| 摘要 |
PURPOSE:To suppress deterioration in transmission characteristic by polishing diagonally the end face of an optical fiber facing a focusing type lens and forming a photodetecting element at the angle reciprocal with the polished surface of the optical fiber surface. CONSTITUTION:An optical fiber 3, a rod lens 6, an APD chip 7, an APD package 8, the locus 10 of the exit light from the fiber 3 and the locus 10 of the reflected light from the chip 7 or the package 8 are illustrated. The end 3b of the fiber 3 is polished or cut diagonal with the optical axis and therefore the Fresnel reflected light at the end face 3b of the optical fiber cannot have backward propagating mode and is radiated as a radiation mode to the outside of the fiber 3. The exit light from the fiber 3 is emitted with inclination by theta/2 of the polishing angle theta with respect to the optical axis. When an imaging magnification is assumed to be one in this embodiment, the exit light from the lens 6 is made incident with inclination by theta/2 to the chip 7 and the reflected light thereof is not made incident again to the fiber 3 as shown by the locus 11 of the reflected light. The angle phi of inclination of the package 8 is highly effected for reflection if said angle is large but if the angle is excessively large, the quantum efficiency decreases. |
