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.
