A fibre endoscope system (100) comprises a catheter (10) with a probe head (10a) for entering into a body cavity (C) adjacent or near a sample region (S). A source fiber (11) has a first fiber ending (11a) and a signal fiber (12) has a second fiber ending (12a) both remote from the probe head (10a) but separate. A sampling fiber (13) has a third fiber ending (13a) disposed at the probe head (10a). A fiber coupler (15) is configured to optically couple at least the source fiber (11) to the sampling fiber (13), and the sampling fiber (13) to the signal fiber (12). A sampling fiber length (L13) of the sampling fiber (13) between a fiber coupler (15) and the third fiber ending (13a) is shorter than a source fiber length (L11) of the source fiber (11) between the fiber coupler (15) and the first fiber ending (11a).