In order to solve the problem of high-cost of the vehicle-assisted driving system and satisfy the requirements of highimaging-quality, the vehicle-mounted infrared optics is light, small, low-cost and mass-produced. In this paper, a compact single-piece free-from prism is used to achieve in-vehicle thermal imaging optical system with waveband of 8~12um, field-of-view of ±14°×±10.5°, F-number of 1 and focal length of 16mm. The optics has a compact structure similar to two-mirror off-axis system, and has the same characteristics with refractive optics of high-quality and low difficulty in installation. Through the process improvement method, the use of molding technology can further reduce the cost of lens, especially suitable for large-volume small-aperture optical systems.
For recent years, with the development of manufacture, free-form surfaces are widely used in optical systems because of the degrees of freedom and the capacity of correcting optical aberrations. Nowadays, commercial optical design software such as Optics Studio are commonly applied to optimize an optical system from a suitable initial structure to obtain high-quality imaging characteristics. The initial structure optimized by software must include the surface types and its parameters. Notice that the free-form surface type is unknown, let alone the parameters. Therefore, the initial structure of a free-form surface cannot be designed by commercial optical design software directly. The software cannot optimize or analyze the system with free-form surfaces either. This paper proposed an integral design method of optical system with free-form surfaces based on theoretical calculation and optimization of optical design software. Firstly, Fermat’s principle, equal optical path length between object and image, is applied to calculate the sampling data points of the free-form surface. Data points are fitted using least-square fitting algorithm to obtain a the surface type and its parameters, which are used as the initial structure. Secondly, a commercial optical design software further optimize the optical system containing the free-form surface. Not only the free-form surface but also other parameters can be optimized by the software. With the powerful functions of image quality and tolerance analysis of the software, we can obtain a high-quality imaging system with free-form surfaces in a short time. This method solves the problem that commercial software cannot design optical systems with free-form surfaces directly. Meanwhile initial structure with free-form surface can be acquired directly by this method. In addition,the powerful functions of the software such as optimization, image quality and tolerance analysis are fully utilized in the process of integral optimization. Since the system will be further optimized by the software, a small amount of sampling data points is enough to calculate the initial structure which speeds up the calculation. A passive ranging and three-dimensional imaging system with chiral phase mask is designed as an example. Different from conventional imaging system, two image points will be obtained by the system when one point is used as the object. Apparently, it is difficult for any commercial optical design software to design. The novel integral method proposed in this paper is applied to this system.Firstly, the system is designed in reverse sequence for the sake of simplification. A doublet with effective focal length 200mm and f-number 8 is used as the initial structure. Two points at (0,0.3,256.1) and (0,-0.3,256.1) are used as Please verify that (1) all pages are present, (2) all figures are correct, (3) all fonts and special characters are correct, and (4) all text and figures fit within the red margin lines shown on this review document. Complete formatting information is available at http://SPIE.org/manuscripts Return to the Manage Active Submissions page at http://spie.org/submissions/tasks.aspx and approve or disapprove this submission. Your manuscript will not be published without this approval. Please contact firstname.lastname@example.org with any questions or concerns. the “object” which will image at (0,0,-63.6) as the “image” in the reverse sequence. A free-form surface is added in front of the doublet, thus the whole system turns to a triplet system. 6X12 sampling data points are calculated to fit an XY polynomial surface. Secondly a commercial optical design software further optimizes the optical system with the free-form surface. Finally, we obtain a high-quality imaging system with a free-form surface. The MTF (Modulation Transfer Function) performance of the system is closed to diffraction limit.
Off-axis reflective optics, due to its no chromatic, no obscuration, small size, compact structure, easy to achieve wide field of view(FOV), high-quality imaging and other features, are widely concerned. In this paper, the conformal ellipsoidal dome of MgF2 material is used to allay the air resistance and reduce the aerodynamic heating effect of the missile head. The compact off-axis four-mirror is used to realize a conformal optical system of the seeker with medium wave infrared(MWIR)，which the working waveband is 3~5μm, F number is 2, FOV is ±1 degree and the focal length is 55mm. The optics achieve 100% cold aperture efficiency and the MTF value of each field at 17lp/mm is greater than 0.7. It has a working distance of 17.4mm and a sapphire window 14.7mm apart from the focal plane, leaving plenty of room for the refrigerant detector. This system can also meet the high accuracy positioning with imaging quality requirements and ensure light design of the seeker.
Using progressive design method, we designed and built a wide field of view (FOV) catadioptric lens for LWIR earth sensors in the 14 to 16 μm range. The prototype lens is compatible with 640×480 uncooled FPA and 25 microns pixel pitch. Its full field of view is 170° and F number is 0.86. The f-theta distortion is less than 1%. Besides, the system works well during a temperature range of -40°C~+60°C.
We designed a compact middle-wave infrared (MWIR) lens with a large focal length ratio (about 1.5:1), used in the 3.7 to 4.8 μm range. The lens is consisted of a compact front group and a re-imaging group. Thanks to the compact front group configuration, it is possible to install a filter wheel mechanism in such a tight space. The total track length of the lens is about 50mm, which includes a 2mm thick protective window and a cold shield of 12mm. The full field of view of the lens is about 3.6°, and F number is less than 1.6, the image circle is about 4.6mm in diameter. The design performance of the lens reaches diffraction limitation, and doesn’t change a lot during a temperature range of -40°C~+60°C. This essay proposed a stepwise design method of infrared optical system guided by the qualitative approach. The method fully utilize the powerful global optimization ability, with a little effort to write code snippet in optical design software, frees optical engineer from tedious calculation of the original structure.
The earth sensors on the satellites measure the attitude by observing the discontinuity between earth radiance and cold space background. As IR detector technology advances, the earth sensor has evolved from traditional scanning sensor to static sensors with uncooled infrared FPA. In order to obtain high pointing accuracy of the earth center and avoid the influence of the cloud layer, the optical system should have the following characteristics such as: excellent f-theta linearity, high MTF at corresponding frequency, and high transmittance in the 14 to 16 μm range. In addition, this earth sensor is intended to be used on a LEO satellite, so the optical system must cover a wide FOV larger than 130°, and be as light and compact as possible.
This paper contains the full design process of a wide-angle lens used for LWIR earth sensors from paraxial power allocation calculation to optimization of lens. The lens has a relative large image circle of 13mm, which is compatible with a 640×480 25μm uncooled FPA, and its full FOV is 180°. Its focal length is 4.177 and F number is 0.8. The f-theta distortion is less than 0.25%. By choosing chalcogenide glasses as lens material, the lens has a higher transmittance compare to Germanium lens. Also by analyzing the chromatic aberration of the lens, applying a DOE surface helps to improve the image quality, and pushes the modulated transfer function towards diffraction limitation.