Mahalanobis Abhijit, Neifeld Mark, Bhagavatula Vijaya Kumar, Haberfelde Thomas, Brady David
Lockheed Martin Missiles and Fire Control, Orlando, Florida 32819, USA.
Appl Opt. 2009 Oct 1;48(28):5212-24. doi: 10.1364/AO.48.005212.
Sparse apertures find imaging applications in diverse fields such as astronomy and medicine. We are motivated by the design of a wide-area imaging system where sparse apertures can be used to construct novel and efficient optical designs. Specifically, we investigate the use of sparse apertures for off-axis imaging at infrared wavelengths while combating the effects of chromaticity to preserve resolution. In principle, several such sparse apertures can be interleaved within a common aperture to simultaneously image in multiple directions. This can ultimately lead to the design of wide-area imaging systems that require considerably less optical and electronic hardware. The resolution achievable using a sparse aperture is the same as that of a fully open aperture. In the case of off-axis imaging, however, the point spread function (PSF) introduces a blur due to chromaticity that degrades the resolution of the system. Of course, the blur can be eliminated by imaging at a single wavelength. However the signal-to-noise ratio (SNR) is poor, which ultimately degrades image quality. To improve SNR, it is necessary to widen the band of wavelengths, which of course degrades resolution due to chromaticity. Hence there is a fundamental trade between the SNR and the resolution as a function of bandwidth. We show that by using a combination of microprisms and phase optimized micropistons it is possible to reduce the chromatic blur over a band of wavelengths and improve the PSF considerably to restore the resolution of the image. The concepts are validated by means of simulations and verified with experimental data to demonstrate the advantages of phase optimized micropistons in off-axis sparse aperture imaging systems.
稀疏孔径在天文学和医学等不同领域有着成像应用。我们的灵感来源于一种广域成像系统的设计，在该系统中稀疏孔径可用于构建新颖且高效的光学设计。具体而言，我们研究了稀疏孔径在红外波长下用于离轴成像的情况，同时应对色度效应以保持分辨率。原则上，几个这样的稀疏孔径可以交错排列在一个共同的孔径内，以便在多个方向上同时成像。这最终可能导致广域成像系统的设计，该系统所需的光学和电子硬件要少得多。使用稀疏孔径可实现的分辨率与完全开放孔径的分辨率相同。然而，在离轴成像的情况下，点扩散函数（PSF）由于色度会引入模糊，从而降低系统的分辨率。当然，通过在单一波长下成像可以消除模糊。然而，信噪比（SNR）很差，这最终会降低图像质量。为了提高信噪比，有必要拓宽波长范围，而这当然会由于色度而降低分辨率。因此，作为带宽的函数，信噪比和分辨率之间存在根本的权衡。我们表明，通过结合使用微棱镜和相位优化的微活塞，可以在一定波长范围内减少色度模糊，并显著改善点扩散函数以恢复图像分辨率。这些概念通过模拟得到验证，并通过实验数据进行了验证，以证明相位优化的微活塞在离轴稀疏孔径成像系统中的优势。
