Optical synthetic aperture (OSA) is a promising solution for very high-resolution imaging while reducing its volume and mass. In this paper, first, the configuration of OSA systems are analyzed and the design methods of two types (Fizeau and Michelson) of OSA systems are summarized and researched. Second, Fizeau and Michelson OSA prototype systems are designed in detail. In the Michelson configuration, the instrument is made of sub-telescopes distributed in entrance pupil and combined by a common telescope via phase delay line. The design of Michelson configuration is more difficult than that of Fizeau configuration. In the design of Fizeau configuration, according to the third aberration theory tworeflective system is designed. Then the primary mirror of the two mirror system is replaced by the synthetic aperture. The whole system was simulated by Zemax software to obtain the Modulation transform function (MTF). In the design of Michelson configuration, the system is first divided into three parts: the afocal interferometric telescopes, beam combiner system and phase delay line. The three parts are designed respectively and then combined in Zemax software to obtain the MTF.
Optical synthetic aperture (OSA) can greatly improve the spatial resolution of the optical system. However, due to its long manufacturing cycle, it is difficult and expensive to manufacture. In this paper, we propose a method for numerical simulation of OSA imaging system, which can simulate the image process of the system before the system is manufactured and thus can greatly reduce the manufacturing costs. Firstly, the relationship of energy on the pixel of image plane between OSA systems of different filling factor are analyzed. Then based on the characteristics of the OSA imaging system, imaging model of optical synthetic aperture is analyzed. Moreover, after those methods of simulating space variant image system and space invariant image system are given. At last, a method assessing of the quality of optical synthetic aperture system was given. Simulation results are presented to demonstrate the feasibility of the proposed technique, in terms of spatially variant and spatially invariant optical synthetic aperture system was achieved.
The temperature of the high speed aircraft optical dome rises rapidly because of aerodynamic heating, which causes severe thermal radiation effect on the detection system in the aerodynamic thermal environment. Therefore, the tracking and acquiring ability of the detector is affected. The temperature distribution of the dome in the aerodynamic thermal environment was investigated through the finite element simulation. The radiative energy factor was used to sample the continuous radiative spectral energy of the dome outside and inside surfaces. The thermal radiation transmission of the dome outside and inside surfaces was simulated numerically using a ray tracing program based on the fourth-order Runge-Kutta algorithm and the Feder method. The number of traced radiative rays of the dome outside and inside surfaces was enormously reduced by introducing the concept of thermal pupil. The irradiance distribution of the dome on the detector’s photosensitive surface was obtained using this ray tracing program. The results showed that the thermal radiation of the dome causes radiation interference for the detection system, and makes the background noise of detection system increase in the aerodynamic thermal environment. Therefore, the thermal radiation of the dome in the aerodynamic thermal environment cannot be neglected.
Scattering phase function on horizontally oriented ice particles near the specular reflective direction is analytically modeled using a mixed method combining direct reflection and Fraunhofer diffraction components, where particles are simply treated as circular facets and the effect of fluttering is introduced under the assumption of Gauss distribution. The obtained model expression reveals that the essence of far-field scattering around specular direction is the diffraction pattern modulated by fluttered geometric reflection. Four groups of experiments are designed to validate this model at different wavelengths and incidence angles, and the calculated phase functions present good agreement both in distributions and peak values with that of T-matrix method in conjunction with a Monte Carlo stochastic process.
Based on the wave theory of aberrations, the Point Spread Functions (PSFs) of optical synthetic aperture imaging system
disturbed by some aberrations, such as Piston error, Tilt error, spherical aberration, astigmatism, were analyzed.
Additionally, the analytical expressions of the central value of the PSF (CVPSF) on Piston error and Tilt error were
deduced, and were simulated by MATLAB. The results show that when one sub-aperture of an N identical sub-apertures
synthetic array is disturbed by Piston error, the PSF fluctuates periodically. Furthermore, the PSF decreased by Piston error,
spherical aberration or astigmatism can be significantly compensated by defocus. And CVPSF is improved from 0.60 to
0.93 for the spherical aberration after it is compensated by defocus.
In this paper, the theory of optical synthetic aperture imaging system is described, with emphasis on the image evaluation by the Point Spread Function (PSF) and Optical Transfer Function (OTF). The optical synthetic aperture imaging technique achieves higher resolution at the cost of decreasing of Modulation Transfer Function (MTF) in near mid-band regions, and of increasing the sidelobes of the PSF. The image evaluation methods for optical synthetic aperture imaging system are given, such as two-point resolution criterion and MTF. The disadvantage of evaluation methods is analyzed by Rayleigh criterion, Sparrow criterion and threshold criterion. The conclusion is that the imaging quality of synthetic aperture system is no better than that of the single sub-aperture system when the sidelobe is 0.5 times of the central lobe of the PSF. Finally, we propose new evaluation criterions, such as the efficiency factor and quality factor, which are directly linked to MTF.