Optical system design of a multi-angle slit-recombinant hyperspectral imager

Long focal lengths and widely separated viewing directions in medium Earth orbit (MEO) multi-angle hyperspectral systems produce large separations between the primary images. Directly coupling these images to a multi-slit spectrometer creates unused detector regions and increases the required slit-plane and downstream optical formats. This study presents a pre-dispersion multi-slit recombination module that provides a compact optical interface between a shared fore-telescope and a shared multi-slit spectrometer. The module uses only plane mirrors to fold and rearrange converging beams without adding optical power. A vector chief-ray tracing model and a baseline-first, matching-second sequential optimization strategy are used to determine the mirror parameters. The method was evaluated using symmetric three-view configurations of 0° and ± 35° and 0° and ± 15° over the 410–900 nm band. In both cases, the module converted widely separated focal images into a compact slit array and reduced the required slit-plane and detector formats. The systems maintained non-overlapping spectral bands, image quality, spectral-distortion control, and common-pupil matching. Monte Carlo tolerance analysis of the primary design also supported the alignment feasibility of the integrated fore-telescope and recombination module. The proposed module enables fixed-view channels to share one powered fore-telescope and one multi-slit spectrometer without an instrument-side view-switching mechanism or separate powered front ends for each view.