View of the Thorlabs fibre bundle with a binocular. The seven dark circles are the cladding of the seven fibres (125 µm diameter). In the centre of each of these fibres, the core (4.5 µm diameter) is visible (bright spots). The science and centring fibres are respectively represented in red and blue and connected with SMF to two power meters. The four retro-injection fibres are represented in green and are connected with SMF to the retro-injection home-built setup. The spare fibre is not labelled.