Image display device and display device

Abstract

An object of the present technology is to provide an image display device in which dark lines and discoloration do not occur in a central portion of a field of view in an image projected on the retina. The present technology provides an image display device. The image display device includes a first reflective volume hologram element and a second reflective volume hologram element that integrally form a transmissive diffractive element. The first reflective body holographic element and the second reflective body holographic element satisfy Bragg conditions for incident light of three colors of red, green and blue. The first reflective body holographic element diffracts incident light incident at an incident angle [theta] i at a connection angle [theta] c, and deflects the incident light to the second reflective body holographic element. The second reflective volume holographic element converges the deflected incident light. The incident angle [theta] i and the connection angle [theta] c satisfy specific conditions.

Description

Technical Field

[0001] The present technical content relates to an image display device and a display device. More specifically, the present technical content relates to an image display device and a display device including the image display device and an imaging device. Background Art

[0002] In a retinal projection device that guides a projection beam to the retina, in order to guide the beam emitted by the projection light source in front to the retina, the entire retinal projection device must be transmissive. However, when this function is realized by a transmissive holographic optical element (HOE), due to its low wavelength selectivity, the spectrum of the diffracted light from each hologram of three colors of red (R), green (G) and blue (B) (hereinafter also referred to as "R / G / B") cannot be completely separated. Therefore, a pseudo-transmissive HOE is realized by combining two reflective HOEs with different functions as shown in FIG. 1. FIG. 1 is a schematic diagram showing a transmissive HOE. In FIG. 1, θi is the incident angle and θc is the connection angle. The two reflective HOEs with different functions are specifically a deflection HOE 101 and a focusing HOE 102 as shown in FIG. 1. The deflection HOE 101 is arranged on the side of the retina, and the focusing HOE 102 is arranged on the side of the projection light source to form a transmissive HOE.

[0003] The function of the deflection HOE 101 is to deflect the incident light incident at a certain incident angle at a certain diffraction angle (connection angle) to the focusing HOE 102. The function of the focusing HOE 102 is to diffract and reflect the deflected light to a certain point. The combination of these HOEs forms a transmission type HOE as a whole.

[0004] In the transmission type HOE, when incident light is transmitted through the focusing HOE 102, the incident light does not satisfy the diffraction condition, thereby passing through it as is and reaching the deflection HOE 101, and when light diffracted by the focusing HOE 102 passes through the deflection HOE 101, it does not satisfy the diffraction condition, thereby passing through as is.

[0005] By utilizing the wavelength selectivity of the reflective HOE, the spectrum can be completely separated, and the corresponding projection beams of R / G / B light can be selectively diffracted in the corresponding holograms of R / G / B. For example, the following patent documents 1 to 3 disclose technologies using this configuration.

[0006] List of existing technologies

[0007] Patent Literature

[0008] Patent Document 1: Japanese Patent Application Laid-Open No. 2000-28925

[0009] Patent Document 2: Japanese Patent Application Laid-Open No. 2003-161820

[0010] Patent Document 3: Japanese Patent Application No. 2017-524962 Summary of the invention

[0011] Problems to be solved by this technical content

[0012] The present inventors have found that, in the case of the configuration of the reflective volume hologram element as described above, a phenomenon in which dark lines or partial discoloration occurs in the image projected on the retina under certain conditions.

[0013] Therefore, an object of the present technical content is to provide an image display device in which dark lines and discoloration are not generated in the central part of the visual field of an image projected on the retina.

[0014] Solution to the problem

[0015] The present invention provides an image display device, comprising:

[0016] The first reflective volume hologram element and the second reflective volume hologram element as a whole form a transmission type diffraction element, wherein

[0017] The first reflective volume hologram element and the second reflective volume hologram element satisfy the Bragg condition for incident light of three colors: red, green and blue.

[0018] The first reflective volume hologram element diffracts the incident light incident at an incident angle θi at a connection angle θc and deflects the incident light to the second reflective volume hologram element.

[0019] The second reflective volume hologram element converges the deflected incident light, and

[0020] The incident angle θi and the connection angle θc satisfy the following condition 1 or condition 2:

[0021] (Condition 1)

[0022] 10 degrees ≤ incident angle θi ≤ 90 degrees, 10 degrees ≤ connection angle θc ≤ 90 degrees, and 4×incident angle θi + connection angle θc ≤ 170 degrees,

[0023] (Condition 2)

[0024] 70 degrees ≤ incident angle θi ≤ 90 degrees, and 70 degrees ≤ connection angle θc ≤ 90 degrees.

[0025] In the image display device, the incident angle θi and the connection angle θc may satisfy the following condition 1a or condition 2:

[0026] (Condition 1a)

[0027] 10 degrees ≤ incident angle θi ≤ 90 degrees, 30 degrees ≤ connection angle θc ≤ 90 degrees, and 6×incident angle θi+connection angle θc ≤ 210 degrees,

[0028] (Condition 2)

[0029] 70 degrees ≤ incident angle θi ≤ 90 degrees, and 70 degrees ≤ connection angle θc ≤ 90 degrees.

[0030] The beam incident surface of the first reflective volume hologram element and the beam incident surface of the second reflective volume hologram element are substantially parallel and face each other.

[0031] The diffraction angle of the central portion of the second reflective volume hologram element is approximately 0 degree.

[0032] The incident light incident on the first reflective volume hologram element may be p-polarized light.

[0033] The incident light may be emitted from an imaging device separate from an image display device.

[0034] In addition, the present technology also provides a display device, including:

[0035] An image display device, wherein

[0036] The image display device includes a first reflective volume hologram element and a second reflective volume hologram element which form a transmission type diffraction element as a whole.

[0037] The first reflective volume hologram element and the second reflective volume hologram element satisfy the Bragg condition for incident light of three colors: red, green and blue.

[0038] The first reflective volume hologram element diffracts the incident light incident at an incident angle θi at a connection angle θc and deflects the incident light to the second reflective volume hologram element.

[0039] The second reflective volume hologram element converges the deflected incident light, and

[0040] The incident angle θi and the connection angle θc satisfy the following condition 1 or condition 2; and

[0041] an imaging device, the imaging device emitting the incident light,

[0042] (Condition 1)

[0043] 10 degrees ≤ incident angle θi ≤ 90 degrees 10 degrees ≤ connection angle θc ≤ 90 degrees, and 4×incident angle θi + connection angle θc ≤ 170 degrees,

[0044] (Condition 2)

[0045] 70 degrees ≤ incident angle θi ≤ 90 degrees, and 70 degrees ≤ connection angle θc ≤ 90 degrees. BRIEF DESCRIPTION OF THE DRAWINGS

[0046] FIG. 1 is a schematic diagram showing a pseudo-transmissive HOE combining two reflective HOEs having different functions.

[0047] FIG. 2 is a schematic diagram showing an example of partial color change.

[0048] FIG. 3 is a schematic diagram showing an example of partial color change.

[0049] FIG. 4 is a schematic diagram showing an example of a partially dark line.

[0050] FIG. 5 is a schematic diagram for explaining that a portion of incident light is diffracted by a focusing HOE.

[0051] FIG. 6 is a schematic diagram for explaining that a portion of diffracted light from a focusing HOE is diffracted by a deflected HOE.

[0052] FIG. 7 is a schematic diagram for explaining the calculation of the diffraction grating in the light-condensing HOE.

[0053] FIG. 8 is a schematic diagram for explaining the calculation of the diffraction condition of incident light incident on the light-condensing HOE at the incident angle θi.

[0054] FIG. 9 is a schematic diagram showing calculation results of the viewing direction and the diffraction wavelength.

[0055] FIG. 10 is a schematic diagram showing an example of the relationship between the incident angle and the connection angle, and the viewing direction in which unnecessary diffraction occurs.

[0056] FIG. 11 is a schematic diagram showing an example of the relationship between the incident angle and the connection angle, and the viewing direction in which unnecessary diffraction occurs.

[0057] FIG. 12 is a schematic diagram for explaining the calculation of the diffraction grating in the deflection HOE.

[0058] FIG. 13 is a schematic diagram for explaining calculation of diffraction conditions of incident light incident on the deflection HOE at an incident angle θv.

[0059] FIG. 14 is a schematic diagram showing calculation results of the viewing direction and the diffraction wavelength.

[0060] FIG. 15 is a schematic diagram showing an example of the relationship between the incident angle and the connection angle, and the viewing direction in which unnecessary diffraction occurs.

[0061] FIG. 16 is a schematic diagram showing an example of the relationship between the incident angle and the connection angle, and the viewing direction in which unnecessary diffraction occurs.

[0062] FIG. 17 is a schematic diagram showing an example of the relationship between the incident angle and the connection angle, and the viewing direction in which unnecessary diffraction occurs.

[0063] FIG. 18 is a schematic diagram showing the optical system during exposure of a focusing HOE.

[0064] FIG. 19 is a schematic diagram showing the optical system during reproduction of a focusing HOE.

[0065] FIG. 20 is a schematic diagram showing an example of the relationship between the incident angle and the connection angle, and the viewing direction in which unnecessary diffraction occurs.

[0066] FIG. 21 is a schematic diagram showing an example of the relationship between the incident angle and the connection angle, and the viewing direction in which unnecessary diffraction occurs.

[0067] FIG. 22 is a schematic diagram showing an example of the relationship between the incident angle and the connection angle, and the viewing direction in which unnecessary diffraction occurs.

[0068] FIG. 23 is a schematic diagram showing an example of the relationship between the incident angle and the connection angle, and the viewing direction in which unnecessary diffraction occurs.

[0069] FIG. 24 is a schematic diagram for explaining the polarization dependence of the transmission spectrum of incident light in the central portion of a focusing HOE.

[0070] FIG. 25 is a schematic diagram illustrating an example of a display device.

[0071] FIG. 26 is a schematic diagram showing an example of a state in which a user uses a display device including an imaging device.

[0072] FIG. 27 is a diagram showing an example of a display device including an imaging device. DETAILED DESCRIPTION

[0073] The preferred embodiments for implementing the present technology will be described below with reference to the accompanying drawings. The embodiments described below show representative embodiments of the present technology, but the scope of the present technology is not limited to these embodiments. The present technology will be described in the following order.

[0074] 1. First Embodiment (Image Display Device)

[0075] 1-1. Overview of the First Embodiment

[0076] 1-2. Dark lines and discoloration

[0077] 1-3. Conditions to prevent the above phenomenon from occurring in the center of the field of vision

[0078] 1-3-1. First Example

[0079] 1-3-2. Second Example

[0080] 1-3-3. Third Example

[0081] 2. Second Embodiment (Display Device)

[0082] 1. First Embodiment (Image Display Device)

[0083] 1-1. Overview of the First Embodiment

[0084] The image display device according to the present embodiment includes a first reflective volume hologram element and a second reflective volume hologram element which form a transmission type diffraction element as a whole. The first reflective volume hologram element and the second reflective volume hologram element satisfy the Bragg condition for incident light of three colors, red, green and blue. The first reflective volume hologram element diffracts incident light incident at an incident angle θi at a connection angle θc and deflects the incident light to the second reflective volume hologram element. The second reflective volume hologram element converges the deflected incident light. The incident angle θi and the connection angle θc satisfy the following condition 1 or condition 2.

[0085] (Condition 1)

[0086] 10 degrees ≤ incident angle θi ≤ 90 degrees, 10 degrees ≤ connection angle θc ≤ 90 degrees, and 4×incident angle θi + connection angle θc ≤ 170 degrees

[0087] (Condition 2)

[0088] 70 degrees ≤ incident angle θi ≤ 90 degrees, and 70 degrees ≤ connection angle θc ≤ 90 degrees

[0089] The first reflective volume hologram element is, for example, a deflecting HOE, and may be the deflecting HOE 101 shown in Fig. 1. The second reflective volume hologram element is, for example, a focusing HOE, and may be the focusing HOE 102 shown in Fig. 1.

[0090] In the image display device according to the present embodiment, the incident angle θi and the connection angle θc are set to satisfy the above-mentioned condition 1 or condition 2. This is because dark lines and discoloration are not generated in the central portion of the visual field in the image projected on the retina.

[0091] In the image display device satisfying the above-mentioned condition 1 or condition 2, the first and second reflective volume hologram elements may be, for example, ideal HOEs. In the case where the second reflective volume hologram element deviates from the ideal HOE, the incident angle θi and the connection angle θc may preferably be a combination satisfying the following condition 1a or condition 2. Note that the ideal HOE will be described separately below.

[0092] (Condition 1a)

[0093] 10 degrees ≤ incident angle θi ≤ 90 degrees, 30 degrees ≤ connection angle θc ≤ 90 degrees, and 6×incident angle θi+connection angle θc ≤ 210 degrees

[0094] (Condition 2)

[0095] 70 degrees ≤ incident angle θi ≤ 90 degrees, and 70 degrees ≤ connection angle θc ≤ 90 degrees

[0096] In a preferred embodiment, the beam incident surface of the first reflective volume hologram element and the beam incident surface of the second reflective volume hologram element are approximately parallel and face each other. Therefore, the connection angle is consistent with the incident angle of the second reflective volume hologram element. "Approximately parallel" includes not only completely parallel but also approximately parallel, and means including a deviation of about several degrees. The deviation is, for example, within ±2 degrees, preferably within ±1 degree, and more preferably within ±0.5 degrees.

[0097] In a preferred embodiment, the diffraction angle of the central part of the second reflective volume hologram element is about 0 degrees. Therefore, the diffracted light from the central part of the second reflective volume hologram element can be the center of the field of view. "About 0 degrees" includes not only the perfect 0 degrees but also about 0 degrees, and means including a deviation of about several degrees. The deviation is, for example, within ±2 degrees, preferably within ±1 degrees, and more preferably within ±0.5 degrees.

[0098] In a preferred embodiment, the incident light incident on the first reflective volume hologram element is p-polarized light. Therefore, the degree of dark lines and discoloration in the image projected on the retina can be reduced.

[0099] In a preferred embodiment, the incident light is emitted from an imaging device separate from the image display device.

[0100] The image display device according to the present embodiment may include a diffraction element other than the above-mentioned diffraction element. The image display device may further include, for example, a diffraction element capable of preventing stray light from being transmitted through the reflective volume hologram element.

[0101] Hereinafter, the phenomenon of dark lines and discoloration occurring in an image projected on the retina will be described in detail. Thereafter, preferred aspects of the present embodiment will be described with reference to specific examples related to conditions for preventing the phenomenon from occurring in the central portion of the visual field.

[0102] 1-2. Dark lines and discoloration

[0103] As described above, the present inventors have found that in the configuration of the reflective volume hologram element as shown in Fig. 1, a phenomenon of dark lines or partial discoloration may occur in the image projected on the retina. This phenomenon will be described below.

[0104] Fig. 2 and Fig. 3 are schematic diagrams showing examples of partial discoloration. Fig. 4 is a schematic diagram showing an example of partial dark lines. In Fig. 2, vertical stripe-like discoloration indicated by arrows A and B can be confirmed. In Fig. 3, ring-like discoloration indicated by arrow C can be confirmed. In Fig. 4, dark lines indicated by arrow D can be confirmed.

[0105] As a result of intensive studies on the above phenomenon, the present inventors have found that unnecessary diffraction occurs in the deflection HOE 101 and the focusing HOE 102 shown in Fig. 1. The unnecessary diffraction is roughly classified into the following two types.

[0106] 1) A portion of the incident light is diffracted at the focusing HOE 102 ( FIG. 5 ).

[0107] 2) A portion of the diffracted light from the focusing HOE 102 is diffracted at the deflection HOE 101 ( FIG. 6 ).

[0108] FIG5 is a diagram for explaining the above 1). In FIG5, L1 represents unnecessary diffracted light. In the figure, when the diffracted light at point P of the focusing HOE 102 is consistent with the direction of the incident light, the incident light at point P is diffracted along the connection angle direction at the focusing HOE 102, so the incident light cannot pass through the focusing HOE 102 or the transmittance is reduced. Therefore, a phenomenon occurs that a part of the incident light (video display light) cannot reach the retina.

[0109] FIG6 is a diagram for explaining the above 2). In FIG6, L2 represents unnecessary diffracted light. In the figure, when the diffracted light at point Q of the deflection HOE 101 is consistent with the direction of the incident light, the diffracted light at point Q is diffracted along the connection angle direction at the deflection HOE 101, and therefore cannot be transmitted through the deflection HOE 101 or the transmittance is reduced. Therefore, a phenomenon occurs in which a part of the incident light (video display light) cannot reach the retina.

[0110] The above phenomenon occurs when the incident light is monochromatic, and occurs in each wavelength band of R / G / B. In addition, since point P and point Q are close to the direction of the incident light, the above two phenomena 1) and 2) occur simultaneously in the three colors. As a result, since the three colors in the video in this direction do not reach the retina, the video appears as a dark line as shown in Figure 4.

[0111] On the other hand, as a more complicated phenomenon, it is necessary to consider unnecessary diffraction caused by the interaction between the hologram and the R / G / B incident light. In the case of a retinal projection device compatible with full color, R / G / B will form diffraction gratings corresponding to them respectively, but the diffraction grating of the R layer will diffract the G light, and unnecessary diffraction will occur between the colors, so that the G light cannot reach the retina.

[0112] This phenomenon does not necessarily occur near the direction of the incident light. In addition, it is relatively rare that three colors are generated at the same position at the same time, and one color of light is not transmitted, making the image appear as striped or ring-shaped color change, as shown in Figures 2 and 3.

[0113] The above-mentioned dark lines and discolored lines depend on the state of the diffraction gratings formed in the deflection HOE 101 and the focusing HOE 102. The inventors have found that the combination of the incident angle θi and the connection angle θc in the deflection HOE 101 and the focusing HOE 102 affects the appearance of the dark lines and the discolored lines. The inventors focused on selecting the incident angle θi and the connection angle θc so that the dark lines and the discolored lines do not enter the field of view, or even if the dark lines and the discolored lines cannot be avoided from entering the field of view, they do not appear in the central part of the field of view, and have completed the content of the present technology. In addition, the inventors have also found that the degree of unnecessary diffraction also depends on the polarization state of the incident light. Selecting the polarization state of the incident light is also effective in suppressing unnecessary diffraction.

[0114] 1-3. Conditions to prevent the above phenomenon from occurring in the center of the field of vision

[0115] The conditions under which dark lines and discolored lines are not generated in the central part of the field of view will be described below using specific examples (first to third examples). In these examples, it is assumed that the image display device is a component in a retinal projection device. In these examples, as shown in FIG. 1 , the retinal projection device includes a deflection HOE 101 and a focusing HOE 102 that form a transmission-type diffraction element as a whole. In addition, the light source of the retinal projection device is assumed to be a semiconductor laser having wavelengths of 644 nm, 520 nm, and 446 nm (reproduction). It is conceivable to select a wavelength other than this, but it will not significantly affect the calculation results described below.

[0116] In addition, the focusing HOE 102 has different diffraction conditions at each point of the two-dimensional expansion. Although it is originally necessary to perform calculations in all two-dimensional areas, when estimating at which viewing angle the dark line appears, it is sufficient to perform calculations in the cross section of the incident surface. Therefore, the calculations in the one-dimensional area of ​​the cross section are performed below.

[0117] 1-3-1. First Example

[0118] As a first example, a case where the deflection HOE and the focusing HOE are ideal HOEs will be described.

[0119] When the incident angle and the connection angle are determined, in the ideal deflection HOE, for the diffraction condition of the incident light incident on the deflection HOE at the incident angle, the diffraction wavelength is consistent with the reproduction wavelength, and the diffraction angle is consistent with the connection angle.

[0120] In an ideal focusing HOE, for incident light incident at a connection angle, the diffracted wavelength matches the reproduced wavelength at any point on the focusing HOE, and the light diffracted at each point is focused on the HOE at one point.

[0121] (1) Calculation of the conditions under which part of the incident light is diffracted by the focusing HOE

[0122] Hereinafter, a process for calculating the conditions under which a portion of incident light is diffracted by a focusing HOE will be described.

[0123] 1) Calculate the diffraction grating (considered as interference between two plane waves) used to diffract the incident light (wavelength is the reproduction wavelength) incident at point P (x = x0) of the focusing HOE at a connection angle θc in the focusing direction (point F) (Figure 7).

[0124] 2) The incident light incident at the diffraction grating at the incident angle θi at the calculated point P satisfies the diffraction condition and the diffraction wavelength is calculated to (Figure 8).

[0125] 3) Find the point P (x=x0) where the diffracted wavelength coincides with the reproduced wavelength, and convert it into the field of view direction (angle) based on the relationship with the focusing position (point F).

[0126] As an example of calculation, FIG9 shows the calculation results of the field of view direction and diffraction wavelength in the red diffraction grating when the incident angle θi = 50 degrees and the connection angle θc = 60 degrees. In FIG9, "Reproduced light wavelength (644nm)" indicates the red reproduced wavelength, "Reproduced light wavelength (520nm)" indicates the green reproduced wavelength, and "Reproduced light wavelength (446nm)" indicates the blue reproduced wavelength.

[0127] Referring to FIG. 9 , it can be seen that in the case where the viewing direction is the incident light (50 degrees), the diffraction wavelength coincides with the red reproduction wavelength. In this viewing direction, similar results occur in green and blue, and therefore, the image is a dark line in which all R / G / B are missing. In addition, even if it is a red diffraction grating, there is a viewing direction in which the diffraction wavelength coincides with the reproduction wavelength of green and blue. In this viewing direction, an image missing green and blue is obtained, and discolored lines are caused.

[0128] 10 and 11 show calculation results of the viewing direction in which the reproduced light of R / G / B is diffracted in the diffraction grating of R / G / B in this manner for the incident angle θi and the connection angle θc.

[0129] Fig. 10 shows the field of view direction in which the diffraction grating of each color diffracts the reproduction light of the same color, where (A) corresponds to red, (B) corresponds to green, and (C) corresponds to blue. In any case, diffraction occurs when the field of view direction coincides with the incident direction. Fig. 11 shows the field of view direction in which the diffraction grating of each color diffracts the reproduction light of another color, where (A) corresponds to the case where the red diffraction grating diffracts the green reproduction light, (B) corresponds to the case where the red diffraction grating diffracts the blue reproduction light, and (C) corresponds to the case where the green diffraction grating diffracts the blue reproduction light.

[0130] The analysis was performed under the assumption that the visual field range is ±10 degrees without dark lines and discolored lines. In the case where the application of the retinal projection device in this embodiment is, for example, an auxiliary screen of a smartphone, assuming a projection distance of 400 mm, a visual field range of ±10 degrees corresponds to 150 mm, and assuming an aspect ratio of 4:3, the image range is 116 mm × 87 mm. Such a size is sufficient for the function of an auxiliary screen of a smartphone.

[0131] Since the visual acuity is high in the central part of the visual field, if dark lines or discolored lines exist in this area, the commercial value is greatly impaired. On the other hand, in the visual field range of ±10 degrees or more, since the visual acuity decreases rapidly, even if dark lines or discolored lines exist in this area, the commercial value is not impaired compared to the case where dark lines or discolored lines exist in the central part of the visual field.

[0132] Under the above conditions, it can be seen from FIG. 10 that for the phenomenon that the diffraction gratings of each color diffract the reproduced light of the same color, it is sufficient to set the incident angle to 10 degrees or more. On the other hand, regarding the phenomenon that the diffraction gratings of each color diffract the reproduced light of another color, FIG. 11 shows the field of view area within ±10 degrees as the field of view area 201. The combination of the incident angle and the connection angle that avoids all the field of view areas 201 shown in (A) to (C) of FIG. 11 is shown by the frame line 202 in (B) and the frame line 203 in (C). By utilizing the combination of the incident angle and the connection angle surrounded by the frame lines 202 and 203, in all cases of (A) to (C) of FIG. 11, dark lines and discolored lines within ±10 degrees in the field of view direction can be avoided.

[0133] (2) Calculate the conditions under which part of the diffracted light from the focusing HOE is diffracted by the deflected HOE

[0134] Hereinafter, a process of calculating the conditions under which a portion of the diffracted light from the focusing HOE is diffracted by the deflected HOE will be described.

[0135] 1) Calculate the diffraction grating (interference of two plane waves, which are the same at any position in the plane) in which the incident light (wavelength is the reproduction wavelength) entering the focusing HOE at an incident angle θi is diffracted at a connection angle θc (Figure 12).

[0136] 2) Calculate the diffraction wavelength that satisfies the diffraction condition for light incident on the calculated diffraction grating at an incident angle θv (Figure 13).

[0137] 3) Find the angle of incidence θv (viewing direction) when the diffracted wavelength coincides with the reproduced wavelength.

[0138] As an example of calculation, the calculation results of the field of view direction and diffraction wavelength in the blue diffraction grating when the incident angle θi = 50 degrees and the connection angle θc = 70 degrees are shown in Figure 14. In Figure 14, "Reproduced light wavelength (520nm)" indicates the green reproduced wavelength, and "Reproduced light wavelength (446nm)" indicates the blue reproduced wavelength.

[0139] As can be seen from FIG14, when the incident angle θv is θi (50 degrees) and -θc (-70 degrees), the diffraction wavelength coincides with the reproduction wavelength of blue. This is obvious from the fact that the blue diffraction grating is formed by interference between plane waves at the incident angles θi and θc. In addition, even if it is a blue diffraction grating, there is a field of view direction in which the diffraction wavelength coincides with the reproduction wavelength of green. In this field of view direction, an image lacking green is obtained, and a discolored line is caused.

[0140] 15 to 17 show calculation results of the viewing direction in which the reproduced light of R / G / B is diffracted in the diffraction grating of R / G / B in this manner for the incident angle θi and the connection angle θc.

[0141] In FIG. 15 , (A) corresponds to the positive side in the field of view direction (the side of incident light), and (B) corresponds to the negative side in the field of view direction (the side opposite to the incident light), where the diffraction gratings of the respective colors diffract the reproduced light of the same color. In (A), in any case of R / G / B, diffraction occurs when the field of view direction coincides with the incident direction. In (B), in any case of R / G / B, diffraction occurs when the field of view direction coincides with the connection angle direction. Note that in (A) and (B), only the case where the red reproduced light is diffracted by the red diffraction grating is described, but the same graphs also apply to the cases of green and blue.

[0142] FIG. 16 and FIG. 17 show the field of view directions of the reproduction light diffracted by the diffraction gratings of different colors, FIG. 16 shows the case where the blue diffraction grating diffracts the green reproduction light, and FIG. 17 shows the case where the green diffraction grating diffracts the red reproduction light. In FIG. 16 and FIG. 17, (A) corresponds to the positive side (the side of the incident light), and (B) corresponds to the negative side (the side opposite to the incident light). The area surrounded by the dividing lines 202 and 203 indicates that when the condition that a part of the incident light is diffracted by the focusing HOE is calculated in (1) above, the occurrence of dark lines and discolored lines within ±10 degrees in the field of view direction can be avoided. In addition, in FIG. 16 and FIG. 17, the field of view area within ±10 degrees is displayed as the field of view area 301.

[0143] In the region where the incident angle θi is small, the allowable range of (1) above (region surrounded by the dividing line 203) is included in the allowable range of (2) above. On the other hand, in the region where the incident angle θi is large, in the case of FIG. 16 (blue diffraction grating → diffracted green reproduction light), the allowable range in (2) above is wider, but in the case of FIG. 17 (green diffraction grating → diffracted red reproduction light), the range of the allowable incident angle θi and connection angle θc is narrower. However, the region 302 shown in FIG. 17 can avoid the field of view region 301 shown in FIGS. 16 and 17. As a result, in the region 302, in both (1) above (the case where a portion of the incident light is diffracted by the focusing HOE) and (2) above (the case where a portion of the diffracted light from the focusing HOE is diffracted by the deflected HOE), dark lines and discolored lines within ±10 degrees in the field of view direction can be avoided.

[0144] (3) Allowable range of incident angle θi and connection angle θc in the first example

[0145] In the first example, a combination of the incident angle θi and the connection angle θc at which dark lines and discolored lines due to the above factors (1) and (2) do not appear within ±10 degrees of the field of view satisfies the following conditions 1 or 2.

[0146] (Condition 1)

[0147] 10 degrees ≤ incident angle θi ≤ 90 degrees, 10 degrees ≤ connection angle θc ≤ 90 degrees, and 4×incident angle θi + connection angle θc ≤ 170 degrees

[0148] (Condition 2)

[0149] 70 degrees ≤ incident angle θi ≤ 90 degrees, and 70 degrees ≤ connection angle θc ≤ 90 degrees

[0150] The above condition 1 corresponds to the region surrounded by the dividing line 203 shown in Fig. 17 (region where the incident angle θi is small). The above condition 2 corresponds to the region 301 shown in Fig. 17 (region where the incident angle θi is large).

[0151] 1-3-2. Second Example

[0152] As a second example, a case where the concentrated HOE deviates from the ideal HOE will be described.

[0153] In the first example, the case where the focusing HOE is an ideal HOE has been described, that is, in the HOE, for light incident at a connection angle, the diffracted wavelength coincides with the reproduced wavelength at any point on the focusing HOE, and the diffracted light at each point converges to one point. However, in reality, there are cases where the focusing HOE may deviate from the ideal HOE due to the following two reasons.

[0154] <Cause 1: The wavelength of the reproduction light is different from the exposure wavelength>

[0155] For ease of operation and cost considerations, in many cases, semiconductor lasers are used for reproduction light. On the other hand, for exposure of a hologram, it is difficult to use semiconductor lasers from the viewpoint of coherence performance and light intensity. Therefore, since the light source is different between the time of reproduction and the time of exposure, the wavelength is also different between the time of reproduction and the time of exposure in many cases.

[0156] <Cause 2: Deformation of the material before and after exposure>

[0157] In many cases, photopolymers are used as hologram materials. In photopolymers, since the diffraction grating is formed by photopolymerization, in many cases, material deformation (contraction) is involved in exposure. Therefore, even if exposure can be performed at the same wavelength as when reproducing, the information of the interference fringes at the time of exposure cannot be accurately reflected on the diffraction grating in the hologram material because the material is deformed after exposure.

[0158] Since the deflection HOE is caused by interference of two plane waves, even when the wavelength at the time of exposure is different from the wavelength at the time of reproduction and material deformation occurs, an ideal HOE can be produced in which the reproduction light incident at the incident angle θi is diffracted at the diffraction angle θc by adjusting the angle at the time of exposure (slightly deviating from θi and θc).

[0159] On the other hand, for a light-concentrating HOE, it is difficult to form interference fringes that satisfy the diffraction condition at all points in the plane at the time of reproduction by adjusting the angle at the time of exposure. However, if the exposure wavelength can be changed relative to the reproduction wavelength by material deformation (in the case of material shrinkage, a longer wavelength is selected due to material shrinkage), a substantially ideal HOE can be produced.

[0160] (1) Calculation of the conditions under which part of the incident light is diffracted by the focusing HOE

[0161] Parameters of the optical system and materials in the second example are shown in the following Tables 1 and 2. In Table 1, the reproduction wavelength and the exposure wavelength are described. In Table 2, the physical property values ​​of the hologram material are described.

[0162] [Table 1]

[0163]

[0164] [Table 2]

[0165]

[0166] Fig. 18 is a schematic diagram showing the optical system during exposure of the focusing HOE. Fig. 19 is a schematic diagram showing the optical system during reproduction of the focusing HOE. For the focusing HOE, as shown in Fig. 19, the angles of the reference light (plane wave) and the signal light (spherical wave) at the time of exposure are adjusted so that the reproduction light incident at the connection angle θc at the time of reproduction is diffracted at a diffraction angle of 0 degrees (a direction perpendicular to the plane) at the center part of the HOE (a point on the optical axis of the lens light at the time of exposure).

[0167] When the exposure angle is determined in this way, the diffraction grating at any point on the focusing HOE after exposure can be calculated. For the diffraction grating calculated in this way, through step 2) and the subsequent steps described in "(1) Calculation of the conditions under which part of the incident light is diffracted by the focusing HOE" in the first example, the field of view direction (angle) when the diffraction wavelength coincides with the reproduction wavelength can be calculated.

[0168] When a diffraction grating is formed on a holographic material as in the second example, the exposure wavelength is usually selected to be longer than the reproduction wavelength in consideration of the shrinkage of the material after exposure. However, if the connection angle is too small, the interval between the diffraction gratings forming the focusing HOE becomes too narrow, and as described above, it is difficult to adjust the angle between the reference light (plane wave) and the signal light (spherical wave) during exposure so that the diffraction angle of the central part of the HOE (the point on the optical axis of the lens light during exposure) is 0 degrees (in the direction perpendicular to the plane). In particular, if the connection angle is 30 degrees or less, the diffraction condition of the central part cannot satisfy the optical parameters in the second example. In order to avoid this, it is preferable to set the connection angle to be 30 degrees or more.

[0169] 20 and 21 show calculation results of the viewing direction under this condition, in which the reproduced light of R / G / B is diffracted in the diffraction grating of R / G / B for the incident angle θi and the connection angle θc.

[0170] FIG20 shows the field of view directions in which the diffraction grating of each color diffracts the reproduction light of the same color, where (A) corresponds to red, (B) corresponds to green, and (C) corresponds to blue. Due to the contraction of the material, as in the first example, although the field of view direction does not completely coincide with the incident direction in any case, diffraction occurs under the condition that the field of view direction is close to the incident direction. Therefore, in order not to generate dark lines and discolored lines within ±10 degrees of the field of view as in the first example, it is sufficient to set the incident angle to 10 degrees or more for the phenomenon that the diffraction gratings of the corresponding colors diffract the reproduction light of the same color.

[0171] FIG. 21 shows the field of view directions in which the diffraction grating of each color diffracts the reproduction light of other colors, wherein (A) corresponds to the case where the red diffraction grating diffracts the green reproduction light, (B) corresponds to the case where the red diffraction grating diffracts the blue reproduction light, and (C) corresponds to the case where the green diffraction grating diffracts the blue reproduction light. In FIG. 21 , the field of view region within ±10 degrees is shown as the field of view region 401. The dividing line 402 in (B) and the dividing line 403 in (C) indicate the combination of the incident angle and the connection angle, and all the field of view regions 401 shown in (A) to (C) of FIG. 21 can be avoided. By the combination of the incident angle and the connection angle surrounded by the dividing lines 402 and 403, in all the cases of (A) to (C) of FIG. 21, dark lines and discolored lines within ±10 degrees in the field of view direction can be avoided.

[0172] (2) Calculate the conditions under which part of the diffracted light from the focusing HOE is diffracted by the deflected HOE

[0173] As described above, for the deflection HOE, the angle at the time of exposure is adjusted so that the reproduction wavelength becomes the diffraction wavelength at each incident angle and connection angle. If the exposure angle is adjusted to such an extent that the exposure wavelength is different from the reproduction wavelength, and even if the material shrinks, an ideal HOE can be generated so that a portion of the diffracted light from the focusing HOE is diffracted by the deflection HOE under the same conditions as in the first example.

[0174] As shown in Fig. 15, in the case where the diffraction gratings of the respective colors diffract the reproduced light of the same color, (A) (positive side, incident light side) shows the diffraction in any R / G / B when the viewing direction coincides with the incident direction, and (B) (negative side, opposite side of the incident light) shows the diffraction in any R / G / B when the viewing direction coincides with the connection angle direction. Therefore, if the incident angle is set to 10 degrees or more and the connection angle is set to 30 degrees or more, dark lines and discolored lines within ±10 degrees in the viewing direction can be avoided.

[0175] Next, the case where the diffraction grating of each color diffracts the reproduced light of other colors will be considered. In the field of view direction, FIG. 22 is similar to FIG. 16 showing the case where the blue diffraction grating diffracts the green reproduced light, and FIG. 23 is similar to FIG. 17 showing the case where the green diffraction grating diffracts the red reproduced light. In FIGS. 22 and 23, (A) corresponds to the positive side (the incident light side), and (B) corresponds to the negative side (the side opposite to the incident light). In the area surrounded by the separation lines 402 and 403, when the condition that part of the incident light is diffracted by the focusing HOE is calculated in (1) above, dark lines and discolored lines within ±10 degrees in the field of view direction can be avoided. In addition, in FIGS. 22 and 23, the field of view area within ±10 degrees is shown as field of view area 501.

[0176] In the region where the incident angle θi is small, the allowable range of (1) above (region surrounded by the dividing line 403) is included in the allowable range of (2) above. On the other hand, in the region where the incident angle θi is large, in the case of FIG. 22 (blue diffraction grating → green reproduction light diffraction), the allowable range in (2) above is wider, but in the case of FIG. 23 (green diffraction grating → red reproduction light diffraction), the range of the incident angle θi and the connection angle θc allowed under this condition is narrower. However, the region 502 shown in FIG. 23 can avoid the field of view region 501 shown in FIGS. 22 and 23. As a result, in the region 502, the dark lines and discolored lines within ±10 degrees in the field of view direction in both (1) above (the case where part of the incident light is diffracted by the focusing HOE) and (2) above (the case where part of the diffracted light from the focusing HOE is diffracted by the deflected HOE) can be avoided.

[0177] (3) Allowable range of the incident angle θi and the connection angle θc in the second example

[0178] In the second example, a combination of the incident angle θi and the connection angle θc such that dark lines and discolored lines due to the above factors (1) and (2) do not appear within ±10 degrees of the field of view satisfies the following condition 1a or 2.

[0179] (Condition 1a)

[0180] 10 degrees ≤ incident angle θi ≤ 90 degrees, 30 degrees ≤ connection angle θc ≤ 90 degrees, and 6×incident angle θi+connection angle θc ≤ 210 degrees,

[0181] (Condition 2)

[0182] 70 degrees ≤ incident angle θi ≤ 90 degrees, 70 degrees ≤ connection angle θc ≤ 90 degrees

[0183] The above condition 1a corresponds to the region surrounded by the dividing line 403 shown in Fig. 23 (region where the incident angle θi is small). The above condition 2 corresponds to the region 501 shown in Fig. 23 (region where the incident angle θi is large).

[0184] 1-3-3. Third Example

[0185] As a third example, the polarization dependence in the case where part of the incident light is diffracted by a focusing HOE will be described.

[0186] As described in the first and second examples, the inventors have discovered that there is polarization correlation in the dark lines and discolored lines where part of the incident light is diffracted by the focusing HOE. FIG. 24 shows the transmission spectral characteristics of light incident at an incident angle of 35 degrees onto the central portion of a green focusing HOE exposed at a connection angle of 50 degrees. It can be seen from the graph shown on the right side of FIG. 24 that, although the diffraction conditions are in the blue region, the decrease in the amount of transmitted light is different between p-polarized light and s-polarized light, and the decrease in p-polarized light is smaller. This indicates that selecting p-polarized light can reduce the degree of dark lines and discolored lines.

[0187] 2. Second Embodiment (Display Device)

[0188] The present technical content also provides a display device, including the image display device described in the above "1. First embodiment (image display device)" and an imaging device that emits incident light. The image display device is as described in the above "1. First embodiment (image display device)", and the description also applies to this embodiment.

[0189] Specifically, the display device according to the present embodiment is a retinal projection display device that displays an image by projecting a light beam (image) onto the retina of a user. In the display device according to the present embodiment, the imaging device may be separated from the image display device. For example, the imaging device may be arranged away from the image display device.

[0190] FIG25 is a schematic diagram showing an example of a display device 1 according to the present embodiment. As shown in FIG25 , the display device 1 includes an image display device 20 and an imaging device 10. The image display device 20 includes a first reflective volume hologram element and a second reflective volume hologram element that form a transmission type diffraction element 21 as a whole. The diffraction element 21 is set in front of the eyes (two eyes or one eye) 3 of the user 2 through the instrument 22. The instrument 22 is, for example, glasses worn on the head of the user 2. The imaging device 10 emits incident light to the diffraction element 21. In other words, the incident light is video display light. That is, the imaging device 10 projects the video display light to the diffraction element 21. The diffraction element 21 diffracts the video display light so that the video display light reaches the retina of the user 2. Therefore, the user 2 of the display device 1 can see the video 4 (still image or moving image) formed by the video display light. In addition, the diffraction element 21 transmits light from the space in front of the instrument 22 (in the direction of the line of sight of the user 2) to reach the eyes of the user 2. Therefore, the user 2 recognizes the video 4 as a video existing in the space.

[0191] The imaging device 10 includes at least one projection optical system. The video display light projected from the projection optical system may be light irradiated by an LED or a CRT. The video display light may be, for example, laser light.

[0192] The projection optical system is configured so that the video display light can be projected toward the diffraction element 21. Those skilled in the art can appropriately select the type of projection optical system used in the present technical content according to, for example, product concepts and the like.

[0193] According to one embodiment of the present technology, the projection optical system may be configured to project video display light to both eyes through a magnifying optical system. The magnifying optical system is an optical system used in, for example, a microscope, a telescope, etc. According to another embodiment of the present technology, the projection optical system may be configured to converge the video display light near the pupil and then emit it to the retina.

[0194] For example, the imaging device 10 may be a portable device such as a smartphone, a mobile phone, or a watch-type terminal. By adopting such a portable device as the imaging device 10 in the display device 1 of the present technical content, the video projection of the present technical content can be performed by a small or ultra-small mobile device.

[0195] FIG26 shows an example of a state in which a user uses a display device of the present technical content including an imaging device, i.e., a smart phone. Glasses 850 are worn on the user's head, and a diffraction element 851 of the present technical content is provided in the glasses 850. In addition, for example, the user carries a smart phone 810 in his hand. Video display light is projected from a projection port 812 of the smart phone 810 toward the diffraction element 851. The video display light is diffracted by the diffraction element 851 and reaches both eyes of the user. Therefore, the user recognizes a video superimposed on an external landscape.

[0196] In addition, the optical characteristics of the diffraction element 851 may be such that it acts as a lens for light within the wavelength range of the video display light and transmits light with wavelengths outside the wavelength range. Therefore, the image of the video display light is superimposed on the external landscape.

[0197] FIG27 shows an example of a display device of the present technical content including an imaging device, i.e., a watch-type terminal. The user wears contact lenses 870 on both eyes. The contact lenses 870 include the diffraction element of the present technical content. In addition, the user wears a watch-type terminal 830, for example, on the wrist. Video display light is projected from the watch-type terminal 830 toward the diffraction element in the contact lens 870. The video display light is diffracted by the diffraction element in the contact lens 870. The user can view a virtual image (e.g., a virtual screen S shown in FIG27 ) through the contact lenses.

[0198] The present technical content can also adopt the following configurations. [1]

[0200] The first reflective volume hologram element and the second reflective volume hologram element as a whole form a transmission type diffraction element, wherein

[0201] The first reflective volume hologram element and the second reflective volume hologram element satisfy the Bragg condition for incident light of three colors: red, green and blue.

[0202] The first reflective volume hologram element diffracts the incident light incident at an incident angle θi at a connection angle θc and deflects the incident light to the second reflective volume hologram element.

[0203] The second reflective volume hologram element converges the deflected incident light, and

[0204] The incident angle θi and the connection angle θc satisfy the following conditions 1 or 2:

[0205] (Condition 1)

[0206] 10 degrees ≤ incident angle θi ≤ 90 degrees, 10 degrees ≤ connection angle θc ≤ 90 degrees, and 4×incident angle θi + connection angle θc ≤ 170 degrees,

[0207] (Condition 2)

[0208] 70 degrees ≤ incident angle θi ≤ 90 degrees, and 70 degrees ≤ connection angle θc ≤ 90 degrees. [2]

[0210] The image display device according to [1], wherein the incident angle θi and the connection angle θc satisfy the following condition 1a or condition 2:

[0211] (Condition 1a)

[0212] 10 degrees ≤ incident angle θi ≤ 90 degrees, 30 degrees ≤ connection angle θc ≤ 90 degrees, and 6×incident angle θi+connection angle θc ≤ 210 degrees,

[0213] (Condition 2)

[0214] 70 degrees ≤ incident angle θi ≤ 90 degrees, and 70 degrees ≤ connection angle θc ≤ 90 degrees. [3]

[0216] The image display device according to [1] or [2], wherein the beam incident surface of the first reflective volume hologram element and the beam incident surface of the second reflective volume hologram element are substantially parallel and face each other. [4]

[0218] The image display device according to any one of [1] to [3], wherein the diffraction angle of the central portion of the second reflective volume hologram element is approximately 0 degree. [5]

[0220] An image display device according to any one of [1] to [4], wherein the incident light incident on the first reflective volume hologram element is p-polarized light. [6]

[0222] The image display device according to any one of [1] to [5], wherein the incident light is emitted from an imaging device separate from the image display device. [7]

[0224] A display device, comprising:

[0225] An image display device, wherein

[0226] The image display device includes a first reflective volume hologram element and a second reflective volume hologram element which form a transmission type diffraction element as a whole.

[0227] The first reflective volume hologram element and the second reflective volume hologram element satisfy the Bragg condition for incident light of three colors: red, green and blue.

[0228] The first reflective volume hologram element diffracts the incident light incident at an incident angle θi at a connection angle θc and deflects the incident light to the second reflective volume hologram element.

[0229] The second reflective volume hologram element converges the deflected incident light, and

[0230] The incident angle θi and the connection angle θc satisfy the following condition 1 or condition 2; and

[0231] an imaging device, the imaging device emitting the incident light,

[0232] (Condition 1)

[0233] 10 degrees ≤ incident angle θi ≤ 90 degrees, 10 degrees ≤ connection angle θc ≤ 90 degrees, and 4×incident angle θi + connection angle θc ≤ 170 degrees,

[0234] (Condition 2)

[0235] 70 degrees ≤ incident angle θi ≤ 90 degrees, and 70 degrees ≤ connection angle θc ≤ 90 degrees.

[0236] Reference numerals

[0237] 1 Display device

[0238] 2 Users

[0239] 3 Eyes

[0240] 4 Videos

[0241] 10 Imaging device

[0242] 20 Image display device

[0243] 21 Diffractive element

[0244] 22 Instruments

[0245] 101 Polarization HOE

[0246] 102 Focus HOE

Claims

1. An image display device, comprising: The first reflective volume hologram element and the second reflective volume hologram element as a whole form a transmission type diffraction element, wherein The first reflective volume hologram element and the second reflective volume hologram element satisfy the Bragg condition for incident light of three colors: red, green and blue. The first reflective volume hologram element diffracts the incident light incident at an incident angle θi at a connection angle θc and deflects the incident light to the second reflective volume hologram element. The second reflective volume hologram element converges the deflected incident light, and The incident angle θi and the connection angle θc satisfy the following conditions 1 or 2: (Condition 1) 10 degrees ≤ incident angle θi ≤ 90 degrees, 10 degrees ≤ connection angle θc ≤ 90 degrees, and 4×incident angle θi + connection angle θc ≤ 170 degrees, (Condition 2) 70 degrees ≤ incident angle θi ≤ 90 degrees, and 70 degrees ≤ connection angle θc ≤ 90 degrees.

2. The image display device according to claim 1, wherein the incident angle θi and the connection angle θc satisfy the following condition 1a or condition 2: (Condition 1a) 10 degrees ≤ incident angle θi ≤ 90 degrees, 30 degrees ≤ connection angle θc ≤ 90 degrees, and 6×incident angle θi+connection angle θc ≤ 210 degrees, (Condition 2) 70 degrees ≤ incident angle θi ≤ 90 degrees, and 70 degrees ≤ connection angle θc ≤ 90 degrees.

3. The image display device according to claim 1, wherein a beam incident surface of the first reflective volume hologram element and a beam incident surface of the second reflective volume hologram element are substantially parallel and face each other.

4. The image display device according to claim 1, wherein a diffraction angle of a central portion of said second reflective volume hologram element is approximately 0 degree.

5. The image display device according to claim 1, wherein the incident light incident on the first reflective volume hologram element is p-polarized light. 6 . The image display device according to claim 1 , wherein the incident light is emitted from an imaging device separate from the image display device.

7. A display device, comprising: An image display device, wherein The image display device includes a first reflective volume hologram element and a second reflective volume hologram element which form a transmission type diffraction element as a whole. The first reflective volume hologram element and the second reflective volume hologram element satisfy the Bragg condition for incident light of three colors: red, green and blue. The first reflective volume hologram element diffracts the incident light incident at an incident angle θi at a connection angle θc and deflects the incident light to the second reflective volume hologram element. The second reflective volume hologram element converges the deflected incident light, and The incident angle θi and the connection angle θc satisfy the following condition 1 or condition 2; as well as an imaging device, the imaging device emitting the incident light, (Condition 1) 10 degrees ≤ incident angle θi ≤ 90 degrees, 10 degrees ≤ connection angle θc ≤ 90 degrees, and 4×incident angle θi + connection angle θc ≤ 170 degrees, (Condition 2) 70 degrees ≤ incident angle θi ≤ 90 degrees, and 70 degrees ≤ connection angle θc ≤ 90 degrees.

Images