Wavefront coding is a typical application technology of computational optical imaging. It can make the optical system insensitive to thermal defocusing through special encoding and computational decoding, thus realizing athermal design. Airborne application scenarios require optical systems to meet the imaging requirements of complex temperature fields while minimizing volume and weight. However, the structure of optical passive athermal scheme is usually complex. Based on this application condition, a group of airborne infrared optical systems are designed in this paper. The system does not use an additional phase plate, but allows the lens of the original system to assume both the power and the phase encoding function. At the same time, it is compared with the optical non thermal scheme, and the imaging simulation of the complex temperature gradient environment is carried out. The research shows that the modulation transfer function of the system is relatively consistent under the environment of - 40 ℃ to 60 ℃ and the large temperature difference of each lens, and the imaging quality is good.
With the development of optical machining and testing, the gap between freeform surface fabrication and design has been filled. Based on the freeform surfaces’ extraordinary feature for balancing asymmetric aberration and compressing system volume, an volume-compression optical design method for off-axis, three-mirror system is presented. Based on the guide of Nodal Aberration Theory for balancing asymmetric aberration, some optimization rules and tricks are shared during the optimization process. In the end, a highly-compact optical system with wide field of view, large entrance pupil and small F number is shown, the image quality is close to diffraction limit at Nyquist frequency.
From the nodal aberration theory, aberration nodes will move to other locations of field of view when the optical element is decentered or tilted in rotationally symmetric system, which will lead to uncorrected off-axis aberration at locations of large field of view; cause the terms of wavefront aberration function are linked directly to the terms of Zernike polynomials, the aberrated wavefront of the system can be fitted by Zernike polynomials. At the same time, specific terms of Zernike polynomials can be selected to correct wavefront aberration efficiently by evaluating full-field display. Based on the method above, an off-axis optical system with field of view of 3°×3°is designed with two freeform surfaces and one aspheric surface, and certain Zernike polynomials are chosen as the descriptor of freeform surfaces. Keywords:Nodal aberration theory, freeform surface, Zernike polynomials, full-field display.
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