Shen Yuecheng, Liu Yan, Ma Cheng, Wang Lihong V
Optical Imaging Laboratory, Department of Biomedical Engineering, Washington University in St. Louis, One Brookings Drive, St. Louis, Missouri, USA, 63130.
Optica. 2017 Jan 20;4(1):97-102. doi: 10.1364/OPTICA.4.000097. Epub 2017 Jan 11.
Optical time-reversal techniques are being actively developed to focus light through or inside opaque scattering media. When applied to biological tissue, these techniques promise to revolutionize biophotonics by enabling deep-tissue non-invasive optical imaging, optogenetics, optical tweezing, and phototherapy. In all previous optical time-reversal experiments, the scattered light field was well-sampled during wavefront measurement and wavefront reconstruction, following the Nyquist sampling criterion. Here, we overturn this conventional practice by demonstrating that even when the scattered field is under-sampled, light can still be focused through or inside scattering media. Even more surprisingly, we show both theoretically and experimentally that the focus achieved by under-sampling can be one order of magnitude brighter than that achieved under the well-sampling conditions used in previous works, where 3×3 to 5×5 pixels were used to sample one speckle grain on average. Moreover, sub-Nyquist sampling improves the signal-to-noise ratio and the collection efficiency of the scattered light. We anticipate that this newly explored under-sampling scheme will transform the understanding of optical time reversal and boost the performance of optical imaging, manipulation, and communication through opaque scattering media.
光学时间反演技术正在积极研发中，用于透过或在不透明散射介质内部聚焦光。当应用于生物组织时，这些技术有望通过实现深层组织无创光学成像、光遗传学、光镊和光疗，给生物光子学带来变革。在之前所有的光学时间反演实验中，散射光场在波前测量和波前重建过程中都按照奈奎斯特采样准则进行了充分采样。在此，我们颠覆了这一传统做法，证明即使散射场采样不足，光仍可透过或在散射介质内部聚焦。更令人惊讶的是，我们通过理论和实验均表明，欠采样实现的聚焦可比之前工作中使用3×3至5×5像素平均采样一个散斑颗粒的充分采样条件下实现的聚焦亮一个数量级。此外，亚奈奎斯特采样提高了散射光的信噪比和收集效率。我们预计，这种新探索的欠采样方案将改变对光学时间反演的理解，并提升通过不透明散射介质进行光学成像、操控和通信的性能。
