| 摘要 |
A small high-performance unidirectional optical power monitor having a directional characteristic of 30 dB or higher is provided. A sleeve in which the center axes of round holes in which a GRIN lens and a photo-diode are inserted and fitted are eccentric from each other is used. The entire sleeve or the inner surfaces are formed by a black non-light-transmissive material. The position of the intermediate wall in the sleeve is at a distance of 0.55 L to 0.8 L from a tap film of the GRIN lens. L is the distance between the tap film and the lens extreme end of the photo-diode. Preferably, the angle of the intermediate wall is in the range from 45 to 135 degrees, the light reflectivity of the wall surfaces of the intermediate wall and the inner wails is 10% or less, the surface roughness is 2 nm or higher, and the undulation is ½ or less of the wavelength of light used.
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