0.4 mm in the X-axis direction and 0.8 mm in the Y-axis direction. Eyebox 200 has a spot size of 12.8 mm in the X-axis direction and 7.2 mm in the Y-axis direction.

[0159] Example 1

[0160] Figure 10 This is a top view of the light guide device 100 of Embodiment 1.

[0161] Figure 11 This is a diagram showing the xz cross section of the light guide device 100 of Embodiment 1.

[0162] The grating of the first part 111 of the light incident section 110 has an orientation of 0 degrees and a grating period of 410 nanometers. The grating of the second part 112 of the light incident section 110 has an orientation of 90 degrees and a grating period of 460 nanometers. The first part 111 and the second part 112 are separated by a boundary line passing through the center of the light incident section 110 and parallel to the y-axis, with both parts having equal areas.

[0163] In Embodiment 1, the light incident section 110 is configured such that the first portion 111 is farther away from the light emitting section 130 than the second portion 112, and the path of light rays from the first portion 111 toward the light emitting section 130 passes through the region of the light guide substrate 150 containing the second portion 112. Specifically, light rays from the first portion 111 toward the first light reflection section 121 travel along the X-axis direction with increasing x-coordinate and pass through the region of the light guide substrate 150 containing the second portion 112. Light rays from the second portion 112 toward the second light reflection section 122 travel along the Y-axis direction with decreasing y-coordinate.

[0164] The grating of the first optical refracting section 121 is oriented at 45 degrees and has a grating period of 290 nanometers. The grating of the second optical refracting section 122 is oriented at 45 degrees and has a grating period of 325 nanometers.

[0165] Table 1 shows the brightness of the light-receiving surface of the eyebox. The brightness values ​​are expressed as a percentage relative to the brightness of the light source. Furthermore, the brightness values ​​in Table 1 and the following tables were obtained through optical simulation (e.g., using VirtualLab optical simulation).

[0166] like Figure 2As shown, the light-receiving surface of the eyebox 200 is parallel to the emission surface of the light-emitting section 130, and the straight line connecting the centers of the two surfaces is the Z-axis direction. Therefore, the position on the light-receiving surface of the eyebox 200 can be determined by the incident angle of the light ray emitted from the center of the emission surface of the light-emitting section 130. The horizontal angles in Table 1 represent the X-axis component of the incident angle, i.e., the coordinates in the X-axis direction, and the vertical angles in Table 1 represent the Y-axis component of the incident angle, i.e., the coordinates in the Y-axis direction.

[0167] The following tables also define the values ​​for brightness, horizontal angle, and vertical angle.

[0168] [Table 1]

[0169]

[0170] Table 2 shows the spacing lengths of the light guide substrates 150 for various incident angles of light in the light guide device 100 of Embodiment 1. The unit of spacing length is millimeters.

[0171] [Table 2]

[0172]

[0173] Table 3 shows the spacing lengths of the light guide substrate 150 for various incident angles of light when the grating period of the second part 112 of the light guide device 100 in Embodiment 1 is changed from 460 nm to 410 nm. The unit of spacing length is millimeters.

[0174] [Table 3]

[0175]

[0176] In Table 3, where the grating period is 410 nm, the spacing length increases compared to Table 2, where the grating period is 460 nm. Thus, shortening the grating period results in an increased spacing length.

[0177] Comparative example

[0178] Figure 12 This is a top view of the comparative example light guide device 100'.

[0179] Figure 13 This is a diagram showing the xz cross section of the light guide device 100' of the comparative example.

[0180] The grating of the first part 111' of the light incident section 110' has an orientation of 0 degrees and a grating period of 410 nanometers. The grating of the second part 112' of the light incident section 110' has an orientation of 90 degrees and a grating period of 460 nanometers. The first part 111' and the second part 112' are divided by a boundary line passing through the center of the light incident section 110' and parallel to the y-axis, with both parts having equal areas.

[0181] In the comparative example, the path of light rays emanating from one of the first and second portions toward the light emitting portion 130' does not pass through the region of the light guide substrate 150' containing the other of the first and second portions. Specifically, light rays emanating from the first portion 111' toward the first light reflecting portion 121' travel along the X-axis direction with increasing x-coordinate, while light rays emanating from the second portion 112' toward the second light reflecting portion 122' travel along the Y-axis direction with decreasing y-coordinate. Thus, light rays emanating from one of the first portion 111' and the second portion 112' do not pass through the region of the light guide substrate 150' containing the other of the first portion 111' and the second portion 112'.

[0182] The grating of the first optical reflector 121' is oriented at 45 degrees and has a grating period of 325 nanometers. The grating of the second optical reflector 122' is oriented at 45 degrees and has a grating period of 290 nanometers.

[0183] Table 4 shows the brightness of the light-receiving surface of the eye chamber.

[0184] [Table 4]

[0185]

[0186] Example 2

[0187] Figure 14 This is a top view of the light guide device 100 of Embodiment 2.

[0188] The grating of the first part 111 of the light incident section 110 has an orientation of 2 degrees and a grating period of 410 nanometers. The grating of the second part 112 of the light incident section 110 has an orientation of 85 degrees and a grating period of 460 nanometers.

[0189] In Embodiment 2, the light incident portion 110 is configured such that the first portion 111 is farther away from the light emitting portion 130 than the second portion 112, and the path of the light from the first portion 111 toward the light emitting portion 130 passes through the area of ​​the light guide substrate 150 having the second portion 112.

[0190] Figure 15 This is a top view of the light incident section 110 of Embodiment 2. The boundary line between the first part 111 and the second part 112 is composed of 4 line segments in the X-axis direction and 5 line segments in the Y-axis direction.

[0191] For example, a straight line passing through the origin of the coordinate system that serves as the center of the light incident section 110 and parallel to the direction of the groove of the diffraction grating in the first part 111 intersects the boundary line at four points.

[0192] The direction of the boundary line between Part 111 and Part 212 is not unidirectional; the maximum difference in angle between the line segment or tangent of the boundary line and the reference direction is 90 degrees.

[0193] Based on a straight line passing through the direction of the groove of the diffraction grating of the first part 111, which is the origin of the coordinates of the center of the light incident part 110, the area occupied by the second part 112 in the region of the light incident part 110 away from the light emitting part 130 is 4.76%.

[0194] Based on a straight line passing through the direction of the groove of the diffraction grating of the first part 111, which is the origin of the coordinates of the center of the light incident part 110, the area occupied by the first part 111 in the region of the light incident part 110 closer to the light emitting part 130 is 13.72%.

[0195] The grating of the first optical refracting section 121 is oriented at 46 degrees and has a grating period of 285 nanometers. The grating of the second optical refracting section 122 is oriented at 42.5 degrees and has a grating period of 310 nanometers.

[0196] Table 5 shows the brightness of the light-receiving surface of the eye chamber.

[0197] [Table 5]

[0198]

[0199] Example 3

[0200] Figure 16 This is a top view of the light guide device 100 of Embodiment 3.

[0201] The grating of the first part 111 of the light incident section 110 has an orientation of 5 degrees and a grating period of 410 nanometers. The grating of the second part 112 of the light incident section 110 has an orientation of 90 degrees and a grating period of 460 nanometers.

[0202] In Embodiment 3, the light incident portion 110 is configured such that the first portion 111 is farther away from the light emitting portion 130 than the second portion 112, and the path of the light from the first portion 111 toward the light emitting portion 130 passes through the area of ​​the light guide substrate 150 having the second portion 112.

[0203] Figure 17This is a top view of the light incident section 110 of Embodiment 3. The boundary line between the first part 111 and the second part 112 is composed of one line segment in the X-axis direction and two line segments in the Y-axis direction.

[0204] The direction of the boundary line between Part 111 and Part 212 is not unidirectional; the maximum difference in angle between the line segment or tangent of the boundary line and the reference direction is 90 degrees.

[0205] Based on a straight line passing through the direction of the groove of the diffraction grating of the first part 111, which is the origin of the coordinates of the center of the light incident part 110, the area occupied by the second part 112 in the region of the light incident part 110 away from the light emitting part 130 is 18.21%.

[0206] Based on a straight line passing through the direction of the groove of the diffraction grating of the first part 111, which is the origin of the coordinates of the center of the light incident part 110, the area occupied by the first part 111 in the region of the light incident part 110 closer to the light emitting part 130 is 18.21%.

[0207] The grating of the first optical refracting section 121 is oriented at 47.5 degrees and has a grating period of 286 nanometers. The grating of the second optical refracting section 122 is oriented at 45 degrees and has a grating period of 325 nanometers.

[0208] Table 6 shows the brightness of the light-receiving surface of the eyebox.

[0209] [Table 6]

[0210]

[0211] Example 4

[0212] Figure 18 This is a top view of the light guide device 100 of Embodiment 4.

[0213] The grating of the first part 111 of the light incident section 110 has a grating direction of 0 degrees and a grating period of 410 nanometers. The grating of the second part 112 of the light incident section 110 has a grating direction of 100 degrees and a grating period of 460 nanometers.

[0214] In Embodiment 4, the light incident portion 110 is configured such that the first portion 111 is farther away from the light emitting portion 130 than the second portion 112, and the path of the light from the first portion 111 toward the light emitting portion 130 passes through the area of ​​the light guide substrate 150 having the second portion 112.

[0215] Figure 19 This is a top view of the light incident section 110 of Embodiment 4. The boundary line between the first part 111 and the second part 112 is a line segment inclined with respect to the y-axis.

[0216] Based on a straight line passing through the direction of the groove of the diffraction grating of the first part 111, which is the origin of the coordinates of the center of the light incident part 110, the area occupied by the second part 112 in the region of the light incident part 110 away from the light emitting part 130 is 14.96%.

[0217] Based on a straight line passing through the direction of the groove of the diffraction grating of the first part 111, which is the origin of the coordinates of the center of the light incident part 110, the area occupied by the first part 111 in the region of the light incident part 110 closer to the light emitting part 130 is 14.96%.

[0218] The grating of the first optical refracting section 121 is oriented at 45 degrees and has a grating period of 290 nanometers. The grating of the second optical refracting section 122 is oriented at 50 degrees and has a grating period of 360 nanometers.

[0219] Table 7 shows the brightness of the light-receiving surface of the eyebox.

[0220] [Table 7]

[0221]

[0222] Example 5

[0223] Figure 20 This is a top view of the light guide device 100 of Embodiment 5.

[0224] The grating of the first part 111 of the light incident section 110 has an orientation of 2 degrees and a grating period of 410 nanometers. The grating of the second part 112 of the light incident section 110 has an orientation of 85 degrees and a grating period of 460 nanometers.

[0225] In Embodiment 5, the light incident portion 110 is configured such that the first portion 111 is farther away from the light emitting portion 130 than the second portion 112, and the path of the light from the first portion 111 toward the light emitting portion 130 passes through the area of ​​the light guide substrate 150 having the second portion 112.

[0226] Figure 21 This is a top view of the light incident section 110 of Embodiment 5. The boundary line between the first part 111 and the second part 112 is composed of one line segment in the X-axis direction and three line segments in the Y-axis direction.

[0227] The direction of the boundary line between Part 111 and Part 212 is not unidirectional; the maximum difference in angle between the line segment or tangent of the boundary line and the reference direction is 90 degrees.

[0228] Based on a straight line passing through the direction of the groove of the diffraction grating of the first part 111, which is the origin of the coordinates of the center of the light incident part 110, the area occupied by the second part 112 in the region of the light incident part 110 away from the light emitting part 130 is 4.28%.

[0229] Based on a straight line passing through the direction of the groove of the diffraction grating of the first part 111, which is the origin of the coordinates of the center of the light incident part 110, the area occupied by the first part 111 in the region of the light incident part 110 closer to the light emitting part 130 is 23.93%.

[0230] Part 2 112 has two parts that are separated from each other by Part 1 111.

[0231] The grating of the first optical refracting section 121 is oriented at 46 degrees and has a grating period of 285 nanometers. The grating of the second optical refracting section 122 is oriented at 42.5 degrees and has a grating period of 310 nanometers.

[0232] Table 8 shows the brightness of the light-receiving surface of the eye chamber.

[0233] [Table 8]

[0234]

[0235] Performance evaluation of the embodiments

[0236] The performance of the embodiments and comparative examples was evaluated according to Tables 1 and 4-8, which show the brightness of the light-receiving surface of the eyebox. First, Table 1 of Embodiment 1 and Table 4 of the comparative examples were compared. When the threshold for observable brightness was set to 0.001%, all values ​​in Table 1 were above the threshold. On the other hand, the values ​​at point 9 (shown in black) in Table 4 were below the threshold. Therefore, the light utilization efficiency of the device of Embodiment 1 is higher than that of the device of the comparative examples. The reason for this is that the diffraction efficiency of the light incident section 110 is higher in the light path of Embodiment 1 compared to the light path of the comparative examples.

[0237] Next, in Tables 1 and 5 to 8, which represent the brightness of Examples 1 to 5, the minimum brightness values ​​are as follows.

[0238] Example 1 (Table 1): 0.007%

[0239] Example 2 (Table 5): 0.022%

[0240] Example 3 (Table 6): 0.015%

[0241] Example 4 (Table 7): 0.027%

[0242] Example 5 (Table 8): 0.022%

[0243] In Examples 2-5, by appropriately determining the boundary line between the first portion 111 and the second portion 112 of the light incident portion 110, the minimum brightness is significantly increased compared to Example 1, which divides the first portion 111 and the second portion 112 into equal areas using a boundary line parallel to the y-axis passing through the center of the light incident portion 110. The reason for this is that in Examples 2-5, by flexibly varying the arrangement of the first portion 111 and the second portion 112, the brightness of the light-receiving surface of the eye chamber can be increased, thereby reducing the brightness difference caused by the position of the light-receiving surface of the eye chamber.

Claims

1. A light guiding device, comprising: A light guide substrate that transmits light through internal reflection; The light incident section has a first part and a second part, which are respectively used as a 1D diffraction grating on the light guide substrate. The first part is configured to allow the received light to propagate as a first beam along a first path in the light guide substrate, and the second part is configured to allow the received light to propagate as a second beam along a second path in the light guide substrate. The first foldback section is a one-dimensional diffraction grating on the light guide substrate, configured to change the direction of the first path of the first beam. The second foldback section is a one-dimensional diffraction grating on the light guide substrate, configured to change the direction of the second path of the second beam; and The light emitting section is a 2D diffraction grating on the light guide substrate, configured to receive the first light beam from the first reflection section and the second light beam from the second reflection section, combine the first light beam and the second light beam, and emit them outward from the light guide substrate. in, The light guide device is configured such that, in the surface of the light guide substrate, the center of the smallest circle including the first portion is farther away from the light emitting portion than the center of the smallest circle including the second portion, and the first path passes through the region of the light guide substrate having the second portion.

2. The light guide device according to claim 1, wherein, The light guide device is configured such that, on the surface of the light guide substrate, with reference to a straight line passing through the center of the smallest circle containing the light incident portion and the direction of the groove of the first part of the diffraction grating, the area occupied by the second part in the region on the side of the light incident portion away from the light emitting portion is 2% or more.

3. The light guiding device according to claim 1, wherein, The light guide device is configured such that, on the surface of the light guide substrate, with reference to a straight line passing through the center of the smallest circle containing the light incident portion and the direction of the groove of the first part of the diffraction grating, the area occupied by the first part is 10% or more in the region closer to the light emitting portion of the light incident portion.

4. The light guiding device according to claim 1, wherein, In the surface of the light guide substrate, the boundary line between the first part and the second part in the light incident portion is configured such that there is a straight line that intersects the boundary line at two or more points, and the straight line is a straight line parallel to the direction of the groove of the diffraction grating of the first part.

5. The light guide device according to claim 1, wherein, The light guide device is configured such that, in the surface of the light guide substrate, the direction of the boundary line between the first part and the second part in the light incident portion is not uniform, and the maximum difference in angle between the line segment or tangent of the boundary line and the reference direction is 75 degrees or more.

6. The light guiding device according to claim 1, wherein, The light guide device is configured such that, in the surface of the light guide substrate, at least one of the first portion and the second portion has at least two portions that are separated from each other by the other of the first portion and the second portion.

7. The light guide device according to claim 1, wherein, The light guide device is configured such that the imaginary horizontal direction and vertical direction when using the light guide device are defined as the x-axis and y-axis, respectively. The direction of the groove of the 1D diffraction grating in the first part is tilted within 5 degrees relative to the y-axis, and the direction of the groove of the 1D diffraction grating in the second part is tilted within 15 degrees relative to the x-axis.

8. The light guide device according to claim 1, wherein, The light guiding device is configured such that the period of the 1D diffraction grating in the first part is less than or equal to the period of the 1D diffraction grating in the second part.

9. The light guide device according to claim 1, wherein, The light guide device is configured such that, on the surface of the light guide substrate, based on a straight line in the vertical direction imaginary when using the light guide device, passing through the center of the smallest circle containing the light incident portion, the area occupied by the second part in the region on the side of the light incident portion away from the light emitting portion is 2% or more.

10. The light guide device according to claim 1, wherein, The light guide device is configured such that, on the surface of the light guide substrate, based on a straight line in the vertical direction imaginary when using the light guide device, passing through the center of the smallest circle containing the light incident portion, the area occupied by the first part in the region closer to the light emitting portion of the light incident portion is 10% or more.

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