The present invention relates to an optical shape sensing system, comprising an optical fiber sensor comprising an optical fiber having embedded therein a number of at least four fiber cores (1 to 6) arranged spaced apart from a longitudinal center axis (0) of the optical fiber, the fiber cores each having a resonance wavelength in response to light introduced into the fiber cores (1 to 6) in an unstrained state thereof. The system further comprises an optical interrogation unit (21) configured to interrogate the fiber cores (1 to 6) with light in a scan wavelength range including the resonance wavelengths of the fiber cores in an unstrained state of the fiber cores (1 to 6). The scan wavelength range is set such that a center wavelength of the scan wavelength range is decentered with respect to the resonance wavelength of at least one of the fiber cores (1 to 6).