Display apparatus

Claim 2

A display apparatus, comprising: a display unit for emitting light; a first diffraction grating for causing light from said display unit to be diffracted; and a second diffraction grating for causing the light diffracted by said first diffraction grating to be diffracted and directing it toward a pupil of an observer, wherein said apparatus satisfies the following condition; ##EQU2## where l 1 is a distance between said display unit and said first diffraction grating, l 2 is a distance between said first diffraction grating and said second diffraction grating, P 1 is a grating pitch of said first diffraction grating, P 2 is a grating pitch of said second diffraction grating, θ 1 is an incident angle of the light on said first diffraction grating, θ 2 is an exit angle of the light from said first diffraction grating, and θ 3 is an incident angle of the light on said second diffraction grating.

Claim 3

An apparatus according to claim 1, further satisfying a condition θ 1 >θ 2 .

Claim 4

An apparatus according to claim 2, further satisfying a condition of (cos θ 2 /cos θ 1 )≧1.2.

Claim 5

An apparatus according to claim 2, further satisfying a condition of l 2 >l 1 .

Claim 6

An apparatus according to claim 4, wherein said second diffraction grating is composed of a hologram.

Claim 7

An apparatus according to claim 5, wherein said hologram is composed of a material principally consisting of poly (N-vinylcarbazol), dichromic acid gelatin or gum Arabic.

Claim 8

An apparatus according to claim 6, wherein said first diffraction grating is composed of a relief-type diffraction grating.

Claim 9

An apparatus according to claim 7, wherein said relief-type diffraction grating is formed on a rear surface of a transparent substrate.

Claim 10

An apparatus according to claim 8, further satisfying the following condition; P.sub.1 =λ.sub.0 | sin θ.sub.1 -sin θ.sub.2 | P.sub.2 =λ.sub.0 | sin θ.sub.4 -sin θ.sub.3 | where λ 0 is the central wavelength of the light and θ 4 is an exit angle of the light from said second diffraction grating.

Claim 11

A headup display apparatus, comprising: a display unit for emitting light; a first diffraction grating for causing light from said display unit to be diffracted; and a beam combiner having a second diffraction grating for causing the light diffracted by said first diffraction grating to be reflectively diffracted and directing it toward a pupil of an observer; wherein said apparatus satisfies the following condition, ##EQU3## P.sub.1 =λ.sub.0 | sin θ.sub.1 -sin θhd 2| P.sub.2 =λ.sub.0 | sin θ.sub.4 -sin θ.sub.3 | where λ 1 is a distance between said display unit and said first diffraction grating, λ 2 is a distance between said first diffraction grating and said second diffraction grating, P 1 is a grating pitch of said first diffraction grating, P 2 is a grating pitch of said second diffraction grating, θ 1 is an incident angle of the light on said first diffraction grating, θ 2 is an exit angle of the light from said first diffraction grating, θ 3 is an incident angle of the light on said second diffraction grating, θ 4 is an exit angle of the light from said second diffraction grating and λ 0 is the central wave length of the light.

Claim 12

A headup display apparatus, comprising: a display unit for emitting light; a first diffraction grating for causing light from said display unit to be diffracted; and a beam combiner having a second diffraction grating for causing the light diffracted by said first diffraction grating to be reflectively diffracted and directing it toward a pupil of an observer; wherein said apparatus satisfies the following condition, ##EQU3## P.sub.1 =λ.sub.0 | sin θ.sub.1 -sin θhd 2| P.sub.2 =λ.sub.0 | sin θ.sub.4 -sin θ.sub.3 | where λ 1 is a distance between said display unit and said first diffraction grating, λ 2 is a distance between said first diffraction grating and said second diffraction grating, P 1 is a grating pitch of said first diffraction grating, P 2 is a grating pitch of said second diffraction grating, θ 1 is an incident angle of the light on said first diffraction grating, θ 2 is an exit angle of the light from said first diffraction grating, θ 3 is an incident angle of the light on said second diffraction grating, θ 4 is an exit angle of the light from said second diffraction grating and λ 0 is the central wave length of the light.

Claim 13

An apparatus according to claim 10, further satisfying a condition of θ 1 >θ 2 .

Claim 14

An apparatus according to claim 11, further satisfying a condition of (cos θ 2 /cos θ 1 )≧1.2.

Claim 15

An apparatus according to claim 11, further satisfying a condition of l 2 >l 1 .

Claim 16

An apparatus according to claim 13, wherein said second diffraction grating is composed of a hologram.

Claim 17

An apparatus according to claim 14, wherein said hologram is composed of a material principally consisting of poly (N-vinylcarbazol), dichromic acid gelatin or gum Arabic.

Claim 18

An apparatus according to claim 15, wherein said first diffraction grating is composed of a relief-type diffraction grating.

Claim 19

An apparatus according to claim 16, wherein said relief-type diffraction grating is formed on a rear surface of a transparent substrate.