The present invention relates to an optical transmittance device including an optical fiber having a tilted incident plane and a silicon optical bench (SiOB) with a mirror plane. In accordance with the present invention, there provided an optical device, including: a substrate having a groove with a tilted surface, wherein the groove has a mirror plane on the tilted surface; a light emitting means aligned to the substrate; and an optical fiber including a tilted incident plane, wherein a reflected light from the mirror plane is incident to the tilted incident plane.