Patent ID: 8641258
Filing Date: 2014-02-04
Classification: G02B

Abstract:
1. A light guide panel comprising: a plate-shaped, light-transmissive light guide panel main body having predetermined width, depth, and thickness, and having a first surface on which coherent light is incident, a second surface disposed adjacent to the first surface in a width direction and perpendicular to a thickness direction in which outgoing light based on the coherent light incident on the first surface is extracted, and a third surface disposed parallel with the second surface in a position facing the second surface in the thickness direction, wherein a reflective sub-wavelength diffraction grating is provided on the third surface, the reflective sub-wavelength diffraction grating being composed of a fine periodic structure in which a plurality of projecting sections, formed integrally with the light guide panel main body and elongated in the depth direction, are disposed along the width direction in an array at an interval smaller than the wavelength of the coherent light, and a reflective film covering the fine periodic structure, and only zero-order light and minus first-order light are generated by incidence of the coherent light onto the reflective sub-wavelength diffraction grating, the generated zero-order light entering the second surface at an angle of incidence greater than a critical angle, being totally reflected, and then incident on the reflective sub-wavelength diffraction grating, while on the other hand, the generated minus first-order light enters the second surface at an angle of incidence smaller than the critical angle and is emitted from the second surface, and subsequently, generation of only new zero-order light and minus first-order light as a result of incidence of the zero-order light onto the reflective sub-wavelength diffraction grating, incidence of the generated new zero-order light onto the reflective sub-wavelength diffraction grating after total reflection by the second surface, and emission of the generated new minus first-order light from the second surface are repeated a plurality of times, as a result of each conditional expression expressed by the following expressions (1) to (3) being satisfied: where, λ: wavelength of the light n: refractive index of the light guide panel main body Λ: period of the reflective sub-wavelength diffraction grating θ