Diffractive light guide plate and display device comprising same
A diffractive light guide plate and a display device including the same, the diffractive light guide plate including a light guide unit; a first diffractive optical element including a linear grating repeatedly formed at a predetermined pitch; and a second diffractive optical element disposed in a region distinct from a region where the first diffractive optical element is disposed and including a two-dimensional pattern provided in a region where a virtual first linear pattern repeatedly arranged at a predetermined pitch along a first direction and a virtual second linear pattern repeatedly arranged at a predetermined pitch along a second direction intersect each other, where a horizontal section of the two-dimensional pattern has an elliptical shape and an angle between the long axis of the elliptical shape and a direction perpendicular to an extension direction of the linear grating in the first diffractive optical element is less than 20°.
1. A diffractive light guide plate comprising:
a light guide unit configured to guide lights;
a first diffractive optical element including a linear grating repeatedly formed at a predetermined pitch such that lights output from a light source are received and guided on the light guide unit, and configured to diffract the received lights; and
a second diffractive optical element disposed in a region distinct from a region where the first diffractive optical element is disposed on one surface of the light guide unit, and including a two-dimensional pattern provided in a region where a virtual first linear pattern repeatedly arranged at a predetermined pitch along a first direction and a virtual second linear pattern repeatedly arranged at a predetermined pitch along a second direction different from the first direction intersect each other,
wherein a horizontal section of the two-dimensional pattern has an elliptical shape and an angle formed between the long axis of the elliptical shape and a direction perpendicular to an extension direction of the linear grating included in the first diffractive optical element is 10° or more but less than 18°,
wherein the two-dimensional pattern protrudes from the one surface of the light guide unit, and
wherein a protruding height of the two-dimensional pattern is 0.084 times to 0.113 times a wavelength of the light output from the light source.
2. The diffractive light guide plate according to claim 1 , wherein the short axis of the elliptical shape is 0.50 times to 0.921 times the pitch of the linear grating, the first linear pattern and the second linear pattern.
3. The diffractive light guide plate according to claim 1 , wherein the long axis of the elliptical shape is 0.150 times to 1.324 times the pitch of the linear grating, the first linear pattern and the second linear pattern.
4. The diffractive light guide plate according to claim 1 , wherein each of the linear grating, the first linear pattern and the second linear pattern has a grating vector defined by a size inversely proportional to each pitch thereof and a direction perpendicular to a direction in which the linear grating, the first linear pattern and the second linear pattern are extended, and
a sum of grating vectors of the linear grating of the first diffractive optical element and the first linear pattern and the second linear pattern of the second diffractive optical element has a value of 0.
5. The diffractive light guide plate according to claim 4 , wherein the grating vectors of the linear grating of the first diffractive optical element and the first linear pattern and the second linear pattern of the second diffractive optical element have the same size.
6. The diffractive light guide plate according to claim 4 , wherein the grating vectors of the linear grating of the first diffractive optical element and the first linear pattern and the second linear pattern of the second diffractive optical element form an angle of 60° therebetween.
7. A display device comprising:
a light source configured to output an image light that forms an image; and
the diffractive light guide plate according to claim 1 .