Super directional light guide film and thin film type back light unit for flat panel display using the same

1. A back light unit comprising:

a light guide film including a light guiding part having a first side and a second side, a light entering part at the first side, a light reflecting part at the second side and the light guiding part between the light entering part and the light reflecting part;

a light radiating part on an upper surface of the light guide film; and

a light source adjacent to the light entering part of the light guide film, the light source providing an expanded light toward the light entering part,

wherein the light entering part permits entry among the expanded light, incident light of the expanded light that satisfies a total reflection condition to propagate from the first side to the second side of the light guiding part,

the light reflecting part that receives the incident light provided from the light guiding part converts the incident light into collimated light and propagates the collimated light to the light guiding part, and

the light radiating part provides back light to a display panel as the collimated light propagates from the second side to the first side of the light guiding part,

wherein the light guide film including the light entering part, the light guiding part and the light reflecting part is a high refractive film,

the light radiating part includes a light radiating pattern that radiates the back light using a first portion of the collimated light and reflects a second portion of the collimate light into the light guiding part, and

the high refractive film has a refractive index greater than the light radiating pattern.

2. The back light unit according to claim 1 , further comprising a reflective pattern at the light reflecting part that collimates the incident light in a first direction, and a reflective surface at the light reflecting part that collimates the incident light in a second direction different from the first direction.

3. The back light unit according to claim 2 , wherein the reflective surface at the light reflecting part has any one of an inclined surface and an inclined arc surface, and has a wedge angle with respect to a surface of the light guiding part.

4. The back light unit according to claim 2 , wherein the reflective pattern includes at least any one of:

a first reflective pattern on the reflective surface; and

a second reflective pattern on an upper surface of the high refractive film, facing the reflective surface.

5. The back light unit according to claim 1 , wherein the light radiating pattern refracts the first portion of the collimated light of which incident angle is less than a total reflective critical angle at an interface between the high refractive film and the light radiating pattern into the light radiating pattern, and reflects the second portion of the collimated light into the high refractive film, and

the first portion of the collimated lights refracted into the light radiating pattern is radiated outside.

6. The back light unit according to claim 1 , wherein the light guide film further comprises a low refractive film attached on an upper surface of the high refractive film, and

the low refractive film has a refractive index lower than the high refractive film and the light radiating pattern.

7. The back light unit according to claim 1 , wherein the light entering part further includes a light absorbing pattern on an upper surface of the entering part that removes a portion of the expanded light of which incident angle is smaller than a critical angle satisfying a total reflection condition.

8. The back light unit according to the claim 1 , wherein the light guide film includes:

a first long side and a second long side which are parallel with each other; and

a first short side at the light entering part and a second short side at the light reflecting part which are parallel with each other and are crossing the first long side and the second long side, and

the light source is disposed along the first short side.

9. The back light unit according to claim 8 , wherein the light source further includes a 3D light source adjacent to any one of the first long side and the second long side.

10. The back light unit according to claim 1 , wherein the light radiating pattern includes any one of a surface grating pattern and a volume grating pattern.

11. A light guide film comprising:

a light guiding part having a first side and a second side;

a light entering part at the first side; and

a light reflecting part at the second side, the light guiding part being between the light entering part and the light reflecting part,

wherein the light entering part permits entry among expanded light, incident light of the expanded light provided from a light source that satisfies a total reflection condition to propagate from the first side to the second side of the light guiding part, and

the light reflecting part that receives the incident light provided from the light guiding part converts the incident light into collimated light and propagates the collimated light to the light guiding part,

wherein the light guide film including the light entering part, the light guiding part and the light reflecting part is a high refractive film,

wherein a light radiating pattern at an upper surface of the high refractive film and configured to radiate back light using a first portion of the collimated light and to reflect a second portion of the collimate light into the light guiding part, and

wherein the high refractive film has a refractive index greater than the light radiating pattern.

12. The light guide film according to claim 11 , further comprising:

a reflective surface at the light reflecting part and configured to collimate the incident light in a first direction; and

a reflective pattern at the light reflecting part and configured to collimate the incident lights in a second direction different from the first direction.

13. The light guide film according to claim 12 , wherein the reflective surface at the light reflecting part has any one of an inclined surface and an inclined arc surface, and has a wedge angle to a surface of the light guiding part.

14. The light guide film according to claim 12 , wherein the reflective pattern includes at least any one of:

a first reflective pattern disposed on the reflective surface; and

a second reflective pattern disposed on an upper surface of the high refractive film, facing the reflective surface.

15. The light guide film according to claim 13 , wherein the light radiating pattern is configured to refract the first portion of the collimated light of which incident angle is less than a total reflective critical angle at an interface between the high refractive film and the light radiating pattern into the light radiating pattern, and

to reflect the second portion of the collimated light into the high refractive film, and

wherein the first portion of the collimated light refracted into the light radiating pattern is radiated outside.

16. The light guide film according to the claim 12 , further comprising a low refractive film attached on an upper surface of the high refractive film,

wherein the low refractive film has a refractive index lower than the high refractive film and the light radiating pattern.

17. The light guide film according to the claim 12 , wherein the light radiating pattern includes any one of a surface grating pattern and a volume grating pattern.

18. The light guide film according to the claim 11 , wherein the light entering part further includes a light absorbing pattern disposed on an upper surface of the light entering part and configured to remove a portion of the expanded light of which incident angle is smaller than a critical angle satisfying a total reflection condition.

19. The light guide film according to the claim 11 , further comprising:

a first long side and a second long side which are parallel with each other; and

a first short side disposed at the light entering part and a second short side disposed at the light reflecting part which are parallel with each other and are crossing with the first long side and the second long side.