| 摘要 |
PURPOSE: To simplify the manufacturing work and prevent the reduction of mechanical strength of an optical fiber by expanding mode field diameter (MFD) of core layers to optically connect core layers to each other. CONSTITUTION: In an optical fiber 4, two core layers 1, 2 which differ in diffractive indexes from each other are arranged in a single clad layer 3 at a distance at which they are not optically connected. Heaters 5 are arranged in close proximity to two places in the longitudinal direction of the optical fiber 4. Temperature of the heaters 5 is kept at a fixed temperature to heat the optical fiber 4 locally. Consequently, the MFD of the core layers 1, 2 is expanded so that a directivity connector portion 9 in which the core layers l, 2 are optically connected to each other is obtained. Although the physical length of the core layers 1, 2 between the directivity connector portions 9 is equal to each other, their diffractive indexes differ from each other. Consequently, their optical length differs from each other to constitute a Mach-Zehnder interference system. |
