Optical element and method for producing the same
An optical element is provided includes an optical layer having a flat incident surface on which light is incident and a wavelength-selective reflective layer disposed in the optical layer. Of light incident on the incident surface at an incident angle (θ, φ), the optical element selectively directionally reflects light in at least one specific wavelength range in at least one direction other than a specular reflection direction (−θ, φ+180°) while transmitting light in at least one wavelength range other than the specific wavelength range, and is transparent to light in at least one wavelength range other than the specific wavelength range.
1. An optical element comprising:
an optical layer having a flat incident surface on which light is incident;
a plurality of beads embedded on one side of the optical layer;
a focusing layer formed over a surface of each bead opposite the optical layer; and
a wavelength-selective reflective layer disposed on the focusing layer opposite each bead; wherein:
θ is the angle of light incident on the first surface or reflected light exiting through the first surface with respect to a normal of the first surface,
φ is the angle of a component of the light incident on the first surface or the reflected light projected on the first surface with respect to a specific line in the first surface, and
of light incident on the first surface at an incident angle (θ, φ), the optical element selectively directionally reflects the light in at least one specific wavelength range in at least one direction other than a specular reflection direction (−θ, φ+180°) while transmitting light in at least one wavelength range other than the specific wavelength range, and is transparent to light in at least one wavelength range other than the specific wavelength range.
2. The optical element according to claim 1 , wherein a value of transmitted-image clarity measured according to JIS K 7105 using an optical comb with a comb width of 0.5 mm in the wavelength range where light is transmitted is 50 or more.
3. The optical element according to claim 1 , wherein the sum of values of transmitted-image clarity measured according to JIS K 7105 using optical combs with comb widths of 0.125 mm, 0.5 mm, 1.0 mm, and 2.0 mm in the wavelength range where light is transmitted is 230 or more.
4. The optical element according to claim 1 , wherein the angle φ of the directionally reflected light in the specific wavelength range is −90° to 90°.
5. The optical element according to claim 1 , wherein the angle of the directionally reflected light in the specific wavelength range lies near (θ, −φ).
6. The optical element according to claim 1 , wherein the angle of the directionally reflected light in the specific wavelength range lies near (θ, φ).
7. The optical element according to claim 1 , wherein the directionally reflected light mainly includes near infrared light in a wavelength range from 780 to 2,100 nm.
8. The optical element according to claim 1 , wherein
the wavelength-selective reflective layer has a surface profile including a one-dimensional array of columns extending in one direction; and
of light incident on the incident surface at an incident angle (θ, φ), wherein θ is the angle of light incident on the incident surface or reflected light exiting through the incident surface with respect to a normal to the incident surface; and φ is the angle of a component of the incident light or the reflected light projected on the incident surface with respect to a line perpendicular to ridges of the columns in the incident surface, the optical element selectively directionally reflects light in at least one specific wavelength range in at least one (θ 0 , −φ) direction (wherein 0°<θ 0 <90°) while transmitting light in at least one wavelength range other than the specific wavelength range.
9. The optical element according to claim 1 , wherein
the wavelength selective reflective layer is a transparent conductive layer mainly containing a conductive material transparent in the visible region or a functional layer mainly containing a chromic material whose reflection performance changes reversibly in response to external stimuli.
10. The optical element according to claim 1 , wherein
the wavelength-selective reflective layer includes a plurality of wavelength selective reflective layers inclined with respect to the incident surface; and
the wavelength-selective reflective layers are arranged parallel to each other.
11. The optical element according to claim 1 , wherein
the wavelength-selective reflective layer has first and second main surfaces;
the optical layer includes a first optical layer on the first main surface of the wavelength-selective reflective layer and a second optical layer on the second main surface of the wavelength-selective reflective layer; and
the first optical layer has a one- or two-dimensional array of structures on a surface on which the wavelength-selective reflective layer is disposed.
12. The optical element according to claim 11 , wherein the first and second optical layers have a refractive index difference of 0.010 or less.
13. The optical element according to claim 11 , wherein
the first and second optical layers are formed of the same resin transparent in the visible region; and
the second optical layer contains an additive.
14. The optical element according to claim 11 , wherein the structures have a prism shape, a cylindrical shape, a hemispherical shape, or a corner cube shape.
15. The optical element according to claim 11 , wherein
the major axis of the structures is inclined in a direction in which the structures are arranged with respect to a normal to the incident surface.
16. The optical element according to claim 11 , wherein the pitch of the structures is from 5 μm to 5 mm.
17. The optical element according to claim 1 , wherein the optical layer absorbs light in at least one specific wavelength range in the visible region.
18. The optical element according to claim 1 , further comprising a light scatterer at one or more of a surface of the optical layer, an inside of the optical layer, and an interface between the optical layer and the wavelength-selective reflective layer.
19. The optical element according to claim 1 , wherein the maximum absolute value of difference in the chromaticity coordinate x of light incident on the incident surface or a surface opposite to the incident surface in the range of incident angle e from 0° to 60° and specularly reflected by the optical element and the maximum absolute value of difference in the chromaticity coordinate y of the light are each 0.05 or less for each surface.
20. A window article comprising:
an optical element, the optical element including:
an optical layer having a flat incident surface on which light is incident;
a plurality of beads embedded on one side of the optical layer;
a focusing layer formed over a surface of each bead opposite the optical layer; and
a wavelength-selective reflective layer disposed on the focusing layer opposite each bead; wherein:
θ is the angle of the light incident on the first surface or reflected light exiting through the first surface with respect to a normal of the first surface,
φ is the angle of a component of the light incident on the first surface or the reflected light projected on the first surface with respect to a specific line in the first surface,
of the light incident on the first surface at an incident angle (θ, φ), the optical element selectively directionally reflects the light in at least one specific wavelength range in at least one direction other than a specular reflection direction (−θ, φ+180°) while transmitting light in at least one wavelength range other than the specific wavelength range, and is transparent to light in at least one wavelength range other than the specific wavelength range.