Optical device and virtual image display
An optical device includes: a light guide plate receiving, for each of N types of wavelength bands, a plurality of parallel light beams with different incident angles each corresponding to view angles, and guiding the received parallel light beams; a first and a second volume hologram gratings of reflection type having a diffraction configuration which includes N types of interference fringes each corresponding to the N types of wavelength bands, and diffracting/reflecting the parallel light beams. The optical device satisfies for each wavelength band, a relationship of ‘P>L’, where ‘L’ represents a central diffraction wavelength in the first and second volume hologram gratings, defined for a parallel light beam corresponding to a central view angle, and ‘P’ represents a peak wavelength of the parallel light beams.
1. An optical device comprising:
a light source;
a light guide plate configured to receive light, and to guide the received light;
a first deflecting element configured to deflect light entering the light guide plate; and
a second deflecting element configured to deflect light which has been propagated through the light guide plate,
wherein a peak wavelength of the light source is closer to a central diffraction wavelength of the light with a first view angle +θ than to a central diffraction wavelength of the light with a second view angle −θ, θ being an angle relative to a normal to a surface of the light guide plate, and
wherein a first deflected light by the first deflecting element corresponds to the first view angle +θ and a second deflected light by the first deflecting element corresponds to the second view angle −θ, and a first portion of the second deflecting element where the first deflected light is deflected is located farther away from the first deflecting element than a second portion of the second deflecting element where the second deflected light is deflected.
2. The optical device of claim 1 , wherein the light source and the first and second deflecting elements are configured such that a number of times that the first deflected light is reflected in the light guide plate when reaching the second deflecting element is higher than a number of times that the second deflected light is reflected in the light guide plate when reaching the second deflecting element.
3. The optical device of claim 1 , wherein the second deflecting element is thinner than the first deflecting element.
4. The optical device of claim 1 , wherein the light source is a LED device.
5. The optical device of claim 1 , wherein the light source is configured to emit red light.
6. The optical device of claim 1 , wherein the light source is configured to emit light including 635 nm.
7. The optical device of claim 1 , wherein the first deflecting element includes a plurality of laminated hologram layers, each hologram layer corresponding to a different wavelength band.
8. The optical device of claim 7 , wherein pitches of interference fringes in different hologram layers are different from each other.
9. The optical device of claim 8 , wherein in any one of the hologram layers, the interference fringes have the same pitch irrespective of position.