An optical coupler including: a substrate; a cladding layer formed on the substrate; and a slab waveguide formed on the cladding layer, wherein the slab waveguide comprises a first waveguide area on which a laser beam is incident and a second waveguide area having an incident surface capable of converging and outputting the laser beam passing through the first waveguide in a width direction. The optical coupler may optically couple one of an optical fiber and a laser diode with the slab waveguide, and more particularly, and a photonic crystal waveguide, with high efficiency.