Optical design of compact unobscured ground-based diffractive telescope

The present invention provides an aberration-eliminating film telescopic system based on a movable optical element. The system comprises a film primary mirror, a field diaphragm, an eyepiece, a tilting mirror, a deformable mirror, an imaging lens, an imaging CCD and an adaptive optical control system, wherein the film primary mirror, the field diaphragm, the eyepiece, the tilting mirror, the deformable mirror, the imaging lens, the imaging CCD and the adaptive optical control system are sequentially arranged along an optical path. Firstly, a hartmann sensor is adopted to replace an imaging objective lens in the optical path and an imaging CCD. Secondly, the ideal laser is adopted as the incident light and the inherent aberration of the film telescopic system is detected by the hartmann sensor. Thirdly, based on the detected aberration, the tilting mirror and the deformable mirror are controlled to realize the surface type compensation of the telescopic system. In this way, the aberration of the system is eliminated and the control voltage at the current moment is recorded. Finally, the imaging objective lens and the imaging CCD are moved back into the optical path, and a recorded static voltage is loaded. As a result, the aberration compensation of the telescope system is finished. The system of the present invention is simple, reliable and easy to implement, and the imaging quality of film telescope system can be significantly improved.

Aberration-eliminating film telescopic system based on movable optical element

In this paper, we present a model that analyzes the influence of the temperature on the modulation transfer function (MTF) of an infrared membrane diffraction optical system. Based on the physical imaging mechanism of diffractive optical systems, the imaging characteristics of the diffraction optical system are characterized by using diffraction efficiency. Then we establish the corresponding calculation model and MTF analysis model based on scalar diffraction theory. In particular, considering the material properties of flexible membrane optical elements and thermal environment effect, the Zernike polynomials are used to establish the thickness distribution model of the membrane diffractive optical components combined with the finite element analysis. After that, we modify the MTF calculation model of diffraction optical system and accordingly propose the model of the infrared membrane diffraction optical system. Finally, we present some experimental results for a 2-m infrared membrane diffraction optical system. The results show that when the temperature is −40°C and wavelength band is 80 nm at the center field of view, the diffraction efficiency is reduced to 81%, and MTF at 75 l p/mm is reduced to 0.12. And when the temperature is −40°C at edge field of view, the efficiency at center wavelength is reduced to 71%, and MTF at 75 l p/mm is reduced to 0.02. The established model and method can be used to estimate the imaging performance of a space infrared membrane diffractive telescope and provide theoretical guidance for the processing algorithm and imaging system design.

Influence of ambient temperature on the modulation transfer function of an infrared membrane diffraction optical system.

For the simulation of relief-type diffractive surfaces, an efficient method has been developed and described. Based on zone decomposition, our approach maps the transmitted wavefront by ray tracing, while point spread function/modulation transfer function (PSF/MTF) plots are calculated by scalar diffraction, taking light diffracted into multiple orders into account inherently. Using a parametric user-defined surface, our solution makes the analysis and optimization of diffractive lenses possible directly inside optical design software. Implementation was carried out in ZEMAX in the form of a swift Windows Dynamic Link Library extension using an approximative, non-iterative algorithm. The average computation time increments relative to standard built-in surfaces are 38% and 21% for PSF and MTF calculations, respectively. Application of our method is illustrated by the analysis of diffractive intraocular lenses. For validation, numerical results were compared with analytical formulae and industry-standard measurements. The ray-tracing error caused by our approximation proved to be less than ${7} \cdot {{10}^{ - 6}}$7⋅10-6 wavelength, and the difference from the theoretical MTF calculations is 1%-2%. The RMS difference of the simulated-measured through-focus MTF values at 50 lp/mm is 0.031, equaling ${2}\sigma $2σ measuring accuracy.

Simulation of relief-type diffractive lenses in ZEMAX using parametric modelling and scalar diffraction.

Diffractive telescope is an updated imaging technology, it differs from conventional refractive and reflective imaging system, which is based on the principle of diffraction image. It has great potential for developing the larger aperture and lightweight telescope. However, one of the great challenges of design this optical system is that the diffractive optical element focuses on different wavelengths of light at different point in space, thereby distorting the color characteristics of image. In this paper, we designs a long-wavelength infrared diffractive telescope imaging system with flat surface Fresnel lens and cancels the infrared optical system chromatic aberration by another flat surface Fresnel lens, achieving broadband light(from 8μm-12μm) to a common focus with 4.6° field of view. At last, the diffuse spot size and MTF function provide diffractive-limited performance. © 2015 SPIE.

Design of infrared diffractive telescope imaging optical systems

Diffraction image technology is an updated technology. It has more potential for developing the larger aperture and lightweight telescope than the conventional refractive and reflective optics. In order to develop a large aperture diffractive telescope, the key is to solve the problem of large aperture lens stitching. Different stitching patterns have different effects on the image quality. However, the stitching pattern for diffractive telescope is different from the conventional refractive and reflective telescope. This paper, for the first time, studies the theory of stitching pattern for diffractive telescope. On the basis of theoretical analysis, a long-wavelength infrared diffractive telescope of segmented-lens is designed and for the first time, good results through stitching experiments have been achieved. According to theoretical analysis and experiment verification, the paper gives the best stitching pattern on diffractive telescope.

Effects of stitching pattern on diffractive telescope image quality

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Design of infrared diffractive telescope imaging optical systems

Effects of stitching pattern on diffractive telescope image quality