  BlueMUSE (Blue Multi Unit Spectroscopic Explorer) is a blue-optimised, medium
spectral resolution, panoramic integral field spectrograph proposed for the
Very Large Telescope (VLT) and based on the MUSE concept. BlueMUSE will open up
a new range of galactic and extragalactic science cases allowed by its specific
capabilities in the 350 - 580 nm range: an optimised end-to-end transmission
down to 350 nm, a larger FoV (up to $1.4 \times 1.4$ arcmin$^2$) sampled at 0.3
arcsec, and a higher spectral resolution ($\lambda/\Delta \lambda \sim 3500$)
compared to MUSE. To our knowledge, achieving such capabilities with a
comparable mechanical footprint and an identical detector format ($4\text{k}
\times 4\text{k}$, 15 $\mathrm{\mu m}$ CCD) would not be possible with a
conventional spectrograph design. In this paper, we present the optomechanical
architecture and design of BlueMUSE at pre-phase A level, with a particular
attention to some original aspects such as the use of curved detectors.
