Double-core single-mode optical fiber as directional coupler
- Cite this article as:
- Schiffner, G., Schneider, H. & Schöner, G. Appl. Phys. (1980) 23: 41. doi:10.1007/BF00899569
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This work describes the preparation and testing of a double-core single-mode optical fiber intended for use as a directional coupler. A short survey of optical directional coupler theory is followed by a description of the preparation of the double-core preform. The drawn fibers have a core diameter of 5μm with a spacing between core centers of 13μm. Sections of the double-core fiber were tested at λ=633 nm and 876 nm. The coupling factor measured for straight fiber sections of different length was found to be considerably lower than that calculated assuming equal phase velocities for both waveguides. This was concluded to be due to a difference between phase velocities caused mainly by a 4 to 5% difference between core diameters. At 876 nm a maximum coupling ratio of 13% was observed. Bending the fiber section was found to influence the coupling factor due to a change in the phase velocity difference. This effect can be utilized for tuning couplers. A double-core fiber section may be applied as a sensor for measuring the bending angle.