The demand for spatial infrared remote sensors with high spatial resolution and wide imaging swatch becomes more and more urgent. Optical system is an important constraint on the performance of spatial infrared remote sensors. In this paper, a novel off-axis catadioptric optical system configuration with intermediate image is proposed. The imaging principle and the initial configuration solution method are analyzed. And an off-axis catadioptric freeform optical system is designed with the spectrum of 7.8-10.2μm, the aperture of 435 mm, the focal length of 1038 mm, and the field of view (FOV) of 9×1.1°. The modulation transfer function (MTF) value is better than 0.316@25lp/mm. The maximum relative distortion is -0.27%. And this optical system has good image-side telecentricity and image illumination consistency. The results show that the spatial infrared off-axis catadioptric freeform optical system has good imaging quality and engineering feasibility.
With continuous development, the hyperspectral imaging has become a hot topic in the field of remote sensing, since its enormous advantage in obtaining the material composition of atmosphere, land resources, battlefield environment and marine resources while observing the Earth in space. However, some challenges have hindered the application of space-based hyperspectral imaging system. To fulfill the requirements of the spectral imager especially for space use, the lightweight and stable structure is especially important. Here the implementation of a Large Aperture Hyperspectral Imaging Optical System is presented. The optical system achieves hyperspectral imaging from ultraviolet to infrared spectral bands. The different spectral bands share a large common aperture of Ø1.8m. A lightweight primary mirror is designed and supported by bipod structure. To keep the large distance between the primary mirror and second mirror, a Lightweight and high-strength truss has been applied. A hierarchical structure is adopt as the main structure of the whole system. With the diffraction gratings and optical slits, the image information of different spectral bands are detected by the different lines of pixels in a focal plane of planar array. By the creative works of the optical and mechanical design, a hyperspectral imaging optical system is implemented and shows the extensive application potential in space remote sensing.
In order to meet the remote sensing application requirements for high spatial resolution, hyperspectral resolution and wide swatch, the next generation spaceborne high-resolution hyperspectral imager is put forward. The spatial resolution is 15m, the swatch is 90km and the hyperspectral resolution can be better than 5nm and 10nm in the spectral range 0.4μm~1.0μm and 1.0μm~2.5μm respectively. The index parameters are optimized depending on SNR and MTF. Then the telescope optical system and spectral imaging optical system are designed owing to the optical technical parameters. A new reimaging off-axis multi-mirror anastigmatic configuration is adopted and the freeform surface is used on the off-axis mirror to realize the telecentric design with wide field of view and large relative aperture. The results show that the distortion is lower than 0.44%. The Offner configuration is applied in the spectral imaging optical system and off-axis lens are used to deduce the length and obtain higher imaging performance. The keystone and smile both can be controlled within 1/10 pixel. The optical system of spaceborne high-resolution hyperspectral imager has so favorable imaging quality and compact volume that can satisfy the demand of multiple application areas.
There is an urgent need for the imaging spectrometer with high spatial resolution and wide swathing range in the field of environment monitoring, agriculture evaluation and emergency disaster reduction. At the same time, higher request for the performance of spectrometers, such as signal-to-noise, is put forward to realize high-precision data inversion and quantitative detection. A telescope optical system with long focal length, large relative aperture and wide field-of-view is designed using for imaging spectrometer. The focal length is 1200 mm, the relative aperture is 1/3 and the field-of-view is 10°×1°. A new re-imaging off-axis six-mirror anastigmat (6MA) configuration is adopted. It is beneficial to control the stray light and achieve the telecentric design in the image space. A real entrance pupil is located in front of the system to minimize the aperture of scanning mirror. The whole system is divided into two modules and each module can image perfectly at the axial field of view. Therefore, each module can be aligned and tested individually to reduce the alignment difficulty of the whole system. The off-axis freeform surface is used to control the distortion lower than 0.5% and advance the imaging quality. Finally, the manufacture and alignment tolerance are simulated and analyzed. The design and analysis results show that the six-mirror anastigmat (6MA) off-axis freeform system can satisfy the demand of high-performance hyperspectral imaging for earth monitoring. Good imaging quality and loose tolerances indicate that this optical system is of strong engineering application value.
The acquisition of hyperspectral image dataset of the earth from space with high accuracy of spectrum and radiation is the objective that a number of space missions dedicate to, which is critical to studying and quantifying aquatic environments, wildfires, coastal ecosystem, and atmospheric composition. In this paper, a hyperspectral imager in geostationary orbit ranging from ultraviolet to longwave infrared is proposed. Geostationary perspective has the capability to provide high temporal, spatial, and spectral resolution measurements. The optical system employed in the proposal is composed of an ultra-large aperture afocal system, three telescope subsystems, and five spectral channels with area array image detectors. The key parameters of the system are identified through analyzing and optimizing of system architecture and specification.
Diffractive optical imaging is a new method to realize high-resolution imaging from geostationary orbit(GEO). Technical advantages of diffractive optical imaging is analyzed in the field of space optics. For application of super large diameter space optical system, the system scheme and a new achromatic method is proposed. An imaging system is developed and tested, the result of optical system wavefront is 0.169λ(RMS), optical system MTF is 0.85, and the imaging system MTF is 0.19. Test results show the new achromatic method is feasible. The above conclusions have reference significance for the development of super large diameter diffractive optical imaging system.
Diffractive membrane imaging can be widely used in infrared band due to its longer minimum linewidth and loose requirement of RMS to fabricate more easily and reduce production period and manufacturing cost than used in visible band. A deployable infrared diffractive membrane imaging system was designed, consisting of Φ200mm imaging aperture (actual aperture is Φ500mm) and deployable structure that supports the infrared membrane under tension. Its spectral band width is >1.2μm, field of view is >1°, and diffractive efficiency can be >60%. Stowed size is 150mm×150mm×400mm. Research result of this project can promote the application of diffractive membrane imaging in infrared band and provide an effective and feasible means for achieving extremely large optical primary mirror from compact, lightweight payload.
Transmissive diffractive membrane optic can be used in space optical telescope to reduce the size and mass of imaging system. Based on the international research results about transmissive diffractive membrane, a 4-level diffractive substrate with 100mm apertures was designed and transmissive diffractive membrane was fabricated by spin coating. High-precision support structure for diffractive membrane with surface precision 0.12λ RMS (λ=632.8nm) was introduced, and that can meet the diffractive imaging requirements. Diffraction efficiency of the diffractive membrane supported by support structure was tested, and the test results showed that diffraction efficiency was >50%. The step figure test results illustrated the etched deep precision was less the 10nm. The imaging wavefront test result demonstrated a wavefront error of about 38 nm RMS. The transmissive diffractive membrane optic can be very useful for large aperture imaging system to realize low mass and low cost.
Solar blind UV detecting system has many advantages such as strong environmental adaptability, low error rate, small volume and without refrigeration. To in-depth develop UV solar blind detection system research work has important significance for further improving solar blind UV detection technology. The working principle of solar blind UV detection system and the basic components were introduced firstly, and then the key technology of solar blind UV detection system was deeply analyzed. Finally, large coverage solar blind UV optical imaging system was designed according to the actual demand for greater coverage of the solar blind UV detection system. The result shows that the system has good imaging quality, simple and compact structure. This system can be used in various types of solar blind UV detection system, and is of high application value.
Squeezed light is an important non-classical light field. In this paper, we demonstrated a designed active imaging system
which use squeezed state light instead of coherent light as light source. The squeezed state light is generated by utilizing
the degenerate optical parametric amplifier based on periodically poled KTiOPO4 crystal. In order to obtain better
imaging results, microlens arrays are used for homogenizing the squeezed light. We describe experiment setup and
present some design result.
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