POLARIZATION CONVERSION OPTICAL SYSTEM OF BACK LIGHT UNIT

PURPOSE: A polarization conversion optical system of a back light unit is provided to reduce electric power consumption and prevent a screen from being degraded. CONSTITUTION: A polarization conversion optical system of a back light unit includes a condensing lens(20,60), a polarization prism(30), a polarization splitting plate(40), and a phase shifter(50). A plurality of condensing lenses are installed as a stacked type to a lamp side and focuses non-polarized beam. The polarization prism is installed on the back side of the condensing lens. The polarization splitting plate is installed on the interface of the each polarization prism. The phase shifter is installed between the polarization splitting plates, and converts the phase of the transverse wave reflected from the polarization splitting plate into 90 degree to convert into a longitudinal wave. The longitudinal wave converted by the phase shifter is reflected by a polarization splitting plate of other polarization prism installed on the low part of the polarization prism and is incident to a light guiding plate(2).