Optical system and head-up display system equipped with same

Abstract

This optical system is equipped with: a first expansion region for expanding by increasing the number of beams of light by splitting and replicating a beam of light advancing in a first direction into a beam of light advancing in a second direction, which intersects the first direction; and a second expansion region which corresponds to the image-visible region and expands by increasing the number of beams of light by splitting and replicating the beams of light advancing in the second direction. The first expansion region has a center region which includes the center of the first expansion region, and an end-section region which is located on one or more ends of the first expansion region and in which the diffracted light amount is smaller than half the diffracted light amount inside the center region.

Description

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

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

[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, for example, allowing the driver to view the virtual image together with the actual view outside the vehicle.

[0003] As a device for displaying a virtual image, Patent Document 1 describes an optical system equipped with a waveguide (light guide) for expanding an exit pupil in two directions. The optical system can expand the exit pupil by utilizing a diffractive optical element. Furthermore, Document 2 describes a head-mounted display that keeps the amount of light diffracted from a diffraction grating constant by modulating the height and duty ratio of the diffraction grating.

[0004] US Patent No. 10,429,645 US Patent Application Publication No. 2009 / 0097122

[0005] However, if there is angular variation in the light beam incident on an optical system that expands the exit pupil, defects will appear in the image that emerges from the optical system. Also, there is a demand for displaying images with higher brightness.

[0006] The present disclosure provides an optical system and a head-up display system that prevent image chipping and improve the efficiency of light flux utilization.

[0007] The optical system disclosed herein allows an observer to view an image, and includes: a first expansion region that expands the area by dividing and duplicating a light beam traveling in a first direction into light beams traveling in a second direction intersecting the first direction and increasing the number of the light beams; and a second expansion region that expands the area by dividing and duplicating the light beam traveling in the second direction and increasing the number of the light beams, and corresponds to the visible area of ​​the image. The first expansion region has a central region that includes a center of the first expansion region, and an end region at least on one end side of the first expansion region, in which the amount of diffracted light is less than half the amount of diffracted light in the central region.

[0008] In addition, the head-up display system of the present disclosure includes the above-mentioned optical system, a display unit that emits a light beam before it is expanded by the optical system, and a translucent member that reflects the light beam emitted from the optical system, and displays an image as a virtual image superimposed on the real scene that can be seen through the translucent member.

[0009] According to the optical system and head-up display system of the present disclosure, it is possible to provide an optical system and a head-up display system that prevent image chipping and improve the efficiency of light flux utilization.

[0010] Graph showing the transition of the proportion of the amount of diffracted light when modulation of diffraction efficiency is not performed in the comparative example. Graph showing modulation of diffraction efficiency so that the transition of the proportion of the amount of diffracted light is constant in the comparative example. Graph showing modulation of diffraction efficiency in the first extended region in the embodiment and the transition of the proportion of the amount of diffracted light. Longitudinal cross-section of a diffraction grating arranged in the first extended region in the embodiment. Longitudinal cross-section of a diffraction grating arranged in the first extended region in the embodiment. Longitudinal cross-section of a diffraction grating arranged in the first extended region in the embodiment. a graph showing the modulation of the diffraction efficiency of the first extended region and the transition of the proportion of the amount of diffracted light in the first extended region in the first variation of the embodiment; a graph showing the modulation of the diffraction efficiency of the first extended region and the transition of the proportion of the amount of diffracted light in the second variation of the embodiment; a graph showing the modulation of the diffraction efficiency of the first extended region and the transition of the proportion of the amount of diffracted light in the second variation of the embodiment; a graph showing the modulation of the diffraction efficiency of the first extended region and the transition of the proportion of the amount of diffracted light in the third variation of the embodiment; a graph showing the modulation of the diffraction efficiency of the first extended region and the transition of the proportion of the amount of diffracted light in the third variation of the embodiment; a graph showing the modulation of the diffraction efficiency of the first extended region and the transition of the proportion of the amount of diffracted light in the fourth variation of the embodiment; a graph showing the modulation of the diffraction efficiency of the first extended region and the transition of the proportion of the amount of diffracted light in the fourth variation of the embodiment; a graph showing the modulation of the diffraction efficiency of the first extended region and the transition of the proportion of the amount of diffracted light in the fourth variation of the embodiment; a graph showing the modulation of the diffraction efficiency of the first extended region and the transition of the proportion of the amount of diffracted light in the fifth variation of the embodiment;

[0011] (Outline of the Present Disclosure) An outline 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 an 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 of the light, a first widening region 23 that widens in a first direction, and a second widening region 25 that widens in a second direction. The first direction and the second direction may intersect with each other, for example, be perpendicular to each other.

[0012] The coupling region 21, the first expansion region 23, and the second expansion region 25 each have a diffraction power for diffracting image light, and a diffractive structure element such as 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 image light incident from outside so that it heads toward the first expansion 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 image light by splitting the incident image light by diffraction power into image light traveling in a first direction 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 by 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 into four light beams of image light in the first direction.

[0014] The second expansion region 25, for example, includes a diffractive structure element disposed therein, which uses diffractive power to split incident image light into image light traveling in the second direction and image light emitted from the second expansion region 25 to the outside, thereby duplicating the image light. For example, in FIG. 1 , three points 25p are arranged in each row in the direction in which the image light travels through repeated total reflection in the second expansion region 25, for a total of four rows, each with a diffractive structure element disposed at twelve points 25p. The image light is split at each point 25p, and the split image light is emitted to the outside. As a result, each of the four rows of incident image light beams is expanded by being duplicated into three image light beams in the second direction. In this way, the light guide 13 can duplicate twelve image light beams from a single incident image light beam, thereby expanding the viewing area by duplicating the light beams in both the first and second directions. The observer can visually recognize each of the twelve beams of image light as a virtual image, thereby widening the visual recognition area in which the observer can visually recognize the image light.

[0015] Next, the difference between a pupil dilation 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 a viewing area Ac where 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 incident on the viewing 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] (Embodiments) Hereinafter, embodiments will be described with reference to FIGS. 4 to 6. Note that components having the same functions as those described above are assigned the same reference numerals. Also, the inclination angle of the windshield in the figures is shown for ease of understanding and may vary 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 a HUD system 1 according to the present disclosure. FIG. 5 is an explanatory diagram showing the optical path of a light beam emitted from a display unit. In the embodiments, the HUD system 1 equipped in a 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 , the display unit 11 and the light guide 13 are disposed inside a dashboard (not shown) below the windshield 5 of the 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 the real scene visible through the windshield 5. Because multiple replicated images are projected into the viewing area Ac, the observer D can view the virtual image Iv within the viewing area Ac even if the position of his or her eyes is shifted in the Y-axis and X-axis directions. 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] 4 , the HUD system 1 includes a display unit 11, a light guide 13, a control unit 15, and a windshield 5. The display unit 11 emits a light beam L1 that forms an image 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 L4 to the windshield 5. The light beam L4 reflected by the windshield 5 is displayed as a virtual image Iv superimposed on the actual scene visible through the windshield 5.

[0022] The display unit 11 emits the luminous flux before being expanded by the light guide 13 and displays an image, for example, based on control by an external control unit. The display unit 11 may be, for example, a backlit liquid crystal display (LCD), an organic light-emitting diode (OLED) display, or a plasma display. 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 luminous flux 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 composed of semiconductor elements, etc. The control unit 15 can be configured, for example, by 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 device 17 and performing various arithmetic processing. 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 thereof. The storage device 17 further stores multiple image data representing virtual images Iv. The control unit 15 determines the virtual image Iv to be displayed based on vehicle-related information acquired from an external device. The control unit 15 reads the image data of the determined virtual image Iv from the storage device and outputs it to the display unit 11.

[0024] [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 related to the extended region 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 from the coupling region is defined as the X-axis direction, and the direction perpendicular to the X-axis direction is defined as the Y-axis direction.

[0025] The light guide 13 has a first major surface 13a and a second major surface 13b, which are surfaces. The first major surface 13a and the second major surface 13b are opposed to 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 major surface 13b, and the exit surface 27 is included in the first major surface 13a. Therefore, the first extended region 23 and the second extended region 25 are arranged on the same plane.

[0026] The exit surface 27 faces the second expansion region 25. The coupling region 21, the first expansion region 23, and the second expansion 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 entrance surface 20 is included in the coupling region 21, but it may also be a surface facing the coupling region 21 and included in the first main surface 13a. The exit surface 27 may also be included in the second expansion region 25.

[0027] The coupling region 21, the first expansion region 23, and the second expansion region 25 each have a different diffraction power, and each has a diffractive structure element formed therein. The coupling region 21, the first expansion region 23, and the second expansion region 25 each have a different diffraction angle of image light. The light guide 13 is configured to totally reflect the incident light beam therein. In this way, the light guide 13 includes a diffractive structure element, such as a volume hologram, that diffracts light in part. When the coupling region 21, the first expansion region 23, and the second expansion 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, from which the light beam L1 is emitted as light beam L2. In this embodiment, coupling refers to a state in which the light beam propagates within the light guide 13 under total reflection conditions.

[0029] The first expansion region 23 expands the light beam L2 in a first direction corresponding to the horizontal direction of the virtual image Iv and outputs the light beam L2 to a second expansion region located in a second direction (-Y-axis direction) intersecting the first direction (X-axis direction). In the first expansion region 23 expanding the light beam L2 in the first direction, the length in the first direction is greater than the length in the second direction. Note that, in the embodiment, the light guide 13 is disposed so that the first direction is the horizontal direction (the direction of the X1 axis), but this is not limiting, and the first direction does not have to completely coincide with the horizontal direction. The light beam L2 propagating from the coupling region 21 propagates in the first direction while repeatedly undergoing total reflection at the first principal surface 13a and the second principal surface 13b. The light beam L2 is replicated by the diffractive structure of the first expansion region 23 formed on the second principal surface 13b and then output to the second expansion region 25.

[0030] The second expansion region 25 expands the light beam L3 in a second direction corresponding to the vertical direction of the virtual image Iv and emits the expanded light beam L4 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 L3 propagating from the first expansion region 23 propagates in the second direction while repeatedly undergoing total reflection at the first principal surface 13a and the second principal surface 13b. The light beam L3 is replicated by the diffractive structure of the second expansion region 25 formed on the second principal surface 13b and is then 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 direction of travel changed, in the horizontal direction (the direction of the X1 axis) of virtual image Iv viewed by observer D, and then further expands it in the vertical direction (the direction of the Y1 axis) of virtual image Iv, and emits light beam L4 from exit surface 27. Here, "duplicating the image in the horizontal direction" is not limited to "duplicating only in the completely horizontal direction" but also includes "duplicating in an approximately horizontal direction." Furthermore, "duplicating the image in the vertical direction" is not limited to "duplicating only in the completely vertical direction" but also includes "duplicating in an approximately vertical direction."

[0032] [1-1-3. Order of Pupil Expansion] In the light guide 13 arranged as described above, the magnitude of the wave vector of the first expansion region 23 and the second expansion region 25 in the HUD system 1 differs depending on the order of pupil expansion of the light beam L1 of image light. The order of pupil expansion in this embodiment will be described with reference to FIG. 7. FIG. 7(a) is an explanatory diagram showing the optical path of the center of the light beam emitted from the display unit. FIG. 7(b) is an explanatory diagram showing the wave vectors that the diffraction gratings in each region in FIG. 7(a) give to the light beam.

[0033] The diffractive structure formed in the coupling region 21 changes the propagation direction of the luminous flux L1 of the image light incident on the light guide 13 to the first expansion region 23, which expands the pupil in the horizontal direction (X-axis direction) as a first direction. 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 L2 toward the first expansion region 23.

[0034] The light beam L2 propagating toward the first extension region 23 extending in the first direction is split by the diffractive structure formed in the first extension region 23 while repeatedly undergoing total reflection into the light beam L2 propagating in the first direction and the light beam L3 which is duplicated and changes its propagation direction to the second extension region 25. At this time, the duplicated light beam L3 is affected by the wave vector k2 shown in FIG. 7 and propagates toward the second extension region 25.

[0035] The light beam L3, 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 L3 propagating in the second direction and a light beam L4 that is duplicated and 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 L4 is affected by the wave vector k3 shown in FIG. 7 and propagates in the direction of the exit surface 27 (see FIG. 6).

[0036] [1-1-4. First Expansion Region and Second Expansion Region] The first expansion region 23 includes a first end region 23a, a central region 23b, and a second end region 23c. The first end region 23a and the second end region 23c are regions that do not overlap with the second expansion region 25 when viewed from the second direction. Therefore, the second expansion region 25 exists in the second direction of the central region 23b, and there are regions without the second expansion region 25 in the second direction of the first end region 23a and the second end region 23c.

[0037] The size of the second extension region 25 is determined according to the size of the viewing region Ac. When the size of the output region from which the display unit 11 emits the light beam L1 is larger than the size of the combined region 21, the light beam L1 incident on the combined region 21 includes a light beam incident at an inclined angle other than an incident angle of 0 degrees (perpendicular incidence). If this light beam L1 with an incident angle other than 0 degrees is not guided to the second extension region 25, a portion of the virtual image Iv will be missing in the viewing region Ac. Therefore, by making the length Lga of the first extension region 23 in the first direction longer than the length Lgb of the second extension region 25 in the first direction, this missing portion of the virtual image Iv can be prevented.

[0038] The central region 23b of the first expansion region 23 includes the center of the first expansion region 23 in the first direction and is located between the first end region 23a and the second end region 23c. The first end region 23a is the end region closer to the bonding region 21, and the second end region 23c is the end region farther from the bonding region 21.

[0039] The length in the first direction of the first extension region 23 is Lga, the length in the first direction of the first end region 23a is Lgaa, the length in the first direction of the central region 23b is Lgab, and the length in the first direction of the second end region 23c is Lgac. The relationships between these lengths satisfy the following equations (1) to (3): Lgaa<Lga / 4 (1) Lga / 4≦Lgab≦(3×Lga) / 4 (2) Lgac<Lga / 4 (3)

[0040] Therefore, the first end region 23a is a region that is less than 1 / 4 of the length from the end of the first expansion region 23 on the bonding region 21 side in the first direction, and the second end region 23c is a region that is less than 1 / 4 of the length from the end of the first expansion region 23 opposite the bonding region 21 in the first direction.

[0041] The use of such a first expansion region 23 can achieve the expansion of the light beam as shown in FIG. 8A . Here, expanding the light beam refers to dividing and duplicating the light beam to increase the number of light beams and thereby expanding the viewing area Ac. The first expansion region 23 expands the viewing area Ac in the horizontal direction, and the second expansion region 25 expands the viewing area Ac in the vertical direction. The light beam L2 traveling in the first direction from the combined region 21 through the first expansion region 23 includes light beams L2a, L2b, and L2c. The light beam L3 traveling in the second direction from the first expansion region 23 includes light beams L3aa, L3ab, L3ac, L3ba, L3bb, L3bc, L3ca, L3cb, and L3cc.

[0042] Light beam L2a, the traveling direction of which is changed from that of the component of light beam L1 perpendicularly incident on the coupling region 21, travels in a first direction through the first extended region 23, and light beam L3ab, light beam L3aa, light beam L3ac, light beam L3ac, which is split and diffracted by the first end region 23a, the central region 23b, and the second end region 23c, each travel in a second direction. Light beam L3aa can travel into the second extended region 25, but light beams L3ab and L3ac cannot travel into the second extended region 25, resulting in a loss of light intensity.

[0043] Furthermore, a light beam L2b, the traveling direction of which is changed from that of a component of the light beam L1 that is incident on the coupling region 21 at a positive angle, travels in a first direction through the first extended region 23, and a light beam L3bb, which is split and diffracted at the first end region 23a, a light beam L3ba, which is split and diffracted at the central region 23b, and a light beam L3bc, which is split and diffracted at the second end region 23c, each travel in a second direction. The light beam L3bc travels into the second extended region 25 to prevent chipping of the virtual image Iv, but a portion of the light beam L3ba and the light beam L3bb cannot travel into the second extended region 25, resulting in a loss of light.

[0044] Furthermore, a light beam L2c, the traveling direction of which is changed from that of a component of the light beam L1 that is incident on the coupling region 21 at a negative angle, travels in a first direction through the first extended region 23, and a light beam L3cb that is split and diffracted at the first end region 23a, a light beam L3ca that is split and diffracted at the central region 23b, and a light beam L3cc that is split and diffracted at the second end region 23c each travel in a second direction. The light beam L3cb travels into the second extended region 25 to prevent chipping of the virtual image Iv, but a portion of the light beam L3ca and the light beam L3cc cannot travel into the second extended region 25, resulting in a loss of light.

[0045] In this way, chipping of the virtual image Iv can be prevented, but a loss of light intensity occurs accordingly. Furthermore, the light beams L3bc and L3cb are diffracted less times within the second extended region 25 than the light beam L3aa, and are propagated with little loss of light intensity through repeated total reflection within the light guide 13. Therefore, the light beams L3bc and L3cb have a larger amount of light than the light beam L3aa, which propagates while being split by diffraction within the second extended region 25, and this can cause uneven brightness of the image light emitted from the second extended region 25.

[0046] Therefore, in this embodiment, the loss of light amount and brightness unevenness are reduced while preventing image loss by modulating the transition in the first direction of the amount of light diffracted from the first extension region 23. Specifically, the diffraction efficiency of the first end region 23a and the second end region 23c is modulated so as to reduce the amount of light of the light beams L3ab, L3bb, L3ac, and L3cc.

[0047] Note that the light beams emitted from the second expansion region 25 within the range of the length Lgb of the second expansion region 25 in the first direction shown in FIG. 8A are incident on the viewing region Ac within a horizontal viewing angle θ range of −α≦θ≦α, as shown in FIG. 8B. In the second expansion region 25, the light beam L3aa is diffracted to generate the light beam L4aa, the light beam L3cb is diffracted to generate the light beam L4cb, and the light beam L3bc is diffracted to generate the light beam L4bc. These light beams L4aa, L4cb, and L4bc reach the viewing region Ac. The light beams diffracted from the light beams L3ab, L3bb, L3ac, L3cc, L3ba, and L3ca that do not exit within the range of the length Lgb of the second expansion region 25 in the first direction do not reach the viewing region Ac. For ease of understanding, the windshield 5 is omitted from FIG. 8B.

[0048] 9A, the second expansion region 25 may have regions 41 and 43 extending in the positive direction (positive direction of the X-axis) and negative direction (negative direction of the X-axis), respectively, of the first direction. The HUD system 1 may also include a light guide 13F in which an expansion region 45 having the second expansion region 25, regions 41, and 43 is arranged in the second direction of the first expansion region 23. As in FIGS. 8A and 8B, the light beams L4aa, L4cb, and L4bc reach the viewing region Ac.

[0049] In contrast, light diffracted from the light beams L3ab, L3bb, L3ac, and L3cc that do not exit within the range of the length Lgb in the first direction of the second extended region 25 of the light guide 13F does not reach the viewing region Ac from the light guide 13F. In the second extended region 25, the light beam L3ab is diffracted to generate the light beam L4ab, the light beam L3bb is diffracted to generate the light beam L4bb, the light beam L3ac is diffracted to generate the light beam L4ac, and the light beam L3cc is diffracted to generate the light beam L4cc. As shown in FIG. 9B, these light beams L4ab, L4bb, L4ac, and L4cc do not reach the viewing region Ac. Note that the windshield 5 is omitted from FIG. 9B for ease of understanding. In the extension region 45 , the extension region within the range of length Lgb where light is incident within the viewing angle θ in the range −α≦θ≦α is the second extension region 25 .

[0050] Next, modulation of the proportion of the amount of light diffracted in the first direction in the first expansion region 23 will be described with reference to Figs. 10 to 12. Fig. 10 is a graph showing the transition of the proportion of the amount of light diffracted when modulation of the diffraction efficiency is not performed in a comparative example. Fig. 11 is a graph showing modulation of the diffraction efficiency so that the transition of the proportion of the amount of light diffracted is constant in a comparative example. Fig. 12 is a graph showing modulation of the diffraction efficiency and the transition of the proportion of the amount of light diffracted in an embodiment.

[0051] 10 , when the diffraction efficiency De1 in the first direction is constant without modulation in the first extension region 23, the diffracted light amount ratio Lr1 is highest in the first end region 23a where the number of diffractions is small, and decreases as the number of diffractions in the first direction increases, which causes uneven brightness in the virtual image Iv.

[0052] 11 , the diffraction efficiency De2 in the first expansion region 23 is modulated and gradually increased in the first direction, thereby making it possible to keep the diffracted light quantity ratio Lr2 constant regardless of the number of diffractions. However, in this embodiment, the length Lga of the first expansion region 23 in the first direction is longer than the length Lgb of the second expansion region 25 in the first direction, which causes light quantity loss and brightness unevenness for the reasons described above.

[0053] Therefore, in this embodiment, the diffraction efficiency is modulated as shown in FIG. 12 . In the first extension region 23, the diffracted light intensity ratio Lr3 gradually increases along the first direction and has a flat portion Lr3a where the light intensity ratio Lr3 falls within a certain range Rc within a specific range of the number of diffractions. The certain range Rc in the flat portion Lr3a is within ±10% of the design value Va of the light intensity ratio diffracted in the central region 23b. The design value Va is a specific value designed based on the number of diffractions in the central region 23b. In this embodiment, the design value Va is approximately 13%.

[0054] In this way, in the first expansion region 23, the light intensity ratio Lr3 diffracted in the first end region 23a, which has a low number of diffractions, and the second end region 23c, which has a high number of diffractions, is set lower than the light intensity ratio Lr3 diffracted in the central region 23b. To achieve this transition of the light intensity ratio Lr3, the diffraction efficiency De3 in the first expansion region 23 increases as the number of diffractions increases and decreases when a certain number of diffractions is exceeded. The diffraction efficiency De3 increases in a first direction from the first end region 23a to the central region 23b and decreases in the second end region 23c in the first direction. The diffracted light intensity Le in the first end region 23a and second end region 23c of the first expansion region 23 is less than half the diffracted light intensity Lc in the central region 23b of the first expansion region 23. Therefore, the following conditional expression (4) is established: Le<Lc / 2 (4)

[0055] This reduces the loss of the light quantity of the light beams L3ab and L3ac, thereby increasing the light quantity of the light beam L3aa by the amount of the reduced light quantity. Furthermore, by reducing the loss of the light quantity at a wide viewing angle, such as the light beams L3bb and L3cc, and reducing the light quantities of the light beams L3bc and L3cb, and propagating them to the second extended region 25C, it is possible to prevent image chipping and improve brightness unevenness of the virtual image Iv.

[0056] Diffraction Grating] Next, the diffractive structure of the first expansion region 23 will be described with reference to Fig. 13. Fig. 13 is a vertical cross-sectional view of a diffraction grating 31 disposed in the first expansion region 23.

[0057] A diffraction grating 31 that diffracts the incident light beam is disposed in the first extension region 23. The diffraction grating 31 is, for example, a transparent resin layer and is formed by nanoimprinting. Alternatively, the diffraction grating 31 may be formed by, for example, laminating SiO2 on a glass substrate 35 and then dry etching the laminated SiO2. A similar diffraction grating 31 is disposed in the second extension region 25.

[0058] The diffraction grating 31 is formed periodically at a pitch P. The diffraction grating 31 has structural characteristics determined by a height h from the surface, a width W, and a duty ratio Dr defined by the width W / pitch P. The diffraction grating 37 may have a slant angle.

[0059] The higher the height of the diffraction grating 31, the higher the diffraction efficiency. The height h1 of the grating 31a in the first end region 23a and the second end region 23c of the first extension region 23 is lower than the height h2 of the grating 31a in the central region 23b. By modulating the height of the grating 31a in this way, the amount of light diffracted in the first end region 23a and the second end region 23c can be made smaller than the amount of light diffracted in the central region 23b.

[0060] 14, the absolute value of the difference between the duty ratios Dr1 and 0.5 of the diffraction gratings in the first end region 23a and second end region 23c of the first extension region 23 is greater than the absolute value of the difference between the duty ratios Dr2 and 0.5 of the diffraction gratings in the central region 23b. Therefore, the following conditional expression (5) is established: |Dr1-0.5|>|Dr2-0.5| (5)

[0061] That is, the duty ratio Dr2 of the diffraction grating in the central region 23 b is closer to 0.5 than the duty ratio Dr1 of the diffraction grating in the first end region 23 a and the second end region 23 c. By modulating the duty ratio in this manner, the amount of light diffracted in the first end region 23 a and the second end region 23 c can be made smaller than the amount of light diffracted in the central region 23 b.

[0062] In addition, by combining modulation of the diffraction grating height with modulation of the duty ratio, the amount of light diffracted in the first end region 23a and the second end region 23c may be made smaller than the amount of light diffracted in the central region 23b.

[0063] Next, a first modification of the embodiment will be described with reference to Fig. 15. Fig. 15(a) is an explanatory diagram showing the optical path of a light beam traveling through the first extended region 23A and the second extended region 25A of the light guide 13A in the first modification of the embodiment. Fig. 15(b) is an explanatory diagram showing the wave vectors imparted to the light beam by the coupling region 21 and the diffraction gratings of the extended regions 23A and 25A in Fig. 15(a). The second extended region 25A has a first end region 23Aa and a central region 23Ab.

[0064] As shown in FIG. 15B, the diffraction gratings of the first and second extension regions 23A and 25A are designed so that the wave vector k5 of the diffraction grating of the second extension region 25A is slightly oblique. This allows the sum of the wave vector k1 of the coupling region 21, the wave vector k4 of the first extension region 23A, and the wave vector k5 of the second extension region 25A to be zero. By making the wave vector k5 oblique, the center of the second extension region 25A in the first direction can be positioned on the first direction side of the first extension region 23A, instead of being aligned with the center of the first extension region 23A in the first direction, as shown in FIG. 15A. The sizes of the first end region 23Aa and the central region 23Ab in the first extension region 23A are larger than the sizes of the first end region 23a and the central region 23b in the first embodiment, and are each extended in the first direction.

[0065] By positioning the second expansion region 25A on the opposite side of the first expansion region 23A from the joining region 21 so that it overlaps with the first expansion region 23A when viewed from the second direction, the space at the edge of the second expansion region 25A on the first direction side can be reduced.

[0066] The transition of the proportion of the amount of light diffracted in the first expansion region 23A of the first modification of the embodiment will be described with reference to Fig. 16. Fig. 16 is a graph showing the modulation of the diffraction efficiency of the first expansion region 23A of the first modification of the embodiment and the transition of the proportion of the amount of light diffracted.

[0067] In the first expansion region 23A, the light intensity ratio Lr3A diffracted in the first edge region 23Aa, which has a smaller number of diffractions, is set lower than the light intensity ratio Lr3A diffracted in the central region 23Ab. To achieve this change in the light intensity ratio Lr3A, the diffraction efficiency De3A is increased as the number of diffractions increases. The diffraction efficiency De3A increases in the first direction from the first edge region 23Aa to the central region 23Ab. The diffracted light intensity Le in the first edge region 23Aa of the first expansion region 23A is smaller than half the diffracted light intensity Lc in the central region 23Ab of the first expansion region 23A.

[0068] This reduces the loss of the light amount of the light beam L3Aab and increases the light amount of the light beam L3Aaa by the amount of the reduction. In addition, the loss of the light amount at a wide viewing angle is reduced, and the light amount of the light beam L3Acb is reduced and propagated to the second extended area 25A, thereby improving the brightness unevenness of the virtual image Iv.

[0069] Next, a second modification of the embodiment will be described with reference to Fig. 17. Fig. 17(a) is an explanatory diagram showing the optical path of a light beam traveling through the first extended region 23B and the second extended region 25B of the light guide 13B in the second modification of the embodiment. Fig. 17(b) is an explanatory diagram showing the wave vectors imparted to the light beam by the coupling region 21 and the diffraction gratings of the extended regions 23B and 25B in Fig. 17(a). The second extended region 25B has a central region 23Bb and a second end region 23Bc.

[0070] As shown in FIG. 17B, the diffraction gratings of the first extension region 23B and the second extension region 25B are designed so that the wave vector k7 of the diffraction grating of the second extension region 25B is oblique. This allows the sum of the wave vector k1 of the coupling region 21, the wave vector k6 of the first extension region 23B, and the wave vector k7 of the second extension region 25B to be zero. By making the wave vector k7 oblique, the center of the second extension region 25B in the first direction can be positioned on the coupling region 21 side, instead of being aligned with the center of the first extension region 23B in the first direction, as shown in FIG. 17A. The sizes of the central region 23Bb and the second end region 23Bc in the first extension region 23B are larger than the sizes of the central region 23b and the second end region 23c in the first embodiment, and are extended in the opposite direction from the first direction.

[0071] By positioning the second expansion region 25B on the joining region 21 side of the first expansion region 23B so that it overlaps with the first expansion region 23B when viewed from the second direction, the space on the edge opposite the first direction of the second expansion region 25B can be reduced.

[0072] The transition of the proportion of the amount of light diffracted in the first expansion region 23A of the second modification of the embodiment will be described with reference to Fig. 18. Fig. 18 is a graph showing the modulation of the diffraction efficiency of the first expansion region 23B of the second modification of the embodiment and the transition of the proportion of the amount of light diffracted.

[0073] In the first expansion region 23B, the light intensity ratio Lr3B diffracted in the second edge region 23Bc, which has a large number of diffractions, is set lower than the light intensity ratio Lr3B diffracted in the central region 23Bb. To achieve this transition of the light intensity ratio Lr3B, the diffraction efficiency De3B is increased as the number of diffractions increases and is decreased when a certain number of diffractions is exceeded. The diffraction efficiency De3B is increased along a first direction in the central region 23Bb and decreased along the first direction in the second edge region 23Bc. The diffracted light intensity Le in the second edge region 23Bc of the first expansion region 23B is less than half the diffracted light intensity Lc in the central region 23Bb of the first expansion region 23B.

[0074] This reduces the loss of the light amount of the light beam L3Bac and increases the light amount of the light beam L3Baa by the amount of the reduction. In addition, the loss of the light amount at a wide viewing angle is reduced, and the light amount of the light beam L3Bbc is reduced and propagated to the second extended area 25B, thereby improving the brightness unevenness of the virtual image Iv.

[0075] Next, a third modification of the embodiment will be described with reference to FIG. 19 . FIG. 19( a) is an explanatory diagram showing the optical path of a light beam traveling through the first extension region 23C and the second extension region 25C of the light guide 13C in the third modification of the embodiment. FIG. 19( b) is an explanatory diagram showing the wave vectors imparted to the light beam by the coupling region 21C and the diffraction gratings of the extension regions 23C and 25C in FIG. 19( a). In the third modification of the embodiment, the first direction of the first extension region 23C is the negative direction of the Y-axis, and the second direction of the second extension region 25C is the direction of the X-axis.

[0076] The light beam incident on the coupling region 21C is affected by the wave vector k1 of the diffraction grating of the coupling region 21C and propagates in the direction where the first extension region 23C is located. The light beam propagating to the first extension region 23C is split by the diffraction structure formed in the first extension region 23C while repeatedly undergoing total reflection into a light beam propagating in the first direction and a light beam that is duplicated and changes its propagation direction toward the second extension region 25C. At this time, the duplicated light beam is affected by the wave vector k9 and propagates in the direction where the second extension region 25C is located. The light beam that has changed its propagation direction toward the second extension region 25C is split by the diffraction structure formed in the second extension region 25C into a light beam propagating in the second direction and a light beam that is duplicated and emitted from the second extension region 25C to the outside of the light guide 13C. At this time, the duplicated light beam is affected by the wave vector k10 of the diffraction grating of the second extension region 25C and emits to the outside of the light guide 13C.

[0077] In the first expansion region 23C, the diffracted light intensity ratio Lr3C in the first end region 23Ca, which has a low number of diffractions, and the second end region 23Cc, which has a high number of diffractions, is set lower than the diffracted light intensity ratio Lr3C in the central region 23b. To achieve this transition of the light intensity ratio Lr3C, the diffraction efficiency De3C increases as the number of diffractions increases and decreases once a certain number of diffractions is exceeded. As shown in FIG. 20 , the diffraction efficiency De3C increases in a first direction from the first end region 23Ca to the central region 23Cb and decreases in the second end region 23Cc in the first direction. The diffracted light intensity Le in the first end region 23Ca and the second end region 23Cc of the first expansion region 23C is less than half the diffracted light intensity Lc in the central region 23Cb of the first expansion region 23C.

[0078] This reduces the loss of light intensity of the light beams L3Cab and L3Cac, thereby increasing the amount of light intensity of the light beam L3Caaa by the amount of the reduced light intensity. Furthermore, by reducing the loss of light intensity at high viewing angles and reducing the amount of light intensity of the light beams L3Cbc and L3Ccb and propagating them to the second expansion region 25C, it is possible to prevent image chipping and improve brightness unevenness of the virtual image Iv. Furthermore, by aligning the first expansion direction by the first expansion region 23C along the Y-axis, it is possible to shorten the size of the light guide 13C in the Y-axis direction.

[0079] Next, a fourth modification of the embodiment will be described with reference to FIG. 21 . FIG. 21( a) is an explanatory diagram showing the optical path of a light beam traveling through the first extension region 23D and the second extension region 25D of the light guide 13D in the fourth modification of the embodiment. FIG. 21( b) is an explanatory diagram showing the wave vectors imparted to the light beam by the coupling region 21D and the diffraction gratings of each extension region 23D, 25D in FIG. 21( a). The fourth modification of the embodiment is an example that combines the first and third modifications. The diffraction gratings of the first and second extension regions 23D, 25D are designed so that the wave vector k12 produced by the diffraction grating of the second extension region 25D is oblique. This allows the sum of the wave vector k8 of the coupling region 21D, the wave vector k11 of the first extension region 23D, and the wave vector k12 of the second extension region 25D to be zero. By making the wave vector k12 oblique, the center of the second expansion region 25D in the first direction can be arranged on the first direction side of the first expansion region 23D, instead of being aligned with the center of the first expansion region 23D in the first direction, as shown in Fig. 21(a) . The sizes of the first end region 23Da and the central region 23Db in the first expansion region 23D are larger than the sizes of the first end region 23Ca and the central region 23Cb in Modification 3, and each is expanded in the first direction.

[0080] By positioning the second expansion region 25D on the opposite side of the first expansion region 23D from the joining region 21D so that it overlaps with the first expansion region 23D when viewed from the second direction, the space at the edge of the second expansion region 25D on the first direction side can be reduced.

[0081] The transition of the proportion of the amount of light diffracted in the first expansion region 23D of the fourth modification of the embodiment will be described with reference to Fig. 22. Fig. 22 is a graph showing the modulation of the diffraction efficiency of the first expansion region 23D of the fourth modification of the embodiment and the transition of the proportion of the amount of light diffracted.

[0082] In the first expanded region 23D, the light intensity ratio Lr3D diffracted in the first edge region 23Da, which has a smaller number of diffractions, is set lower than the light intensity ratio Lr3D diffracted in the central region 23Db. To achieve this change in the light intensity ratio Lr3D, the diffraction efficiency De3D is increased as the number of diffractions increases. The diffraction efficiency De3D increases in the first direction from the first edge region 23Da to the central region 23Db. The diffracted light intensity Le in the first edge region 23Da of the first expanded region 23D is smaller than half the diffracted light intensity Lc in the central region 23Db of the first expanded region 23D.

[0083] This reduces the loss of the light amount of the light beam L3Dab and increases the light amount of the light beam L3Daa by the amount of the reduction. Also, by reducing the loss of the light amount at a wide viewing angle and reducing the light amount of the light beam L3Dcb so that it propagates to the second extended region 25D, it is possible to prevent image chipping and improve the brightness unevenness of the virtual image Iv.

[0084] Next, a fifth modification of the embodiment will be described with reference to Fig. 23. Fig. 23(a) is an explanatory diagram showing the optical path of a light beam traveling through the first extended region 23E and the second extended region 25E of the light guide 13E in the fifth modification of the embodiment. Fig. 23(b) is an explanatory diagram showing the wave vectors given to the light beam by the coupling region 21E and the diffraction gratings of the extended regions 23E and 25E in Fig. 23(a). The fifth modification of the embodiment is an example in which the second modification and the third modification are combined.

[0085] The diffraction gratings of the first extension region 23E and the second extension region 25E are designed so that the wave vector k14 of the diffraction grating of the second extension region 25E is oblique. This allows the sum of the wave vector k8 of the coupling region 21E, the wave vector k13 of the first extension region 23E, and the wave vector k14 of the second extension region 25E to be zero. By making the wave vector k14 oblique, the center of the second extension region 25E in the first direction can be positioned on the coupling region side 21 instead of being aligned with the center of the first extension region 23E in the first direction. The sizes of the central region 23Eb and the second end region 23Ec in the first extension region 23E are larger than the sizes of the central region 23b and the second end region 23c in the first embodiment, and are extended in the opposite direction from the first direction.

[0086] By positioning the second expansion region 25E on the joining region 21 side of the first expansion region 23E so that it overlaps with the first expansion region 23E when viewed from the second direction, the space on the edge opposite the first direction of the second expansion region 25E can be reduced.

[0087] The transition of the proportion of the amount of light diffracted in the first expansion region 23E of the fifth modification of the embodiment will be described with reference to Fig. 24. Fig. 24 is a graph showing the modulation of the diffraction efficiency of the first expansion region 23E of the fifth modification of the embodiment and the transition of the proportion of the amount of light diffracted.

[0088] In the first expansion region 23E, the light intensity ratio Lr3E diffracted in the second edge region 23Ec, which has a large number of diffractions, is set lower than the light intensity ratio Lr3E diffracted in the central region 23Eb. To achieve this transition of the light intensity ratio Lr3E, the diffraction efficiency De3E increases as the number of diffractions increases and decreases when a certain number of diffractions is exceeded. The diffraction efficiency De3E increases along a first direction in the central region 23Eb and decreases along the first direction in the second edge region 23Ec. The diffracted light intensity Le in the second edge region 23Ec of the first expansion region 23E is less than half the diffracted light intensity Lc in the central region 23Eb of the first expansion region 23E.

[0089] This reduces the loss of the light amount of the light beam L3Eac and increases the light amount of the light beam L3Eaa by the amount of the reduction. Also, by reducing the loss of the light amount at a wide viewing angle and reducing the light amount of the light beam L3Ebc so that it propagates to the second extended region 25E, it is possible to prevent image chipping and improve the brightness unevenness of the virtual image Iv.

[0090] [1-2. Effects, etc.] The light guide 13, which is an optical system according to the present disclosure, is an optical system that allows the observer D to view a virtual image Iv. The light guide 13 includes a first expansion region 23 that expands the light guide 13 by dividing and duplicating a light beam L2 traveling in a first direction into a light beam L3 traveling in a second direction intersecting the first direction, thereby increasing the number of light beams, and a second expansion region 25 that expands the light guide 13 by dividing and duplicating the light beam traveling in the second direction, thereby increasing the number of light beams, and corresponds to the viewing region Ac of the virtual image Iv. The first expansion region 23 includes a central region 23b that includes the center of the first expansion region 23, and at least one of a first end region 23a and a second end region 23c, at least one of which has an amount of diffracted light that is less than half the amount of diffracted light in the central region 23b, on at least one of the ends of the first expansion region 23.

[0091] Since the diffracted light amount Le in the first end region 23 a or the second end region 23 c is smaller than half the diffracted light amount Lc in the central region 23 b of the first extended region 23, the amount of light diffracted in the first end region 23 a or the second end region 23 c can be reduced, thereby reducing light loss. Furthermore, the light diffracted in the first end region 23 a or the second end region 23 c and reaching the second extended region 25 is a light beam with high brightness due to a small number of diffractions, but since the amount of this light beam can be reduced, brightness unevenness can be reduced.

[0092] Furthermore, the second extension region 25 is present in the second direction in the central region 23b, and regions without the second extension region 25 are present in the second direction in the first end region 23a and the second end region 23c. The regions without the second extension region 25 can reduce the transmission of light beams to the observer D outside the viewing region Ac. Furthermore, if an extension region other than the second extension region 25 exists in a region exceeding the length Lgb in the first direction, the light beams from the first end region 23a and the second end region 23c are diffracted by this extension region and do not reach the viewing region Ac. However, the presence of regions without the second extension region 25 in the second direction in the first end region 23a and the second end region 23c reduces this diffraction and increases the amount of light that reaches the viewing region Ac.

[0093] Furthermore, the length Lga in the first direction of the first extended region 23 is longer than the length Lgb in the first direction of the second extended region 25. This makes it possible to prevent image loss due to the light beam that is diffracted at the first end region 23a or the second end region 23c and reaches the second extended region 25.

[0094] Furthermore, by projecting light emitted from the light guide 13 as an optical system onto the windshield 5 of the vehicle 3, a flawless virtual image Iv with appropriate brightness can be displayed to the observer D driving the vehicle 3.

[0095] (Other Embodiments) As described above, the above-mentioned embodiments have been described as examples of the technology disclosed in the present application. However, the technology in the present disclosure is not limited to these, and can be applied to embodiments in which modifications, substitutions, additions, omissions, etc. are made as appropriate. Therefore, other embodiments will be described below as examples.

[0096] In the above embodiment, the divided 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 divided and replicated light beam L2 may be reflected by the combiner to allow the observer D to view the virtual image Iv.

[0097] 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 visible to the user 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.

[0098] In the above embodiment, the light guide 13 is used in the HUD system 1 that displays the virtual image Iv, but the present invention is not limited to this. The light guide 13 may also be used for an HMD.

[0099] In the above embodiment, the light guide 13 is used in the HUD system 1 that displays the virtual image Iv, but the present invention is not limited to this. The light guide 13 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 a person who directly views the image formed by the emitted light beam, and is therefore not limited to a passenger in a moving vehicle.

[0100] (Summary of the embodiment) (1) The optical system of the present disclosure is an optical system that allows an observer to view an image, and includes a first expansion region that expands by dividing and duplicating a light beam traveling in a first direction into a light beam traveling in a second direction intersecting the first direction, thereby increasing the number of light beams, and a second expansion region that expands by dividing and duplicating the light beam traveling in the second direction, thereby increasing the number of light beams, and corresponds to the visible region of the image, and the first expansion region has a central region that includes the center of the first expansion region, and an end region at at least one end side of the first expansion region, in which the amount of diffracted light is less than half the amount of diffracted light in the central region.

[0101] Since the amount of diffracted light in at least one of the end regions is less than half the amount of diffracted light in the central region of the first extended region, the amount of light diffracted in the end regions can be reduced, thereby reducing light loss. Furthermore, the light diffracted in the end regions and reaching the second extended region is a light beam with high brightness due to a small number of diffractions, but since the amount of light of this light beam can be reduced, brightness unevenness can be reduced.

[0102] (2) In the optical system of (1), a second extension region exists in the second direction of the central region, and a region without the second extension region exists in the second direction of the edge region. The region without the second extension region can reduce the light beam from the edge region from reaching the viewer in a region other than the second extension region that does not reach the viewer in the visible region, and can increase the amount of light that reaches the viewer in the visible region.

[0103] (3) In the optical system of (1) or (2), the length of the first extension region in the first direction is longer than the length of the second extension region in the first direction, thereby preventing a missing image due to a light beam diffracted at the end region and reaching the second extension region.

[0104] (4) In the optical system of any one of (1) to (3), in the transition of the proportion of the amount of diffracted light in the first direction in the first expansion region, the proportion of the amount of diffracted light in the central region of the first expansion region, which overlaps with the second expansion region when viewed from the second direction, is within a range of ±10% of the design value. This makes it possible to keep constant the amount of light diffracted from the central region of the first expansion region in the second direction, thereby reducing brightness unevenness.

[0105] (5) In the optical system of any one of (1) to (4), in the edge region of the first extended region, the amount of diffracted light increases from the end of the edge region opposite to the central region toward the central region of the first extended region. As a result, the amount of diffracted light increases in the edge region of the first extended region toward the central region, thereby reducing the amount of light diffracted at the end of the edge region and reducing light loss.

[0106] (6) In the optical system of any one of (1) to (5), the central region of the first extension region is a region that is at least 1 / 4 and not more than 3 / 4 of the length from the end in the first direction, and the end region is a region that is less than 1 / 4 of the length from the end in the first direction.

[0107] (7) In any one of the optical systems (1) to (5), a coupling region is provided that changes the direction of travel of the incident light beam toward the first expansion region, and the end region of the first expansion region is the region closer to the coupling region.

[0108] (8) In any one of the optical systems (1) to (6), a coupling region is provided that changes the direction of travel of the incident light beam toward the first expansion region, and the end region of the first expansion region is the region farther from the coupling region.

[0109] (9) In the optical system of any one of (1) to (8), the first extension region has a diffraction grating, and the height of the diffraction grating in the end region of the first extension region is lower than the height of the diffraction grating in the central region, thereby allowing the diffraction efficiency of the first extension region to be modulated to a desired profile.

[0110] (10) In the optical system of any one of (1) to (8), the first extension region has a diffraction grating, and the difference between the duty ratio value of the diffraction grating in the edge region of the first extension region and 0.5 is larger than the difference between the duty ratio value of the diffraction grating in the central region and 0.5. This allows the diffraction efficiency of the first extension region to be modulated to a desired progression.

[0111] (11) In the optical system of any one of (1) to (8), the first extension region has a diffraction grating, and the difference between the duty ratio of the diffraction grating in the edge regions of the first extension region and 0.5 is different from the difference between the duty ratio of the diffraction grating in the central region and 0.5, and the height of the diffraction grating in the edge regions of the first extension region is different from the height of the diffraction grating in the central region. This allows the diffraction efficiency of the first extension region to be modulated to a desired progression.

[0112] (12) The head-up display system of the present disclosure comprises any one of the optical systems (1) to (11), a display unit that emits a light beam before being expanded by the optical system, and a light-transmitting member that reflects the light beam emitted from the optical system, and displays the image as a virtual image superimposed on a real scene that can be seen through the light-transmitting member.

[0113] (13) In the head-up display system of (12), the light-transmitting member is a windshield of a moving object.

[0114] The present disclosure is applicable to optical systems and head-up display systems that replicate and display images.

[0115] 1 Head-up display system 3 Vehicle 3a Center line 5 Windshield 11 Display unit 13, 13A, 13B, 13C, 13D, 13E, 13F Light guide 13a First main surface 13b Second main surface 15 Control unit 17 Storage device 20 Incident surface 21 Coupling region 23 First extension region 23a First end region 23b Central region 23c Second end region 25 Second extension region 25p Point 27 Exit surface 31 Diffraction grating 31a Grating Ac Viewing region D Observer Iv Virtual image k1, k2, k3, k4, k5, k6, k7, k8, k9, k10, k11, k12, k13, k14 Wave vector L1, L1A, L1B, L2, L2a, L2b, L2c, L3, L3aa, L3ba, L3ca, L3ab, L3bb, L3cb, L3ac, L3bc, L3cc, L4, L4aa, L4bc, L4cb, L4ab, L4bb, L4ac, L4cc Luminous flux

Claims

1. An optical system that allows an observer to view an image, a first expansion region that expands the area by dividing and duplicating a light beam traveling in a first direction into light beams traveling in a second direction intersecting the first direction, thereby increasing the number of the light beams; a second expansion area corresponding to a visible area of ​​the image, the second expansion area being expanded by dividing and duplicating the light beams traveling in the second direction to increase the number of the light beams; the first expansion region has a central region including a center of the first expansion region and an end region at least on one end side of the first expansion region, in which the amount of diffracted light is less than half the amount of diffracted light in the central region; optical system.

2. the second extension region is in the second direction of the central region; a region in the second direction of the end region where the second extension region is absent; The optical system of claim 1 .

3. The length of the first expansion region in the first direction is longer than the length of the second expansion region in the first direction. The optical system of claim 1 .

4. In the transition of the ratio of the amount of diffracted light along the first direction in the first expansion region, a ratio of the amount of diffracted light in a central region of the first extended region that overlaps with the second extended region when viewed from the second direction is within a range of ±10% of a design value; The optical system of claim 1 .

5. In the end region of the first expanded region, the amount of diffracted light increases from an end of the end region opposite to the central region side toward the central region of the first expanded region. The optical system of claim 1 .

6. a central region of the first expansion region that is a region that is ¼ to ¾ of the length from an end in the first direction, and a terminal region that is a region that is less than ¼ of the length from an end in the first direction; The optical system of claim 1 .

7. a coupling region for changing the direction of the incident light beam toward the first expansion region; The end region of the first expansion region is a region closer to the bonding region. The optical system of claim 1 .

8. a coupling region for changing the direction of the incident light beam toward the first expansion region; The end region of the first expansion region is the region farther from the bonding region. The optical system of claim 1 .

9. the first extension region has a diffraction grating; the height of the diffraction grating in the end regions of the first extension region is lower than the height of the diffraction grating in the central region; The optical system of claim 1 .

10. the first extension region includes a plurality of diffraction gratings; A duty ratio Dr1 of the diffraction grating in the edge regions of the first extension region and a duty ratio Dr2 of the diffraction grating in the central region satisfy the following conditional expression: |Dr1-0.5|>|Dr2-0.5| The optical system of claim 1 .

11. the first extension region includes a plurality of diffraction gratings; an absolute value of a difference between the duty ratio value of the diffraction grating in the end regions of the first extension region and 0.5 is different from an absolute value of a difference between the duty ratio value of the diffraction grating in the central region and 0.5; the height of the diffraction grating in the end regions of the first extension region is different from the height of the diffraction grating in the central region; The optical system of claim 1 .

12. The optical system of any one of claims 1 to 11; a display unit that emits a light beam before being expanded by the optical system; a light-transmitting member that reflects the light beam emitted from the optical system, The image is displayed as a virtual image superimposed on a real scene visible through the light-transmitting member. Head-up display system.

13. The light-transmitting member is a windshield of a moving object. The head-up display system of claim 12.