In order to break through the limitations of super-miniaturization, super-long focal length and super-wide field of view on optical system, a miniaturized four field of view medium-wave infrared optical system is proposed and designed. The optical system adopts double optical path structure, including super-small field of view optical path and small field of view/medium field of view/wide field of view optical path. Two optical paths share a relay group. The super-small field of view optical path is stereo-folded four times, and the small/medium/wide field of view optical path is folded twice, totally six times. The shape size of the whole dual paths optical system is effectively constrained, and the envelope is in the range of 250mm×155mm×90mm (local 140 mm), the optical system has high integration; the dual-path optical system includes four fields of view: super-small field of view, small field of view, medium field of view and wide field of view. The super-small field of view focal length is 733mm, the field of view is 0.75 degrees, the wide field of view focal length is 10.78 mm, and the field of view is 48 degrees, which realizes both super-long focal length and super-wide field of view with a zoom ratio of 68× and the super-small field of view optical system only adopts with five lenses, the transmittance is high, and the whole optical system with two optical paths has compact structure and small volume, thus realizing the miniaturization. The design and test results show that the optical system has good image quality and meets the requirements of high performance thermal imager.
In this research, we designed an MWIR optical system, which is equipped with long focal length, large aperture, optically athermalization. The optical system has been athermalized under wide temperature range (-40 to 70 DEG C) by means of optically passive compensation of more two-optical-material and one housing material combination. The optical system only is composed of six lenses, the transmission of the optical system is high. The final optical system has a 1200mm focal length and a 0.46°×0.37° field of view. The modulation transfer function of the optical system is close to the diffraction-limit, the 4-bar target image of the MWIR imager is very legible. The design and test results show that the image quality of the optical system is perfect, and it can meet the requirements of the high definition and high performance MWIR imager and needn't focus from minus 40 degrees centigrade to positive 70 degrees centigrade.
A novel common aperture dual waveband imaging optical system for a MWIR/SWIR polarization imager is presented in
this paper. The optical system consists of an all-reflective telescope with focal ratio 4, a dichroic beam-splitter, a MWIR
refractive optical arm with effective focal length 60 mm, a SWIR refractive optical arm with effective focal length 60
mm. The effective focal length of the whole optical system is 240 mm, the f-number is 2 and the efficiency of the cold
stop is 100%. The MWIR arm includes a secondary refractive telescope, a MWIR polarimetric analyzer, a re-imaging
objective and a MWIR 320×256 FPA. The SWIR arm includes a secondary refractive telescope, a SWIR polarimetric
analyzer, a focusing lens and a SWIR 320×256 FPA. The common axis all-reflective telescope has a minimal central
obstacle ratio of 0.3, which is composed of a first paraboloid, a mirror with two operational faces, a second paraboloid.
In order to minimize the apertures of the first paraboloid, the
beam-splitter and the polarizer, the thrice imaging
technique is taken to design the MWIR arm, that is, the remote scene is imaged three times and the cold stop is imaged
twice from the image space to the object space. The first real image of the remote scene is focused on the common focus
of the first paraboloid and the second paraboloid, i.e., the small hole centered on the mirror with two operational faces,
the second real image is focused on the intermediate real image plane of the re-imaging objective, and the third real
image is focused on the FPA. The first real image of the cold stop is located nearby the beam-spiltter, the second real
image (the entrance pupil) is located nearby the first paraboloid, so that the clear apertures of the first paraboloid, the
beam-splitter and the polarizer are compressed within Φ 125mm, Φ 45mm and Φ 30mm respectively. The image quality
of the dual waveband optical system is optimized perfect well, and it can fulfill the requirements and the specifications of
the dual waveband IR polarization imager.