Light deflection device
In a light deflection device, the radiation efficiency of radiated light beams is to be improved. The light deflection device is configured by a photonic crystal waveguide having a lattice array with low refractive index parts periodically arrayed in a surface of a high refractive-index member. The lattice array has a dual-periodic structure consisting of a first periodic array and a second periodic array which differ from each other in periodic arrangement of the low refractive index parts. A line defect where no low refractive index parts are arrayed constitutes a waveguide core for propagating incident light. The cross section of at least either the first periodic array or the second periodic array constituting the periodic arrays of the dual-periodic structure is asymmetrical in the thickness direction of the low refractive index parts.
1. A light deflection device comprising a photonic crystal waveguide having a lattice array with low refractive index parts periodically arranged in a surface of a high refractive-index member, the lattice array constituting the waveguide, wherein
the lattice array includes a dual-periodic structure including a first periodic array and a second periodic array different from each other in periodic arrangement of the low refractive index parts, and
the low refractive index parts have an asymmetrical cross-sectional shape with reference to a thickness direction in at least either of the first and second periodic arrays of the dual-periodic structure, and thereby increasing intensity of radiation of light in one direction of a thickness directions, the light propagating through waveguide core formed in the lattice array.
2. The light deflection device according to claim 1 , wherein side walls of the low refractive index parts having the asymmetrical cross-sectional shape each have a wall shape of either an inclined wall or a stepped wall in a thickness direction, the stepped wall being defined by at least two walls selected from the group consisting of an inclined wall, a perpendicular wall, and a horizontal wall.
3. The light deflection device according to claim 1 , wherein the dual-periodic structure is configured such that:
circular holes having different diameters are arranged in the low refractive index parts of the first periodic array and the second periodic array;
the circular holes are arranged at predetermined intervals in a propagation direction of the waveguide comprising the periodic arrays;
the circular holes of the first periodic array and the circular holes of the second periodic array are alternately arranged in rows extending in the propagation direction of the waveguide; and
out of large-diameter and small-diameter circular holes differing from each other in diameter, the small-diameter circular holes have an asymmetrical cross-sectional shape.
4. The light deflection device according to claim 1 , wherein the dual-periodic structure is configured such that:
circular holes having different diameters are arranged in the low refractive index parts of the first periodic array and the second periodic array;
the circular holes are arranged at predetermined intervals in a propagation direction of the waveguide comprising the periodic arrays;
the circular holes of the first periodic array and the circular holes of the second periodic array are alternately arranged in rows extending in the propagation direction of the waveguide; and
out of large-diameter and small-diameter circular holes differing from each other in diameter, the large-diameter circular holes have an asymmetrical cross-sectional shape.
5. The light deflection device according to claim 1 , wherein the dual-periodic structure is configured such that:
the circular holes having the different diameters are arranged in the low refractive index parts of the first periodic array and the second periodic array;
the circular holes are arranged at predetermined intervals in a propagation direction of the waveguide comprising the periodic arrays;
the circular holes of the first periodic array and the circular holes of the second periodic array are alternately arranged in rows extending in the propagation direction of the waveguide; and
large-diameter and small-diameter circular holes differing from each other in diameter have an asymmetrical cross-sectional shape.
6. The light deflection device according to claim 1 , wherein the dual-periodic structure is configured such that:
the circular holes having different diameters are arranged in the low refractive index parts of the first periodic array and the second periodic array, the circular holes being arranged at predetermined intervals in the propagation direction of a waveguide of the periodic arrays;
the circular holes of the first periodic array and the circular holes of the second periodic array are alternately arranged in the same row extending in the propagation direction of the waveguide; and
circular holes of either periodic array of the first periodic array and the second periodic array have an asymmetrical cross-sectional shape.
7. The light deflection device according to claim 3 , wherein the periodic array of the circular holes having the asymmetrical cross-sectional shape is a second-row periodic array from a line defect devoid of the circular holes among the rows in the propagation direction of the waveguide.
8. The light deflection device according to claim 3 , wherein, among the circular holes provided in the lattice array, dual-periodic circular holes of even-number lattice rows in the propagation direction of the waveguide have a diameter enlarged or reduced as compared with the circular holes in other locations.
9. The light deflection device according to claim 2 , wherein the perpendicular wall surface is a side wall of a groove formed by removing part of the surfaces of a plurality of the low refractive index parts having an asymmetrical cross-sectional shape and the high refractive-index member.