Optical Design of Visible and Short-wave Infrared
Common-Aperture Imaging Spectrum System
Pei Linlin, Wang Jianwei, Lv Qunbo
Academy of Opto-electronics, Chinese Academy of Sciences, No 9, Deng Zhuang South Road, HaiDian District, Beijing,100094, China
pll@aoe.ac.cn
Abstract: in this paper, we design a common-aperture imaging spectrum system. We choose
reflective lenses as the main structure, and three refractive lenses to correct axial aberrations.
The system is just 260mm in length. The image quality is good.
OCIS codes: (110.0110) Imaging system; (300.0300) Spectroscopy; (310.0310) Thin films
1. Introduction
There are many classification methods for imaging spectrum system. According to the splitting method, the
system can be divided into prism dispersion type, grating diffraction type, interference type, and filter type
[1]
.
We can directly place a linear gradient filter on the image plane of the imaging lens to achieve a filter type
imaging spectrum system. The other several imaging spectral techniques are very complex.
In this paper, we design a imaging spectrum system based on the linear gradient filter, which can be used to
obtain high-spectrum acquisition in a limited space and volume range. We use common-aperture to achieve a
wider spectrum.
2. Optical system design
A spatially-divided filter is used as a light-splitting element, which is placed at a position facing the
surface of the detector. Several rows of pixels of the detector are corresponding to one spectral band, and
the entire surface of the detector is corresponding to many spectral bands. Each time a photograph is taken
to obtain two-dimensional spatial information of a certain area target and spectral information of a specific
spectral band. Through the platform flight to achieve the sweep of the spatial dimension, which is
equivalent to sweeping in the spectral dimension, to obtain the complete data of the target.
Visible and short-wave infrared light can go through many kind of glass materials, but they cannot present
on one detector, means the detctor cannot response such a wide spectrum of wavelength. We design a splitting
prism to achieve one way visible light and one way short-wave infrared light
[2]
. The specific indicators of the
optical system determined by the project demand decomposition index are as follows:
Focal length: 890mm
Field of view: 1.96°
F/#: 3.5
Number of bands: 60
To analysis the optical system indexes, it belongs to medium focal length optical systems. The total length
of the system is limited to 300mm. Therefore, the classical Cassegrain optical structure is adopted. The design
results are shown in the Fig.1. The multiple structures are used in Zemax. The reflection way at a wavelength of
420 nm to 900 nm is imaged by a linearly graded filter on a visible light detector. The transmit way at a
wavelength of 900 nm to 1700 nm is imaged by a linearly graded filter on a short wave infrared detector.
Fig.1. Optical system diagram
3. Filter design
The filter array is a key technical component of this system, and its processing level is directly related to the
spectral resolution of the final acquired image. The entire filter array is divided into two parts: the coated
