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Slim planar apparatus for converting LED light into collimated polarized light uniformly emitted from its top surface

Tun-Chien Teng and Li-Wei Tseng

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Abstract

This study proposes a slim planar apparatus for converting nonpolarized light from a light-emitting diode (LED) into an ultra-collimated linearly polarized beam uniformly emitted from its top surface. The apparatus was designed based on a folded-bilayer configuration comprising a light-mixing collimation element, polarization conversion element, and polarization-preserving light guide plate (PPLGP) with an overall thickness of 5 mm. Moreover, the apparatus can be extended transversally by connecting multiple light-mixing collimation elements and polarization conversion elements in a side-by-side configuration to share a considerably wider PPLGP, so the apparatus can have theoretically unlimited width. The simulation results indicate that the proposed apparatus is feasible for the maximal backlight modules in 39-inch liquid crystal panels. In the case of an apparatus with a 480 × 80 mm emission area and two 8-lumen LED light sources, the average head-on polarized luminance and spatial uniformity over the emission area was 5000 nit and 83%, respectively; the vertical and transverse angular distributions of the emitting light were only 5° and 10°, respectively. Moreover, the average degree of polarization and energy efficiency of the apparatus were 82% and 72%, respectively. As compared with the high-performance ultra-collimated nonpolarized backlight module proposed in our prior work, not only did the apparatus exhibit outstanding optical performance, but also the highly polarized light emissions actually increased the energy efficiency by 100%.

© 2014 Optical Society of America

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Figures (9)
Fig. 1
Fig. 1 Illustration of the polarization conversion within a single PCU: (a) perspective 3D-structure view of a PCU; (b) perspective view of the PCU; (c) side view of the PCU; (d) top view of the PCU.

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Fig. 2
Fig. 2 Polarization conversion element composed of one pair of connected PCUs: (a) perspective exploded view; (b) top assembling view ; (c) ray path diagram (black: nonpolarized light, blue: original p-wave, green: original s-wave); (d) transversely extending of multiple PC elements.

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Fig. 3
Fig. 3 Light-mixing and collimation element, V-cut CPC: (a) perspective view; (b) top view.

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Fig. 4
Fig. 4 Schematic illustration of optical model of the apparatus: (a) perspective view; (b) side view (not proportionally scaled).

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Fig. 5
Fig. 5 Impact of both the half-angle of incident light and refractive index of the PCU on the coupling efficiency of PC element.

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Fig. 6
Fig. 6 Distributions of the light emitted from the PPLGP: (a) spatial distribution; (b) angular distribution.

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Fig. 7
Fig. 7 Spatial degree of polarization distribution of the light emitted from PPLGP: (a) spatial distribution; (b) spatial distribution along the longitudinal central line.

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Fig. 8
Fig. 8 Angular degree of polarization distribution of the light emitted from PPLGP: (a) angular distribution; (b) angular distribution along the longitudinal and transverse central lines across the intensity peak.

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Fig. 9
Fig. 9 Feasible manufacture and assembling way for the polarization conversion element.

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Tables (2)

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Table 1 Simulation analysis for various apex angles of V-groove microstructures on V-cut CPCs

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Table 2 Energy efficiency for the components of the apparatus

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Equations (3)

Equations on this page are rendered with MathJax. Learn more.

t 1 t 2 = n 2 sin θ 2 n 1 sin θ 1 ,
A 1 A 2 = ( n 2 sin θ 2 ) 2 ( n 1 sin θ 1 ) 2 .
D O P = ( I s − I p ) / ( I s + I p ) × 100 % .
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