Backlight containing formed birefringence reflective polarizer

1. A backlight unit comprising in order:

(1) a light source;

(2) a light guide plate (LGP) having an incident face toward the light source and having a refractive index n LGP ;

(3) a reflective polarizer having formed birefringence in optical contact with the LGP including a layer having:

(a) an elongated non-conductive first material with refractive index n 1 ;

(b) an elongated non-conductive second material with a refractive index n 2 different by at least 0.2 from that of to first material;

 in which the first material and the second materials are aligned in a direction generally perpendicular to the incident face of the LGP; wherein:

(i) the cross-sectional dimensions of the first and second materials, in a plane parallel to the light incident face of the LGP, are smaller tan 100 nm in their width dimensions; and

(ii) the parameters of the reflective polarizer are selected to provide R 0 >0.8 for one polarization state and T 90 >0.8 for the orthogonal polarization state, for light of wavelength of 550 nm, for least one reflective polarizer angle of light incidence θ a , wherein the parameters selected include pitch, thickness, cross-sectional width, n 1 , n 2 , n LGP , location of reflective polarizer, and fill factor.

2. The backlight unit of claim 1 wherein the reflective polarizer has a thickness d that is less than 5 microns.

3. The backlight unit of claim 1 wherein the reflective polarizer has a thickness d that is less than 1 micron.

4. The backlight unit of claim 1 wherein the light guide plate is tapered.

5. The backlight unit of claim 4 further comprising a light redirecting film.

6. The backlight unit of claim 1 wherein the light guide plate is non-tapered.

7. The backlight unit of claim 1 wherein the reflective polarizer is sandwiched between the light guide plate and a layer of transparent substrate.

8. The backlight unit of claim 1 wherein the reflective polarizer is disposed closer to the top of the light guide plate than to the bottom of the light guide plate.

9. The backlight unit of claim 5 further comprising a light extraction article on the top face of the light guide plate.

10. The backlight unit of claim 1 wherein the reflective polarizer is disposed closer to the bottom of the light guide plate than to the top of the light guide plate.

11. The backlight unit of claim 10 further comprising a light extraction article on the bottom face of the light guide plate.

12. The backlight unit of claim 1 wherein the light guide plate is fabricated from a material taken from the group consisting of PMMA and polycarbonate.

13. The backlight unit of claim 1 wherein the first material is air.

14. The backlight unit of claim 1 wherein the first material or the second material is birefringent.

15. A backlight unit comprising in order:

(1) a light source;

(2) a light guide plate (LGP) having an incident face toward the light source and having a refractive index n LGP ;

(3) a reflective polarizer having formed birefringence in optical contact with the LGP including a layer having:

(a) an elongated non-conductive first material with refractive index n 1 ;

(b) an elongated non-conductive second material with a refractive index n 2 different by at least 0.2 from that of the first material;

 in which the first material and the second materials are aligned in a direction generally perpendicular to the incident face of the LGP; wherein:

(i) the cross-sectional dimensions of the first and second materials, in a plane parallel to the light incident face of the LGP, are smaller than 100 nm in their width dimensions; and

(ii) the parameters of the reflective polarizer are selected to provide R 0 >0.8 for one polarization state and T 90 >0.8 for the orthogonal polarization state, for light of wavelength of 550 nm, for least one reflective polarizer angle of light incidence θ a , wherein the parameters selected in part (ii) satisfy the requirements over at least 20° for θ a .

16. A backlight unit comprising in order:

(1) a light source;

(2) a light guide plate (LGP) having an incident face toward the light source and having a refractive index n LGP ;

(3) a reflective polarizer having formed birefringence in optical contact with the LGP including a layer having:

(a) an elongated non-conductive first material with refractive index n 1 ;

(b) an elongated non-conductive second material with a refractive index n 2 different by at least 0.2 from that of the first material;

 in which the first material and the second materials are aligned in a direction generally perpendicular to the incident face of the LGP; wherein:

(i) the cross-sectional dimensions of the first and second materials, in a plane parallel to the light incident face of the LGP, are smaller than 100 nm in their width dimensions; and

(ii) the parameters of the reflective polarizer are selected to provide R 0 >0.8 for one polarization state and T 90 >0.8 for the orthogonal polarization state, for light of wavelength of 550 nm, for least one reflective polarizer angle of light incidence at an angle between

90

0

-

sin

-

1

⁡

(

1

n

LGP

)

 and 89 degrees.

17. A backlight unit comprising in order:

(1) a light source;

(2) a light guide plate (LGP) having an incident face toward the light source and having a refractive index n LGP ;

(3) a reflective polarizer having formed birefringence in optical contact with the LGP including a layer having:

(a) an elongated non-conductive first material with refractive index n 1 ;

(b) an elongated non-conductive second material with a refractive index n 2 different by at least 0.2 from that of the first material;

 in which the first material and the second materials are aligned in a direction generally perpendicular to the incident face of the LGP; wherein:

(i) the cross-sectional dimensions of the first and second materials, in a plane parallel to the light incident face of the LGP, are smaller than 100 nm in their width dimensions; and

(ii) the parameters of the reflective polarizer are selected to provide R 0 >0.8 for one polarization state and T 90 >0.8 for the orthogonal polarization state, for light of wavelength of 550 nm, for least one reflective polarizer angle of light incidence θ a , wherein T 0 for light having the first polarization axis substantially parallel to the incident face of the light guide plate exceeds 0.88.

18. A backlight unit comprising in order:

(1) a light source;

(2) a light guide plate (LGP) having an incident face toward the light source and having a refractive index n LGP ;

(3) a reflective polarizer having formed birefringence in optical contact with the LGP including a layer having:

(a) an elongated non-conductive first material with refractive index n 1 ;

(b) an elongated non-conductive second material with a refractive index n 2 different by at least 0.2 from that of the first material;

 in which the first material and the second materials are aligned in a direction generally perpendicular to the incident face of the LGP; wherein:

(i) the cross-sectional dimensions of the first and second materials, in a plane parallel to the light incident face of the LGP, are smaller than 100 nm in their width dimensions; and

(ii) the parameters of the reflective polarizer are selected to provide R 0 >0.8 for one polarization state and T 90 >0.8 for the orthogonal polarization state, for light of wavelength of 550 nm, for least one reflective polarizer angle of light incidence θ a , wherein R 90 for light having a second polarization axis substantially perpendicular to the first polarization axis exceeds 0.88.

19. A backlight unit comprising in order:

(1) a light source;

(2) a light guide plate (LGP) having an incident face toward the light source and having a refractive index n LGP ;

(3) a reflective polarizer having formed birefringence in optical contact with the LGP including a layer having:

(a) an elongated non-conductive first material with refractive index n 1 ;

(b) an elongated non-conductive second material with a refractive index n 2 different by at least 0.2 from that of the first material;

 in which the first material and the second materials are aligned in a direction generally perpendicular to the incident face of the LGP; wherein:

(i) the cross-sectional dimensions of the first and second materials, in a plane parallel to the light incident face of the LGP, are smaller than 100 nm in their width dimensions; and

(ii) the parameters of the reflective polarizer are selected to provide R 0 >0.8 for one polarization state and T 90 >0.8 for the orthogonal polarization state, for light of wavelength of 550 nm, for least one reflective polarizer angle of light incidence θ a , wherein the ratio of the cross-sectional dimension of the first material to the pitch P, wherein the pitch P equals the sum of the cross-sectional dimension of the first material plus the cross-sectional dimension of the second material of the reflective polarizer, is in the range between 0.2 and 0.8 micron.

20. A backlight unit comprising in order:

(1) a light source;

(2) a light guide plate (LGP) having an incident face toward the light source and having a refractive index n LGP ;

(3) a reflective polarizer having formed birefringence in optical contact with the LGP including a layer having:

(a) an elongated non-conductive first material with refractive index n 1 ;

(b) an elongated non-conductive second material with a refractive index n 2 different by at least 0.2 from that of the first material;

 in which the first material and the second materials are aligned in a direction generally perpendicular to the incident face of the LGP; wherein:

(i) the cross-sectional dimensions of the first and second materials, in a plane parallel to the light incident face of the LGP, are smaller than 100 nm in their width dimensions; and

(ii) the parameters of the reflective polarizer are selected to provide R 0 >0.8 for one polarization state and T 90 >0.8 for the orthogonal polarization state, for light of wavelength of 550 nm, for least one reflective polarizer angle of light incidence θ a , wherein the reflective polarizer provides both the transmission and the reflection exceeding 80% for all light incident to the reflective polarizer surface at an angle between

90

0

-

sin

-

1

⁡

(

1

n

LGP

)

 and 89 degrees.

21. A backlight unit comprising in order:

(1) a light source;

(2) a light guide plate (LGP) having an incident face toward the light source and having a refractive index n LGP ;

(3) a reflective polarizer having formed birefringence in optical contact with the LGP including a layer having:

(a) an elongated non-conductive first material with refractive index n 1 ;

(b) an elongated non-conductive second material with a refractive index n 2 different by at least 0.2 from that of the first material;

 in which the first material and the second materials are aligned in a direction generally perpendicular to the incident face of the LGP; wherein:

(i) the cross-sectional dimensions of the first and second materials, in a plane parallel to the light incident face of the LGP, are smaller than 100 nm in their width dimensions; and

(ii) the parameters of the reflective polarizer are selected to provide R 0 >0.8 for one polarization state and T 90 >0.8 for the orthogonal polarization state, for light of wavelength of 550 nm, for least one reflective polarizer angle of light incidence θ a , wherein the first and second materials are aligned in alternating channels running in a direction generally perpendicular to the incident face of the light guide plate and having a pitch less than 150 nm, the reflective polarizer layer providing both transmission of a first polarization state and reflection of the second orthogonal polarization state for some light incident to the reflective polarizer surface at an angle between

90

0

-

sin

-

1

⁡

(

1

n

LGP

)

 and 89 degrees, both the transmission of the first polarization state and the reflection of the second polarization state exceeding 80% for light at the wavelength of 550 nm, and the first polarization axis being substantially parallel to the incident face of the light guide plate.