Assemblies of the microlenses on the front-end fibres of MOONS

MOONS (Multi-Object Optical and near-Infrared Spectrograph) will be a fibre-fed, optical to near-infrared multi-objet spectrograph designed to utilise the full 25 arcminute diameter field-of-view of the Very Large Telescope and with a multiplex capability of over 1000 fibres. The baseline design includes a single focal plate and fibre positioning subsystem, consisting of up 1024 small dual radial arm modules, which are used to place each fibre, in the exact x, y and z position in the telescope focal plane. Each fibre has a microlens to focus the beam into the fibre at a relatively fast focal ratio of F/3.65 to reduce the Focal Ratio Degradation (FRD). The light is then fed through the fibres to two identical, cryogenic triple arm spectrographs, mounted on the instrument platform. In each spectrograph, the light from 512 fibres, arranged in a pseudo-slit, is split by dichroic filters into three channels (RI, YJ and H) and dispersed on to 4k x 4k detectors in each channel.