Dual fibre optical apparatus

First and second optical conduits contain first 310 and second 320 optical fibres whose ends are arranged side-by-side and parallel to one another so that the central axes of their respective outputs are parallel. A separation between the optical axes of their end sections is less than or equal to half the sum of the maximum diameters of the first and second conduits. For the same optical inputs, the outputs of the optical conduits differ in at least one optical characteristic due to their different configurations. This characteristic includes divergence due to the different core profiles of their optical fibres. The optical conduits may have at least one first optical component contiguous with their respective optical fibres. The output ends 315, 325 of the optical conduits may be offset from each other in a direction parallel to the optical axes of the end sections. The two end sections may be mounted in a single mount. The optical characteristic may comprise polarisation and the first optical output may be linearly polarised whilst the second optical output is circularly polarised. An atom interferometer, fluorescence microscope, laser machining apparatus or a Raman spectrometer may include the device.