Abstract: There is provided a beam expander including a first optical element, a second optical element, a composite waveguide including a plurality of waveguide elements, and a dichroic coating provided between the plurality of waveguide elements. The first optical element inputs a collimated incident beam from the outside into the composite waveguide, and the second optical element outputs, from the composite waveguide, collimated incident beam, input to the composite waveguide, wherein the collimated incident beam input into the composite waveguide is divided into multiple wavefronts by the dichroic coating, and the multiple wavefronts are mixed by total internal reflection in the composite waveguide. When the beam expander is used, coherency and collimation of an output beam may be maintained and speckles may be reduced or eliminated while improving the efficiency of an optical system.

Abstract: Provided are an eye-tracking device that may rapidly and accurately track an observer's eye and may be made compact, and a display apparatus including the eye-tracking device. The eye-tracking device includes: a light source configured to emit an illumination light; a light guide plate configured to transmit the illumination light emitted from the light source to an observer's eye and transmit the illumination light reflected from the observer's eye in a direction opposite to a propagation direction of the illumination light emitted from the light source; a photodetector array configured to detect the illumination light reflected from the observer's eye; and a signal processor configured to determine an angle of rotation of the observer's eye based on a two-dimensional (2D) intensity distribution of the illumination light detected by the photodetector array.

Abstract: A beam expander includes first and second optical elements spaced apart from each other, and a light diffuser having an angular aperture that diffuses incident light through the angular aperture, wherein the first optical element in-couples the diffused light such that light exiting the first optical element has a first cross-sectional shape and light having a second cross-sectional shape different from the first cross-sectional shape is incident on the second optical element, and the second optical element out-couples light incident from the first optical element.

Abstract: Provided is a device configured to enlarge an exit pupil area of a visual optical apparatus, the device including a diffraction grating configured to output a plurality of diffracted light beams of a plurality of diffraction orders by diffracting an incident light beam, and a waveguide provided on the diffraction grating and configured to form an exit pupil based on a first diffracted light beam among the plurality of diffracted light beams output from the diffraction grating and to form exit pupil orders based on a second diffracted light beam among the plurality of diffracted light beams output from the diffraction grating.

Abstract: A beam expander includes first and second optical elements spaced apart from each other, and a light diffuser having an angular aperture that diffuses incident light through the angular aperture, wherein the first optical element in-couples the diffused light such that light exiting the first optical element has a first cross-sectional shape and light having a second cross-sectional shape different from the first cross-sectional shape is incident on the second optical element, and the second optical element out-couples light incident from the first optical element.

Abstract: There is provided a beam expander including a first optical element, a second optical element, a composite waveguide including a plurality of waveguide elements, and a dichroic coating provided between the plurality of waveguide elements. The first optical element inputs a collimated incident beam from the outside into the composite waveguide, and the second optical element outputs , from the composite waveguide, collimated incident beam, input to the composite waveguide, wherein the collimated incident beam input into the composite waveguide is divided into multiple wavefronts by the dichroic coating, and the multiple wavefronts are mixed by total internal reflection in the composite waveguide. When the beam expander is used, coherency and collimation of an output beam may be maintained and speckles may be reduced or eliminated while improving the efficiency of an optical system.

Abstract: A beam expander includes first and second optical elements spaced apart from each other, and a light diffuser having an angular aperture that diffuses incident light through the angular aperture, wherein the first optical element in-couples the diffused light such that light exiting the first optical element has a first cross-sectional shape and light having a second cross-sectional shape different from the first cross-sectional shape is incident on the second optical element, and the second optical element out-couples light incident from the first optical element.

Abstract: Provided is a device configured to enlarge an exit pupil area of a visual optical apparatus, the device including a diffraction grating configured to output a plurality of diffracted light beams of a plurality of diffraction orders by diffracting an incident light beam, and a waveguide provided on the diffraction grating and configured to form an exit pupil based on a first diffracted light beam among the plurality of diffracted light beams output from the diffraction grating and to form exit pupil orders based on a second diffracted light beam among the plurality of diffracted light beams output from the diffraction grating.

Abstract: Provided is a backlight unit including a light source emitting coherent light, a light guide plate propagating the light emitted by the light source, an input grating inputting the light from the light source into the light guide plate, an output grating provided on one surface of the light guide plate and diffracting light incident from inside the light guide plate and outputting the light, in a direction toward the outside of the light guide plate, a first recuperation element provided on one surface of the light guide plate and including a first recycle grating, and a second recuperation element provided opposite to the first recuperation element and directing, to the first recuperation element, incident light that is propagating inside the light guide plate.

Abstract: Provided are an eye-tracking device that may rapidly and accurately track an observer's eye and may be made compact, and a display apparatus including the eye-tracking device. The eye-tracking device includes: a light source configured to emit an illumination light; a light guide plate configured to transmit the illumination light emitted from the light source to an observer's eye and transmit the illumination light reflected from the observer's eye in a direction opposite to a propagation direction of the illumination light emitted from the light source; a photodetector array configured to detect the illumination light reflected from the observer's eye; and a signal processor configured to determine an angle of rotation of the observer's eye based on a two-dimensional (2D) intensity distribution of the illumination light detected by the photodetector array.

Abstract: Provided is a backlight unit including a light source emitting coherent light, a light guide plate propagating the light emitted by the light source, an input grating inputting the light from the light source into the light guide plate, an output grating provided on one surface of the light guide plate and diffracting light incident from inside the light guide plate and outputting the light, in a direction toward the outside of the light guide plate, a first recuperation element provided on one surface of the light guide plate and including a first recycle grating, and a second recuperation element provided opposite to the first recuperation element and directing, to the first recuperation element, incident light that is propagating inside the light guide plate.