The ultra-thin imaging system using reflective multiple-fold structure has smaller volume and less weight while
maintaining high resolution compared with conventional optical systems. The multi-folded approach can significantly
extend focal distance within wide spectral range without incurring chromatic aberrations. In this paper, we present a dual
infrared imaging system of four-folded reflection with two air-spaced concentric reflective surfaces. The dual brand IR
system has 107mm effective focal length, 0.7NA, ±4° FOV, and 50mm effective aperture with 80mm outer diameter
into a 25mm total thickness, which spectral response is 3~12μm.