Optical lens having sub-wavelength structure containing aluminum or aluminum oxide, method of manufacturing optical lens, and imaging optical system including optical lens
An optical element includes an optically effective area and an optically ineffective area partly or entirely coated with a coating opaque at wavelengths used. The opaque coating contains a cured product prepared from an epoxy resin and a curing agent containing an alicyclic acid anhydride. The alicyclic acid anhydride is preferably methylhexahydrophthalic anhydride or hexahydrophthalic anhydride.
1. An optical element, comprising:
an optically effective area coated with a coating having an optical function; and
an optically ineffective area partly or entirely coated with a opaque coating,
wherein the opaque coating contains a cured product prepared from an epoxy resin and a curing agent containing an alicyclic acid anhydride,
wherein the optically effective area has a sub-wavelength structure which is disposed on at least one surface of the optically effective area, and
wherein the sub-wavelength structure contains aluminum or aluminum oxide.
2. The optical element according to claim 1 , wherein the alicyclic acid anhydride is methylhexahydrophthalic anhydride or hexahydrophthalic anhydride.
3. The optical element according to claim 1 , wherein the opaque coating contains at least one selected from the group consisting of tar, pitch, dye, pigment, mica particles, and silica particles.
4. The optical element according to claim 1 , wherein the optically effective area has a sub-wavelength structure which is disposed on at least one surface thereof,
wherein the sub-wavelength structure contains aluminum or aluminum oxide, and
wherein the sub-wavelength structure includes a repetitive structure having pitch dimensions less than a wavelength used.
5. The optical element according to claim 4 , wherein the sub-wavelength structure is formed of crystals principally containing a hydroxide of aluminum or a hydrate of aluminum oxide.
6. The optical element according to claim 5 , wherein the sub-wavelength structure increases the anti-reflective properties of the at least one surface on which the sub-wavelength structure is disposed.
7. The optical element according to claim 1 , wherein the optical element is a lens and the optically ineffective area is located at the edge of the lens.
8. An imaging optical system focusing light from an object to form an image of the object, comprising the optical element according to claim 1 .
9. The optical element according to claim 1 , wherein the sub-wavelength structure is formed of crystals principally containing a hydroxide of aluminum or a hydrate of aluminum oxide.
10. The optical element according to claim 1 , wherein the sub-wavelength structure is formed of crystals principally containing boehmite crystals.
11. The optical element according to claim 1 , wherein the sub-wavelength structure increases anti-reflective properties of the at least one surface on which the sub-wavelength structure is disposed.
12. The optical element according to claim 1 , wherein the optically ineffective area is located at the edge of the lens.
13. The optical element according to claim 1 , wherein the optically ineffective area is located at the edge of the optical element, the sub-wavelength structure containing aluminum or aluminum oxide is manufactured by processes of applying a coating material containing aluminum or aluminum oxide onto the optical element coated with the opaque coating, forming the coating material by heating the coating material, and immersing the coating material or the opaque coating in hot water at a temperature of 60° C. to 100° C.