A medical device, system, and method having a flexible shaft and a multi-core fiber (200) within the flexible shaft. The multi-core fiber (200) includes a plurality of optical cores dedicated for shape sensing sensors, and a plurality of optical cores dedicated for force sensing sensors. A medical device flexing structure assembly can comprise a multi-core fiber (200) comprising a plurality of cores (510), and a flexing structure (616) comprising at least one slot (618). Each of the plurality of cores (510) can comprise a fiber Bragg grating, and the flexing structure (616) can be configured to bend in response to a force imparted on the flexing structure (616).
