JP2010145721A - Optical path combiner, image display device and head mount display - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To prevent ghost light from being made incident to an optical pupil even when an observed picture angle gets into widd, and thereby to enable a user to observe a high quality color image. <P>SOLUTION: An optical path combiner has a plurality of diffraction peak wavelengths discretely existing with respect to light rays made incident to the center of the optical pupil from the center of the optical path combiner when the observed picture angle gets into ≥16 degrees, and, in all of the combinations among the plurality of diffraction peak wavelengths, satisfies the following relations: 380<λa<λb<780 nm and λb/λa>1.13, wherein one side diffraction peak wavelength is λa and the other side diffraction peak wavelength is λb. Since the mutual diffraction peak wavelengths are adequately separated from each other, it is avoided, for example, that the diffraction wavelength region of B light on the optical path combiner and the diffraction wavelength region of G light are partially superimposed, and it is avoided that G light is diffracted on HOE where B light is diffracted and is made incident to an optical pupil as ghost light. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to an optical path combiner having a hologram optical element (hereinafter also referred to as HOE), an image display apparatus including the optical path combiner, and capable of observing a color image with a wide observation angle by overlapping with the outside, and the image display The present invention relates to a head mounted display (hereinafter also referred to as HMD) provided with the device.

  Using a film with reflection and transmission characteristics formed on a transparent substrate, the image light from the display element is reflected in the direction of the observer's pupil, and at the same time the external light is transmitted, and the image (virtual image) and the external environment are superimposed. As devices that are visually recognized, devices known as head-up displays (hereinafter also referred to as HUDs) and HMDs are well known. By using a see-through device that can observe the image and the outside world at the same time, it is possible to additionally observe the necessary information displayed without diverting the line of sight from the outside world in front of various scenes. Is very useful.

  For example, HOE has been used as a film having this reflection / transmission characteristic, that is, an excellent optical path combiner that superimposes external light and image light (see Patent Document 1). By using HOE, high external light transmittance can be obtained. Further, since the HOE has optical power, the apparatus can be reduced in size and weight.

JP 2004-61731 A

  However, the HOE has been used so far only when the observation angle of view is narrow. When observing an image with a wider observation angle of view, a ghost may occur in the conventional HOE. There was found.

  For example, in Patent Document 1, the HOE is manufactured using lasers of three colors having wavelengths of 476 nm, 532 nm, and 647 nm. Then, the position of the reference light source for exposing the hologram photosensitive material at the time of manufacturing the HOE is shifted from the optical pupil center at the time of use in a direction closer to the HOE or away from the HOE, thereby manufacturing the HOE. When the HOE produced in this way is used, the angle shift between the light beam at the time of manufacture and the light beam at the time of observation is small in the optical pupil at both the center and the pupil end of the optical pupil. small). However, in the field angle direction from the center of the observation screen toward the screen edge, the angle shift between the light beam at the time of manufacture and the light beam at the time of observation is larger toward the screen edge (color unevenness in the field angle direction is larger).

  Since the HOE has wavelength selectivity and angle selectivity, when the angle shift in the field angle direction increases, the shift amount of the diffraction peak wavelength for each color also increases. That is, for each color, the diffraction peak wavelength for light at the top of the angle of view incident on the optical pupil center is shifted to, for example, the short wavelength side, and the diffraction peak wavelength for light at the bottom of the angle of view incident on the optical pupil center is, for example, a long wavelength. Shift to the side. As the viewing angle of view of the display image becomes wider, this effect becomes greater, and the wavelength range of light that is simultaneously incident on the optical pupil increases for each color. For this reason, for example, the diffraction wavelength range of the B light that is diffracted by the HOE and enters the optical pupil may partially overlap with the diffraction wavelength range of the G light. In this case, since the G light is diffracted by the HOE that diffracts the B light and enters the optical pupil as ghost light, a high-quality color image cannot be observed.

  The present invention has been made in order to solve the above-described problems, and the object of the present invention is to make ghost light optical even when the observation angle of view is wide when observing an image superimposed on the outside. An object of the present invention is to provide an optical path combiner capable of observing a high-quality color image while avoiding incident on the pupil, an image display device including the optical path combiner, and an HMD including the image display device. .

The optical path combiner of the present invention diffracts and reflects the image light from the display element in the direction of the optical pupil, while transmitting the external light and guiding it to the optical pupil, so that the virtual image of the display image and the external environment are transmitted at the position of the optical pupil. An optical path combiner having a volume phase type reflection type hologram optical element, and a perpendicular line at the center of the optical path combiner and a straight line connecting the center of the optical path combiner and the center of the optical pupil. A diffraction peak with respect to a light ray incident from the center of the optical path combiner to the center of the optical pupil when a maximum angle difference between the light rays emitted from the optical path combiner and incident on the optical pupil center is 16 degrees or more. There are a plurality of discrete wavelengths, and in all combinations of a plurality of diffraction peak wavelengths, one diffraction peak wavelength is λa, and the other diffraction peak The over peak wavelength as λb,
380 nm <λa <λb <780 nm and λb / λa> 1.13
It is characterized by satisfying.

  In the optical path combiner of the present invention, it is desirable that the hologram optical element has a planar shape.

The optical path combiner of the present invention is
1.2 <λb / λa <1.5
It may be the composition which satisfies.

The optical path combiner of the present invention is
500 nm <λa <535 nm and 620 nm <λb <680 nm,
Or
440 nm <λa <490 nm and 620 nm <λb <680 nm
It may be the composition which satisfies.

  In the optical path combiner of the present invention, the hologram optical element is manufactured using a laser having an emission wavelength of 510 to 535 nm and a laser of 630 to 680 nm, or a laser of 440 to 490 nm and a laser of 630 to 680 nm. May be.

  In the optical path combiner of the present invention, the hologram optical element may be manufactured using a laser having an emission wavelength of 440 nm to 460 nm, a laser of 525 nm to 535 nm, and a laser of 630 nm to 680 nm.

  An image display device according to the present invention includes a display element that displays an image, an optical member that totally reflects image light from the display element, and an optical pupil that reflects image light guided through the optical member. And an optical path combiner that transmits external light and guides it to the optical pupil. The optical path combiner includes the above-described optical path combiner of the present invention.

  In the image display device of the present invention, the hologram optical element of the optical path combiner has an axially asymmetric positive optical power, and at least a part of the eyepiece optical system that guides the image light from the display element to the optical pupil is provided. You may comprise.

  The HMD of the present invention includes the above-described video display device of the present invention and support means for supporting the video display device in front of an observer's eyes.

  According to the present invention, it is possible to observe an image (virtual image) superimposed on the outside by using an optical path combiner having a volume phase type reflection type HOE. At this time, when observing an image with a wide observation angle of view where the maximum angle difference between the light rays incident on the center of the optical pupil is 16 degrees or more, all the combinations of the diffraction peak wavelengths that exist discretely are described above. By satisfying the above conditional expression, the diffraction peak wavelengths are sufficiently separated from each other. Thereby, for example, it is possible to avoid that the diffraction wavelength range of the B light that is diffracted by the HOE and enters the optical pupil and the diffraction wavelength range of the G light partially overlap, and the HOE in which the G light diffracts the B light. It can be avoided that the light is diffracted by the light and enters the optical pupil as ghost light. As a result, it is possible to observe a high-quality color image even when the observation angle of view is wide.

  Note that the ghost light is, for example, a HOE that uses the light beam on the optical pupil side as parallel light out of the two light beams that expose the hologram photosensitive material, and the observer's pupil is positioned at the center of the optical pupil to widen the image. However, the HOE is produced by using the light beam on the optical pupil side as the divergent light from the point light source, and the observer's pupil is shifted from the position of the point light source that is the divergent center of the divergent light from the point light source. This can occur in the same way even when an image is observed at a wide angle at the optical pupil position. According to the present invention, in any of the above cases, ghost light can be prevented from entering the observer's pupil, and a high-quality color image can be observed at a wide angle.

  An embodiment of the present invention will be described below with reference to the drawings.

(About video display device)
FIG. 1 is an explanatory view schematically showing a configuration of a video display device 1 of the present invention. The video display device 1 includes a display element 2 and an optical path combiner 3. The display element 2 is a light modulation element that displays an image by modulating light from a light source (not shown) based on image data, and is composed of, for example, a transmissive liquid crystal display element.

  The optical path combiner 3 is an optical member that reflects video light from the display element 2 and guides it to the optical pupil E, and transmits external light and guides it to the optical pupil E. Therefore, the observer can observe the virtual image of the display image and the outside world superimposed at the position of the optical pupil E.

  The optical path combiner 3 only needs to have both functions of reflection and transmission. For example, the optical path combiner 3 can be composed of a half mirror, a reflection hologram (HOE) in which interference fringes are recorded in layers, a multilayer film, and the like. Among them, the reflective HOE is desirable because it can reflect only an arbitrary wavelength region due to its wavelength selectivity, and can also serve as a part of an eyepiece optical system by giving optical power. By matching the reflection wavelength with the image light wavelength, the image light can be observed brightly, and external light other than the reflection wavelength can be transmitted, so that the external environment can also be observed brightly. Since the HOE has wavelength selectivity and angle selectivity, if the reflection angle on the optical path combiner 3 is different, the reflection wavelength of the image light is also different.

  The optical path combiner 3 having a narrow reflection wavelength range can be easily manufactured by using a volume phase type reflection type HOE. Volume phase type reflection type HOEs are manufactured by interference exposure with coherent light. Depending on the refractive index difference (Δnd) of materials used, manufacturing conditions (exposure amount, post-exposure processing (temperature)), etc. The reflection wavelength range can be arbitrarily controlled. Examples of the hologram photosensitive material for producing the HOE used for such applications include photopolymers, silver salt materials, dichromated gelatin, and the like, among which photopolymers that can be easily manufactured by a dry process are desirable. In the following, it is assumed that a volume phase type reflective HOE is used as the optical path combiner 3.

(Comparative example)
Next, in order to facilitate understanding of the present invention, a comparative example will be described first before describing an embodiment of the present invention.

  FIG. 2 is an explanatory diagram schematically showing the optical path of the exposure light beam when the optical path combiner 3 (HOE) is manufactured and the optical path of the reproduction light beam when in use (during reproduction). The reflection type HOE is produced by irradiating the hologram photosensitive material 3a with two light beams (exposure rays 1 and 2 having a wavelength λa) from opposite sides and recording these interference fringes.

Here, since the reflection type HOE has wavelength selectivity and angle selectivity, when the incident angle is different, the diffraction peak wavelength indicating the maximum diffraction efficiency is also different. The relationship between the incident angle and the diffraction peak wavelength satisfies the following black condition. That is, in the diffraction by the reflection type HOE, the diffraction intensity of the light diffracted in the direction in which the following two expressions are simultaneously established becomes the maximum.
(Sin θ ₁ −sin θ ₂ ) / λa = (sin θ ₃ −sin θ ₄ ) / λb
(Cos θ ₁ −cos θ ₂ ) / λa = (cos θ ₃ −cos θ ₄ ) / λb
However,
λa (nm): Manufacturing wavelength (exposure wavelength)
θ ₁ (°): Incident angle of object light (exposure ray 1) to HOE
(An angle formed between the normal line of the HOE and the exposure light beam 1)
θ ₂ (°): Incident angle of reference beam (exposure beam 2) to HOE
(An angle formed between the normal line of the HOE and the exposure light beam 2)
λb (nm): reproduction wavelength (use wavelength, diffraction wavelength)
θ ₃ (°): complementary angle of the incident angle of the reconstructed beam with respect to HOE
(Supplementary angle between HOE normal and reconstructed incident light beam 3)
θ ₄ (°): exit angle of reconstructed light from HOE
(An angle formed by the normal line of the HOE and the regenerative light beam 4)
It is.

  Next, the influence of the wavelength selectivity and angle selectivity of the HOE when using a reflective HOE combiner will be considered. Here, in order to facilitate understanding of the explanation, as shown in FIG. 3, the reflective HOE includes a parallel light beam (exposure light beam 1) from the optical path combiner 3 toward the display element and a parallel beam from the optical pupil toward the optical path combiner 3. It is assumed that the hologram photosensitive material 3a is produced by exposing the light beam (exposure light beam 2) with two light beams.

  When the parallel reproduction light beam from the display element enters the optical path combiner 3, the reproduction light beam having the same wavelength as the exposure light beam is diffracted and reflected by the optical path combiner 3 in parallel to the pupil direction and observed as an image. Since the reconstructed ray is reflected parallel to the pupil direction, even if the observer's pupil position is slightly shifted up and down, the same display image (no color change) as when the observer's pupil is at the center of the optical pupil is observed. it can.

However, in the field angle direction, the angle difference between the light beam incident on the center of the pupil from the optical path combiner 3 and the exposure light beam 2 increases as α ₁ and α ₂ toward the end of the observation field angle, and diffraction of the light beam is performed. The shift amount of the peak wavelength from the wavelength λa of the exposure light increases. That is, as shown in FIG. 4, the diffraction peak wavelength of the light at the top of the angle of view incident on the pupil center (light in the direction in which the emission angle from the recorded interference fringe increases) is shifted by a short wavelength and incident on the pupil center. The diffraction peak wavelength of the light at the lower end of the angle of view (the light in the direction in which the emission angle from the recorded interference fringes becomes smaller) is shifted by a long wavelength. The wider the viewing angle of the displayed image, the greater the influence of this wavelength shift.

Next, in consideration of the size of the optical pupil, light rays that are simultaneously incident on the optical pupil (observer's pupil) during actual observation are examined. FIG. 5 is an explanatory diagram schematically showing the optical path of the reproduction light beam that is diffracted and reflected by the optical path combiner 3 and enters the optical pupil E. As described above, the light beam during the exposure so as the wavelength shift amount angle difference is large between the light beam during reproduction is large, the maximum angle difference alpha ₁ of the light beam (ray of angle bottom) L1 incident on the pupil upper end, By studying the diffraction peak wavelength for the light ray L3 having the maximum angle difference α ₂ incident on the lower end of the pupil (the light ray at the upper end of the angle of view), the wavelength range of light incident simultaneously on the pupil (the diffraction wavelength range in the HOE) is determined. (At least light in the wavelength region between the two diffraction peak wavelengths is incident on the pupil).

  Here, under the following conditions, the light beam L1 having the maximum angle difference incident on the upper end of the pupil, the light beam L2 having the central angle of view incident on the pupil center, and the light beam L3 having the maximum angular difference incident on the lower end of the pupil. The diffraction peak wavelength was calculated. The HOEs that diffract and reflect blue light, green light, and red light are B-HOE, G-HOE, and R-HOE, respectively, and the diffraction peak wavelength is calculated using the above black diffraction formula, as shown in FIG. become.

<Calculation model conditions>
-The HOE combiner is flat and is inclined 30 degrees with respect to the vertical plane.
The hologram photosensitive material was exposed using parallel light incident at 30 degrees with respect to the normal line of the HOE combiner and parallel light reflected at -30 degrees to produce a HOE combiner.
-The distance between the center of the HOE combiner and the optical pupil was 15 mm.
-The pupil size (the pupil diameter simultaneously incident on the pupil) was 3 mm.
The laser wavelength of HOE is Ar ⁺ 476.5 nm, YAG: Nd ³⁺ (double wave) 532 nm, Kr ⁺ 647.1 nm.
・ It was assumed that the hologram photosensitive material did not shrink.
・ HOE diffraction half width is not considered.
-The viewing angle of view of the video was set to 20 degrees.
• For simplicity, the HOE has no optical power.

  From FIG. 6, light in the wavelength region of 445 to 498 nm is incident on the pupil by diffraction reflection at B-HOE, and light in the wavelength region of 497 to 556 nm is incident on the pupil by diffraction reflection at G-HOE. It can be seen that light in the wavelength range of 605 to 677 nm is incident on the pupil by diffraction reflection at the R-HOE. That is, light in these wavelength ranges is incident on the pupil at the same time.

  Here, the required diffraction wavelength regions partially overlap between B-HOE and G-HOE. For this reason, for example, light having a wavelength of 497 nm is diffracted and reflected by both B-HOE and G-HOE and reaches the pupil. Therefore, even if one of the images (for example, a G image) is to be displayed, the G light is diffracted and reflected by B-HOE and reaches the pupil, so that this appears as a ghost.

  Here, for simplification, the half-value wavelength width of the diffraction efficiency of the HOE is not considered, so the overlapping region of the diffraction wavelength regions in the B-HOE and G-HOE is 1 nm. Since the light of the wavelength width reaches the pupil, the overlapping region of necessary diffraction wavelength regions becomes larger, and ghosts are generated more. Further, as the viewing angle of view of the display image becomes wider, the maximum angle difference α1 and α2 of light rays simultaneously incident on the pupil increases, and the shift amount of the diffraction peak wavelength increases, so that the influence of the ghost increases. In consideration of the half-value wavelength width (for example, 20 nm) of the HOE, a ghost is generated even when the observation field angle is narrower than 20 degrees (for example, the field angle is 16 degrees).

Example 1
Next, an embodiment of the present invention will be described as Embodiment 1. In Example 1, HOE was manufactured under the same conditions as the calculation model conditions of the comparative example, except that the laser wavelength for manufacturing the HOE was Ar ⁺ 457.9 nm, YAG: Nd ³⁺ (second harmonic) 532 nm, and He—Ne 633 nm. Was made. FIG. 7 shows diffraction peak wavelengths in the HOE (B-HOE, G-HOE, R-HOE) for the light beams L1, L2, and L3.

In the first embodiment, the diffraction peak wavelength of the light beam L2 having the angle of view incident on the center of the pupil, that is, the light beam incident on the center of the optical pupil E from the center of the optical path combiner 3, exists in each wavelength region of RGB. There are a plurality of discretely. Moreover, in all combinations of the plurality of diffraction peak wavelengths, one diffraction peak wavelength is λa (nm) and the other diffraction peak wavelength is λb (nm).
380 nm <λa <λb <780 nm (1)
λb / λa> 1.13 (2)
Are satisfied at the same time. That is, in the example of FIG. 7, when λa = 458 nm and λb = 532 nm, λb / λa = 1.162, and when λa = 532 nm and λb = 633 nm, λb / λa = 1.190. When λa = 458 nm and λb = 633 nm, λb / λa = 1.382, and both satisfy the conditional expressions (1) and (2) at the same time.

  5 includes a plane including a perpendicular line at the center of the optical path combiner 3 and a straight line connecting the center of the optical path combiner 3 and the center of the optical pupil E. In the above, when the maximum angle difference α (observation angle of view) of the light beams emitted from the optical path combiner 3 and incident on the center of the optical pupil E is 16 degrees or more, the diffraction peak wavelengths that are discretely present are mutual. By satisfying the conditional expressions (1) and (2) for all the combinations, it is possible to avoid that the diffraction peak wavelengths are sufficiently separated from each other and the diffraction wavelength regions required by the HOE overlap between different colors. That is, in the example of FIG. 7, the diffraction wavelength range required for B-HOE is 428 to 479 nm, the diffraction wavelength range required for G-HOE is 497 to 556 nm, and the diffraction required for R-HOE. The wavelength range is 592 to 662 nm, and these do not overlap each other. Therefore, as in the comparative example, it is possible to avoid light having the same wavelength from being diffracted by two types of HOEs and entering the optical pupil E at the same time. As a result, it is possible to observe a good color image (high-quality full-color image by RGB) that does not generate ghosts even with a wide observation angle of view of 16 degrees or more.

  At this time, it is desirable that the HOE constituting the optical path combiner 3 has a planar shape (see FIG. 1 and the like). If the HOE is planar, for example, an optical path combiner 3 is manufactured by pasting a film-shaped hologram photosensitive material in an unexposed state on the substrate, or an optical path combiner 3 is pasted on the substrate after the hologram recording. The optical path combiner 3 can be easily manufactured.

  By the way, the emission wavelength of the laser for manufacturing the HOE is not limited to the above values (457.9 nm, 532 nm, and 633 nm). For example, by using a laser having an emission wavelength of 440 nm or more and 460 nm or less, a laser of 525 nm or more and 535 nm or less, and a laser of 630 nm or more and 680 nm or less, HOE (optical path combiner 3) satisfying conditional expressions (1) and (2) is satisfied. Can be realized. That is, by realizing the three-color HOE that diffracts the BGR three-color light using the above lasers, the effect of the present invention that enables high-quality images to be observed even with a wide observation angle of view can be obtained.

In Example 1, since the incident angle and the emission angle of the reproduction light beam toward the pupil center with respect to the HOE are the same as the incident angles of the two exposure light beams with respect to the HOE (hologram photosensitive material) (assuming that there is no contraction of the HOE). However, in actuality, it contracts by about 2% and shifts the wavelength by a corresponding amount (2%), so that the diffraction peak wavelength for the reproduction light beam toward the center of the pupil is equal to the exposure wavelength of the laser. However, since the wavelength of the laser beam that can be produced is discrete and limited, if necessary, the angle between the reproduction light beam and the exposure light beam toward the pupil center is shifted (the incident direction of the reference light at the time of exposure is set to the pupil center). By making the HOE (shifted from the direction), it is possible to arbitrarily set the diffraction peak wavelength of the reconstructed light beam toward the pupil center. At this time, by selecting any of the following laser groups and using them in combination with BGR, a laser in the above-mentioned wavelength region can be realized.
B laser group: He—Cd ⁺ 441.6 nm,
Ar ⁺ 457.9 nm, 476.5 nm, 488.0 nm
G laser group: Ar ⁺ 514.5 nm,
Kr ⁺ 530.9 nm,
YAG: Nd ³⁺ (2nd harmonic) 532nm
R laser group: He-Ne 633 nm
Kr ⁺ 647.1 nm, 676.4 nm

(Example 2)
Next, another embodiment of the present invention will be described as a second embodiment. In the second embodiment, the optical path combiner 3 is configured by a two-color HOE that diffracts light of any two colors of RGB. For example, FIG. 8A shows the diffraction characteristics of a two-color HOE that diffracts light of two colors G and R, and FIG. 8B shows the two-color HOE that diffracts light of two colors B and R. The diffraction characteristics are shown. These two-color HOEs can be produced, for example, by exposing a hologram photosensitive material using a laser having the following emission wavelength.
Two colors G and R: YAG: Nd ³⁺ (double wave) 532 nm, Kr ⁺ 647.1 nm
Two colors B and R: Ar ⁺ 476.5 nm, Kr ⁺ 647.1 nm

  From the viewpoints of “corresponding to a wider viewing angle of view” and “corresponding to a case where the half-value wavelength width of the HOE is wide (bright image)”, it is desirable to increase the difference between the diffraction peak wavelengths. By producing a two-color HOE that diffracts light of two colors, G and R or B and R, instead of the three colors of BGR, the difference between the diffraction peak wavelengths can be easily increased. .2 <λb / λa <1.5 can be realized. Therefore, by producing a two-color HOE, it is possible to avoid the ghost light from entering the pupil, even when observing an image at a wider angle or when the half-value wavelength width of the HOE is wide, and to produce a high-quality color image. Can be observed.

  Incidentally, in the above-described two-color HOE of G and R, if λa = 532 nm and λb = 647.1 nm, λb / λa = 1.216, and in the two-color HOE of B and R, λa = 476.5 nm, If λb = 647.1 nm, then λb / λa = 1.358, both satisfying 1.2 <λb / λa <1.5. That is, in the above-mentioned two-color HOE of G and R or B and R, the value of λb / λa is larger than that of the first embodiment (the difference between the diffraction peak wavelengths is further increased), and an image can be displayed at a wider angle. It is possible to easily cope with observation or when the half-value wavelength width of the HOE is wide.

From the above, if the optical path combiner 3 satisfies the following conditional expression (3), the ghost light is incident on the pupil even when observing an image at a wider angle or when the half-value wavelength width of the HOE is wide. It can be said that high-quality color images can be observed by avoiding the above. That is,
1.2 <λb / λa <1.5 (3)
It is.

  By the way, the emission wavelength of the laser for producing the two-color HOE is not limited to the above value. For example, a laser with a wavelength of 510 nm to 535 nm and a laser with a wavelength of 630 nm to 680 nm or a laser with a wavelength of 440 nm to 490 nm and a laser of 630 nm to 680 nm can be used. By producing a two-color HOE of G and R or B and R using a laser having such a light emission wavelength, the above-described effect by using the two-color HOE can be obtained.

In addition, when such a combination of lasers is used, it is possible to realize a two-color HOE that satisfies the following expression by, for example, producing the HOE by shifting the angle between the reproduction beam and the exposure beam toward the pupil center. Become. That is,
500 nm <λa <535 nm and 620 nm <λb <680 nm,
Or
440 nm <λa <490 nm and 620 nm <λb <680 nm
It is.

  By realizing such a two-color HOE of G and R or B and R, the following effects can be obtained in addition to increasing the difference in diffraction peak wavelength. That is, by using the two-color HOE, two colors and their intermediate colors can be expressed. That is, although it is not full color, it is possible to observe a single color and a multicolor image of a different color. In addition, when two colors are expressed by the HOE1 layer (when the HOE has an interference fringe that diffracts light of two colors), the diffraction efficiency of each color can be improved as compared to the case where three colors are expressed by the HOE1 layer. Can brighten the image. Further, in the case of two-color HOE, for example, a light source having two colors can be used as a light source for illuminating the display element. However, when the power consumption of the light source is the same, the light source has two colors rather than three colors. The intensity of illumination light per color can be increased, and the image can be brightened. If the illumination light source is the same, the wider the field of view, the larger the area of the observation image, so it will be observed darker. Therefore, the wider the field of view, the more important it is to make the image brighter and more observable. .

(Example 3)
Next, still another embodiment of the present invention will be described as a third embodiment. FIG. 9 is an explanatory diagram showing the optical paths of the exposure light beam when producing the HOE constituting the optical path combiner 3 and the reproduction light beam when using the HOE. In Example 3, the position of the reference light source (point light source of the exposure light beam 2) at the time of HOE production is arranged farther from the HOE than the center of the optical pupil E at the time of use to produce the HOE. In Example 3, the degree of wavelength shift in the field angle direction is smaller than that in Examples 1 and 2 in which the reference light (exposure light beam 2) is parallel light, but the wavelength shift still exists, so that the observation angle of view becomes wider. Ghost is likely to occur. In Example 3, the ghost was considered under the following calculation model conditions. FIG. 10 shows the diffraction peak wavelength obtained under the calculation model conditions.

<Calculation model conditions>
-The HOE combiner is inclined 30 degrees with respect to the vertical plane.
A HOE combiner was produced with parallel light incident at 30 degrees with respect to the normal of the HOE combiner, and divergent light at a distance of −30 degrees from the normal at the center of the combiner and at a distance of 30 mm from the center of the combiner. .
-The distance between the center of the HOE combiner and the optical pupil was 15 mm.
-The pupil size (the pupil diameter simultaneously incident on the pupil) was 3 mm.
-Production laser wavelength of HOE is Ar ⁺ 457.9 nm or Ar ⁺ 476.5 nm, YAG: Nd3 + (second harmonic) 532 nm, Kr 647.1 nm.
・ It was assumed that the hologram photosensitive material did not shrink.
・ HOE diffraction half width is not considered.
-The viewing angle of view of the video was 30 degrees.

In FIG. 10, HOE produced using an Ar ⁺ 457.9 nm laser is B-HOE (1), and HOE produced using an Ar ⁺ 476.5 nm laser is B-HOE (2). . When the HOE is manufactured with three colors of lasers of 476.5 nm, 532 nm, and 647.1 nm, the required diffraction wavelength range of B-HOE (2) and G-HOE is 447 to 492 nm for B-HOE (2), G-HOE is very close to 500 to 550 nm. In this calculation, the half-value wavelength width of the diffraction efficiency of the HOE is not taken into consideration. However, if the half-value wavelength width is 20 nm, for example, the necessary diffraction wavelength regions overlap each other and a ghost is generated.

  Therefore, it is desirable to produce B-HOE (1) having a diffraction peak wavelength of 458 nm instead of B-HOE (2) having a diffraction peak wavelength of 476 nm. In this case, the necessary diffraction wavelength region of B-HOE (1) is 430 to 474 nm, which is sufficiently away from the necessary diffraction wavelength region of G-HOE, so that it is possible to reliably avoid the occurrence of ghost, It is possible to observe images with resolution. Incidentally, when λa = 458 nm and λb = 532 nm, λb / λa = 1.16, which satisfies the conditional expressions (1) and (2).

(About the arrangement of the optical path combiner)
Next, arrangement | positioning of the optical path combiner 3 mentioned above is demonstrated. FIG. 11A shows a vertical insertion configuration of image light, that is, an angle φ ₁ so that the lower end of the optical path combiner 3 is closer to the optical pupil E side than the upper end with respect to the vertical plane P facing the optical pupil E. Only the optical path combiner 3 is shown tilted. In this configuration, image light from a display element (not shown) enters the optical path combiner 3 from above and is reflected by the optical path combiner 3 in the pupil direction. In this case, the above-described wavelength shift in the viewing angle direction occurs with respect to the observation viewing angle in the vertical direction.

On the other hand, FIG. 11B shows the horizontal insertion configuration of the image light, that is, the angle at which the left end of the optical path combiner 3 is closer to the optical pupil E side than the right end with respect to the vertical plane P facing the optical pupil E. The state where the optical path combiner 3 is tilted by φ ₂ is shown. In this configuration, image light from a display element (not shown) enters the optical path combiner 3 from the right direction and is reflected by the optical path combiner 3 in the pupil direction. In this case, the above-described wavelength shift in the view angle direction occurs with respect to the observation view angle in the left-right direction.

  According to the configurations of the first to third embodiments described above, the surface having high wavelength selectivity and angle selectivity of the HOE constituting the optical path combiner 3, that is, the perpendicular line at the center of the optical path combiner 3, the center of the optical path combiner 3, and the optical When the observation angle of view in a direction parallel to the plane including the straight line connecting the center of the pupil E is a wide angle, it is possible to avoid the generation of ghost light and observe a high-quality color image. Therefore, when the optical path combiner 3 is arranged as shown in FIG. 11A, the above-described effects of the present invention can be obtained when the observation angle of view in the vertical direction becomes a wide angle. On the other hand, when the optical path combiner 3 is arranged as shown in FIG. 11B, the above-described effects of the present invention can be obtained when the observation angle of view in the left-right direction becomes a wide angle.

(Specific examples applied to HMD)
Next, a specific configuration when the video display device 1 described above is applied to an HMD will be described.

  FIG. 12 is a cross-sectional view showing a schematic configuration of the video display device 11 applied to the HMD. The video display device 11 allows the observer to observe the outside world through see-through, displays the video, and provides it to the viewer as a virtual image, and corresponds to the video display device 1 (see FIG. 1 and the like) described above. ing. The video display device 11 includes a video display unit 21 and an eyepiece optical system 31. The video display unit 21 includes a light source 22, a unidirectional diffuser plate 23, a condenser lens 24, and an LCD 25.

  The light source 22 is composed of an RGB integrated LED that emits light in three wavelength bands whose central wavelengths are 465 nm, 520 nm, and 635 nm, for example. The RGB light emitting units of the light source 22 are arranged side by side in the horizontal direction. The unidirectional diffuser plate 23 diffuses illumination light from the light source 22, but the degree of diffusion differs depending on the direction. More specifically, the unidirectional diffuser plate 23 diffuses incident light by about 40 ° in a direction perpendicular to the paper surface (horizontal direction) in FIG. 12, and in a direction parallel to the paper surface (a direction perpendicular to the horizontal direction). Diffuses incident light by about 0.2 °.

  The condenser lens 24 is an illumination optical system that condenses the light diffused by the unidirectional diffuser plate 23. The condenser lens 24 is arranged so that the diffused light efficiently forms the optical pupil E. The LCD 25 is a display element that displays an image by modulating light from the light source 22 on a pixel-by-pixel basis based on an image signal. For example, the LCD 25 includes a transmissive liquid crystal display element. The LCD 25 corresponds to the display element 2 (see FIG. 1 and the like) described above.

  On the other hand, the eyepiece optical system 31 guides the image light from the LCD 25 to the optical pupil E, and transmits the external light to the optical pupil E so that the external world is displayed together with the virtual image of the display image at the position of the optical pupil E. Let them see through. The eyepiece optical system 31 includes a cemented prism (a cemented optical member), and configures a telecentric optical system. Specifically, the eyepiece optical system 31 is formed by joining an eyepiece prism 32 and a deflection prism 33, which are optical members, with an optical path combiner 34 interposed therebetween.

  The eyepiece prism 32 and the deflection prism 33 are joined with an adhesive. The eyepiece prism 32 is formed in a shape in which the lower end portion of the parallel plate is wedge-shaped and the upper end portion is thickened, and guides the image light from the LCD 25 by totally reflecting it internally. The eyepiece prism 32 has surfaces 32a, 32b, and 32c. The surface 32a is an incident surface on which the image light from the image display unit 21 is incident, and the surfaces 32b and 32c are surfaces facing each other. Among these, the surface 32b is a total reflection surface and an emission surface.

  The deflection prism 33 is configured to be a substantially parallel flat plate integrated with the eyepiece prism 32 by forming the upper end portion of the parallel plate along the lower end portion of the eyepiece prism 32. When the deflecting prism 33 is not joined to the eyepiece prism 32, external light is refracted when passing through the wedge-shaped lower end portion of the eyepiece prism 32, so that the external field image observed through the eyepiece prism 32 is distorted. However, the deflection prism 33 is joined to the eyepiece prism 32 to form an integral substantially parallel plate, whereby the deflection when the external light passes through the wedge-shaped lower end of the eyepiece prism 32 is canceled by the deflection prism 33. Can do. As a result, it is possible to prevent distortion in the external image observed through the see-through.

  The optical path combiner 34 is a reflective optical element that reflects the image light from the LCD 25 guided inside the eyepiece prism 32 and guides it to the optical pupil E, and transmits external light to the optical pupil E, for example, a volume phase. It is composed of a type and reflection type HOE. The optical path combiner 34 corresponds to the optical path combiner 3 (see FIG. 1 and the like) described above, and the diffraction peak wavelengths of the respective colors are set so as to satisfy the conditional expressions (1) and (2) described above. The HOE constituting the optical path combiner 34 has an axially asymmetric positive optical power for enlarging an image displayed on the LCD 25.

  The optical path combiner 34 is attached to the inclined surface at the lower end of the eyepiece prism 32, and as a result, is sandwiched between the eyepiece prism 32 and the deflection prism 33. By forming the HOE between the two transparent members (the eyepiece prism 32 and the deflection prism 33), the HOE does not come into contact with the outside air, so that the optical performance can be kept stable.

  In the above configuration, the light emitted from the light source 22 of the video display unit 21 is diffused by the unidirectional diffusion plate 23, condensed by the condenser lens 24, and enters the LCD 25. The light incident on the LCD 25 is modulated for each pixel based on the video signal and is emitted as video light. At this time, a color image is displayed on the LCD 25.

  The image light from the LCD 25 enters the eyepiece prism 32 of the eyepiece optical system 31 from its upper end surface (surface 32a), is totally reflected a plurality of times by the two opposing surfaces 32b and 32c, and enters the optical path combiner 34. To do. The light incident on the optical path combiner 34 is diffracted and reflected there, is emitted through the surface 32b, and reaches the optical pupil E. Therefore, at the position of the optical pupil E, the observer can observe an enlarged virtual image of the image displayed on the LCD 25.

  On the other hand, the eyepiece prism 32, the deflecting prism 33, and the optical path combiner 34 transmit almost all the external light, so that the observer can observe the external world. Therefore, the virtual image of the image displayed on the LCD 25 is observed while overlapping a part of the outside world. From the above, it can be said that the optical path combiner 34 is a combiner that guides the image light and the external light simultaneously to the eyes of the observer.

  As described above, the eyepiece optical system 31 includes the optical path combiner 34 made of a volume phase type and a reflection type HOE. Volume phase type reflection type HOE has high diffraction efficiency, and the half-value wavelength width of the diffraction efficiency peak is narrow. Therefore, a bright image can be observed by using such a HOE and adopting a configuration in which the image light from the LCD 25 is diffracted and reflected by the HOE and guided to the optical pupil E. In addition, since the transmittance of external light is increased, a bright external environment can be observed.

  In addition, since the image light is guided using total reflection in the eyepiece prism 32, the thickness can be reduced to the same level as that of a normal spectacle lens (for example, about 3 mm), and the eyepiece prism 32 can be made compact. While being able to be lightweight, the transmittance of external light becomes high and the external environment can be observed well. Further, the LCD 25 can be disposed on one end side of the eyepiece optical system 31, that is, in the vicinity of the visual field, and a wide external field viewing angle can be ensured.

  Further, the HOE has an axially asymmetric positive optical power and constitutes at least a part of the eyepiece optical system 31. Therefore, each of the optical elements constituting the apparatus while the eyepiece optical system 31 is made compact. The degree of freedom of arrangement of members can be increased, the apparatus can be reduced in size and weight, and an image with good aberration correction can be observed.

  Further, since the optical path combiner 34 is composed of a volume phase type reflection type HOE that diffracts only light having a specific wavelength at a specific incident angle, image light from the LCD 25 is supplied to the eyepiece prism 32, the deflection prism 33, and the optical path. The external light transmitted through the combiner 34 is not affected. Therefore, the observer can observe the outside world normally and clearly through the eyepiece prism 32, the deflection prism 33 and the optical path combiner 34 while observing the virtual image of the display image on the LCD 25 through the optical path combiner 34. .

  Next, an HMD to which the video display device 11 is applied will be described. FIGS. 13A, 13B, and 13C are a plan view, a front view, and a side view showing a schematic configuration of the HMD, respectively. The HMD includes the above-described video display device 11 and support means 12 that supports the video display device 11, and as a whole looks like one lens (for example, for the left eye) is removed from general glasses. Yes. In the video display device 11, a portion corresponding to the right eye lens of the glasses is configured by bonding the eyepiece prism 32 and the deflection prism 33.

  The support unit 12 supports the video display device 11 in front of the observer's eyes (for example, in front of the right eye), and includes a bridge 13, a frame 14, a temple 15, a nose pad 16, and a cable 17. is doing. The frame 14, the temple 15 and the nose pad 16 are provided as a pair on the left and right sides. However, when these are distinguished from each other, the right frame 14R, the left frame 14L, the right temple 15R, the left temple 15L and the right nose pad 16R. The left nose pad 16L is expressed.

  One end of the video display device 11 is supported by the bridge 13. The bridge 13 supports the left frame 14 </ b> L and the nose pad 16 in addition to the video display device 11. The left frame 14L supports the left temple 15L so as to be rotatable. On the other hand, the other end of the video display device 11 is supported by the right frame 14R. An end of the right frame 14R opposite to the support side of the video display device 11 supports the right temple 15R so as to be rotatable. The cable 17 is a wiring for supplying an external signal (for example, a video signal, a control signal) and power to the video display device 11, and is provided along the right frame 14R and the right temple 15R.

  When the observer uses the HMD, the right temple 15R and the left temple 15L are brought into contact with the right and left heads of the observer, and the nose pad 16 is placed on the nose of the observer so as to wear general glasses. The HMD is attached to the observer's head. When an image is displayed on the image display device 11 in this state, the observer can observe the image on the image display device 11 as a virtual image and can observe the outside world through the image display device 11 in a see-through manner. it can.

  As described above, since the video display device 11 is supported by the support means 12, the observer can observe the video provided from the video display device 11 in a hands-free manner. In addition, since the observation direction of the observer is determined in one direction, there is an advantage that the observer can easily search for a display image even in a dark environment.

  The HMD may have a configuration in which two video display devices 11 are arranged in front of both eyes of the observer.

  Of course, it is possible to configure the optical path combiner, the video display device, and thus the HMD by appropriately combining the configurations described in this embodiment.

  Note that the optical path combiner and the video display device described in this embodiment can be applied to, for example, a HUD.

  The present invention is applicable to HMD and HUD.

It is explanatory drawing which shows typically the structure of the video display apparatus of this invention. It is explanatory drawing which shows typically the optical path of the exposure light beam at the time of preparation of the optical path combiner of the said video display apparatus, and the optical path of the reproduction light beam at the time of use (at the time of reproduction | regeneration). It is explanatory drawing which shows typically the optical path of the exposure light beam at the time of producing an optical path combiner using two parallel light beams, and the optical path of the reproduction light beam which is diffracted by the optical path combiner and enters the center of the optical pupil. In the said optical path combiner, it is explanatory drawing which shows a mode that a diffraction peak wavelength shifts according to an angle of view. It is explanatory drawing which shows typically the optical path of the reproduction | regeneration light beam which is diffracted and reflected by the said optical path combiner, and simultaneously injects into the optical pupil with a fixed magnitude | size. In a comparative example, it is explanatory drawing which shows the diffraction peak wavelength in HOE about each light ray which injects into an optical pupil. In Example 1, it is explanatory drawing which shows the diffraction peak wavelength in HOE about each light ray which injects into an optical pupil. (A) is explanatory drawing which shows the diffraction characteristic of 2 color HOE which diffracts the light of 2 colors of G and R, (b) is the diffraction of 2 color HOE which diffracts the light of 2 colors of B and R It is explanatory drawing which shows a characteristic. It is explanatory drawing which shows the optical path of the exposure light beam when producing another optical path combiner, and the optical path of the reproduction light beam at the time of use. In Example 3, it is explanatory drawing which shows the diffraction peak wavelength in HOE about each light ray which injects into an optical pupil. (A) is explanatory drawing which shows the vertical insertion structure of image light, (b) is explanatory drawing which shows the horizontal insertion structure of image light. It is sectional drawing which shows the structure of the outline of the video display apparatus applied to HMD. (A) (b) (c) is the top view, front view, and side view which respectively show the structure of the outline of the said HMD.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Video display apparatus 2 Display element 3 Optical path combiner 11 Video display apparatus 12 Support means 25 LCD (display element)
31 Eyepiece optical system 32 Eyepiece prism (optical member)
34 Optical path combiner (hologram optical element)
E Optical pupil

Claims (9)

The image light from the display element is diffracted and reflected in the direction of the optical pupil, while the external light is transmitted and guided to the optical pupil, thereby superimposing the virtual image of the display image and the external environment at the position of the optical pupil. An optical path combiner having a volume phase type reflection type hologram optical element,
In a plane including a perpendicular at the center of the optical path combiner and a straight line connecting the center of the optical path combiner and the center of the optical pupil, the maximum angle difference between the light rays emitted from the optical path combiner and incident on the optical pupil center is 16 When there are multiple diffraction peak wavelengths discretely for light rays incident on the center of the optical pupil from the center of the optical path combiner, and in all combinations of the plurality of diffraction peak wavelengths, The diffraction peak wavelength of λa is λa, and the other diffraction peak wavelength is λb.
380 nm <λa <λb <780 nm and λb / λa> 1.13
An optical path combiner characterized by satisfying   The optical path combiner according to claim 1, wherein the hologram optical element has a planar shape. 1.2 <λb / λa <1.5
The optical path combiner according to claim 1 or 2, wherein: 500 nm <λa <535 nm and 620 nm <λb <680 nm,
Or
440 nm <λa <490 nm and 620 nm <λb <680 nm
The optical path combiner according to any one of claims 1 to 3, wherein:   The hologram optical element is manufactured using a laser having an emission wavelength of 510 to 535 nm and a laser of 630 to 680 nm, or a laser of 440 to 490 nm and a laser of 630 to 680 nm. The optical path combiner according to any one of claims 1 to 4.   The hologram optical element is manufactured using a laser having an emission wavelength of 440 nm to 460 nm, a laser of 525 nm to 535 nm, and a laser of 630 nm to 680 nm. The optical path combiner described in 1. A display element for displaying an image;
An optical member that totally reflects image light from the display element inside;
An optical path combiner that reflects the image light guided inside the optical member and guides it to the optical pupil while transmitting the external light to the optical pupil,
7. The image display device according to claim 1, wherein the optical path combiner comprises the optical path combiner according to any one of claims 1 to 6.   The hologram optical element of the optical path combiner has an axially asymmetric positive optical power, and constitutes at least a part of an eyepiece optical system that guides image light from the display element to an optical pupil. The video display device according to claim 7. The video display device according to claim 7 or 8,
A head-mounted display comprising: support means for supporting the video display device in front of an observer's eyes.

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