Abstract: A confocal microscope (100) based on a large mode area photonic crystal fibre (5) is described. The microscope may comprise an optical pump source (1) for exciting a sample under study (9), a dichroic beamsplitter (2) to combine the optical paths of the pump and fluorescent light, a lens (3) to couple pump light into the fibre and collimate fluorescent light emerging from the fibre, a large mode area photonic crystal fibre (5), a lens (7) to collimate pump light emerging from the fibre and couple fluorescent light into the fibre, and a lens (8) to focus pump light onto the sample and collimate the resulting fluorescent light. The fluorescent light emitted by the sample (9) is detected by a detector (10). The core (32) of the fibre (5) acts as the aperture of the confocal microscope (100). The large mode area photonic crystal fibre may operate as a single mode fibre over a wide wavelength range (e.g. 400 nm to 2000 nm).