Discussed is a flat panel display device embedding an optical imaging sensor such as a fingerprint image sensor. The device includes: a display panel including a display area and a non-display area, and having a top surface; and a directional optical unit attached to the top surface of the display panel, the directional optical unit having a length along a length axis of the display panel, a width along a width axis of the display panel and a thickness along a thickness axis of the display panel, wherein the directional optical unit provides a sensing light to the display area, and wherein the sensing light is collimated and directionized along a predetermined direction of the directional optical unit.