Thermal assisted magnetic recording head having spot size converter

A spot size converter, comprising:

• a second core that operates to introduce a light beam and to taper light from the light beam,
• a first core that is linked to the second core, and
• a clad that surrounds a periphery of a core coupling body formed by linking the first and second cores, wherein
• when the refractive index of the second core is nC2, the refractive index of the first core is nC1, and the refractive index of the clad is nad, the condition of nC1>nC2>nad is satisfied;
• the second core has a rectangular cross-sectional area that gradually decreases as the second core advances internally from the optical incident end surface, and that has a taper portion that is a triangular plate-like part when viewed from a level plane;
• the first core has a tapered coupling part that is integrated within the taper portion of the second core, and a waveguide core part that is linked with the tapered coupling part and that propagates primarily in a single mode, and
• the tapered coupling part is structured such that its shape viewed from a level plane is a triangular plate-like coupling part, and the level plane in which the rectangular cross-sectional area gradually increases in relation to an advancing direction of the light.