Minimizing group index variations in a multicore endoscope fiber

We describe a multicore endoscope fiber where variation in group index is minimized between cores of the fiber, allowing simultaneously launched pulses to arrive at the distal end of the fiber synchronously. Minimization of group index variation between cores is achieved at a V parameter of 3 owing to a turning point in the relationship between the group index and V parameter. For synchronized arrival times single-mode propagation is important. By tapering a short length of the fiber at the launch end the V value is brought below 2.405 allowing a pure fundamental mode to be launched into each core.