Objective High function density electro-optical (EO) system is becoming an important development direction at present and in the near future. With the gradual maturity of wide-band infrared detector technology, VIS-SWIR (from visible to short wave infrared) wide-band confocal zoom optical system, which can support various operational modes such as color imaging, fog penetration, and low-light conditions, effectively simplify the overall design of EO systems, turns into an important mean to realize the high functional density and SWaP&C (Size, Weight, Power, and Cost) of EO system, but optical materials show great differences in dispersion characteristics within this band, which makes design of continuous zoom system difficult and time-consuming. Studying of the corresponding optical system design method become necessary and urgent.
Methods In order to solve this problem, a wide band zoom optical design model (Eq. (1)-Eq. (3)) is established with the combination of classical continuous zoom system design model and the achromatic conditions in the design of wide-band optical system. The parameters affecting the color aberration distribution of the whole system are explicitly demonstrated in the model. Based on the proposed model, the methods of optical power distribution and material selection are further discussed. Considering the dispersion characteristics of glass materials in different bands, some material using guidelines with examples in Tab.1 of wideband zoom lens design is provided. The extraordinary applications of the cemented elements, especially the synthetic abnormal dispersion characteristics and its synthetic method, are pointed out explicitly.
Results and Discussions A wideband (VIS-SWIR) optical system under the requirements of F≤5.5, focal length 10-300 mm, horizontal field of view 38.8°-1.25°, waveband of 0.48-1.7 μm, 1 080 P InGaAs detector with pixel size of 3.45 μm is designed (Fig.3) to fulfill multi-band imaging by switching filters, and realize the common aperture integration of different functions such as color/fog-penetrating/laser/low-light imaging through a switching mechanism or a dichroic prism (Fig.4-Fig.5). It can be observed from Tab.3 that at a frequency of 100 lp/mm and 145 lp/mm, the MTF values at the edge of the field of view are approximately 0.3 and 0.1 across the wide wavelength range of 0.48 μm to 1.7 μm, the relative distortion at each focal length position is less than 2%; the chromatic focus shift at each focal length position is within the focal depth (162 μm) as 1.1 μm is taken as the central wavelength. The zoom lens system, which uses 7 kinds of optical glass, consists of 18 lenses, total length 190 mm, has good image quality and tolerance character through the full zoom range.
Conclusions Starting from the zoom system design model, a design method for a wide-band zoom system is discussed with consideration of the achromatic conditions within and between bands of a wide-band system. Material selection criteria for different components of the zoom system are provided, which reduces the time-consuming and tedious trial-and-error process of traditional methods. This approach can effectively guide the design and development of related optical systems. As an example, a continuous zoom optical system with a wide wavelength range of 0.48 μm to 1.7 μm is designed using only commonly used optical glass. This system achieves integration of a common aperture and common focal plane for the visible light, near-infrared, and short-wave infrared bands. It features a telephoto ratio better than 0.64 and a zoom ratio of 30×. Additionally, it demonstrates excellent imaging quality throughout the entire zoom range and is compatible with multi-band, multi-mode, and multi-purpose applications, making it promising for widespread use in related fields.
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