Optical element, display device, master, and method for manufacturing optical element
There is provided an optical element including: a substrate; and a plurality of microlenses formed on the substrate. A reflecting surface of the microlens is an aspherical surface and asymmetrical with respect to an optical axis of the microlens. A pitch between adjacent ones of the microlenses is 10 to 230 μm. A depth of the microlens is 3.2 to 15.4 μm.
1. An optical element comprising:
a substrate; and
a plurality of microlenses formed on the substrate,
wherein a reflecting surface of each microlens of the plurality of microlenses is an aspherical surface and asymmetrical with respect to an optical axis of the microlens,
wherein the plurality of microlenses have shapes different from each other,
wherein each outer edge of each microlens is in contact with a respective outer edge of an adjacent microlens of the plurality of microlenses,
wherein a pitch between adjacent ones of the plurality of microlenses is 10 to 230 μm, and
wherein a depth of each microlens is 3.2 to 15.4 μm.
2. The optical element according to claim 1 , wherein the pitch between adjacent ones of the plurality of microlenses is different between various combinations of adjacent ones of the plurality microlenses.
3. The optical element according to claim 1 , wherein the depth of each microlens is different between the plurality of microlenses.
4. The optical element according to claim 1 , wherein an aperture plane of each microlens is in a shape deviated from a regular polygon.
5. The optical element according to claim 4 , wherein the aperture plane of each microlens is in a shape deviated from a regular hexagon.
6. The optical element according to claim 4 , wherein the aperture plane of each microlens is in a shape deviated from a square.
7. The optical element according to claim 1 , wherein an arithmetic average roughness Ra of the reflecting surface of each microlens is 27 nm or less.
8. The optical element according to claim 1 , wherein an amount of shift of the optical axis of each microlens from a centroid of the microlens is 2.5% to 15% of a radius of the microlens.
9. The optical element according to claim 1 , wherein an intensity distribution of reflected light forms a top hat shape.
10. The optical element according to claim 9 , wherein a sum of intensities of the reflected light is 4% or less of an intensity of incident light.
11. A display device comprising the optical element according to claim 1 .
12. A master for manufacturing the optical element according to claim 1 , the master comprising:
a base material for the master; and
a resist layer formed on the base material for the master,
wherein a plurality of transfer units each having an inverted shape of a respective microlens of the plurality of microlenses are formed on the resist layer.
13. A method for manufacturing an optical element for manufacturing the optical element according to claim 1 , the method comprising:
forming a resist layer on a base material for a master;
pulse-applying laser light to the resist layer to form a latent image pattern having an inverted shape of each microlens of the plurality of microlenses on the resist layer;
developing the resist layer to form a transfer unit having the inverted shape of each microlens of the plurality of microlenses on the resist layer; and
transferring the inverted shape of the transfer unit to the substrate.
14. The optical element according to claim 1 , wherein each outer edge of each microlens is in contact along substantially its entire length with the respective outer edge of the adjacent microlens.