Optical element
To provide a volume-type optical element in which a self-cloning photonic crystal is used. An optical element is provided with half-wave plates of photonic crystals formed on the xy plane and laminated in the z-axis direction in a three-dimensional space x, y, z. The groove direction of the photonic crystals is a curved line, and the angle in relation to the y-axis direction changes continuously in the range of 0°-180°. Light entering the optical element in the axial direction is emitted from the optical element upon being divided and converted into clockwise circularly polarized light in the direction facing the x-axis by a given angle from the z-axis and anticlockwise circularly polarized light in the direction facing the −x-axis by a given angle from the z-axis. Laminating or placing a quarter-wave plate comprising a photonic crystal on one or both surfaces makes it possible to divide light entering from the z-axis direction of the optical element into two orthogonal linearly polarized lights.
1. An optical element comprising a half wavelength plate of photonic crystal which is formed on an xy plane and in which two types of transparent media with different refractive indices are stacked alternately, each over multiple layers, in a three-dimensional space x, y and z, wherein
the optical element includes one or a plurality of single or repeated regions in an x axis direction,
the regions are partitioned into a plurality of sub regions of belt-like shapes in the x axis direction,
in a groove direction of the photonic crystal comprising protrusion parts and recess parts,
an angle with respect to a y axis direction changes stepwise in a range of 0° to 180° in the region, and
the angle with respect to the y axis direction is uniform in the sub region, and
the optical element splits and converts light entering in the z axis direction into
right-handed circularly polarized light in a direction which travels toward an x axis by a certain angle from a z axis, and
left-handed circularly polarized light in a direction which travels toward an x axis by the same angle from the z axis to emit.
2. An optical element comprising a half wavelength plate of photonic crystal which is formed on an xy plane and in which two types of transparent media with different refractive indices are stacked alternately, each over multiple layers, in a three-dimensional space x, y and z, wherein
the optical element includes one or a plurality of single or repeated regions in an x axis direction,
a groove direction of the photonic crystal comprising protrusion parts and recess parts
is a curve, and
an angle with respect to a y axis direction continuously changes within a range of 0° to 180°, and
the optical element splits and converts light entering in the z axis direction into
right-handed circularly polarized light in a direction which travels toward an x axis by a certain angle from a z axis, and
left-handed circularly polarized light in a direction which travels toward an x axis by the same angle from the z axis to emit.
3. The optical element according to claim 2 , wherein
where a pitch of a pattern consisting of the protrusion parts and the recess parts in a center part of the regions is p 0 , at edge parts of the regions, the protrusion parts and the recess parts are joined so that a pitch of a pattern consisting of the protrusion parts and the recess parts in the edge parts is in a variation range of 0.5 p 0 to 2.0 p 0 .
4. The optical element according to claim 3 , wherein,
when a width of the region is D,
the curve is expressed by y=(D/π)log(cos(πx/D))+a constant.
5. The optical element according to claim 1 or 2 , wherein
an inter-groove unit period of the photonic crystal is 40 nm or more and is ¼ or less than a wavelength of the entering light, and
a period in a thickness direction is ¼ or less than the wavelength of the entering light.
6. The optical element according to claim 1 or 2 , wherein
a ¼ wavelength plate made of the photonic crystal is stacked or disposed on a single surface or both surfaces, and
light entering from the z axis direction of the optical element is split into two beams of orthogonal linearly polarized light.
7. A composite optical element comprising two optical elements according to claim 1 or two optical elements according to claim 2 , wherein
a first optical element and a second optical element are disposed at an interval of a certain propagation length,
the composite optical element comprises:
a ¼ wavelength plate which is provided at a stage subsequent to the second optical element; and
a pair of lenses which are provided at the stage subsequent to the ¼ wavelength plate, and have a function of condensing linearly polarized light and diffusing linearly polarized light orthogonal to the linearly polarized light, and
splits light entering from a side of the first optical element into two linearly polarized light components to condense.