| 摘要 |
<p>A photocoupler used for splitting signal light in an optical transmission line at a predetermined ratio. A substrate is provided with a single-layer beam splitter formed by vacuum depositing a film material having a refractive index below a square root of the refractive index of the substrate so that an optical film thickness attains a predetermined value, and means for holding the single-layer beam splitter in the optical transmission line so that the angle of incidence is kept at about 45°. Alternatively, four-, five- or seven-layered thin film is formed by using three kinds of film materials having refractive indices of 1.46 ± 0.10, 1.65 ± 0.10 and 2.30 ± 0.10, respectively, on a substrate having a refractive index of 1.51 ± 0.10 or 3.50 ± 0.20, and the combination of the thin film layers and the optical film thickness of each thin film layer are selected so that dependence of a split ratio on polarized wave becomes small, and a branching film can be formed. The photocoupler further includes this beam splitter and means for holding the beam splitter in the optical transmission line at an angle of about 45°. Furthermore, the photocoupler may comprise a beam splitter formed by forming 4- to 14-layered thin film layer using two kinds of film materials having refractive indices of 1.46 ± 0.10 and 2.30 ± 0.10 on a substrate having a refractive index of 1.51 ± 0.10 to 3.50 ± 0.20 and selecting the combination of the thin film layers and the optical film thickness of each layer so that the dependence of the split ratio on polarized wave becomes small, and means for holding the beam splitter in the optical transmission line at an angle of about 45°.</p> |
