Spliced optical fiber coupler

Abstract

In general, the mode field pattern of a single-mode polarization-maintaining fiber is symmetric. There are preferred axes for the polarization states, but the intensity pattern emerging from the fiber is rotationally symmetric. If a short piece of multi-mode fiber is spliced onto the end of a polarization-maintaining single-mode fiber, it is possible to change the apparent shape of the mode field. The use of a fusion splicer affects the stress pattern in polarization-preserving fiber, and introduces asymmetry into the shape of the fiber mode field. If the spliced fiber is cleaved near the splice, and the asymmetry of the fiber mode field is matched to the asymmetry of a laser diode beam, then the laser beam is coupled efficiently into the fiber without the use of additional beam-shaping optics. The asymmetric beam from the laser is brought to a focus, which is also asymmetric. By matching the asymmetries of the focused spot and the distorted mode field (caused by the addition of the short piece of multi-mode fiber), good coupling is achieved into the fiber. Once the light has entered the spliced fiber and propagated past the splice, the mode field returns to its original symmetric pattern and the light propagates in a single mode, as it would in an unspoiled, single-mode polarization-maintaining fiber. The output from the unspoiled end is still symmetric, and there is little attenuation caused by the splice.

Dependencies are inferred from the claim text.