Abstract: Described herein is a photonic spectrograph for accurately measuring and displaying spectra from radiation signals received from a telescope. One embodiment provides a photonic imaging device, in the form of a spectrograph, including a plurality of input ports for receiving an arbitrary incident electromagnetic radiation field containing one or more spatial propagation modes; a coupling device attached to the multi-mode optical fibre for efficiently coupling the incident electromagnetic radiation field into an arbitrary plurality (N) of single-mode optical fibres; an optical manipulation device which selectively combines the single-mode signals into a continuous optical spectrum; and an optical detector for detecting the continuous optical spectrum.