Backlight unit providing uniform light and display apparatus including the same

A display apparatus comprising:

• a backlight unit comprising:
• a light source configured to emit light;
• a light guide plate comprising a first surface, a second surface that is opposite to the first surface in a first direction, a third surface, and a fourth surface that is opposite to the third surface in a second direction, the second direction being different from the first direction;
• an input grating provided on the light guide plate adjacent to the third surface, the input grating being configured to input the light emitted by the light source into the light guide plate such that the light input is totally reflected inside of the light guide plate;
• an output grating provided on one of the first surface and the second surface of the light guide plate, the output grating being configured to diffract light that is incident on the output grating from inside of the light guide plate and output the light toward an outside of the light guide plate;
• a first recuperation element provided on the one of the first surface and the second surface of the light guide plate and adjacent to the fourth surface, the first recuperation element comprising a first recycle grating;
• and
• a second recuperation element provided on the other one of the first surface and the second surface of the light guide plate opposite to the first recuperation element in the first direction, the second recuperation element being configured to direct, to the first recuperation element, the light propagating inside the light guide plate that is incident on the second recuperation element;
• and
• a spatial light modulator configured to form a hologram image based on the light from the backlight unit.