Optical shape 
sensing system for sensing a position and / or shape of a 
medical device (20) using 
backscatter reflectometry, comprising a 
broadband light source (12) for generating input light of multiple wavelengths of a 
broadband spectrum, an interferometer arrangement (11) comprising a plurality of interferometers including a multi-
core optical fiber (22m, 30), the multi-
core optical fiber (22m, 30) comprising at least two 
fiber cores (31, 32a,b,c), wherein each of the interferometers is configured to perform 
backscatter reflectometry separately with a corresponding one of a plurality of input light beams divided from the input light and comprises a 
fiber splitter (14) for dividing the corresponding input 
light beam into a 
reference beam and a device beam, an additional 
optical fiber (22s) for guiding the 
reference beam, a corresponding 
fiber core (31, 32a,b,c) of the multi-
core optical fiber (22m, 30) for guiding the device beam to be reflected within the 
medical device (20) and for guiding the reflected device beam, and a 
fiber coupler (18) for 
coupling the reflected device beam with the 
reference beam to form an output 
light beam, the optical shape 
sensing system further comprising a 
spectrometer (28) for receiving and interacting with the output 
light beam, the 
spectrometer (28) comprising a 
detector unit (26) for detecting the output light beam.