Optical element and information recording medium for counterfeit prevention
There is provided an optical element for counterfeit prevention that has both high counterfeit preventing property and designability by a multi-optical element structure. The optical element has a second layer ( 3 ) having a relief structure on a front surface, a first layer ( 2 ) disposed on the second layer ( 3 ), and a third layer ( 6 ) in a thin film interposed between the second layer ( 3 ) and the first layer ( 2 ) and formed along a front surface of the relief structure. The second layer ( 3 ) has a refractive index lower than a refractive index of the first layer ( 2 ) and the third layer ( 6 ) has a refractive index higher than the refractive index of the first layer ( 2 ). The optical element has at least a first region ( 4 ) and a second region ( 5 ) in a plan view. In the first region ( 4 ), an electromagnetic wave that enters from a side of the first layer ( 2 ) in a specific angle range is configured to be totally reflected. In the second region ( 5 ), a relief structure that causes at least one of diffraction, interference, scattering, refraction, and absorption of an electromagnetic wave is disposed and the electromagnetic wave entering from the first layer ( 2 ) side is configured to be reflected by a refractive index difference between the first layer ( 2 ) and the third layer ( 6 ).
1. An optical element for counterfeit prevention comprising:
a second layer having a relief structure disposed on a front surface;
a first layer disposed in a side of the front surface of the second layer; and
a third layer interposed between the second layer and the first layer, the third layer being formed along a front surface of the relief structure, wherein
the second layer has a refractive index lower than a refractive index of the first layer,
the third layer has a refractive index higher than the refractive index of the first layer,
the optical element comprises at least a first region and a second region in a plan view,
the relief structure disposed in the second region causes at least one of diffraction, interference, scattering, refraction, and absorption of an electromagnetic wave,
the first region is configured such that an electromagnetic wave entering from a side of the first layer in a preliminarily set specific angle range is totally reflected due to at least one of a ratio of the refractive index of the second layer to the refractive index of the first layer and the relief structure disposed in the first region, and
the second region is configured such that the electromagnetic wave entering from the first layer side is reflected by a refractive index difference between the first layer and the third layer.
2. The optical element for counterfeit prevention according to claim 1 , wherein
at least a part of a visible light is reflected at an interface between the first layer and the third layer, and
at least a part of the visible light having passed through the third layer is totally reflected at an incident angle greater than a critical angle at an interface between the third layer and the second layer.
3. The optical element for counterfeit prevention according to claim 1 , wherein
the relief structure disposed in the first region has a plurality of aligned inclined surfaces inclined with respect to an optical element plane, and
the relief structure disposed in the second region has a repeated unevenness in a cross-sectionally rectangular shape or a cross-sectionally wavy form.
4. The optical element for counterfeit prevention according to claim 1 , wherein
the relief structure disposed in the first region has a plurality of inclined surfaces inclined with respect to an optical element plane,
when an observation is made from any observation point with a light source placed in an observation point side,
Equation (1) is satisfied, where
an incident angle to the inclined surface of the relief structure disposed in the first region is θ f1 ,
a refractive index of the first layer in the first region is N 1 , and
a refractive index of the second layer in the first region is N 2 ,
θ f1 arcsin( N 2 /N 1 ) Equation (1).
5. The optical element for counterfeit prevention according to claim 1 , comprising
a fourth layer disposed to contact any layer of the first layer, the second layer, and the third layer, wherein
the fourth layer is a print layer on which at least one of a character, an image pattern, and a code is printed.
6. The optical element for counterfeit prevention according to claim 1 , comprising
a fifth layer disposed on a surface opposite to a surface of the second layer where the relief structure is disposed, wherein
the fifth layer is a colored layer.
7. The optical element for counterfeit prevention according to claim 6 , comprising
a sixth layer disposed on a surface opposite to a surface of the fifth layer opposing the second layer, wherein
the sixth layer is an electromagnetic wave absorbing layer.
8. The optical element for counterfeit prevention according to claim 1 , comprising:
a seventh layer disposed on a surface opposite to a surface of the first layer opposing the second layer, the seventh layer being a colored layer, and
an eighth layer disposed on a surface opposite to a surface of the second layer opposing the first layer, the eighth layer being an electromagnetic wave absorbing layer.
9. An optical element for counterfeit prevention, comprising
two or more laminated optical elements for counterfeit prevention according to claim 1 .
10. The optical element for counterfeit prevention according to claim 9 , wherein
the relief structure of at least two optical elements of each of the laminated optical elements is periodic relief structure, and
the periodic relief structures is configured to generate a moire.
11. The optical element for counterfeit prevention according to claim 1 , wherein
the relief structure has at least partially a periodic structure and further includes a ninth layer configured to generate a moire and the periodic structure, and
the ninth layer is a colored layer colored by a preliminarily set patterning.
12. The optical element for counterfeit prevention according to claim 1 , wherein
at least one region of the first region and the second region generates a parallax image based on an angle of convergence determined by positions of both eyes and the optical element when an observation is made from a perpendicular direction with respect to an optical element plane.
13. The optical element for counterfeit prevention according to claim 1 , wherein
the third layer is interposed at least in a part between the second layer and the first layer to contact the relief structure.
14. The optical element for counterfeit prevention according to claim 13 , wherein
the third layer is interposed only in a part between the second layer and the first layer to contact the relief structure, and
a metal reflection layer is disposed at least in a part of a portion of the relief structure where the third layer does not contact.
15. The optical element for counterfeit prevention according to claim 1 , wherein
a metal reflection layer contacting the relief structure is disposed in a part in at least one of the first region and the second region.
16. The optical element for counterfeit prevention according to claim 1 , wherein
a smooth surface is disposed in any of the first region, the second region, and between the first region and the second region.
17. The optical element for counterfeit prevention according to claim 1 , comprising:
a plurality of the first regions, and
a metal reflection layer surrounding at least one of the first regions.
18. An information recording medium comprising
the optical element for counterfeit prevention according to claim 1 .
19. The optical element for counterfeit prevention according to claim 2 , wherein
the relief structure disposed in the first region has a plurality of aligned inclined surfaces inclined with respect to an optical element plane, and
the relief structure disposed in the second region has a repeated unevenness in a cross-sectionally rectangular shape or a cross-sectionally wavy form.
20. The optical element for counterfeit prevention according to claim 2 , wherein
the relief structure disposed in the first region has a plurality of inclined surfaces inclined with respect to an optical element plane,
when an observation is made from any observation point with a light source placed in an observation point side,
Equation (1) is satisfied, where
an incident angle to the inclined surface of the relief structure disposed in the first region is θ f1 ,
a refractive index of the first layer in the first region is N 1 , and
a refractive index of the second layer in the first region is N 2 ,
θ f1 ≥arcsin( N 2 /N 1 ) Equation (1).