Abstract:The application of wire grid polarizers as efficient polarizing beam splitters for visible light is studied. The large differences between the transmissivity for different polarizations are explained qualitatively by using the theory of metallic wave guides. The results of rigorous calculations obtained by using the finite element method are compared with experiments for both classical and conical mount. Furthermore the application of wire-grid polarizers in liquid crystal on silicon display systems is considered.
A polarized backlight for LCD illumination is designed and fabricated in which s-polarized light is extracted owing to selective total internal reflection at microstructures in the anisotropic layer. From the measurement, the contrast ratio in normal viewing direction can be as high as 64. Luminous uniformity of higher than 80% is achieved for polarized backlights. Furthermore, 1.6 gain in efficiency is obtained aiming for high-efficiency LCD illumination.
Abstract—
A new polarized backlight system for liquid‐crystal displays (LCDs) is presented in which one linear polarization is preferentially coupled out by anisotropic scattering. The lightguide consists of a polymeric polarization‐dependent scattering film adhered to a transparent polymeric substrate. By changing the scattering power of the film, the polarized light outcoupling angles can be influenced and optimized to achieve a maximum outcoupling centered along the normal direction. The other linear polarization is mainly trapped in the lightguide and is shown to be recycled to enhance the overall light and/or energy efficiency. With a proper substrate choice, the achieved local contrast exceeds 14 over a 50‐mm range. A collimated light input further enhances the polarized contrast to well over 17.
The efficiency of luminescent solar concentrators could be enhanced by use of wavelength-selective filters, reducing the amount of luminescent light lost. To accomplish this, polarization-independent filters with reflectivity >97% were made by combining layers of cholesteric liquid crystals, either a right- with a left-handed layer, or two right-handed layers with a half-lambda waveplate. Normal cholesteric filters have a reflection bandwidth which is narrower than the spectral and angular range of the luminescent emission. The reflection band is broadened from 80 to 200 nm by employing a pitch gradient in the cholesteric layer. The measured transmission bands compare well with calculations.
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