Designs of compact off-axis three-mirror afocal optical system

Opti-electronic loads with multi-sensor are widely applied in the fields of atmosphere sounding and optical remote sensing. For the purpose of achieving high performance, miniaturization and light weight of multi-band photoelectric load, this paper proposes a structure with common aperture and partial common optical path, then light enters each subsequent light path after decomposed. This structure can improve system stability and avoids boresight errors caused by multi-apertures. The essay analyzes the aberration formula and initial structural parameter's calculation method of the three-mirror system with the constraint of afocal condition, then eliminate the center occlusion through shifting the optic aperture and design a compact off-axis three-mirror afocal optical system with a folding mirror. The system magnification is 6(x), the max aperture is 140 mm, and the max field of view is 4 degrees x2.1 degrees. The modulation transfer function of optical system reaches more than 90% of the diffraction limit. The mirror surface adopts paraboloid and hyperboloid, which are easy to be processed and tested. The size of system is 167 x145 x211 mm, and the structure is compact enough to meet the application requirements.