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Light beams with spatially variant states of polarization (SOPs) have attracted increasing interest recently because their vector nature brings unique perspectives to optics and photonics. Nevertheless, their applications are challenged when transposed to scattering media, because of the inherent depolarization effects arising from multiple scattering. Wavefront shaping techniques are expected to confront these challenges; however, shaping spatially variant SOPs in addition to amplitude and phase of light through scattering media has not been explored yet. Here, we present a general framework based on the vector transmission matrix to simultaneously tailor these properties. Further, we demonstrate its use in producing multiple focal spots and structured light beams with spatially variant SOPs behind the scattering media, which is confirmed by simulations. As a particular application, by encoding information into light's spatially distributed SOPs, we are able to directly encrypt multiplexed grayscale images into a single laser beam behind a scattering medium. Our work is expected to find potential applications such as optical imaging in deep tissues, optical encryption, and communication. [ABSTRACT FROM AUTHOR]

Mid-infrared (2–20 μm) light has been attracting great attention in many areas of science and technology. Beyond the extended wavelength range from visible and near-infrared to mid-infrared, shaping spatial structures may add opportunities to grooming applications of mid-infrared photonics. Here, we design and fabricate a reflection-enhanced plasmonic metasurface and demonstrate efficient generation of structured light with the phase helix and intensity helix at 2 μm. This work includes two distinct aspects. First, structured light (phase helix, intensity helix) generation at 2 μm, which is far beyond the ability of conventional spatial light modulators, is enabled by the metasurface with sub-wavelength engineered structures. Second, the self-referenced intensity helix against environmental noise is generated without using a spatially separated light. The demonstrations may open up advanced perspectives to structured light applications at 2 μm, such as phase helix for communications and non-communications (imaging, sensing) and intensity helix for enhanced microscopy and advanced metrology. [ABSTRACT FROM AUTHOR]

It has been shown that in the asymptotic case of infinite-key length, the 2-decoy state Quantum Key Distribution (QKD) protocol outperforms the 1-decoy state protocol. Here, we present a finite-key analysis of the 1-decoy method. Interestingly, we find that for practical block sizes of up to 108 bits, the 1-decoy protocol achieves for almost all experimental settings higher secret key rates than the 2-decoy protocol. Since using only one decoy is also easier to implement, we conclude that it is the best choice for QKD, in most common practical scenarios. [ABSTRACT FROM AUTHOR]