JP6171740B2 - Optical device and image display apparatus - Google Patents

Description

  The present invention relates to an optical device using a light guide plate and a diffractive optical element, and an image display apparatus including the optical device.

  In recent years, head mounted displays that display images from an image display device as one of the image projection devices in front of the viewer's eyes using a light guide plate have been commercialized, resulting in further miniaturization and wider angle of view. Development related to high efficiency is being carried out. Among them, an apparatus using a diffractive optical element is proposed as one of elements for entering and exiting the light guide plate (for example, Patent Document 1 and Patent Document 2).

  In such an apparatus using a diffractive optical element, light propagating through the light guide plate enters the diffractive optical element a plurality of times in the diffractive optical element region for output, and is taken out of the light guide plate each time. Reach the eyes. Therefore, a virtual image can be observed even if the position of the observer's eyes slightly moves in the horizontal direction.

  However, since the diffraction characteristics of the diffractive optical element have a large wavelength dependency, the color unevenness of the observed virtual image may increase. Therefore, conventionally, in an apparatus using a diffractive optical element, measures for improving color unevenness have been taken.

  In the image display device disclosed in Patent Document 1, in order to reduce the efficiency difference for each color due to the wavelength dependence of diffraction efficiency, a plurality of light guide plates are prepared, and the colors (wavelength components) propagate through the respective light guide plates. Is limited.

  In the image display device disclosed in Patent Document 2, the diffraction efficiency of the diffractive optical element for emission is changed depending on the position, the difference due to the position of the emitted light amount is reduced, and the distribution of the emitted light amount is made uniform. Technology is disclosed.

  On the other hand, when it is desired to increase the size of the virtual image to be observed, it is necessary to increase the angle range of light incident on the light guide plate (for example, 20 degrees or more in all angles). As a diffractive optical element capable of increasing the diffraction efficiency over a large angle range, a surface relief type diffraction grating is more preferable than a volume hologram, and an apparatus using such a surface relief type diffraction grating has also been proposed ( For example, Patent Document 3).

Special table 2008-523434 gazette Special table 2008-535032 gazette Special table 2009-539129

  However, in the apparatus of Patent Document 1, the diffraction efficiency of the diffractive optical element for output is constant regardless of the position. There is a problem that the distribution of the emitted light quantity in the optical element is not uniform.

  Further, in the apparatus of Patent Document 2, the diffraction efficiency of the diffractive optical element for emission is changed depending on the position to reduce the difference due to the position of the emitted light amount. However, light having a long wavelength propagates through the light guide plate at a large angle, and the number of times it enters the diffraction grating in the diffractive optical element region for emission is small. In this case, there is a problem that the total amount of light extracted outside is reduced by changing the diffraction efficiency depending on the position.

  Furthermore, in the apparatus of Patent Document 3, since the surface relief type diffraction grating is used as the diffractive optical element, the angle range of the light incident on the light guide plate can be increased. Since the diffraction efficiency is not changed depending on the position, there is a problem that the distribution of the emitted light quantity is not uniform.

  Accordingly, in consideration of the above-described circumstances, the present invention can reduce color unevenness and make the emitted light amount distribution uniform in a light guide plate structure using a surface relief type diffractive optical element that can increase diffraction efficiency over a wide angle range. It is an object of the present invention to provide an optical device structure that can be realized.

In order to solve the above problems, a first aspect of the optical device according to the present invention includes a first light guide including a first light incident portion and a first light emitting portion, a second light incident portion, A second light guide including two light emitting portions; and at least a part of the light guided in the second light guide and provided in the second light emitting portion of the second light guide. A first diffractive optical element that is diffracted and taken out of the second light guide;
At least a part of the light that is provided in the first light emitting part of the first light guide and guided through the inside of the first light guide and at least a part of the light extracted by the first diffractive optical element A second diffractive optical element for taking out light, and a part of incident light incident on the first light guide and the second light guide is from the first light incident portion of the first light guide. Light that enters and is guided to the inside, and part of the light that enters the second light guide from the second light incident portion and is guided to guide the inside of the second light guide. Includes more light having a longer wavelength than the light guided inside the first light guide, and the second diffractive optical element includes a side closer to the first light incident part, and the first light incident part. The first diffractive optical element includes a portion where the diffraction efficiency is different on the side far from the distance, and the diffraction efficiency is substantially constant.

  According to the first aspect of the optical device according to the present invention described above, a part of the incident light incident on the first light guide is incident on the inside of the first light guide from the first light incident part. The other part is incident on the inside of the second light guide from the second light incident part and guided. At least a portion of the light that enters and is guided into the first light guide is extracted from the first light guide by the second diffractive optical element provided in the first light emitting portion of the first light guide. It is. At least a part of the light that enters the second light guide and is guided by the second light guide is provided by the first diffractive optical element provided in the second light emitting portion of the second light guide. Take out to the outside. Furthermore, at least a part of the light extracted by the first diffractive optical element is extracted by the second diffractive optical element. At this time, since the second diffractive optical element includes a portion where the diffraction efficiency is different between the side closer to the first light incident portion and the side far from the first light incident portion, the emitted light quantity distribution is made uniform. In addition, since the diffraction efficiency of the first diffractive optical element is substantially constant, light containing light having a longer wavelength than the light guided into the first light guide is guided into the second light guide. Even when the number of times of propagation through the light guide at a large angle and incidence on the first diffractive optical element is small, the amount of emitted light is increased. As described above, according to this aspect, by using the two light guides of the first light guide and the second light guide, the efficiency difference for each color due to the wavelength dependency of the diffraction efficiency is reduced, The two diffractive optical elements are provided with portions having different diffraction efficiencies so that the distribution of the quantity of emitted light is made uniform, and the diffraction efficiency of the first diffractive optical element is substantially constant. Thus, an optical device that can obtain a large amount of emitted light, and uniforms the emitted light amount distribution and suppresses color unevenness as a whole is provided.

  In the first aspect of the optical device according to the present invention described above, the first diffractive optical element is a surface relief type diffraction grating having a first concavo-convex structure on one surface, and the second light guide In a cross-sectional view including both the second light incident portion and the second light emitting portion, a surface that intersects the second light emitting portion among the surfaces constituting the convex portion of the first uneven structure is the first light emitting portion. It is preferable to incline with respect to the direction perpendicular to the two light emitting portions. In this case, the surface relief type diffraction grating is used for the first diffractive optical element, so that the diffraction efficiency can be increased over a wide angle range, and a sufficient amount of emitted light can be obtained even for light on the long wavelength side. As a whole, an optical device is provided in which the emitted light quantity distribution is made uniform and color unevenness is suppressed.

  In the first aspect of the optical device according to the present invention described above, the second diffractive optical element is a surface relief type diffraction grating having a second concavo-convex structure on one surface, and the first light guide In a cross-sectional view including both the first light incident portion and the first light emitting portion, a surface that intersects the first light emitting portion among the surfaces constituting the convex portion of the second uneven structure is the first light emitting portion. It is preferable to incline with respect to the direction perpendicular to the one light emitting part. In this case, the surface relief type diffraction grating is used for the second diffractive optical element, so that the diffraction efficiency can be increased over a wide angle range, and a sufficient amount of emitted light can be obtained even for light on the long wavelength side. As a whole, an optical device is provided in which the emitted light quantity distribution is made uniform and color unevenness is suppressed.

  In the first aspect of the optical device according to the present invention described above, the second diffractive optical element is a surface relief type diffraction grating having a second concavo-convex structure on one surface, and the first light guide In a cross-sectional view including both the first light incident portion and the first light emitting portion, the depth of the concave portion of the second concavo-convex structure is from the side closer to the first light incident portion. It is preferable to change gradually or stepwise from the part to the far side. In this case, the amount of light reaching the side closer to the first light incident part is larger than the light reaching the side farther from the first light incident part, but from the side closer to the first light incident part, Since it changes gradually or in steps from one light incident part to the far side, the diffraction efficiency changes, and as a result, the emitted light quantity distribution is made uniform.

  In the first aspect of the optical device according to the present invention described above, the second diffractive optical element is a surface relief type diffraction grating having a second concavo-convex structure on one surface, and the first light guide In a cross-sectional view including both the first light incident part and the first light emitting part, the filling ratio of the second uneven structure is from the side close to the first light incident part, from the first light incident part. It is preferable to change gradually or in steps from the far side. In this case, the amount of light reaching the side closer to the first light incident part is larger than the light reaching the side farther from the first light incident part, but from the side closer to the first light incident part, Since it changes gradually or in steps from one light incident part to the far side, the diffraction efficiency changes, and as a result, the emitted light quantity distribution is made uniform.

  In the first aspect of the optical device according to the present invention described above, the second diffractive optical element is a cross-sectional view including both the first light incident portion and the first light emitting portion of the first light guide. In the above, it is preferable that a surface intersecting the first light emitting portion among the surfaces constituting the convex portion of the second concavo-convex structure is inclined with respect to a direction perpendicular to the first light emitting portion. In this case, it is possible to increase the diffraction efficiency and obtain a sufficient amount of emitted light.

  1st aspect of the optical device which concerns on this invention mentioned above WHEREIN: It is provided in the said 1st light-incidence part of a said 1st light guide, and diffracts a part of said incident light, and the inside of a said 1st light-guide A third diffractive optical element that is incident on the second light guide and the second light incident portion of the second light guide, and diffracts the other part of the incident light to enter the second light guide. It is preferable to have a fourth diffractive optical element. In this case, incident light can be efficiently introduced into the first light guide and the second light guide to guide the light.

  In the first aspect of the optical device according to the present invention described above, the grating period of the third diffractive optical element is a grating period different from the grating period of the fourth diffractive optical element, and the second diffractive optical element Preferably, the grating period of the fourth diffractive optical element is the same as the grating period of the first diffractive optical element. In this case, light having the same wavelength as the light diffracted by the second diffractive optical element and incident on the first light guide can be extracted from the first light guide by the third diffractive optical element. Light having the same wavelength as the light incident on the first light guide after being diffracted by the optical element can be extracted from the first light guide by the second diffractive optical element, and diffracted by the fourth diffractive optical element to obtain the second light. Light having the same wavelength as the light incident on the light guide can be extracted from the second light guide by the first diffractive optical element.

  In the first aspect of the optical device according to the present invention described above, it is preferable that the grating period of the third diffractive optical element is shorter than the grating period of the fourth diffractive optical element. In this case, light having a wavelength longer than the wavelength of light incident on the first light guide can be incident on the second light guide.

  In the first aspect of the optical device according to the present invention described above, the third diffractive optical element is a surface relief type diffraction grating having a third concavo-convex structure on one surface, and the first light guide In a cross-sectional view including both the first light incident portion and the first light emitting portion, a surface that intersects the first light incident portion among the surfaces constituting the convex portion of the third uneven structure is the first The fourth diffractive optical element is a surface relief type diffraction grating having a fourth concavo-convex structure on one surface, which is inclined with respect to a direction perpendicular to one light incident part, and the second light guide In a cross-sectional view including both the second light incident portion and the second light emitting portion, a surface that intersects the second light incident portion among the surfaces constituting the convex portion of the fourth uneven structure is the second It is preferable to incline with respect to the direction perpendicular to the light incident part. In this case, the third diffractive optical element and the fourth diffractive optical element use a surface relief type diffraction grating having a concavo-convex structure having an inclined surface to increase the diffraction efficiency over a wide angle range, A sufficient amount of emitted light can be obtained even for light on the long wavelength side, and as a whole, an optical device is provided in which the emitted light amount distribution is made uniform and color unevenness is suppressed.

  In the first aspect of the optical device according to the present invention described above, the fourth diffractive optical element has the first diffractive optical element more than the third diffractive optical element in a plan view as viewed from a direction perpendicular to the second light incident portion. The first diffractive optical element is located on the side of the second light emitting part, and the first diffractive optical element is closer to the second light incident part than the second diffractive optical element in a plan view as viewed from a direction perpendicular to the second light emitting part. Preferably it is located. In this case, since each diffractive optical element is arranged along the optical axis of incident light and outgoing light, the loss at the time of incident and outgoing is reduced.

  Next, an image display apparatus according to the present invention includes the above-described optical device according to the present invention and an image forming unit that emits image light. Such an image display device may include an image forming unit such as a liquid crystal display and a collimating optical system, and can be adapted to a form mounted on the observer's head such as a head-mounted display.

  As described above, according to the present invention, even in an image display device that is mounted on the observer's head, such as a head-mounted display, the manufacturing difficulty is reduced and the manufacturing cost is reduced. In addition, it is possible to obtain an optical device that can improve the fitting property to the face of the observer and can obtain a wide angle of view.

  In the image display device according to the present invention, the “image forming unit” refers to, for example, a liquid crystal display that displays an image, a laser scanning display that causes an observer to recognize an image by scanning laser light, and the like. It includes an optical system that collects and converts image light emitted from the image display.

It is a perspective view which shows an example of the whole image of the head mounted display which concerns on 1st Embodiment. It is principal part sectional drawing which shows an example of the internal structure of the optical system for left eyes of the head mounted display which concerns on 1st Embodiment, and a waveguide. It is principal part sectional drawing explaining the aspect of the diffraction in the diffraction grating without an inclination. It is principal part sectional drawing explaining the aspect of diffraction in the diffraction grating with an inclination. It is an enlarged view of the part by which the 2nd diffractive optical element is arrange | positioned. It is an enlarged view of the part by which the diffractive optical element of the comparative example compared with a 2nd diffractive optical element is arrange | positioned. It is a figure which shows an example of the emitted light quantity distribution of a 2nd diffractive optical element and a comparative example. It is an enlarged view of the part by which the 4th diffractive optical element is arrange | positioned. It is explanatory drawing explaining an example of the arrangement position of a 1st diffractive optical element, a 2nd diffractive optical element, a 3rd diffractive optical element, and a 4th diffractive optical element. It is explanatory drawing explaining an example of the arrangement position of a 1st diffractive optical element, a 2nd diffractive optical element, a 3rd diffractive optical element, and a 4th diffractive optical element. It is an enlarged view of the part by which the 2nd diffractive optical element in 2nd Embodiment is arrange | positioned. It is explanatory drawing explaining the filling factor of the 2nd diffractive optical element in 2nd Embodiment. It is an enlarged view of the part by which the 2nd diffractive optical element in 3rd Embodiment is arrange | positioned. It is an enlarged view of the part by which the 2nd diffractive optical element in 4th Embodiment is arrange | positioned.

  Hereinafter, various embodiments according to the present invention will be described with reference to the accompanying drawings. In the drawings, the ratio of dimensions of each part is appropriately changed from the actual one. In the embodiment described below, the optical device of the present invention is described as an example applied to a head-mounted display that is an example of an image display device that is mounted on the head of an observer. The embodiment shows one embodiment of the present invention, and does not limit the present invention, and can be arbitrarily changed within the scope of the technical idea of the present invention.

<A: First Embodiment>
(Overall configuration of head mounted display)
FIG. 1 is a perspective view showing an example of the entire image of the head mounted display 100 according to the first embodiment. As shown in FIG. 1, the head mounted display 100 according to the present embodiment is a head mounted display having an appearance like glasses, and recognizes image light based on a virtual image for an observer wearing the head mounted display 100. It is possible to cause the observer to observe the outside world image with see-through.

  Specifically, the head mounted display 100 includes a light guide plate 20, a pair of left and right temples 131 and 132 that support the light guide plate 20, and a pair of image forming apparatuses 111 and 112 attached to the temples 131 and 132. Here, in the drawing, the first display device 100A in which the left side of the light guide plate 20 and the image forming device 111 are combined is a portion that forms a virtual image for the right eye, and functions alone as an image display device. In the drawing, the second display device 100B in which the right side and the image forming device 112 are combined with the light guide plate 20 is a portion that forms a virtual image for the left eye, and functions alone as an image display device.

  The internal structure and light guide plate of the head mounted display 100 will be described. FIG. 2 is a main part sectional view schematically showing an example of the internal structure and the light guide plate of the head mounted display according to the present embodiment. FIG. 2 is a cross-sectional view of the main part showing the internal structure of the left-eye optical system and the light guide plate according to the present embodiment. In addition, although illustration is abbreviate | omitted, about the internal structure and light guide plate of the optical system for right eyes, it has the structure which reversed FIG. 2 and replaced right and left. As shown in FIG. 2, the first display device 100 </ b> A and the second display device 100 </ b> B include an image forming unit 10 and a light guide plate 20.

  The image forming unit 10 includes an image display device 11 and a projection optical system 12. Among these, the image display apparatus 11 is a liquid crystal display device in this embodiment, and is illuminated by a light source to generate image light 13 including three colors of red (R), green (G), and blue (B), The light is emitted toward the projection optical system 12. An organic EL panel can also be used as the image display device 11. On the other hand, the projection optical system 12 is a collimating lens that converts the image light emitted from each point on the image display device 11 into a light beam in a parallel state and enters the light guide plate 20. In particular, in the present embodiment, the image forming unit 10 is arranged to be inclined with respect to the normal direction perpendicular to the panel in order to obtain a wide angle of view.

  The light guide plate 20 includes a first light guide plate 101 and a second light guide plate 201. The overall appearance of the first light guide plate 101 and the second light guide plate 201 is formed by a flat plate-like member extending parallel to the YX plane in the drawing. The first light guide plate 101 and the second light guide plate 201 are plate-like members formed of glass or a light-transmitting resin material.

  The first light guide plate 101 includes a first panel surface 101a disposed to face the image forming unit 10, and a second panel surface 101b facing the first panel surface 101a, and the first panel surface 101a. The image light is incident through the light incident surface 101c formed at one end of the first image surface, and the incident image light is totally reflected by the first panel surface 101a and the second panel surface 101b, and in front of the observer's eyes. The light is guided to the formed light exit surface 101d.

  The second light guide plate 201 has a first panel surface 201a disposed opposite to the first light guide plate 101, and a second panel surface 201b opposed to the first panel surface 201a. The image light is incident through the light incident surface 201c formed at one end of the surface 201a, and the incident image light is totally reflected by the first panel surface 201a and the second panel surface 201b, and the first The light is guided to the light exit surface 201d formed at the other end of the panel surface 201a.

  The first and second panel surfaces 101a and 101b of the first light guide plate 101 and the first and second panel surfaces 201a and 201b of the second light guide plate 201 are not provided with a reflective coating, and the panel External light that is incident on the surfaces 101a, 101b, 201a, and 201b from the external side may pass through the first light guide plate 101 and the second light guide plate 201 with high transmittance. Thereby, the 1st light guide plate 101 and the 2nd light guide plate 201 can be made into the see-through type which can see through an external field image.

  The light incident surface 101c of the first light guide plate 101 is provided with a first diffractive optical element 102 that diffracts incident light in the direction of the end surface on the light exit surface 101d side, and the light exit surface 101d is connected to the light exit surface 101d. A second diffractive optical element 103 is provided that diffracts image light toward the outside and projects it as virtual image light onto the observer's eye EY.

  The light incident surface 201c of the second light guide plate 201 is provided with a third diffractive optical element 202 that diffracts incident light in the direction of the end surface on the light exit surface 201d side. A fourth diffractive optical element 203 that diffracts image light toward the outside and projects the image light as virtual image light onto the observer's eye EY via the first light guide plate 101 is provided.

  In the present embodiment, as an example, the first diffractive optical element 102, the second diffractive optical element 103, the third diffractive optical element 202, and the fourth diffractive optical element 203 are all surface relief type diffraction gratings.

(First light guide plate)
In the first diffractive optical element 102 provided on the light incident surface 101c of the first light guide plate 101, the grating surface is inclined in the direction shown in FIG. 2 in order to increase the diffraction efficiency. When the diffracted light is ordered in the order of 0th order, ± 1st order,... From the side closer to the central axis of the incident light, as shown in FIG. The next diffracted light and the −1st order diffracted light have substantially the same intensity.

  However, when the grating surface of the surface relief type diffraction grating is inclined, if the inclination of the grating surface and the direction of incident light are in a relationship as shown in FIG. 4, the diffracted light is caused by Bragg reflection on the grating surface. Therefore, the intensity of the + 1st order diffracted light becomes higher than the intensity of the −1st order diffracted light. As a result, it is possible to increase the diffraction efficiency for light diffracted in the direction in which image light propagates toward the light exit surface.

  As shown in FIG. 2, the grating surface of the second diffractive optical element 103 provided on the light exit surface 101d of the first light guide plate 101 is not inclined. However, as shown in FIG. 2, the second diffractive optical element 103 has a diffraction grating whose depth changes stepwise, and becomes deeper as it approaches the end surface of the first light guide plate 101 on the light exit surface 101 d side. It has become. Details will be described later.

  Since the light emitted from the second diffractive optical element 103 needs to have the same angle as the image light 13, the grating period of the first diffractive optical element 102 and the second diffractive optical element 103 (in the X direction in FIG. 2) The period) is the same.

  As shown in FIG. 2, the diffraction angle by the diffraction grating varies depending on the wavelength, and the shorter the wavelength, the smaller the diffraction angle. Therefore, the angle introduced into the first light guide plate 101 by the first diffractive optical element 102 differs depending on the blue light 13B, the green light 13G, and the red light 13R. In the present embodiment, the grating period of the first diffractive optical element 102 is determined so that the blue light 13B can propagate through the first light guide plate 101 over a wide incident angle range. If comprised in this way, the diffraction angle with respect to red light 13R will become large, and the diffraction efficiency with respect to red light 13R will fall large. Therefore, the first light guide plate 101 substantially propagates the blue light 13B and the green light 13G.

  The light propagated while repeating total reflection in the first light guide plate 101 reaches the second diffractive optical element 103 and is taken out little by little every time it enters the diffraction grating surface and reaches the eye EY of the observer. The blue light 13B having a short wavelength propagates through the first light guide plate 101 at a small angle (standing angle), and enters the second diffractive optical element 103 in the region where the second diffractive optical element 103 is provided. The number of times to perform increases compared to the green light 13G and the red light 13R. FIG. 2 shows an example in which the blue light 13B is incident on the second diffractive optical element 103 five times.

(Second diffractive optical element)
FIG. 5 shows an enlarged portion where the second diffractive optical element 103 is provided. As shown in FIG. 5, the second diffractive optical element 103 is divided into five regions 103A, 103B, 103C, 103D, and 103E, and the depth of the diffraction grating is different in each region. The depth of the diffraction grating in the region 103E farthest from the first diffractive optical element 102 is the deepest, and the depth of the diffraction grating in the region 103E is blue light that propagates through the first light guide plate 101 at a small angle. For 13B, the depth is such that the first-order diffraction efficiency is maximized. As the depth of the diffraction grating becomes closer to the regions 103D, 103C, 103B, and 103A and the first diffractive optical element 102, the depth of the diffraction grating becomes gradually smaller.

  As shown in FIG. 6, when the second diffractive optical element 103 ′ having the same depth as a whole is provided on the first light guide plate 101, much light is extracted in the region 103 </ b> A closest to the first diffractive optical element 102. The amount of light reaching the farthest region 103E from the first diffractive optical element 102 is reduced.

  FIG. 7 shows a comparison result of the amount of emitted light when the second diffractive optical element 103 whose depth changes stepwise and when the second diffractive optical element 103 ′ having the same depth as a whole is used. In FIG. 7, a curve a indicates the distribution of the emitted light amount when the second diffractive optical element 103 ′ having the same depth as a whole is used. Curve b shows the distribution of the emitted light quantity when the second diffractive optical element 103 whose depth changes stepwise is used.

  As shown in FIG. 7, when the second diffractive optical element 103 ′ having the same depth as a whole is used, a lot of light is extracted in the region 103A closest to the first diffractive optical element 102, and the first diffractive optical element It can be seen that the amount of light decreases as the area is farther from the element 102.

  However, as shown in FIG. 7, when the second diffractive optical element 103 whose depth changes stepwise is used, from the region 103 </ b> A closest to the first diffractive optical element 102, from the first diffractive optical element 102. The distribution of the amount of emitted light is almost uniform up to the farthest region 103E. This is because the diffraction efficiency in the region 103A closest to the first diffractive optical element 102 is made shallow to reduce the diffraction efficiency, so that the amount of light remaining in the first light guide 101 after the region 103A is also reduced. This is because light can be delivered to the region 103E farthest from the first diffractive optical element 102.

(Second light guide plate)
The light 23 transmitted without being diffracted by the first diffractive optical element 102 of the first light guide plate 101 enters a third diffractive optical element 202 provided on the light incident surface 201 c of the second light guide plate 201. The light incident on the third diffractive optical element 202 is diffracted and introduced into the second light guide plate 201.

  The third diffractive optical element 202 provided on the light incident surface 201c of the second light guide plate 201 is inclined in the direction shown in FIG. 2 in order to increase the diffraction efficiency. The configuration in which the grating surface is inclined is the same as that of the first diffractive optical element 102. However, the grating period of the third diffractive optical element 202 is different from the grating period of the first diffractive optical element 102. Since the grating period of the third diffractive optical element 202 is made different from the grating period of the first diffractive optical element 102 in this way, light having a wavelength range different from that of the light propagating through the first light guide plate 101 is transmitted to the second guide. It can be propagated into the light plate 201. Specifically, the grating period of the third diffractive optical element 202 is such that the green light 23G can propagate through the second light guide plate 201 with total reflection over a wide incident angle range. The grating period is set longer than the period. Accordingly, depending on the incident angle, the diffraction angle with respect to the blue light becomes small, and the second light guide plate 201 is transmitted without being totally reflected at the interface between the second light guide plate 201 and the air. As a result, in the second light guide plate 201, the green light 23G and the red light 23R are substantially propagated.

  As with the third diffractive optical element 202, the fourth diffractive optical element 203 provided on the light exit surface 201d of the second light guide plate 201 is inclined in the direction shown in FIG. 2 in order to increase the diffraction efficiency. doing. Details will be described later.

  The light emitted from the fourth diffractive optical element 203 needs to have the same angle as that of the image light 23, and therefore the grating period of the third diffractive optical element 202 and the fourth diffractive optical element 203 (in the X direction in FIG. 2). The period) is the same.

  In the second light guide plate 201, the green light 23G and the red light 23R are propagated. Among them, it is important to propagate the red light 23R with high efficiency. This is because green light is propagated also in the first light guide plate 101.

  Since the red light 23R having a long wavelength is diffracted by the third diffractive optical element 202 at a large angle, the red light 23R propagates through the second light guide plate 201 at a large angle. Accordingly, in the region where the fourth diffractive optical element 203 is provided, the number of times of incidence on the fourth diffractive optical element 203 is small. FIG. 2 shows an example in which the red light 23R enters the fourth diffractive optical element 203 twice.

(Fourth diffractive optical element)
As described above, when the number of times of incidence on the fourth diffractive optical element 203 is small, the diffraction efficiency of the region close to the incident side diffractive optical element is divided into a plurality of regions as in the second diffractive optical element 103. Even if it is lowered, there is little effect of making the distribution of the emitted light quantity uniform, and the observed virtual image may become darker as the emitted light quantity decreases.

  Therefore, in the present embodiment, as shown in FIG. 8, the amount of emitted light is increased by inclining the grating surface of the fourth diffractive optical element 203 to form an inclined surface relief diffraction grating.

(Positional relationship of diffractive optical elements)
As shown in FIG. 9, since the optical axis of the light incident on the first diffractive optical element 102 of the first light guide plate 101 is inclined at a predetermined angle, the third diffractive optical of the second light guide plate 201 is used. The position of the element 202 is a position moved to the central portion side of the second light guide plate 201 as compared with the first diffractive optical element 102.

  Similarly, since the optical axis of the light emitted from the second diffractive optical element 103 of the first light guide plate 101 is inclined at a predetermined angle, the position of the fourth diffractive optical element 203 of the second light guide plate 201 is changed. Is a position moved to the center side of the second light guide plate 201 as compared with the first diffractive optical element 102.

  Accordingly, when viewed from the front side of the first light guide plate 101, as shown in FIG. 10, the first diffractive optical element 102 and the third diffractive optical element 202, and the second diffractive optical element 103 and the fourth diffractive optical element are provided. The position 203 has a positional relationship shifted in the longitudinal direction of the first light guide plate 101. In FIG. 10, each diffractive optical element is represented by a frame only. By disposing each diffractive optical element at such a position, it is possible to reduce the loss at the time of incidence and at the time of emission.

  As described above, according to this embodiment, the light is separated into the first light guide plate 101 that shares green light from the blue light and the second light guide plate 201 that shares red light from the green light. The second diffractive optical element 103 having a different diffraction efficiency depending on the region is applied to blue light having a large number of reflections on the exit surface 101d, and for red light having a small number of reflections on the exit surface 201d, Since the fourth diffractive optical element 203 having an inclined grating surface is applied, it is possible to provide an image display device that can display a virtual image in which the distribution of emitted light quantity is nonuniform or color unevenness is suppressed.

<B: Second Embodiment>
Next, a second embodiment of the present invention will be described. The present embodiment is an example in which the filling rate of the diffraction grating of the second diffractive optical element 103 is changed depending on the region in order to change the diffraction efficiency of the second diffractive optical element 103 depending on the region. FIG. 11 is an enlarged view of a portion provided with the second diffractive optical element 103 in the present embodiment. FIG. 12 is a diagram for explaining the filling factor of the diffraction grating.

  As shown in FIG. 12, the filling factor of the diffraction grating is a ratio of the width of the diffraction grating to the grating period of the diffraction grating, and the interval between two adjacent diffraction gratings, that is, the grating period is P, and the width of the diffraction grating is When L, it is expressed as L / P.

  Since the grating period P is the same throughout the second diffractive optical element 103, in this embodiment, in order to change the filling factor of the diffraction grating, diffraction is performed in each of the plurality of regions 103A to 103E as shown in FIG. The width of the lattice was changed. Specifically, the filling rate of the diffraction grating in the region 103E farthest from the first diffractive optical element 102 is the highest, and the closer to the region 103D, the region 103C, the region 103B, the region 103A and the first diffractive optical element 102, the closer to the diffraction grating The filling rate is low. As a result of such a configuration, the diffraction efficiency of the region 103E farthest from the first diffractive optical element 102 is highest, and the diffraction efficiency decreases as the region 103D, region 103C, region 103B, region 103A and the first diffractive optical element 102 are closer to each other. The diffraction efficiency is lowest in the region 103A closest to the first diffractive optical element 102.

  According to this embodiment, the first light guide plate 101 that shares green light from blue light and the second light guide plate 201 that shares red light from green light are separated and guided, and the light exit surface 101d The second diffractive optical element 103 having a different diffraction efficiency depending on the region is applied to the blue light having a large number of reflections of the light, and the red light having a small number of reflections on the exit surface 201d is applied with the inclined grating surface. Since the four-diffractive optical element 203 is applied, it is possible to provide an image display device capable of displaying a virtual image in which the distribution of the emitted light quantity is not uniform or the color unevenness is suppressed.

<C: Third Embodiment>
Next, a third embodiment of the present invention will be described. In this embodiment, in order to change the diffraction efficiency in the second diffractive optical element 103 depending on the region, the depth of the diffraction grating of the second diffractive optical element 103 is changed depending on the region, and the diffraction grating is inclined. FIG. 13 is an enlarged view of a portion provided with the second diffractive optical element 103 in the present embodiment.

  As shown in FIG. 13, for the blue light 13B that has the deepest diffraction grating in the region 103E farthest from the first diffractive optical element 102 and propagates in the first light guide plate 101 at a small angle, The depth is such that the first-order diffraction efficiency is maximized. As the depth of the diffraction grating becomes closer to the regions 103D, 103C, 103B, and 103A and the first diffractive optical element 102, the depth of the diffraction grating becomes gradually smaller. As a result of such a configuration, the diffraction efficiency of the region 103E farthest from the first diffractive optical element 102 is highest, and the diffraction efficiency decreases as the region 103D, region 103C, region 103B, region 103A and the first diffractive optical element 102 are closer to each other. The diffraction efficiency is lowest in the region 103A closest to the first diffractive optical element 102.

  Furthermore, in this embodiment, the diffraction grating of the second diffractive optical element 103 is inclined as shown in FIG. As a result, the amount of light emitted from the second diffractive optical element 103 can be increased.

  According to this embodiment, the first light guide plate 101 that shares green light from blue light and the second light guide plate 201 that shares red light from green light are separated and guided, and the light exit surface 101d The second diffractive optical element 103 having a different diffraction efficiency depending on the region is applied to the blue light having a large number of reflections of the light, and the red light having a small number of reflections on the exit surface 201d is applied with the inclined grating surface. Since the four-diffractive optical element 203 is applied, it is possible to provide an image display device capable of displaying a virtual image in which the distribution of the emitted light quantity is not uniform or the color unevenness is suppressed.

<D: Fourth Embodiment>
Next, a fourth embodiment of the present invention will be described. In this embodiment, in order to change the diffraction efficiency in the second diffractive optical element 103 depending on the region, the filling rate of the diffraction grating of the second diffractive optical element 103 is changed depending on the region, and the diffraction grating is inclined. FIG. 14 is an enlarged view of a portion provided with the second diffractive optical element 103 in the present embodiment.

  In this embodiment, as shown in FIG. 14, the width of the diffraction grating is changed in each of the plurality of regions 103A to 103E, and the filling factor of the diffraction grating is changed. Specifically, the filling rate of the diffraction grating in the region 103E farthest from the first diffractive optical element 102 is the highest, and the closer to the region 103D, the region 103C, the region 103B, the region 103A and the first diffractive optical element 102, the closer to the diffraction grating The filling rate is low. As a result of such a configuration, the diffraction efficiency of the region 103E farthest from the first diffractive optical element 102 is highest, and the diffraction efficiency decreases as the region 103D, region 103C, region 103B, region 103A and the first diffractive optical element 102 are closer to each other. The diffraction efficiency is lowest in the region 103A closest to the first diffractive optical element 102.

  Furthermore, in this embodiment, the diffraction grating of the second diffractive optical element 103 is inclined as shown in FIG. As a result, the amount of light emitted from the second diffractive optical element 103 can be increased.

  According to this embodiment, the first light guide plate 101 that shares green light from blue light and the second light guide plate 201 that shares red light from green light are separated and guided, and the light exit surface 101d The second diffractive optical element 103 having a different diffraction efficiency depending on the region is applied to the blue light having a large number of reflections of the light, and the red light having a small number of reflections on the exit surface 201d is applied with the inclined grating surface. Since the four-diffractive optical element 203 is applied, it is possible to provide an image display device capable of displaying a virtual image in which the distribution of the emitted light quantity is not uniform or the color unevenness is suppressed.

<E: Modification>
In the first to fourth embodiments described above, surface relief type diffraction gratings are used as the first diffractive optical element 102 and the third diffractive optical element 202 which are diffractive optical elements on the incident side. However, the present invention is not limited to this. However, it is also possible to use an optical element such as a volume hologram, a mirror, or a prism. In the first to fourth embodiments, an example in which an inclined surface relief diffraction grating is used as the first diffractive optical element 102, the third diffractive optical element 202, and the fourth diffractive optical element 203 has been described. It is also possible to apply a blazed diffraction grating.

  Furthermore, in the above-described first to fourth embodiments, the example in which the second diffractive optical element 103 is divided into five regions has been described for convenience. However, the number of divisions may be further increased. Alternatively, instead of changing the depth of the diffraction grating and the filling rate of the diffraction grating for each region, it is possible to continuously change the depth of the diffraction grating and the filling rate of the diffraction grating.

DESCRIPTION OF SYMBOLS 10 ... Image formation part, 11 ... Image display apparatus, 12 ... Projection optical system, 13 ... Image light, 13B ... Blue light, 13G ... Green light, 13R ... Red light, 20 ... Light guide plate, 23 ... Image light, 23G ... Green light, 23R ... red light, 100 ... head mounted display, 100A, 100B ... display device, 101 ... first light guide plate, 101a, 101b ... panel surface, 101c ... first light incident surface, 101d ... first light emitting surface , 102 ... 1st diffractive optical element, 103 ... 2nd diffractive optical element, 103A, 103B, 103C, 103D, 103E ... area, 111, 112 ... image forming apparatus, 131, 132 ... temple, 201 ... 2nd light guide plate, 201a, 201b ... panel surface, 201c ... second light incident surface, 201d ... second light exit surface, 202 ... third diffractive optical element, 203 ... fourth diffractive optical element.

Claims (12)

A first light guide including a first light incident portion and a first light emitting portion;
A second light guide including a second light incident portion and a second light emitting portion;
A first light provided at the second light emitting portion of the second light guide and diffracting at least a part of the light guided inside the second light guide to be taken out of the second light guide. A diffractive optical element;
At least a part of the light that is provided in the first light emitting part of the first light guide and guided through the inside of the first light guide and at least a part of the light extracted by the first diffractive optical element A second diffractive optical element for taking out
A part of the incident light incident on the first light guide and the second light guide is incident on the inside of the first light guide from the first light incident part, and is guided to the other part. Is incident on the inside of the second light guide from the second light incident part, is guided,
The light that guides the inside of the second light guide includes more light having a longer wavelength than the light that guides the inside of the first light guide,
The second diffractive optical element includes a portion where the diffraction efficiency is different between a side closer to the first light incident part and a side far from the first light incident part,
The optical device according to claim 1, wherein the first diffractive optical element has substantially constant diffraction efficiency. The optical device according to claim 1.
The first diffractive optical element is a surface relief type diffraction grating having a first concavo-convex structure on one surface, and includes a second light incident part and a second light output part of the second light guide. In a cross-sectional view including both, a surface intersecting the second light emitting portion among the surfaces constituting the convex portion of the first concavo-convex structure is inclined with respect to a direction perpendicular to the second light emitting portion. An optical device characterized by that. The optical device according to claim 1 or 2,
The second diffractive optical element is a surface relief type diffraction grating having a second concavo-convex structure on one surface, and includes the first light incident part and the first light output part of the first light guide. In a cross-sectional view including both, a surface that intersects the first light emitting portion among the surfaces constituting the convex portion of the second concavo-convex structure is inclined with respect to a direction perpendicular to the first light emitting portion. An optical device characterized by that. The optical device according to claim 1 or 2,
The second diffractive optical element is a surface relief type diffraction grating having a second concavo-convex structure on one surface, and includes the first light incident part and the first light output part of the first light guide. In a cross-sectional view including both, the depth of the concave portion of the second concavo-convex structure changes gradually or stepwise from the side closer to the first light incident portion to the side farther from the first light incident portion. An optical device characterized by that. The optical device according to claim 1 or 2,
The second diffractive optical element is a surface relief type diffraction grating having a second concavo-convex structure on one surface, and includes the first light incident part and the first light output part of the first light guide. In a cross-sectional view including both, the filling factor of the second concavo-convex structure changes gradually or stepwise from the side closer to the first light incident part to the side farther from the first light incident part. An optical device. The optical device according to claim 4 or 5,
The second diffractive optical element has a surface constituting a convex portion of the second concavo-convex structure in a cross-sectional view including both the first light incident portion and the first light emitting portion of the first light guide. Among these, the optical device is characterized in that a surface intersecting with the first light emitting portion is inclined with respect to a direction perpendicular to the first light emitting portion. The optical device according to any one of claims 1 to 6,
A third diffractive optical element that is provided in the first light incident portion of the first light guide and diffracts a part of the incident light to enter the first light guide;
A fourth diffractive optical element provided at the second light incident portion of the second light guide and diffracting another part of the incident light to be incident on the second light guide. An optical device characterized by. The optical device according to claim 7.
The grating period of the third diffractive optical element is a grating period different from the grating period of the fourth diffractive optical element, and is the same as the grating period of the second diffractive optical element,
The optical device according to claim 4, wherein a grating period of the fourth diffractive optical element is the same as a grating period of the first diffractive optical element. The optical device according to claim 8.
An optical device, wherein the grating period of the third diffractive optical element is a grating period shorter than the grating period of the fourth diffractive optical element. The optical device according to any one of claims 7 to 9,
The third diffractive optical element is a surface relief type diffraction grating having a third concavo-convex structure on one surface, and includes a first light incident portion and a first light emitting portion of the first light guide. In a cross-sectional view including both, a surface that intersects the first light incident portion among the surfaces constituting the convex portion of the third uneven structure is inclined with respect to a direction perpendicular to the first light incident portion,
The fourth diffractive optical element is a surface relief type diffraction grating having a fourth concavo-convex structure on one surface, and includes the second light incident portion and the second light emitting portion of the second light guide. In a cross-sectional view including both, a surface that intersects the second light incident portion among the surfaces constituting the convex portion of the fourth concavo-convex structure is inclined with respect to a direction perpendicular to the second light incident portion. An optical device characterized by that. The optical device according to any one of claims 7 to 10,
The fourth diffractive optical element is located closer to the second light emitting part than the third diffractive optical element in a plan view as viewed from a direction perpendicular to the second light incident part;
The first diffractive optical element is located closer to the second light incident part than the second diffractive optical element in a plan view as viewed from a direction perpendicular to the second light emitting part. Optical device. An image display apparatus comprising: the optical device according to claim 1; and an image forming unit that emits image light.

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