Optical microscope observation method of a single-mode optical-fiber core for precise core-axis alignment

A new method is presented for observing a single-mode optical-fiber core by the use of an optical microscope to achieve precise core-axis alignment. The formation mechanism of a core image and its observation condition have been investigated using a ray tracing method. Simulation results show good accordance with practical observed results. Precise alignment of cores can be achieved when the dimension of a core image becomes equal to the core diameter multiplied by the magnification of the observation system. In the core aligning experiment for a single-mode fiber with a large core eccentricity of 3.4 μm, the average misalignment was 0.6 μm.