Superpixel-based spatial amplitude and phase modulation using a digital micromirror device.

This is the final version of the article. Available via open access from Optical Society of America via the DOI in this record.We present a superpixel method for full spatial phase and amplitude control of a light beam using a digital micromirror device (DMD) combined with a spatial filter. We combine square regions of nearby micromirrors into superpixels by low pass filtering in a Fourier plane of the DMD. At each superpixel we are able to independently modulate the phase and the amplitude of light, while retaining a high resolution and the very high speed of a DMD. The method achieves a measured fidelity F = 0.98 for a target field with fully independent phase and amplitude at a resolution of 8 × 8 pixels per diffraction limited spot. For the LG10 orbital angular momentum mode the calculated fidelity is F = 0.99993, using 768 × 768 DMD pixels. The superpixel method reduces the errors when compared to the state of the art Lee holography method for these test fields by 50% and 18%, with a comparable light efficiency of around 5%. Our control software is publicly available.We thank Duygu Akbulut, Hasan Yılmaz, Henri Thyrrestrup, Michael J. Van De Graaff, Pepijn W.H. Pinkse, Ad Lagendijk and Willem L. Vos for discussions. This work is part of the research program of the Stichting voor Fundamenteel Onderzoek der Materie (FOM). A.P.M. acknowledges European Research Council grant no. 279248

High-fidelity multimode fibre-based endoscopy for deep brain in vivo imaging

Progress in neuroscience constantly relies on the development of new techniques to investigate the complex dynamics of neuronal networks. An ongoing challenge is to achieve minimally-invasive and high-resolution observations of neuronal activity in vivo inside deep brain areas. A perspective strategy is to utilise holographic control of light propagation in complex media, which allows converting a hair-thin multimode optical fibre into an ultra-narrow imaging tool. Compared to current endoscopes based on GRIN lenses or fibre bundles, this concept offers a footprint reduction exceeding an order of magnitude, together with a significant enhancement in resolution. We designed a compact and high-speed system for fluorescent imaging at the tip of a fibre, achieving micron-scale resolution across a 50 um field of view, and yielding 7-kilopixel images at a rate of 3.5 frames/s. Furthermore, we demonstrate in vivo observations of cell bodies and processes of inhibitory neurons within deep layers of the visual cortex and hippocampus of anesthetised mice. This study forms the basis for several perspective techniques of modern microscopy to be delivered deep inside the tissue of living animal models while causing minimal impact on its structural and functional properties.Comment: 10 pages, 2 figures, Supplementary movie: https://drive.google.com/file/d/1Fm0G3TAIC49LVX6FaEiAtlefkWx1T2a5/vie

Secure communication with coded wavefronts

Communication between a sender and receiver can be made secure by encrypting the message using public or private shared keys. Quantum key distribution utilizes the unclonability of a quantum state to securely generate a key between the two parties [1]. However, without some way of authentication of either the sender or the receiver, a man-in-the-middle attack with an eavesdropper mimicking the receiver can break the security of the protocol

Asymmetric cryptography with physical unclonable keys

\u3cp\u3eSecure communication is of paramount importance in modern society. Asymmetric cryptography methods such as the widely used RSA cryptosystem allow secure exchange of information between parties who have never previously shared keys. However, the existing asymmetric cryptographic schemes rely on unproven mathematical assumptions for security. Further, the digital keys used in their implementation are susceptible to copying that might remain unnoticed. Here, we introduce a secure communication method based on Physical Unclonable Keys (PUKs), which we call PUK-Enabled Asymmetric Communication (PEAC). PEAC uses physical keys and thus overcomes the problem of unnoticed copying. As all the information about the PUK is allowed to be public, PEAC does not require the safekeeping of any digital information. Using optical PUKs realized in opaque scattering materials, we transmit messages in an error-corrected way employing off-the-shelf equipment. Information is transmitted as patterned wavefronts of few-photon wavepackets which can be successfully decrypted only with the receiver's PUK. The security of PEAC assumes technological constraints in distinguishing between different few-photon wavefronts. A heuristic argument for the security of PEAC is outlined focusing on a specific attack, namely state estimation. We demonstrate secure transmission of messages over a 2 m free-space line-of-sight quantum channel. PEAC enables new directions for physical key based cryptography.\u3c/p\u3

Asymmetric cryptography with physical unclonable keys

Secure communication is of paramount importance in modern society. Asymmetric cryptography methods such as the widely used RSA method allow secure exchange of information between parties who have not shared secret keys. However, the existing asymmetric cryptographic schemes rely on unproven mathematical assumptions for security. Further, the digital keys used in their implementation are susceptible to copying that might remain unnoticed. Here we introduce a secure communication method that overcomes these two limitations by employing Physical Unclonable Keys (PUKs). Using optical PUKs realized in opaque scattering materials and employing off-the-shelf equipment, we transmit messages in an error-corrected way. Information is transmitted as patterned wavefronts of few-photon wavepackets which can be successfully decrypted only with the receiver's PUK. The security of PUK-Enabled Asymmetric Communication (PEAC) is not based on any stored secret but on the hardness of distinguishing between different few-photon wavefronts