Optical design of a reflective omnidirectional optical system to be used simultaneously in visible and LWIR wavelength range

Abstract

We design an omnidirectional optical system that is composed of pseudo-Cassegrain collecting mirror part making narrow field of view(FOV) and a reverse pseudo-Cassegrain imaging mirror part, which can be used simultaneously in visible and long wavelength infrared(LWIR) light. The FOV is set to 40° to 110° and the F/number is 1.55. Because a CMOS sensor (CMOSIS, CMV2000) for visible and a micro bolometer sensor (semiconductor device, Bird 384) for LWIR are chosen, respectively, the common size of image should be determined by 5.9 mm × 5.9 mm. After the optimizing design, the ratio of the image height about two cases of 40° and 110° is 48.97 %. We can obtain that two MTFs for visible and LWIR at 20 lp/mm about the FOV of 110° are 0.425 and 0.385, respectively. The total length of this system is about 280 mm. When the MTF at 20 lp/mm and 110° is 0.3, the cumulative probabilities of the tolerance in visible and LWIR are 90.69 % and 99.79 %, respectively. After the athermalization analysis in the temperature range of - 32°C to 55°C, we choose the secondary mirror of the imaging part as a compensator to improve the collapsed MTF.