Patent ID: 7412137

Claim:
An optical power monitor comprising: two optical fibers, each having a core in its center and a cladding layer around the core, which are disposed on an upstream side and on a downstream side of a light transmission direction, respectively, and which end surfaces face and are fusion-spliced to each other at a fusion splicing portion with their core optical axes offset from each other; a light reflection surface disposed in the cladding layer of the downstream-side optical fiber, facing part of the end surface of the upstream-side optical fiber core, which is offset and protrudes from the end surface of the downstream-side optical fiber core at the fusion splicing portion, and being at an angle of 38° to 45° with the core optical axis of the downstream-side optical fiber; and a photo-diode disposed opposite to the light reflection surface with respect to the downstream-side optical fiber core to detect lights that are transmitted through the upstream-side optical fiber core, leaked into the cladding layer of the downstream-side optical fiber from the part of the end surface of the upstream-side optical fiber core offset and protruding from the end surface of the downstream-side optical fiber core, and reflected by the light reflection surface, wherein the light reflection surface is located at a position, that the lights leaked into the cladding layer of the downstream-side optical fiber from the part of the end surface of the upstream-side optical fiber core interfere and strengthen each other, and at a distance of 4.5 mm to 7.5 mm from the fusion splicing portion, and wherein the optical fibers are curved in an arc-like shape, having a curvature radius of 0.85 m to 0.111 m or 0.347 m to 2.667 m, to rise in a direction opposite to the photo-diode and to have a peak of the arc-like shape substantially at a mid-point between the fusion splicing portion and the light reflection surface.