Aspects of the disclosure relate to an integrated spectral unit including a micro-electro-mechanical systems (MEMS) interferometer fabricated within a first substrate and a light redirecting structure integrated on a second substrate, where the second substrate is coupled to the first substrate. The light redirecting structure includes at least one mirror for receiving an input light beam propagating in an out-of-plane direction with respect to the first substrate and redirecting the input light beam to an in-plane direction with respect to the first substrate towards the MEMS interferometer.