Optical system and head-up display system equipped with the same

Abstract

This optical system is provided with a light-guide body. A light beam which enters the light-guide body from a display unit is replicated by diffraction by means of a diffraction structure for an augmented area, in a first direction corresponding to the horizontal direction of an image, or a second direction corresponding to the perpendicular direction of the image. A direction normal to the light-guide body in the augmented area is taken as the Z-axis direction, and a plane tangential to the light tube as the XY-plane. In the XY-plane, where the advancing direction of the center ray of the light beam incident on the augmented area is the X-axis and a direction perpendicular to the X-axis is the Y-axis, then the diffraction structure for the augmented area is formed so that a light beam which is the light beam incident on the augmented area and which is replicated when transmitted through the XY-plane of the augmented area from the Z-axis positive direction, and a light beam which is the augmented-area incident beam replicated when transmitted from the Z-axis negative direction are contained within the field of view angle through which images are visible. The diffraction structure for the augmented area is inclined with respect to the Z-axis direction.

Description

[Technical Field]

[0001] The present disclosure relates to an optical system used to display an image and a head-up display system including the same. [Background technology]

[0002] A vehicle information projection system that uses a head-up display device to display augmented reality (AR) information has been disclosed. The head-up display device projects light representing a virtual image onto the windshield of the vehicle, allowing the driver to view the virtual image together with the real view outside the vehicle.

[0003] As a device for displaying a virtual image, Patent Document 1 describes an optical element having a waveguide (light guide) for expanding an exit pupil in two directions. The optical element can expand the exit pupil by utilizing a diffractive optical element. Furthermore, Document 2 describes a head-mounted display that performs augmented reality (AR) display using a volume hologram diffraction grating. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] U.S. Patent No. 10,429,645 [Patent Document 2] International Publication No. 2018 / 198587 Summary of the Invention [Problem to be solved by the invention]

[0005] However, for example, when an expanded-pupil hologram used in a head-mounted display is realized in a head-up display, the field of view in which the image can be seen is narrow.

[0006] The present disclosure aims to provide an optical system and a head-up display system that expands the range of view in which an image can be seen. [Means for solving the problem]

[0007] The optical system disclosed herein includes a display unit that emits a light beam that is visually recognized by an observer as an image, and a light guide that replicates the light beam. The light guide has an incident surface onto which the light beam from the display unit is incident and an exit surface from which the light beam exits the light guide. A central ray of the light beam that exits the display unit is incident on the incident surface of the light guide. The light beam that enters the incident surface of the light guide is changed in its traveling direction by diffraction due to a diffractive structure in a coupling region within the light guide. The light beam whose traveling direction has been changed is expanded by being replicated in a first direction corresponding to the horizontal direction of the image viewed by the observer, a second direction corresponding to the vertical direction of the image, or both directions by diffraction due to a diffractive structure in an expansion region within the light guide, and then exits from the exit surface. When the normal direction to the surface of the light guide at the center or center of gravity of the extended region is defined as the Z-axis direction, the tangential plane is defined as the XY plane, and the direction perpendicular to the X-axis in the XY plane is defined as the X-axis and the direction perpendicular to the X-axis is defined as the Y-axis, the diffractive structure of the extended region is formed so that the duplicated luminous flux when the luminous flux incident on the extended region passes through the XY plane of the extended region from the positive direction of the Z-axis and the duplicated luminous flux when the luminous flux passes through the XY plane of the extended region from the negative direction of the Z-axis are contained within a viewing angle at which the image can be viewed, and the diffractive structure of the extended region is inclined with respect to the Z-axis direction.

[0008] In addition, the head-up display system of the present disclosure includes the above-mentioned optical system and a translucent member that reflects the light beam emitted from the light guide, and displays an image as a virtual image superimposed on the actual scene that can be seen through the translucent member. [Effects of the Invention]

[0009] The optical system and head-up display system of the present disclosure can expand the field of view in which images can be seen. [Brief explanation of the drawings]

[0010] [Figure 1] FIG. 1 is a schematic perspective view showing the configuration of a light guide body. [Figure 2]An explanatory diagram showing the direction of incident light and emitted light to a light guide of a head-mounted display. [Figure 3] FIG. 1 is an explanatory diagram showing the directions of incident light and emitted light to a light guide of a head-up display; [Figure 4] 1 is a YZ plane cross-sectional view of a vehicle equipped with a head-up display system according to an embodiment of the present invention; [Figure 5A] FIG. 1 is an explanatory diagram showing the optical path of a light beam emitted from a display unit. [Figure 5B] An explanatory diagram showing the horizontal field of view of a virtual image [Figure 5C] An explanatory diagram showing the vertical field of view of a virtual image [Figure 6] FIG. 1 is a perspective view showing a configuration of a light guide according to an embodiment. [Figure 7] An explanatory diagram showing the central optical path of a light beam emitted from a display unit. [Figure 8] Plan view of the first expansion area [Figure 9] IX-IX cross section of Figure 8 [Figure 10] Plan view of the first expansion area [Figure 11] FIG. 1 is an explanatory diagram showing a light beam incident on a diffractive structure and a replicated light beam; [Figure 12] Table showing the numerical values ​​for each example and comparative example [Figure 13] FIG. 1 is an explanatory diagram showing a field of view of a virtual image in Example 1. [Figure 14] FIG. 10 is an explanatory diagram showing the field of view of a virtual image in Comparative Example 1. [Figure 15] FIG. 10 is an explanatory diagram showing the field of view of a virtual image in Example 2. [Figure 16] FIG. 10 is an explanatory diagram showing the field of view of a virtual image in Example 3. [Figure 17] FIG. 10 is an explanatory diagram showing the field of view of a virtual image in Example 4. [Figure 18] FIG. 10 is an explanatory diagram showing the field of view of a virtual image in Example 5. [Figure 19] FIG. 10 is an explanatory diagram showing the field of view of a virtual image in Example 6. [Figure 20] FIG. 13 is an explanatory diagram showing the field of view of a virtual image in Example 7. [Figure 21] FIG. 10 is an explanatory diagram showing the field of view of a virtual image in Comparative Example 2. [Figure 22] Graph showing the relationship between viewing angle and normalized diffraction efficiency [Figure 23] Graph showing the relationship between viewing angle and normalized diffraction efficiency DETAILED DESCRIPTION OF THE INVENTION

[0011] (Summary of the Disclosure) An overview of the present disclosure will first be described with reference to Fig. 1. Fig. 1 is a schematic diagram showing the configuration of a light guide 13. A so-called pupil widening type light guide 13 is used in an optical system used in a head-mounted display (hereinafter referred to as HMD) or the like. The pupil widening type light guide 13 includes a coupling region 21 that receives image light from a display unit 11 and changes the direction of travel, a first widening region 23 that widens the light beam incident in a first direction, and a second widening region 25 that widens the light beam incident in a second direction. The first direction and the second direction intersect with each other and may be, for example, perpendicular to each other.

[0012] The coupling region 21, the first extension region 23, and the second extension region 25 each have a diffraction power for diffracting image light, and an embossed hologram or a volume hologram is formed therein. The embossed hologram is, for example, a diffraction grating. The volume hologram is, for example, a periodic refractive index distribution in a dielectric film. The coupling region 21 changes the traveling direction of the image light incident from the outside so that it heads toward the first extension region 23 by using the diffraction power.

[0013] The first expansion region 23 has, for example, a diffractive structure element disposed therein, and replicates the incident image light by splitting the incident image light into image light traveling in a first direction using diffractive power and image light traveling to the second expansion region 25. For example, in FIG. 1 , the first expansion region 23 has diffractive structure elements disposed at four points 23p aligned in the direction in which the image light travels after repeated total reflection. The diffractive structure element splits the image light at each point 23p, and causes the split image light to travel to the second expansion region 25. As a result, the incident light beam is expanded by being replicated in the first direction into four light beams of image light.

[0014] The second expansion region 25 has, for example, a diffractive structure element disposed therein, and replicates the image light by splitting the incident image light into image light traveling in the second direction using diffractive power and image light emitted from the second expansion region 25 to the outside. For example, in FIG. 1 , three points 25p are arranged in each row in the direction in which the image light travels after repeated total reflection in the second expansion region 25, with a diffractive structure element disposed at each of four rows for a total of 12 points 25p. The image light is split at each point 25p, and the split image light is emitted to the outside. As a result, the incident image light beams in the four rows are each replicated into three image light beams in the second direction, thereby expanding the field of view. In this way, the light guide 13 can replicate 12 image light beams from a single incident image light beam, and can replicate the light beams in both the first and second directions to expand the field of view. The observer can visually recognize each of the twelve beams of image light as a virtual image, and the visual recognition area in which the observer can visually recognize the image light can be widened.

[0015] Next, the difference between a pupil widening type HMD and a head-up display (hereinafter referred to as HUD) will be explained with reference to Figures 2 and 3. Figure 2 is an explanatory diagram showing incident light and outgoing light of an HMD. Figure 3 is an explanatory diagram showing incident light and outgoing light of an HUD.

[0016] 2, the light guide 13 in the HMD faces substantially directly toward the viewing area Ac in which the observer can view a virtual image. Image light incident perpendicularly from the display unit 11 is split within the light guide 13, and the split image light is emitted perpendicularly from the exit surface 27 of the light guide 13 toward the viewing area Ac.

[0017] 3, in the case of a HUD, the image light emitted from the light guide 13 is reflected by, for example, the windshield 5 and made to enter the visible area Ac, so that the divided image light is emitted in an oblique direction from the emission surface 27 of the light guide 13. The optical system for a HUD will be described below.

[0018] (Embodiment) Hereinafter, an embodiment will be described with reference to Figures 4 to 6. Note that components having the same functions as those described above are given the same reference numerals. Also, the inclination angle of the windshield in the figures is shown for ease of understanding and may differ depending on the figure. [1-1.Configuration] [1-1-1. Overall configuration of optical system and head-up display system] A specific embodiment of a head-up display system 1 (hereinafter referred to as HUD system 1) according to the present disclosure will be described. FIG. 4 is a diagram showing a cross section of a vehicle 3 equipped with the HUD system 1 according to the present disclosure. FIG. 5A is an explanatory diagram showing the optical path of a light beam emitted from a display unit. In the embodiment, the HUD system 1 equipped in the vehicle 3 will be described as an example.

[0019] The directions related to the HUD system 1 will be described below based on the X1 axis, Y1 axis, and Z1 axis shown in FIG. 4. The Z1 axis direction is the direction in which the observer views the virtual image Iv from the visibility area Ac in which the observer can view the virtual image Iv. The X1 axis direction is a horizontal direction perpendicular to the Z1 axis. The Y1 axis direction is a direction perpendicular to the X1Z1 plane formed by the X1 axis and the Z1 axis. Therefore, the X1 axis direction corresponds to the horizontal direction of the vehicle 3, the Y1 axis direction corresponds to the approximately vertical direction of the vehicle 3, and the Z1 axis direction corresponds to the approximately forward direction of the vehicle 3.

[0020] As shown in FIG. 4, an optical system 2 is disposed inside a dashboard (not shown) below a windshield 5 of a vehicle 3. An observer D sitting in the driver's seat of the vehicle 3 recognizes the image projected from the HUD system 1 as a virtual image Iv. In this way, the HUD system 1 displays the virtual image Iv superimposed on a real scene visible through the windshield 5. Because multiple replicated images are projected into the visibility area Ac, the observer D can view the virtual image Iv within the visibility area Ac even if the position of his or her eyes shifts in the Y1-axis direction and the X1-axis direction. Regarding the range of the virtual image Iv viewed by the observer D, an angle θh indicating the horizontal viewing angle of the virtual image Iv viewed by the observer D is shown in FIG. 5B, and an angle θv indicating the vertical viewing angle of the virtual image Iv is shown in FIG. 5C. The observer D is a passenger in a moving body such as the vehicle 3, for example, the driver or a passenger sitting in the passenger seat.

[0021] Referring to Figure 4, the HUD system 1 includes an optical system 2 and a windshield 5. The optical system 2 includes a display unit 11, a light guide 13, and a control unit 15. The display unit 11 emits a light beam L1 that forms an image that is visually recognized by the observer as a virtual image Iv. The light guide 13 divides and copies the light beam L1 emitted from the display unit 11, and guides the copied light beam L2 to the windshield 5. The light beam L2 reflected by the windshield 5 is displayed as a virtual image Iv superimposed on the actual scene that is visible through the windshield 5.

[0022] The display unit 11 displays an image under the control of an external control unit. For example, a backlit liquid crystal display, an organic light-emitting diode (OLED) display, or a plasma display can be used as the display unit 11. Alternatively, the display unit 11 may generate an image using a screen that diffuses or reflects light, a projector, or a scanning laser. The display unit 11 can display image content including various information such as road navigation guidance, the distance to the vehicle ahead, the remaining battery charge, and the current vehicle speed. In this way, the display unit 11 emits a light beam L1 including image content that is visually recognized by the observer D as a virtual image Iv.

[0023] The control unit 15 can be realized by a circuit configured with semiconductor elements, etc. The control unit 15 can be configured with, for example, a microcomputer, a CPU, an MPU, a GPU, a DSP, an FPGA, or an ASIC. The control unit 15 realizes predetermined functions by reading data and programs stored in a built-in storage unit (not shown) and performing various arithmetic processing. The control unit 15 also includes a storage device 17.

[0024] The storage device 17 is a storage medium that stores programs and data necessary to realize the functions of the control unit 15. The storage device 17 can be realized, for example, by a hard disk drive (HDD), an SSD, a RAM, a DRAM, a ferroelectric memory, a flash memory, a magnetic disk, or a combination of these. The storage device 17 stores multiple image data representing the virtual image Iv. The control unit 15 determines the virtual image Iv to be displayed based on vehicle-related information acquired from an external source. The control unit 15 reads out the image data of the determined virtual image Iv from the storage device and outputs it to the display unit 11.

[0025] [1-1-2. Light guide] The configuration of the light guide 13 will be described with reference to FIG. 6. FIG. 6 is a perspective view showing the configuration of the light guide 13. The directions of the extended regions of the light guide 13 will be described below based on the X-axis, Y-axis, and Z-axis shown in FIG. 6. The normal direction to the surface of the light guide 13 at the center or center of gravity of the first extended region 23 is defined as the Z-axis direction, and the tangential plane is defined as the XY plane. In the XY plane, the traveling direction of the central ray of the light beam incident on the first extended region 23 is defined as the X-axis direction, and the direction perpendicular to the X-axis direction is defined as the Y-axis direction. Similarly, the normal direction to the surface of the light guide 13 at the center or center of gravity of the second extended region 25 is defined as the Za-axis direction, and the tangential plane is defined as the XaYa plane. In the XaYa plane, the traveling direction of the central ray of the light beam incident on the second extended region is defined as the Xa-axis direction, and the direction perpendicular to the Xa-axis direction is defined as the Ya-axis direction.

[0026] The light guide 13 has a first main surface 13a and a second main surface 13b. The first main surface 13a and the second main surface 13b are opposite each other. The light guide 13 has an incident surface 20, a coupling region 21, a first extended region 23, a second extended region 25, and an exit surface 27. The incident surface 20, the coupling region 21, the first extended region 23, and the second extended region 25 are included in the second main surface 13b, and the exit surface 27 is included in the first main surface 13a. The exit surface 27 faces the second extended region 25. Note that the coupling region 21, the first extended region 23, and the second extended region 25 may be located between the first main surface 13a and the second main surface 13b. The first main surface 13a faces the windshield 5. In this embodiment, the incident surface 20 is included in the coupling region 21, but it may also be included in the first main surface 13a as a surface facing the coupling region 21. Furthermore, the exit surface 27 may be included in the second expansion region 25 .

[0027] The coupling region 21, the first extended region 23, and the second extended region 25 each have a different diffraction power, and each has a diffractive structure element formed therein. The coupling region 21, the first extended region 23, and the second extended region 25 each have a different diffraction angle of image light. The light guide 13 is configured to totally reflect the incident light beam inside. The light guide 13 is formed, for example, of a glass or resin plate with a mirror-finished surface. The light guide 13 is not limited to a flat shape, but may also have a curved shape. In this way, the light guide 13 includes a diffractive structure element, such as a volume hologram, that partially diffracts light. When the coupling region 21, the first extended region 23, and the second extended region 25 include a volume hologram, they become three-dimensional regions.

[0028] The coupling region 21 is a region where the light beam L1 emitted from the display unit 11 enters through the incident surface 20 and changes the traveling direction of the light beam L1. The coupling region 21 has diffractive power, and changes the propagation direction of the incident light beam L1 toward the first extended region 23, and emits it as light beam L1A. In this embodiment, coupling refers to a state where the light beam L1 propagates within the light guide 13 under total reflection conditions.

[0029] The first extended region 23 extends the light beam L1A in a first direction corresponding to the horizontal direction of the virtual image Iv and outputs the light beam L1A to the second extended region 25 in a second direction intersecting the first direction. In the first extended region 23 extending the light beam L1A in the first direction, the length in the first direction is greater than the length in the second direction. In the embodiment, the light guide 13 is disposed so that the first direction is the horizontal direction (the direction of the X1 axis). However, the first direction does not have to completely coincide with the horizontal direction. The light beam L1A propagating from the coupling region 21 propagates in the first direction while repeatedly being totally reflected by the first principal surface 13a and the second principal surface 13b. The light beam L1A is replicated by the diffractive structure of the first extended region 23 formed on the second principal surface 13b and is output to the second extended region 25.

[0030] The second extended region 25 extends the light beam L1B in a second direction corresponding to the vertical direction of the virtual image Iv and emits the extended light beam L2 from the exit surface 27. The second direction is, for example, perpendicular to the first direction. Note that the light guide 13 is disposed such that the second direction is the Z1-axis direction. The light beam L1B propagating from the first extended region 23 propagates in the second direction while repeatedly being totally reflected by the first principal surface 13a and the second principal surface 13b. The light beam L1B is replicated by the diffractive structure of the second extended region 25 formed on the second principal surface 13b and is emitted to the outside of the light guide 13 via the exit surface 27.

[0031] Therefore, from the viewpoint of observer D, light guide 13 expands light beam L1, which has been incident on incident surface 20 and has its traveling direction changed, by replicating it in the horizontal direction (the direction of the X1 axis) of virtual image Iv viewed by observer D, and then further expands it by replicating it in the vertical direction (the direction of the Y1 axis) of virtual image Iv, and emits light beam L2 from exit surface 27. Here, replicating the image in the horizontal direction is not limited to replicating it in the completely horizontal direction, but also includes replicating it in an approximately horizontal direction. Furthermore, replicating the image in the vertical direction is not limited to replicating it in the completely vertical direction, but also includes replicating it in an approximately vertical direction.

[0032] [1-1-3. Order of pupil dilation] In the light guide 13 arranged as described above, the magnitude of the wave vector of the first extended region 23 and the second extended region 25 in the HUD system 1 differs depending on the order of pupil expansion of the light beam L1 of the image light. The order of pupil expansion in this embodiment will be described with reference to Fig. 7. Fig. 7 is an explanatory diagram showing the optical path of the center of the light beam emitted from the display unit.

[0033] The luminous flux L1 of image light incident on the light guide 13 changes its propagation direction to the first expansion region 23, which expands the pupil in the horizontal direction (X-axis direction) as a first direction, due to the diffractive structure formed in the coupling region 21. Therefore, after being obliquely incident on the coupling region 21, the luminous flux L1 is affected by the wave vector k1 shown in FIG. 7 and propagates as the luminous flux L1A toward the first expansion region 23.

[0034] Light beam L1A propagating toward the first extended region 23 extending in the first direction is split by the diffractive structure formed in the first extended region 23 while repeatedly undergoing total reflection into light beam L1A propagating in the first direction and light beam L1B, which is duplicated and changes its propagation direction toward the second extended region 25. At this time, the duplicated light beam L1B is affected by the wave vector k2 shown in FIG. 7 and propagates toward the second extended region 25.

[0035] The light beam L1B, whose propagation direction has been changed to the second extended region 25 extending along the negative direction of the Z1 axis as the second direction, is split by the diffractive structure formed in the second extended region 25 into the light beam L1B propagating in the second direction and a duplicated light beam L2 that is emitted from the second extended region 25 to the outside of the light guide 13 via the exit surface 27. At this time, the duplicated light beam L2 is affected by the wave vector k3 shown in FIG. 7 and propagates in the direction of the exit surface 27.

[0036] [1-1-4. Diffraction structure] Next, the diffractive structure of the first extended region 23 will be described with reference to Fig. 8 and Fig. 9. Fig. 8 is a plan view of the first extended region 23, and Fig. 9 is a cross-sectional view taken along line IX-IX in Fig. 8.

[0037] If the diffractive structure of the first extended region 23 is, for example, a volume hologram, interference fringes 31 are formed as the diffractive structure in the first extended region 23. In the first extended region 23, the angle between the direction in which the interference fringes 31 extend on the XY plane and the direction in which the light beam L1A travels is defined as α. Furthermore, in a vertical cross-sectional view of the diffractive structure, i.e., in a cross-sectional view taken along the arrows IX-IX in FIG. 8 , the inclination angle of the interference fringes 31 with respect to the vertical direction is defined as β.

[0038] As shown in Figure 10, a light beam L1A propagating toward the first extended region 23 extending in a first direction is split into a light beam L1A propagating in the first direction and a light beam L1B that is duplicated and changes its propagation direction to the second extended region 25 by the diffractive structure formed in the first extended region 23 while repeatedly undergoing total reflection.

[0039] 11 shows, in a spherical coordinate system, a light beam L1B that is duplicated when the light beam L1A passes through the XY plane of the first extended area 23 from the negative direction to the positive direction of the Z axis. When the viewing angle of the virtual image Iv seen by the observer D is ±F degrees, the angle of the central ray of the light beam L1A with respect to the Z axis is θA degrees, and the angle of the central ray of the light beam L1B with respect to the Z axis is θB degrees, the following formulas (1) and (2) are satisfied. |θA-θB| < |F| / 2 (1) |β|×2×cos(α) ≦ |F|-|θA-θB|···(2) formula However, β≠0.

[0040] The horizontal viewing angle of the virtual image Iv is 2×|F|=θh, and the vertical viewing angle of the virtual image Iv is 2×|F|=θv (see FIGS. 5B and 5C). The horizontal viewing angle will be described below, but the same relationship applies to the vertical viewing angle.

[0041] In equation (1), |θA-θB| determines the center between two peaks of the diffraction efficiency when light passes from the positive direction to the negative direction along the Z axis and when it passes from the negative direction to the positive direction. Furthermore, |β|×2×cos(α) in equation (2) determines the distance between the two peaks of the diffraction efficiency when light passes from the positive direction to the negative direction along the Z axis and when it passes from the negative direction to the positive direction. When β=0, the light beam L1B copied when the light beam L1A passes through the first extension region 23 from the positive direction to the negative direction along the Z axis and the light beam L1B copied when the light beam L1A passes through the first extension region 23 from the negative direction to the positive direction along the Z axis have the same diffraction efficiency, and therefore the horizontal angle of view does not widen. Conversely, when β≠0, the light beam L1A copied when it passes through the first extension region 23 from the positive direction of the Z axis to the negative direction and the light beam L1B copied when it passes through the first extension region 23 from the negative direction of the Z axis to the positive direction have different diffraction efficiencies, and therefore the horizontal angle of view can be expanded.

[0042] Next, each example and comparative example will be described with reference to FIGS. 12 to 21. FIG. 12 is a table of parameters for each example and comparative example. FIGS. 13 to 21 show the diffraction efficiency at different viewing angles for each example and comparative example. FIGS. 13(a) to 21(a) show the diffraction efficiency of the light beam L1B replicated when the light beam L1A passes through the first extended region 23 from the negative direction of the Z axis to the positive direction of the Z axis under each condition. FIGS. 13(b) to 21(b) show the diffraction efficiency of the light beam L1B replicated when the light beam L1A passes through the first extended region 23 from the positive direction of the Z axis to the negative direction under each condition. In each example and comparative example, the thickness of the volume hologram is 5 μm.

[0043] In Example 1 to Comparative Example 2, the viewing angle F is 3.50 degrees. The viewing angle F in Example 1 to Comparative Example 2 indicates the horizontal (left-right) viewing angle (horizontal viewing angle). A similar relationship holds for the vertical viewing angle (vertical viewing angle). In Example 1 shown in FIG. 13, the angles θA and θB described in relation to equations (1) and (2) are 50.00 degrees, the angle α is 45.00 degrees, and the tilt angle β is 1.24 degrees. FIG. 13(c) shows the diffraction efficiency of the light beam L1B that has traveled through the first extended region 23 once around the Z axis. That is, FIG. 13(c) shows the diffraction efficiency obtained by adding together the diffraction efficiency of the light beam L1B that is duplicated when it passes through the first extended region 23 from the negative direction to the positive direction of the Z axis and the diffraction efficiency of the light beam L1B that is duplicated when it passes through the first extended region 23 from the positive direction to the negative direction of the Z axis. The diffraction efficiency is shown in stages from level A1 to A5, with the diffraction efficiency increasing from level A1 to A4. Level A1 indicates a diffraction efficiency of 0% or more and less than 10%, level A2 indicates a diffraction efficiency of 10% or more and less than 20%, level A3 indicates a diffraction efficiency of 20% or more and less than 30%, and level A4 indicates a diffraction efficiency of 30% or more and less than 40%.

[0044] According to the first embodiment, β≠0 and formulas (1) and (2) are satisfied, so that the diffraction efficiency peaks are separated on the left and right sides of the angle of view, and high diffraction efficiency can be obtained over a wide range, as shown in Figures 13(a) and 13(b). This allows for the effect of widening the angle of view.

[0045] 14, the angles θA and θB are 50.00 degrees, the angle α is 45.00 degrees, and the tilt angle β is 0 degree. Because β=0, the peak positions of the diffraction efficiency within the viewing angle are the same whether light passes through the first extension region 23 from the positive direction of the Z axis or from the negative direction. Therefore, even if the diffraction efficiency in the center is good, the effect of widening the viewing angle cannot be obtained.

[0046] In the case of Example 2 shown in FIG. 15, the angle θA is 49.00 degrees, the angle θB is 50.00 degrees, the angle α is 44.57 degrees, and the tilt angle β is 0.71 degrees. According to Example 2, β≠0, and formulas (1) and (2) are satisfied. As shown in FIG. 15(a), the diffraction efficiency of the light beam L1B copied when it passes through the first extended region 23 from the negative direction to the positive direction of the Z axis is high at the center of the field of view. Also, as shown in FIG. 15(b), the diffraction efficiency of the light beam L1B copied when it passes through the first extended region 23 from the positive direction to the negative direction of the Z axis is high at the right side of the field of view. As such, the peak positions of the diffraction efficiencies are separated, thereby achieving the effect of widening the field of view.

[0047] In Example 3 shown in FIG. 16, the angle θA is 59.00 degrees, the angle θB is 60.00 degrees, the angle α is 44.71 degrees, and the tilt angle β is 0.71 degrees. According to Example 3, β≠0, satisfying formulas (1) and (2). In FIG. 16(a), level A1a indicates a diffraction efficiency of 0% or more and less than 5%, level A1b indicates a diffraction efficiency of 5% or more and less than 10%, level A2a indicates a diffraction efficiency of 10% or more and less than 15%, level A2b indicates a diffraction efficiency of 15% or more and less than 20%, and level A3a indicates a diffraction efficiency of 20% or more and less than 25%. As shown in FIG. 16(a), the diffraction efficiency of the light beam L1B replicated when passing through the first extension region 23 from the negative direction to the positive direction of the Z axis is high at the center of the field angle. 16(b), the diffraction efficiency of the light beam L1B that is duplicated when it passes through the first extension region 23 from the positive direction to the negative direction of the Z axis is higher on the right side of the angle of view. In this way, the peak positions of the diffraction efficiencies are separated, which provides the effect of widening the angle of view.

[0048] In the case of Example 4 shown in FIG. 17, the angle θA is 59.00 degrees, the angle θB is 58.50 degrees, the angle α is 50.76 degrees, and the tilt angle β is −0.32 degrees. According to Example 4, β≠0, and formulas (1) and (2) are satisfied. As shown in FIG. 17(a), the diffraction efficiency of the light beam L1B copied when it passes through the first extended region 23 from the negative direction to the positive direction of the Z axis is high at the center of the field of view. As shown in FIG. 17(b), the diffraction efficiency of the light beam L1B copied when it passes through the first extended region 23 from the positive direction to the negative direction of the Z axis is high at the left side of the field of view. As such, the peak positions of the diffraction efficiencies are separated, thereby achieving the effect of widening the field of view.

[0049] In the case of Example 5 shown in FIG. 18, the angle θA is 59.00 degrees, the angle θB is 59.55 degrees, the angle α is 34.85 degrees, and the tilt angle β is 0.48 degrees. According to the angle example 5, β≠0, which satisfies formulas (1) and (2). In FIG. 18, level A5 indicates a diffraction efficiency of 40% or more and less than 50%. As shown in FIG. 18(a), the diffraction efficiency of the light beam L1B copied when passing through the first extended region 23 from the negative direction to the positive direction of the Z axis is high at the center of the field of view. Also, as shown in FIG. 18(b), the diffraction efficiency of the light beam L1B copied when passing through the first extended region 23 from the positive direction to the negative direction of the Z axis is high on the right side of the field of view. Since the peak positions of the diffraction efficiencies are separated, the effect of widening the field of view can be achieved.

[0050] In Example 6 shown in FIG. 19, the angle θA is 50.00 degrees, the angle θB is 46.00 degrees, the angle α is 46.80 degrees, and the tilt angle β is −2.83 degrees. In FIG. 19, level A1c indicates a diffraction efficiency of 0% or more and less than 2%, level A1d indicates a diffraction efficiency of 2% or more and less than 4%, level A1e indicates a diffraction efficiency of 4% or more and less than 6%, level A1f indicates a diffraction efficiency of 6% or more and less than 8%, and level A1g indicates a diffraction efficiency of 8% or more and less than 10%. According to Example 6, β≠0, but equations (1) and (2) are not satisfied. Therefore, as shown in FIGS. 19(a) and 19(b), the peak positions of the diffraction efficiencies within the viewing angle are different when light passes through the first extension region 23 from the positive direction of the Z axis and when it passes through the first extension region 23 from the negative direction. This results in an expanded viewing angle. However, since the formulas (1) and (2) are not satisfied, the diffraction efficiency peaks further outward in the angle of view, and as shown in FIG. 19(b), the diffraction efficiency within the angle of view of the light beam L1B that is replicated when passing through the first extension region 23 from the positive direction to the negative direction of the Z axis is low, and the effect of widening the angle of view is smaller than in Examples 1 to 5.

[0051] In Example 7 shown in FIG. 20 , the angle θA is 50.00 degrees, the angle θB is 53.00 degrees, the angle α is 43.81 degrees, and the tilt angle β is 2.12 degrees. According to Example 7, although β≠0, formulas (1) and (2) are not satisfied. Therefore, as shown in FIGS. 20(a) and 20(b), the peak positions of the diffraction efficiencies within the viewing angle are different when light passes through the first extended region 23 from the positive direction of the Z axis and when light passes through the first extended region 23 from the negative direction of the Z axis. This results in a wider viewing angle. However, because formulas (1) and (2) are not satisfied, the diffraction efficiency within the viewing angle of the light beam L1B, which is replicated when light passes through the first extended region 23 from the positive direction to the negative direction of the Z axis, is low, as shown in FIG. 20(b). This results in a smaller widening effect of the viewing angle than in Examples 1 to 5.

[0052] 21, the angles θA and θB are 59.00 degrees, the angle α is 52.97 degrees, and the tilt angle β is 0. Although the value of α is different from that of Comparative Example 1, β=0 as in Comparative Example 1. Therefore, the peak positions of the diffraction efficiency within the viewing angle are the same whether light is transmitted through the first extension region 23 from the positive direction of the Z axis or from the negative direction. Therefore, even though the diffraction efficiency in the center is good, the effect of widening the viewing angle cannot be obtained.

[0053] Furthermore, even when the thickness T in the Z direction of the volume hologram shown in FIG. 9 and the light beam L1A with a wavelength λ [μm] satisfy the following relational expression, the diffraction efficiency is improved by this embodiment. T>(-2.3576×λ+0.0952)×|F|+(22.3540×λ-0.9125) ···(3) formula

[0054] 22 is a graph showing an example of normalized diffraction efficiency when the thickness T of equation (3) is near the lower limit. When the thickness T is greater than the value on the right side of equation (3), the diffraction efficiency may become zero within the range of the viewing angle. This results in a loss of part of the image, degrading the quality. However, this embodiment improves the diffraction efficiency, making it possible to adopt a volume hologram thickness that satisfies the relationship of equation (3).

[0055] Furthermore, even when the thickness T in the Z direction of the volume hologram shown in FIG. 9 and the light beam L1A with a wavelength λ [μm] satisfy the following relational expression, the diffraction efficiency is improved by this embodiment. T < (-3.8645×λ-0.2185)×|F|+(37.4910×λ+1.5298) ···(4) formula

[0056] 23 is a graph showing an example of normalized diffraction efficiency when the thickness T of equation (4) is near the upper limit. When the thickness T is smaller than the value on the right side of equation (4), the diffraction efficiency becomes zero or greater within half the range of the viewing angle. As a result, when the thickness T is equal to or greater than the value on the right side of equation (4), the range in which the diffraction efficiency becomes zero or greater becomes too narrow. However, in the range below the value on the right side of equation (4), the present embodiment improves the diffraction efficiency, making it possible to display images over the entire range of the viewing angle.

[0057] In this embodiment, the second expansion region 25 also has a structure similar to the diffractive structure of the first expansion region 23. Such a structure may be provided in only one of the first expansion region 23 and the second expansion region 25, or the optical system 2 may further include another expansion region that has such a diffractive structure. Alternatively, the functions of the first expansion region 23 and the second expansion region 25 may be realized by a single expansion region, and this single expansion region may have, for example, two-dimensional interference fringes, thereby replicating the incident light beam in both the horizontal and vertical directions.

[0058] [1-2. Effects, etc.] The optical system 2 of the present disclosure includes a display unit 11 that emits a light beam L1 that is viewed by an observer D as a virtual image Iv, and a light guide 13 that replicates the light beam L1. The light guide 13 has an incident surface 20 onto which the light beam L1 from the display unit 11 is incident, and an exit surface 27 from which the light beam L2 from the light guide 13 is emitted. A central ray of the light beam L1 that is emitted from the display unit 11 is incident on the incident surface 20 of the light guide 13. The light beam L1 that is incident on the incident surface 20 of the light guide 13 is diffracted by a diffractive structure in a coupling region within the light guide 13, and its traveling direction is changed. The light beam whose traveling direction has been changed is expanded by being diffracted by a diffractive structure in an extension region within the light guide 13, and is then output from the exit surface 27. When the normal direction to the surface of the light guide 13 at the center or center of gravity of the extended region is defined as the Z-axis direction, the tangential plane is defined as the XY plane, the light beam entering the extended region is defined as light beam L1A, the light beam diffracted by the extended region and emitted as light beam L1B, and in the XY plane, the direction of travel of the central ray of light beam L1A is defined as the X-axis, and the direction perpendicular to the X-axis is defined as the Y-axis, the diffraction structure of the extended region is formed so that the duplicated light beam L1B when light beam L1A passes through the XY plane of the extended region from the positive direction of the Z-axis and the duplicated light beam L1B when light beam L1A passes through the XY plane of the extended region from the negative direction of the Z-axis are contained within a viewing angle at which a virtual image can be viewed, and the diffraction structure of the extended region is inclined with respect to the Z-axis direction.

[0059] Because the diffractive structure of the extended region is tilted with respect to the Z-axis direction, the peaks of the diffraction efficiencies of the duplicated light beam L1B when light beam L1A passes through the XY plane of the extended region from the positive direction of the Z-axis and the duplicated light beam L1B when light beam L1A passes through the XY plane of the extended region from the negative direction of the Z-axis can be formed at different positions within the field of view. This makes it possible to provide an optical system with an expanded field of view in which a virtual image can be seen.

[0060] Furthermore, by projecting the light emitted from the optical system 2 onto the windshield 5 of the vehicle 3, a virtual image Iv suitable for the observer D driving the vehicle 3 can be displayed.

[0061] (Other embodiments) As described above, the above embodiment has been described as an example of the technology disclosed in the present application. However, the technology in the present disclosure is not limited to this, and can be applied to embodiments in which appropriate modifications, substitutions, additions, omissions, etc. are made. Therefore, other embodiments will be exemplified below.

[0062] In the above embodiment, the diffraction structure of the extended area is an interference pattern, but it is not limited to this. For example, it may be a physical uneven structure filled with resin.

[0063] In the above embodiment, the split and replicated light beam L2 is reflected by the windshield 5 to allow the observer D to view the virtual image Iv, but this is not limiting. A combiner may be used instead of the windshield 5, and the split and replicated light beam L2 may be reflected by the combiner to allow the observer D to view the virtual image Iv.

[0064] In the above embodiment, the first direction in which the light beam L1A is expanded in the first expansion region 23 and the second direction in which the light beam L1B is expanded in the second expansion region 25 are perpendicular to each other, but this is not limited to this. As shown in Fig. 6, the light beam L1A is expanded in the first direction in the first expansion region 23 as long as the component expanding in the horizontal direction is larger than the component expanding in the direction along the Z axis, and the light beam L1B is expanded in the second direction in the second expansion region 25 as long as the component expanding in the direction along the Z axis is larger than the component expanding in the horizontal direction.

[0065] In the above embodiment, the HUD system 1 is described as being applied to a vehicle 3 such as an automobile. However, the object to which the HUD system 1 is applied is not limited to the vehicle 3. The object to which the HUD system 1 is applied may be, for example, a train, a motorcycle, a ship, or an airplane, or may be an amusement machine that does not involve movement. In the case of an amusement machine, the light beam from the display unit 11 is reflected by a transparent curved plate that serves as a translucent member that reflects the light beam emitted from the display unit 11 instead of the windshield 5. Furthermore, the actual scene that the user can view through the transparent curved plate may be an image displayed by another image display device. In other words, a virtual image generated by the HUD system 1 may be superimposed on an image displayed by another image display device. In this manner, any of the windshield 5, a combiner, and a transparent curved plate may be used as the translucent member in the present disclosure.

[0066] In the above embodiment, the optical system 2 is used in the HUD system 1 that displays the virtual image Iv, but the present invention is not limited to this. The optical system 2 may be used in, for example, an image display system in which the observer directly observes the light beam emitted from the emission surface 27, rather than viewing the virtual image through a light-transmitting member. In this case, the observer is someone who directly views the image formed by the emitted light beam, and is therefore not limited to a passenger on a moving object.

[0067] (Outline of the embodiment) (1) The optical system disclosed herein includes a display unit that emits a light beam that is visually recognized by an observer as an image, and a light guide that replicates the light beam. The light guide has an incident surface onto which the light beam from the display unit is incident and an exit surface from which the light beam exits the light guide. A central ray of the light beam that exits the display unit is incident on the incident surface of the light guide. The light beam that enters the incident surface of the light guide is changed in its traveling direction by diffraction due to a diffractive structure in a coupling region within the light guide. The light beam whose traveling direction has been changed is expanded by being replicated in a first direction corresponding to the horizontal direction of a virtual image perceived by the observer, a second direction corresponding to the vertical direction of the image, or both directions by diffraction due to a diffractive structure in an expansion region within the light guide, and then exits from the exit surface. When the normal direction to the surface of the light guide at the center or center of gravity of the extended region is defined as the Z-axis direction, the tangential plane is defined as the XY plane, and the direction perpendicular to the X-axis in the XY plane is defined as the X-axis and the direction perpendicular to the X-axis is defined as the Y-axis, the diffractive structure of the extended region is formed so that the duplicated luminous flux when the luminous flux incident on the extended region passes through the XY plane of the extended region from the positive direction of the Z-axis and the duplicated luminous flux when the luminous flux passes through the XY plane of the extended region from the negative direction of the Z-axis are contained within a viewing angle at which the image can be viewed, and the diffractive structure of the extended region is inclined with respect to the Z-axis direction.

[0068] Because the diffractive structure of the extended region is tilted with respect to the Z-axis direction, the peaks of the diffraction efficiencies of the replicated light beams when a light beam incident on the extended region passes through the XY plane of the extended region from the positive direction of the Z-axis and the replicated light beams when the light beam passes through the XY plane of the extended region from the negative direction of the Z-axis can be formed at different positions within the field of view, thereby providing an optical system with an expanded field of view in which an image can be seen.

[0069] (2) In the optical system of (1), when the viewing angle of the image seen by the observer is ±F degrees, the angle between the diffractive structure of the extended area in the XY plane and the traveling direction of the light beam incident on the extended area is α degrees, the tilt angle between the diffractive structure and the Z axis is β degrees, the angle between the central ray of the light beam incident on the extended area and the Z axis is θA degrees, and the angle between the central ray of the light beam diffracted by the extended area and emitted from the extended area is θB degrees, the following relationship is satisfied. |θA-θB| < |F| / 2, and |β|×2×cos(α) ≦ |F|-|θA-θB|, However, β ≠ 0

[0070] (3) In the optical system of (2), the optical system has two expansion regions, one of which expands the light beam incident on it by replicating it in a first direction corresponding to the horizontal direction of the image seen by the observer, and the other expansion region expands the light beam incident on it by replicating it in a second direction corresponding to the vertical direction of the virtual image seen by the observer.

[0071] (4) In the optical system of (3), the relational expression is satisfied in the extended region having the narrower diffraction pitch of the diffractive structure among the two extended regions.

[0072] (5) In the optical system of any one of (1) to (4), the extended region includes a transmission volume hologram.

[0073] In the optical system of (6)(5), the thickness T of the volume hologram in the Z direction and the wavelength λ [μm] of the light beam incident on the volume hologram satisfy the following relational expression. T>(-2.3576×λ+0.0952)×|F|+(22.3540×λ-0.9125)

[0074] (7) In the optical system of (5) or (6), the thickness T of the volume hologram in the Z direction and the wavelength λ [μm] of the light beam incident on the volume hologram satisfy the following relational expression. T < (-3.8645×λ-0.2185)×|F|+(37.4910×λ+1.5298)

[0075] (8) In any one of the optical systems (1) to (7), the central ray of the light beam emitted from the display unit is incident at an angle with respect to the normal direction of the incident surface of the light guide, and the central ray of the light beam emitted from the light guide is emitted toward the translucent member at an angle with respect to the normal direction of the exit surface of the light guide.

[0076] (9) The head-up display system of the present disclosure comprises any one of the optical systems (1) to (8) and a light-transmitting member that reflects the light beam emitted from the light guide, and displays an image as a virtual image superimposed on a real scene visible through the light-transmitting member.

[0077] (10) In the head-up display system of (9), the light-transmitting member is a windshield of a moving object. [Industrial Applicability]

[0078] The present disclosure is applicable to optical systems and head-up display systems that replicate and display images. [Explanation of symbols]

[0079] 1 Head-up display system 3 vehicles 3a center line 5 Windshield 11 Display section 13 Light guide 13a First main surface 13b Second principal surface 15 Control Unit 17 Storage device 20 Entrance plane 21 Combined area 23 First Expansion Area 23a points 25 Second Expansion Area 25a points 27 Exit surface Ac Visibility Zone D. Observer IV Virtual Image k1, k2, k3 wave vectors L1, L1A, L1B, L2 luminous flux

Claims

1. a display unit that emits a light beam that is visually recognized by an observer as the image; a light guide that replicates the light beam; the light guide has an incident surface onto which the light flux from the display unit is incident and an exit surface from which the light flux exits the light guide, a central ray of light emitted from the display unit is incident on an incident surface of the light guide, the direction of travel of the light beam incident on the incident surface of the light guide is changed by diffraction due to the diffractive structure of the coupling region within the light guide, the light beam whose propagation direction has been changed is expanded by being diffracted by a diffractive structure in an expanded region of the light guide in a first direction corresponding to the horizontal direction of the image visually recognized by an observer, or in a second direction corresponding to the vertical direction of the image, or in both directions, and then output from the output surface; a normal direction to the surface of the light guide at the center or center of gravity of the extended region is defined as a Z-axis direction, and a tangential plane is defined as an XY plane; In the XY plane, when the traveling direction of the central ray of the light beam incident on the extended area is the X axis and the direction perpendicular to the X axis is the Y axis, the diffractive structure of the extended region is formed so that a duplicated light beam when a light beam incident on the extended region passes through the XY plane of the extended region from the positive direction of the Z axis and a duplicated light beam when the light beam passes through the XY plane of the extended region from the negative direction of the Z axis are contained within a viewing angle at which the image can be viewed, The diffractive structure of the extended region is inclined with respect to the Z-axis direction. optical system.

2. When the viewing angle of the image seen by the observer is ±F degrees, the angle between the diffractive structure of the extended area in the XY plane and the traveling direction of the light beam incident on the extended area is α degrees, the tilt angle between the diffractive structure and the Z axis is β degrees, the angle between the central ray of the light beam incident on the extended area and the Z axis is θA degrees, and the angle between the central ray of the light beam diffracted by the extended area and emitted from the extended area is θB degrees, the following relational expressions are satisfied: The optical system of claim 1 . |θA−θB| < |F| / 2, and |β|×2×cos(α) ≦ |F|−|θA−θB|, However, β ≠ 0

3. the optical system has two of the extended regions; one of the extension areas extends the light beam incident on the one extension area by duplicating it in the first direction corresponding to the horizontal direction of the image visually recognized by the observer, the other extension area extends the light beam incident on the other extension area by replicating it in the second direction corresponding to the vertical direction of the image viewed by the observer; The optical system according to claim 2 .

4. the relational expression is satisfied in the extension region having a narrower diffraction pitch of the diffractive structure in the two extension regions; The optical system according to claim 3 .

5. the expansion region includes a transmission volume hologram; 5. The optical system according to claim 1.

6. The thickness T [μm] of the volume hologram in the Z direction and the wavelength λ [μm] of the light beam incident on the volume hologram satisfy the following relational expression: The optical system according to claim 5 . T>(-2.3576×λ+0.0952)×|F|+(22.3540×λ-0.9125)

7. The thickness T [μm] of the volume hologram in the Z direction and the wavelength λ [μm] of the light beam incident on the volume hologram satisfy the following relational expression:

7. The optical system according to claim 5 or 6. T < (-3.8645×λ-0.2185)×|F|+(37.4910×λ+1.5298)

8. a central ray of the light flux emitted from the display unit is incident at an angle with respect to a normal direction to the incident surface of the light guide, and a central ray of the light flux emitted from the light guide is emitted at an angle with respect to a normal direction to the exit surface of the light guide; 8. The optical system according to claim 1.

9. The optical system according to any one of claims 1 to 8; a light-transmitting member that reflects the light beam emitted from the light guide, The image is displayed as a virtual image superimposed on a real scene visible through the light-transmitting member. Head-up display system.

10. The light-transmitting member is a windshield of a moving object. The head-up display system of claim 9.

Images