IMAGE DISPLAY APPARATUS

• US 20090147362A1
• Filed: 12/09/2008
• Published: 06/11/2009
• Est. Priority Date: 12/11/2007
• Status: Active Grant

• Current Assignee: Canon Kabushiki Kaisha (Canon Inc.)
• Original Assignee: Canon Kabushiki Kaisha (Canon Inc.)
• Inventors: Saito, Kenichi
• Granted Patent: US 8,169,704 B2
• Time in Patent Office: Days
• US Class Current: 359/574
• CPC Class Codes: G02B 2027/0116 comprising devices for correcting chromatic aberration
• CPC Class Codes: G02B 27/0037 with diffracting elements G02B27/0056 takes precedence; holographic optical elements G02B5/32; zone systems G02B5/1876
• CPC Class Codes: G02B 27/0101 characterised by optical features G02B27/0172 takes precedence
• CPC Class Codes: G02B 27/4211 correcting chromatic aberrations G02B27/0056, G02B27/4222, G02B27/4227 take precedence
• CPC Class Codes: G02B 27/4277 being separated by an air space
• CPC Class Codes: G02B 5/18 Diffraction gratings holographic optical elements G02B5/32, G03H; integrally combined with optical fibres G02B6/02057; for coupling light guides G02B6/34; integrally combined with optical integrated light guides G02B6/12; grating systems G02B27/44
• CPC Class Codes: G02B 5/1876 Diffractive Fresnel lenses; Zone plates; Kinoforms G02B5/1842, G02B5/1847 take precedence; optical systems having diffractive correction means G02B27/0037; Fresnel lenses operating by refraction G02B3/08

Abstract

The image display apparatus includes an image-forming element, an optical system guiding light from the image-forming element to an exit pupil, and a diffractive optical element disposed between the image-forming element and the optical system or between the optical system and the exit pupil. The diffractive optical element includes plural diffraction grating portions formed of mutually different materials. Each of the diffraction grating portions includes plural grating rings each having a grating surface and a grating side surface. In each of the grating rings, the grating side surface is inclined oppositely to the grating surface with respect to a normal to an enveloping surface passing through apexes of the plural grating rings. The diffractive optical element satisfies the following conditions at least when k=k_E: θ_d(j, k)=sin⁻¹ [{n_i·sin θ_i(j, k)−m(j, k)·λ/P(j, k)}/n_d]≦θ_i(j, k), M(k)=Σ{m(j, k)}=const, and θ_d(j, k)≦θ_i(j, k).

Claims

1. An image display apparatus comprising:

an image-forming element configured to form an original image;

an optical system configured to guide light from the image-forming element to an exit pupil; and

a diffractive optical element disposed between the image-forming element and the optical system or between the optical system and the exit pupil,

wherein the diffractive optical element includes plural diffraction grating portions formed of mutually different materials, the plural diffraction grating portions being disposed with a gap therebetween,

wherein each of the diffraction grating portions includes plural grating rings each having a grating surface and a grating side surface,

wherein, in each of the grating rings, the grating side surface is inclined oppositely to the grating surface with respect to a normal to an enveloping surface passing through apexes of the plural grating rings, and

wherein the diffractive optical element satisfies the following conditions for a k-th grating ring of the plural grating rings in a j-th diffraction grating portion of the plural diffraction grating portions, at least when k=k_E;

${\mathrm{\theta <br><br>}}_d<br><br>\left(j,k\right)={\sin }^{-1}<br><br>\left[\left\{n_i·<br><br>\sin <br><br><br><br>{\mathrm{\theta <br><br>}}_i<br><br>\left(j,k\right)-m<br><br>\left(j,k\right)·<br><br>\mathrm{\lambda <br><br>}/P<br><br>\left(j,k\right)\right\}/n_d\right]\le <br><br>{\mathrm{\theta <br><br>}}_i<br><br>\left(j,k\right)$ $M<br><br>\left(k\right)=\underset{j=1}{\overset{s}{\sum <br><br>}}<br><br>\left\{m<br><br>\left(j,k\right)\right\}=\mathrm{const}.<br><br>{\mathrm{\theta <br><br>}}_d<br><br>\left(j,k\right)\le <br><br>\mathrm{\theta <br><br>}\le <br><br>{\mathrm{\theta <br><br>}}_i<br><br>\left(j,k\right)$

where;

λ

represents a design wavelength of the diffractive optical element;

θ

_i(j, k) represents an angle formed by a light ray passing through the k-th grating ring in the j-th diffraction grating portion and the exit pupil with the normal to the enveloping surface, |θ

_i(j, k)| being smaller than a maximum view angle of the optical system;

θ

_d(j, k) represents a diffraction angle of light of a design diffraction order at the k-th grating ring in the j-th diffraction grating portion;

m(j, k) represents the design diffraction order of the k-th grating ring in the j-th diffraction grating portion;

P(j, k) represents a pitch between the k-th grating ring and a (k−

1)-th grating ring;

k_E represents a number of the grating ring where the pitch is minimum or where θ

_i(j, k) is maximum;

M(k) represents a diffraction order of the diffractive optical element;

n_i and n_d respectively represent refractive indexes of an entrance side medium and a diffraction side medium in the j-th diffraction grating portion;

s represents a total number of the plural grating rings in the j-th diffraction grating portion; and

θ

represents an angle which the grating side surface forms with the normal to the enveloping surface.

2. An image display apparatus according to claim 1, wherein the diffractive optical element further satisfies the following condition:

d(j,k)≦

m(j,k)·

λ

/{n_i·

cos θ

_i(j,k)−

n_d·

cos θ

_d(j,k)}

where d(j, k) represents a height of the k-th grating ring in the j-th diffraction grating portion in a direction along the normal.

3. An image display apparatus according to claim 1, wherein θ

_i(j, k) represents an incident angle of a light ray onto the diffractive optical element, the light ray passing through a specific point on an optical axis of a display optical system including the diffractive optical element and the optical system, and the specific point being located farther from the diffractive optical element than an exit pupil of the display optical system.

4. An image display apparatus, comprising:

an image-forming element configured to form an original image;

an optical system configured to guide light from the image-forming element to an exit pupil; and

a diffractive optical element disposed between the image-forming element and the optical system or between the optical system and the exit pupil,

wherein the diffractive optical element includes plural diffraction grating portions formed of mutually different materials, the plural diffraction grating portions being disposed with a gap therebetween,

wherein each of the diffraction grating portions includes plural grating rings each having a grating surface and a grating side surface,

wherein in each of the grating rings, the grating side surface is inclined to a same side as the grating surface with respect to a normal to an enveloping surface passing through apexes of the plural grating rings, and

wherein the diffractive optical element satisfies the following conditions for a k-th grating ring of the plural grating rings in a j-th diffraction grating portion of the plural diffraction grating portions, at least when k=k_E;

${\mathrm{\theta <br><br>}}_d<br><br>\left(j,k\right)={\sin }^{-1}<br><br>\left[\left\{n_i·<br><br>\sin <br><br><br><br>{\mathrm{\theta <br><br>}}_i<br><br>\left(j,k\right)-m<br><br>\left(j,k\right)·<br><br>\mathrm{\lambda <br><br>}/P<br><br>\left(j,k\right)\right\}/n_d\right]\ge <br><br>{\mathrm{\theta <br><br>}}_i<br><br>\left(j,k\right)$ $M<br><br>\left(k\right)=\underset{j=1}{\overset{s}{\sum <br><br>}}<br><br>\left\{m<br><br>\left(j,k\right)\right\}=\mathrm{const}.<br><br>{\mathrm{\theta <br><br>}}_i<br><br>\left(j,k\right)\le <br><br>\mathrm{\theta <br><br>}\le <br><br>{\mathrm{\theta <br><br>}}_d<br><br>\left(j,k\right)$

where;

λ

represents a design wavelength of the diffractive optical element;

θ

_i(j, k) represents an angle formed by a light ray passing through the k-th grating ring in the j-th diffraction grating portion and the exit pupil with the normal to the enveloping surface,

|θ

_i(j, k)| being smaller than a maximum view angle of the optical system;

θ

_d(j, k) represents a diffraction angle of light of a design diffraction order at the k-th grating ring in the j-th diffraction grating portion;

m(j, k) represents the design diffraction order of the k-th grating ring in the j-th diffraction grating portion;

P(j, k) represents a pitch between the k-th grating ring and a (k−

1)-th grating ring;

k_E represents a number of the grating ring where the pitch is minimum or where θ

_i(j, k) is maximum;

M(k) represents a diffraction order of the diffractive optical element;

n_i and n_d respectively represent refractive indexes of an entrance side medium and a diffraction side medium in the j-th diffraction grating portion;

s represents a total number of the plural grating rings in the j-th diffraction grating portion; and

θ

represents an angle which the grating side surface forms with the normal to the enveloping surface.

5. An image display apparatus according to claim 4, wherein the diffractive optical element further satisfies the following condition:

d(j,k)≧

m(j,k)·

λ

/{n_i·

cos θ

_i(j,k)−

n_d·

cos θ

_d(j,k)}

where d(j, k) represents a height of the k-th grating ring in the j-th diffraction grating portion in a direction along the normal.

6. An image display apparatus according to claim 4, wherein θ

_i(j, k) represents an incident angle of a light ray onto the diffractive optical element, the light ray passing through a specific point on an optical axis of a display optical system including the diffractive optical element and the optical system, and the specific point being located farther from the diffractive optical element than an exit pupil of the display optical system.