Photonic crystal surface emission laser

A photonic crystal surface emission laser, comprising:

• an active layer;
• a first photonic crystal layer made of a plate-shaped slab provided with modified refractive index areas having a refractive index different from that of the slab, the modified refractive index areas being arranged on lattice points of a first rhombic-like lattice;
• and
• a second photonic crystal layer made of a plate-shaped slab provided with modified refractive index areas arranged on a second rhombic-like lattice in which two diagonals are parallel to those of the first rhombic-like lattice and a length of only one of the two diagonals is different from that of the first rhombic-like lattice, wherein:
• ax1, ax2, ay, and n satisfy a following inequality:
• 
• 1
• a
• x
• ⁢
• ⁢
• 1
• -
• 1
• a
• x
• ⁢
• ⁢
• 2
• 
• (
• 1
• a
• x
• ⁢
• ⁢
• 1
• +
• 1
• a
• x
• ⁢
• ⁢
• 2
• )
• 2
• +
• (
• 2
• a
• y
• )
• 2
• ≤
• 1
• n
• ,
• where ax1 and ay respectively represent a length of the aforementioned one of the two diagonals having a different length and that of an other one of the two diagonals of the first rhombic-like lattice, ax2(ax2≠ax1) and ay respectively represent a length of the aforementioned one of the two diagonals having a different length and that of an other one of the two diagonals of the second rhombic-like lattice, and n represents an equivalent refractive index of the first photonic crystal layer and the second photonic crystal layer in a direction perpendicular to the first photonic crystal layer and the second photonic crystal layer.