  We report on a tapered three-core optical fibre that can be used as a
tip-tilt wavefront sensor. In this device, a coupled region of a few
millimetres at the sensing tip of the fibre converts fragile phase information
from an incoming wavefront into robust intensity information within each of the
cores. The intensity information can be easily converted to linear wavefront
error over small ranges, making it ideal for closed loop systems. The sensor
uses minimal information to infer tip-tilt and is compatible with remote
detector arrays. We explore its application within adaptive optics and present
a validation case to show its applicability to astronomy.
