We analyze the polarization-preserving property of two conventional edge-lit light guide plates (LGPs) based on scattering dots and refractive microgrooves and find that these two structures almost completely depolarize the incident linearly polarized light. We then propose a new edge-lit LGP based on total internal reflection (TIR). Simulation results show that such a TIR-based LGP can largely preserve the polarization state of the incident linearly polarized light. The polarization efficiency is 77.2%. By incorporating a linearly polarized LED to our proposed LGP, the overall optical gain is 1.54 compared with the backlight system with an unpolarized LED. At on-axis, the luminance is $2.4\times$ higher. Because the output light is concentrated near the surface normal direction, no additional brightness enhancement film is needed. This polarization-preserving LGP enables a polarized or partially polarized LED backlight to be used, which in turn greatly enhances the optical efficiency of a LCD.
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