Image display device having maximum emission angle of image light smaller than maximum viewing angle of virtual image

Abstract

The image display device includes an image generating unit that emits first image light, a pupil expanding element that expands a diameter of a light flux included in the first image light from the image generating unit to obtain second image light, a first light condensing optical system that condenses the second image light and forms an intermediate image, and a second light condensing optical system that condenses light from the intermediate image and generates a virtual image on eye of a viewer, in a plane including at least the image generating unit, the pupil expanding element, and the eye of the viewer, a maximum emission angle of the first image light is smaller than a maximum viewing angle of the virtual image, and the diameter of the light flux included in the second image light is greater than that of a light flux included in the virtual image.

Claims

1. An image display device comprising: an image generating unit that emits an image light corresponding to a virtual image; a pupil expanding element that expands a diameter of a light flux of the image light which is incident from the image generating unit, the pupil expanding element emitting the image light that has the diameter of the light flux expanded; and a light condensing optical system that condenses the image light emitted from the pupil expanding element to form an exit pupil, wherein, a maximum emission angle of the image light emitted from the pupil expanding element is smaller than a maximum viewing angle of the virtual image, the diameter of the light flux of the image light emitted from the pupil expanding element is greater than a diameter of a light flux in the exit pupil.

2. The image display device according to claim 1, wherein the image generating unit includes: a light source that emits the image light; and a light scanning device that scans the image light emitted by the light source unit.

3. The image display device according to claim 1, wherein the image generating unit includes an electro-optical device and a collimator lens.

4. The image display device according to claim 1, wherein the pupil expanding element includes a plurality of light guiding materials that are bonded to each other through a half mirror layer.

5. The image display device according to claim 1, wherein the pupil expanding element includes a diffraction element.

6. The image display device according to claim 1, wherein the light condensing optical element includes a first light condensing optical element and a second light condensing optical element, the first light condensing element condenses the image light that is emitted from the pupil expending element to form an intermediate image, and the second light condensing element condenses the image light from the intermediate image to form the exit pupil.

7. The image display device according to claim 6, wherein the first light condensing optical system has at least positive power and negative power, and totally has the positive power.

8. The image display device according to claim 6, wherein the second light condensing optical system is a concave mirror having positive power in a plane including at least the image generating unit, the pupil expanding element, and the eye of the viewer.

9. The image display device according to claim 6, wherein the second light condensing optical system is a reflective type hologram having positive power in the plane including at least the image generating unit, the pupil expanding element, and the eye of the viewer.

Description

BRIEF DESCRIPTION OF DRAWINGS

(1) FIG. 1 is a view illustrating a state in which a HMD of the present embodiment is worn.

(2) FIG. 2 is a perspective view of the HMD of the present embodiment.

(3) FIG. 3 is a plan view illustrating a configuration of each part of a display device.

(4) FIG. 4 is a view for describing a pupil expanding function.

(5) FIG. 5 is a sectional view illustrating a schematic configuration of a pupil expanding element.

(6) FIG. 6 is a view for describing a viewing angle expanding function.

(7) FIG. 7 is a view for describing a pupil expanding function in a HMD of a second embodiment.

(8) FIG. 8 is a view illustrating a configuration of an image generating unit according to a modification example.

(9) FIG. 9 is a view illustrating a configuration of a pupil expanding element according to the modification example.

DESCRIPTION OF EMBODIMENTS

(10) Hereinafter, embodiments will be described in detail with reference to drawings.

(11) Also, there are cases in which a part to be a feature for the sake of convenience in drawings to be used in following description is enlarged and illustrated in order to easily understand features thereof, and a dimensional ratio of each component is not necessary to be the same as that of the actual.

(12) Hereinafter, an embodiment will be described in detail with respect to drawings.

(13) The image display device of the present embodiment is an example of a head mounted display which a user wears on his or her head to use.

(14) In the following description, a head mounted display will be shortened to HMD.

(15) FIG. 1 is a view illustrating a state in which the user wears the HMD of the present embodiment.

(16) FIG. 2 is a perspective view of the HMD of the present embodiment.

(17) As illustrated in FIG. 1, an HMD 300 of the present embodiment is worn on a head portion and used by the user with the feeling of wearing eyeglasses. The HMD 300 of the present embodiment is a see-through type (transmitting type) HMD. According to the HMD 300 of the present embodiment, the user is capable of visually recognizing an image which is generated by an image display unit, and is also capable of visually recognizing an image of the outdoor scenes such as the scenery which is external to the HMD 300.

(18) As illustrated in FIG. 2, the HMD 300 is provided with a display device 100 which has a shape which is similar to eyeglasses, and a control device (controller) 200 which has a size of a degree a user may hold using a hand of the user. The display device 100 and the control device 200 are connected in a wired or a wireless manner to be capable of communication. In the present embodiment, each of a left eye image display unit 110A and a right eye image display unit 110B which form the display device 100, and the control device 200 are connected in a wired manner via a cable 150 to be capable of communication, and communicate image signals, control signals, and the like.

(19) The display device 100 is provided with a main frame (main body of device) 120, the left eye image display unit 110A, and the right eye image display unit 110B. The control device 200 is provided with a display unit 210, and an operation button unit 250. The display unit 210 displays various information, instructions, and the like to be provided to the user, for example. A main frame 120 is provided with a pair of temple portions 122A and 122B for the user to wear on the ears of the user. The main frame 120 is a member which supports the left eye image display unit 110A and the right eye image display unit 110B.

(20) FIG. 3 is a plan view illustrating the configuration of the portions of the display device 100. FIG. 3 illustrates a state of the user wearing the display device 100 as viewed from above the head.

(21) The right eye image display unit 110B and the left eye image display unit 110A have the same configuration, and the configuration elements inside both the image display units are disposed to be left-right symmetrical. Therefore, hereinafter, detailed description will be given of the right eye image display unit 110B simply as the image display unit 110, and description of the left eye image display unit 110A will be omitted.

(22) As illustrated in FIG. 3, the image display unit 110 is provided with an image generating unit 11, a pupil expanding element 12, a first light condensing optical system 13, and a second light condensing optical system 14. The image generating unit 11 emits light which includes image information. The pupil expanding element 12 expands a beam diameter of the light which is emitted from a light scanning device 17 to be described later.

(23) The image generating unit 11 is provided with a light source optical system 15, a mirror 16, and the light scanning device 17. The light source optical system 15 emits light which is generated by an internal semiconductor laser. The mirror 16 reflects the light which is emitted from the light source optical system 15 and turns back the optical path of the light. The light scanning device 17 scans the light which is reflected by the mirror 16.

(24) The light source optical system 15 is provided with a light source unit 25, a pickup lens 26, an optical fiber 27, and a collimator lens 28. For example, the light source unit 25 is provided with a plurality of solid state light sources (not illustrated) including a semiconductor laser which emits red light, a semiconductor laser which emits green light, and a semiconductor laser which emits blue light. The colors of light which are emitted from the semiconductor lasers are modulated according to the image signal, the colors of light which are modulated are combined, and are emitted from the light source unit 25 as image light. The pickup lens 26 transmits the light which is emitted from the light source unit 25 to the optical fiber 27 of a later stage. The optical fiber 27 guides the light, which passes from the light source unit 25, through the pickup lens 26, and is incident on the optical fiber 27, to an optical system of a later stage. A collimator lens 28 parallelizes the light which is incident from the optical fiber 27.

(25) The optical path of the light which is emitted from the light source optical system 15 is turned back due to the light being reflected by the mirror 16, and the light is guided to the light scanning device 17. The light scanning device 17 is provided with an MEMS mirror (not illustrated), for example. The light scanning device 17 causes the posture of the MEMS mirror to change in accordance with a modulation operation of the light source optical system 15, and scans light two-dimensionally. In this manner, the light scanning device 17 emits image light which includes image information.

(26) However, recently, the head mounted display is required to have a widened viewing angle in which the viewing angle is more magnified. In addition, since the head mounted display is used in a state of being worn on the head portion of a user, the head mounted display is further required to be miniaturized.

(27) In the HMD 300 of the present embodiment, miniaturization of a device configuration is achieved by generating image light using the light scanning device 17 including the MEMS mirror. Performance of the MEMS mirror has a trade-off relationship in which the diameter of the mirror and an oscillation angle of the mirror are determined and the oscillation angle is reduced if the diameter of the mirror increases. Meanwhile, if the diameter of the mirror is reduced too much in order to realize high resolution, resolution feeling is lowered due to a diffraction phenomenon, and thus it is not possible to unduly reduce the diameter of the mirror and increase the oscillation angle. Generally, regarding a balanced design value of the diameter of the mirror and the oscillation angle of the mirror, the diameter of the mirror is 1 mm, and the oscillation angle is 10 degrees as a half viewing angle of a light beam angle.

(28) The light scanning device 17 of the present embodiment adopts an MEMS mirror in which a diameter is 1 mm and an oscillation angle is 10 degrees as a half viewing angle.

(29) Generally, if a size of a pupil of an eye of a viewer, movement of an eyeball, individual differences of a width of eyes, or the like is considered, it is thought that a size of an exit pupil is required to be approximately 6 mm to 8 mm.

(30) In the HMD 300 of the present embodiment, a diameter of the MEMS mirror is 1 mm, and thus light from the MEMS mirror is magnified up to 6 mm or more by the pupil expanding element 12.

(31) Here, in the head mounted display, in a case of a half viewing angle of the 10 degrees MEMS mirror, it corresponds to a virtual image size of approximately 40 inches 2.5 m ahead and an aspect 16:9. Accordingly, in order to realize the higher viewing angle of which the viewing angle is wide, it is necessary to increase (widen) the viewing angle by an optical system. However, the viewing angle and a size of the exit pupil have a conflicting relationship with each other, and for example, if the viewing angle is magnified, the size of the exit pupil is reduced.

(32) With respect to the above description, the HMD 300 of the present embodiment is capable of achieving both a pupil expanding function and a viewing angle expanding function by adopting a configuration to be described later.

(33) Here, the pupil expanding function in the HMD 300 of the present embodiment will be described. Hereinafter, the main frame 120 (that is, image generating unit 11 and pupil expanding element 12) and a pupil expanding function in a plane including an eye of a viewer M (in-plane illustrated in FIG. 3) will be described.

(34) FIG. 4 is a view for describing the pupil expanding function. Also, a light flux of the center of an image (virtual image) is only illustrated in FIG. 4. In addition, in FIG. 4, a first light condensing optical system 13 is illustrated as one lens in order to easily see the system.

(35) Here, in FIG. 4, a size of a first image light H1 which is a light emitting portion (corresponding to exit port where image light is emitted) of the MEMS mirror 18 is set to R1, a size of a second image light H2 which is a light emitting portion (corresponding to exit port where magnified image light is emitted) of the pupil expanding element 12 is set to R2, and a diameter of the light flux included in the image light at the time of being incident on the pupil of the viewer M, that is, a size of an exit pupil H is set to R3.

(36) As illustrated in FIG. 4, light emitted from the light source optical system 15 is parallelized by the collimator lens 28 so as to be parallel light. The parallelized light has a changed angle due to the MEMS mirror 18 of the light scanning device 17 so as to constitute the image light. The image light in which the angle is changed due to the MEMS mirror 18 is incident on the pupil expanding element 12.

(37) FIG. 5 is a sectional view illustrating a schematic configuration of the pupil expanding element 12.

(38) As illustrated in FIG. 5, the pupil expanding element 12 includes a plurality of parallel plane plates (light guiding material) 24a and a plurality of half mirrors 24b. The plurality of parallel plane plates 24a are bonded to each other through the half mirror 24b. The pupil expanding element 12 is cut such that a pair of end surfaces is inclined with respect to a thickness direction of the parallel plane plate 24a, and the end surfaces are respectively constitute a light entrance end surface 12a where the image light from the light scanning device 17 is incident, and a light exit end surface 12b where the image light is magnified and emitted. In this manner, a shape of a horizontal section of the pupil expanding element 12 is a trapezoidal shape.

(39) In the pupil expanding element 12, the image light incident from the light entrance end surface 12a is repeatedly transmitted to and reflected by the plurality of half mirrors 24b, and then is emitted from the light exit end surface 12b. A width of the image light emitted from the light exit end surface 12b is magnified with respect to a width of the image light incident on the light entrance end surface 12a. In addition, an incident angle of the image light on the light entrance end surface 12a and an emission angle of the image light from the light exit end surface 12b are matched with each other.

(40) Accordingly, for example, the image light which is vertically incident on the light entrance end surface 12a is vertically emitted from the light exit end surface 12b, and the image light which is incident on the light entrance end surface 12a at a predetermined incident angle is emitted from the light exit end surface 12b at an emission angle which is the same as the incident angle. Accordingly, in FIG. 3, when the image light is transmitted to the pupil expanding element 12, an optical path is bent to a short side of the trapezoidal shape.

(41) Return to FIG. 3, the first light condensing optical system 13 is an optical system at least having positive power and negative power, and totally has the positive power. In the present embodiment, the first light condensing optical system 13 includes a first lens 21, a second lens 22, and a third lens 23 in order from a light incident side. Also, in the present embodiment, the first light condensing optical system 13 is configured with three lenses of the first lens 21, the second lens 22, and the third lens 23, but the number of correction lenses is not particularly limited.

(42) Based on such a configuration, as illustrated in FIG. 4, since the first light condensing optical system 13 totally has the positive power, light emitted from the pupil expanding element 12 is condensed, and an intermediate image GM is formed in front of the second light condensing optical system 14.

(43) The second light condensing optical system 14 forms the exit pupil H near pupils of eyes ME of the viewer M by condensing the light from the intermediate image, and a part of the external light is transmitted. The second light condensing optical system 14 is configured with a half mirror (concave mirror) having the positive power in a plane including the main frame 120 (refer to FIG. 3) and the eye ME of the viewer M.

(44) The image light magnified by the pupil expanding element 12 is condensed by the first light condensing optical system 13, the intermediate image GM is formed in front of the second light condensing optical system 14, and the exit pupil H is formed near the pupil of the eye ME of the viewer M by reflecting the light from the second light condensing optical system 14. Since the second light condensing optical system 14 condenses the light from the intermediate image GM so as to return the light to be approximately parallel light, the viewer M can visually recognize the virtual image G1 in the distance.

(45) Subsequently, the viewing angle expanding function in the HMD 300 of the present embodiment will be described. Hereinafter, the pupil expanding function in the plane (in-plane illustrated in FIG. 3) including the main frame 120 and the eye of the viewer M will be described.

(46) FIG. 6 is a view for describing the viewing angle expanding function. Also, FIG. 6 only illustrates the center of the image (virtual image) and central light beams of both ends. In addition, in FIG. 6, the first light condensing optical system 13 is illustrated as one lens in order to easily see the system.

(47) As illustrated in FIG. 6, the MEMS mirror 18 rotates so as to cause the first image light H1 to be incident on the pupil expanding element 12 at an angle θ.sub.1 of ±10 degrees. Here, the pupil expanding element 12 does not convert the angle of the first image light H1. Therefore, a maximum emission angle θ.sub.2 of the second image light H2 after being magnified in the pupil expanding element 12 becomes ±10 likewise.

(48) In the present embodiment, the first light condensing optical system 13 and the second light condensing optical system 14 constitute an afocal optical system AF. An angular magnification B of the afocal optical system AF is defined as a value of which a substantial focal distance F.sub.1 of the first light condensing optical system 13 illustrated in FIG. 5 is divided by a focal distance F.sub.2 of the second light condensing optical system 14. Otherwise, as illustrated in FIG. 6, the angular magnification B can be also regulated by a ratio of the maximum emission angle θ.sub.2 of the first image light H1 and a maximum viewing angle θ.sub.3 of the virtual image G1.

(49) The maximum viewing angle θ.sub.3 of the virtual image G1 is a value of which the angular magnification B is multiplied by the maximum emission angle θ.sub.2 of the second image light H2. Therefore, in order to obtain the viewing angle expanding function, the angular magnification B is necessary to be set to be greater than 1.

(50) In the present embodiment, a lower limit value of the angular magnification B is set to 1.1. In a case in which the angular magnification B is set to 1.1 or more, for example, a viewing angle of 40 inches can be magnified up to a viewing angle of 44 inches or more.

(51) Meanwhile, a magnitude R2 of the second image light H2 is magnified as the angular magnification B is magnified. Therefore, if the angular magnification B is greater than necessary, the pupil expanding element 12 also becomes great, and thus there is a concern that the entire apparatus including the pupil expanding element 12 increases in size.

(52) For example, in order to secure the exit pupil H as 6.0 mm in a case in which the angular magnification B is set to 3.0 times, the magnitude R2 of the second image light H2 is required to be set to 18 mm. In order to realize that, a magnification ratio of the pupil expanding element 12 is required to be set to 18 times, and the pupil expanding element 12 significantly increases in size. Further, the first light condensing optical system 13 is required to be greater than 18 mm, and the HMD 300 increases in size.

(53) In consideration of such a situation, there is an upper limit in the angular magnification B of which the viewing angle can be magnified with a miniaturized apparatus.

(54) Substantially, the magnitude R2 of the second image light H2 (corresponding to exit port of pupil expanding element 12) is desirably approximately 10 mm. That is, if the magnitude R1 of the first image light H1 (corresponding to exit port of MEMS mirror 18) is 1 mm, the magnification ratio of the pupil expanding element 12 is set to 10 times.

(55) Here, the magnification ratio of the pupil expanding element 12 is set, such that the magnitude R2 of the second image light H2 is equal to or greater than a size of which the angular magnification B is multiplied by a size (6 mm) of a predetermined exit pupil H.

(56) Therefore, in a case in which the magnitude R2 of the second image light H2 is set to approximately 10 mm, an upper limit of the angular magnification B may be set to be equal to or less than 1.7 times.

(57) Also, the substantial upper limit of the magnitude R2 of the second image light H2 after the apparatus configuration is miniaturized is set to approximately 15 mm. In this case, a pupil expanding ratio of the pupil expanding element 12 is set to 15 times, and an upper limit of the angular magnification B may be set to be equal to or lower than 2.5.

(58) In consideration of such a background, in the present embodiment, the angular magnification B of the afocal optical system AF is set to be 1 or more and 2.5 or less, and more desirably, 1.1 or more and 1.7 or less.

(59) Hereinafter, a case in which the angular magnification is set to 1.5 times will be described as an example. In this case, the maximum viewing angle θ.sub.3 of the virtual image G1 is ±15 degrees by multiplying the maximum emission angle θ.sub.2 of the second image light H2 by the angular magnification B. That is, the maximum viewing angle θ.sub.3 of the virtual image G1 is greater than the maximum emission angle θ.sub.2 of the first image light H1 of the image generating unit 11.

(60) That is, in a case in which the angular magnification B is set to 1.0 times (case of not being changed from the maximum emission angle θ.sub.2 (±10 degrees) as it is), a virtual image of a size of approximately 40 inches 2.5 m ahead and an aspect 16:9 is obtained, but if the angular magnification B is set to 1.5 times, a virtual image of a size of approximately 60 inches 2.5 m ahead and an aspect 16:9 is obtained can be obtained.

(61) That is, according to the HMD 300 of the present embodiment, the viewing angle expanding function for expanding the viewing angle of the virtual image G1 can be obtained. The magnitude R2 of the second image light H2 is reduced at a ratio of an inverse number (1/angular magnification B) of the angular magnification B (1.5 times). Therefore, the second image light H2 is approximately 6.6 mm at a position of the pupil of the viewer M. Accordingly, even when considering an influence due to aberration of an actual afocal optical system AF, approximately 6 mm size R3 of the exit pupil H can be secured.

(62) As described above, in the HMD 300 of the present embodiment, the afocal optical system AF in which the angular magnification B is set to be 1 or more and 2.5 or less (more desirably 1.1 or more and 1.7 or less) is provided, and the magnitude R2 of the second image light H2 is set to be greater than the size R3 of the exit pupil H. Specifically, in the present embodiment, the size R1 of the first image light H1 is 1 mm (corresponding to diameter of MEMS mirror 18), the magnitude R2 of the second image light H2 is 10 mm, and the size R3 of the exit pupil H is 6 mm or more. In addition, the maximum emission angle θ.sub.2 of the first image light H1 is ±10 degrees, and the maximum viewing angle θ.sub.3 of the virtual image G1 is ±15 degrees.

(63) According to the HMD 300 of the present embodiment, a size of the exit pupil H is set in consideration of reduction due to the magnified viewing angle of the virtual image G1. Therefore, even when a diameter of the pupil is reduced by expanding the viewing angle of the virtual image G1, a predetermined size (6 mm or more) of the exit pupil H can be obtained.

(64) In addition, since the upper limit of the angular magnification B is regulated in the present embodiment, the pupil expanding element 12 does not increase in size, and the entire apparatus can be miniaturized.

(65) Accordingly, the miniaturized HMD 300 in which both the pupil expanding function and the viewing angle expanding function are achieved is provided.

Second Embodiment

(66) Subsequently, a second embodiment will be described. This embodiment and a first embodiment are different from each other in a point of a structure of the second light condensing optical system, but the others except the point are common to each other, and the same numeral is given to the common component and detailed description thereof will be omitted.

(67) FIG. 7 is a view for describing the pupil expanding function in a HMD 301 of the present embodiment. Also, a light flux of the center of an image (virtual image) is only illustrated in FIG. 7. In FIG. 7, the first light condensing optical system 13 is illustrated as one lens in order to easily see the system.

(68) In the present embodiment, the second light condensing optical system 114 is configured with a reflective type hologram having a positive power in a plane including at least the main frame 120 (refer to FIG. 3) and the eye of the viewer M.

(69) The second light condensing optical system 114 includes a volume hologram, and is capable of randomly adjusting an incident angle and a reflection angle of light by changing a volume hologram pattern.

(70) The second light condensing optical system 114 is capable of expanding a section of the reflected light flux by making an incident angle and a reflection angle of the light. Accordingly, the second light condensing optical system 114 includes the pupil expanding function of expanding the second image light H2 at the time of reflecting the light from the intermediate image when compared a case in which the light is reflected from the second light condensing optical system 14 of the first embodiment.

(71) In the present embodiment, when the size R3 of the exit pupil H (6 mm) same as the first embodiment is obtained, the magnitude R2 of the second image light H2 can be reduced approximately 8 mm as an effect of expanding pupil due to the hologram. Accordingly, as the second image light H2 is reduced, the pupil expanding element 12 and the first light condensing optical system 13 can be miniaturized, and thus the entire apparatus can be miniaturized.

(72) In addition, according to the present embodiment, if the magnitude R2 of the second image light H2 is secured as a magnitude (10 mm), even when the angular magnification B increases, the exit pupil H having a sufficient size due to the effect of expanding pupil of the hologram can be obtained. Accordingly, a higher viewing angle of the virtual image G1 can be achieved.

(73) Otherwise, if the magnitude R2 and the angular magnification B of the second image light H2 are not changed, the exit pupil H can be more magnified as the effect of expanding pupil of the hologram, and thus the HMD 301 can be provided which is excellent in general versatility and is capable of improving that people having various sizes of eyes easily see.

(74) Also, a technical scope of the disclosure is not limited to the embodiments described above, and it is possible to add various modifications without departing from the gist of the disclosure.

(75) For example, in the embodiment described above, a case in which the light scanning device 17 is used as the image generating unit 11 is exemplified, but the configuration of the image generating unit is not limited thereto. For example, as illustrated in FIG. 8, as an image generating unit 111, a display panel (electro-optical device) 112, and a device including a collimator lens 113 may be used.

(76) The display panel 112 includes a backlight 112a and a light modulation element 112b. The backlight 112a is configured with, for example, a set of light sources of each of light emission color such as red, green, and blue. As each light source, for example, a light emitting diode (LED), a laser light source, or the like can be used. As the light modulation element 112b, for example, a liquid crystal display which is a display element or the like can be used. In addition, as the display panel 112, an organic electroluminescence device (organic EL device) or the like can also be adopted.

(77) The collimator lens 113 is configured with, for example, a group of projection lens which are projects image light being incident, and projects the first image light L emitted from the light modulation element of the display panel 112 so that the light is light flux in a parallel state. The first image light L through the collimator lens 113 includes different angular components.

(78) In addition, in the embodiment described above, a structure in which the plurality of parallel plane plates 24a and the plurality of half mirrors 24b are stacked is exemplified as the pupil expanding element 12, but the embodiment is not limited thereto. For example, a pupil expanding element may be formed using an optical element including a plurality of diffraction elements.

(79) For example, as illustrated in FIG. 9, a pupil expanding element 212 including a first optical element 213 and a second optical element 214 may be also used.

(80) The first optical element 213 includes a light incident side diffraction portion (diffraction element) 215 disposed on a light incident surface side 213a side, and a light emission side diffraction portion (diffraction element) 216 disposed on a light emission surface side 213b side. The light incident side diffraction portion 215 and the light emission side diffraction portion 216 include grating patterns 215a and 216a in which a plurality of linear gratings are arranged.

(81) The second optical element 214 includes a light incident side diffraction portion 217 disposed on the light incident surface side 214a side and a light emission side diffraction portion 218 disposed on the light emission surface side 214b side. The light incident side diffraction portion 217 and the light emission side diffraction portion 218 includes grating patterns 217a and 218a in which a plurality of linear gratings are arranged.

(82) As illustrated in FIG. 9, a light flux of light L1 incident on the first optical element 213 increases to be three when being diffracted by the light incident side diffraction portion 215, is emitted from the light emission side diffraction portion 216, and is incident on the second optical element 214. The light flux of each light L1 incident on the second optical element 214 increases to be three when being diffracted by the light incident side diffraction portion 217 as same as above, and is emitted from the light emission side diffraction portion 218. According to such a pupil expanding element 212, the sectional area of the light is magnified by repeatedly diffracting the light such that the second image light can be generated.

(83) For example, in the embodiment described above, a case in which both the pupil expanding function and the viewing angle expanding function are achieved in a plane including the main frame 120 (refer to FIG. 3) and the eye of the viewer M is described; however, the embodiment is not limited thereto. The embodiment can be applied for a case in which both the pupil expanding function and the viewing angle expanding function are achieved in a plane (plane perpendicular to plane of paper of FIG. 3) orthogonal to a plane including the main frame 120 and the eye of the viewer M.

REFERENCE SIGNS LIST

(84) M viewer ME eye G1 virtual image H exit pupil H1 first image light H2 second image light L first image light B angular magnification MG intermediate image F.sub.1, F.sub.2 focal distance 11, 111 image generating unit 12, 212 pupil expanding element 13 first light condensing optical system 14, 114 second light condensing optical system 17 light scanning device 24a parallel plane plate (light guiding material) 24b half mirror (half mirror layer) 25 light source unit 112 display panel (electro-optical device) 113 collimator lens 120 main frame (device main body) 213 first optical element 214 second optical element 215, 217 light incident side diffraction portion (diffraction element) 216, 218 light emission side diffraction portion (diffraction element) 300 HMD (image display device)