Directional backlight unit, method for manufacturing the same, and 3D image display apparatus having the same
A directional backlight unit is provided, including a light guide plate, a light source, and a grating that is formed on a light-emitting surface of the light guide plate. The grating is configured such that an intensity of one ray of light, of the light irradiated by the light source and diffracted and emitted by the grating, is greater than a sum of intensities of all other rays of light, of the light irradiated by the light source and diffracted and emitted by the grating.
1. A directional backlight unit comprising:
a light guide plate;
a light source that irradiates light to the light guide plate; and
a grating formed on a light-emitting surface of the light guide plate, wherein a shape of the grating is configured such that an intensity of one ray of light, of the light irradiated by the light source and diffracted and emitted by the grating is greater than a sum of intensities of all other rays of light, of the light irradiated by the light source and diffracted and emitted by the grating,
wherein the grating comprises a lower grating formed into the light-emitting surface of the light guide plate, and an upper grating connected to the lower grating, and
wherein the lower grating comprises a plurality of round furrows periodically formed in the light-emitting surface of the light guide plate, each of the plurality of round furrows is spaced apart by a flat area of the light-emitting surface of the light guide plate, and the upper grating comprises a plurality of round ridges alternatingly disposed with the plurality of round furrows, each of the plurality of round ridges is directly contacted to the flat area of the light-emitting surface of the light guide plate and protrudes from the light guide plate.
2. The directional backlight unit of claim 1 , wherein the plurality of round ridges are connected to the plurality of round furrows, such that the plurality of round ridges and the plurality of round furrows together form a sinusoidal wave shape.
3. The directional backlight unit of claim 1 , wherein the light guide plate comprises a thermal resistance material which is transparent with respect to visible light, and the grating comprises a polymer material which is transparent with respect to visible light.
4. The directional backlight unit of claim 1 , wherein a refractive index of the grating is substantially the same as a refractive index of the light guide plate.
5. The directional backlight unit of claim 1 , wherein the grating comprises a sinusoidal wave shape.
6. The directional backlight unit of claim 5 , wherein a refractive index of the grating is substantially the same as a refractive index of the light guide plate.
7. The directional backlight unit of claim 6 , wherein the grating comprises a transparent resin material.
8. The directional backlight unit of claim 1 , wherein, a shape of the grating is configured such that, a square of a first Fourier coefficient of a Fourier transformation performed on the shape of the grating is greater than a sum of squares of remaining Fourier coefficients including a second Fourier coefficient of the Fourier transformation.
9. The directional backlight unit of claim 8 , wherein the shape of the grating is configured such that Fourier coefficients, except the first Fourier coefficient, of the Fourier transformation performed on the shape of the grating, are substantially zero.
10. A 3D image display device comprising:
the directional backlight unit according to claim 1 ; and
a display panel disposed on the light-emitting surface of the directional backlight unit.