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Created by hugo.defienne on 10/08/2020
Unscrambling entanglement through a complex medium
[N. H. Valencia, S. Goel, W. McCutcheon, H. Defienne and M. Malik, Nature Physics (2020)] Quantum properties of light may enable unconditionally secure optical communications. In this respect, high-dimensional entangled states offer a way of exceeding the limitations of current approaches to quantum communication (e.g. larger information capacity and increased noise resilience). For example, the orbital angular momentum of photons was first used to establish high-dimensional quantum key distribution (HD-QKD) protocols in free-space, but with a limited range due to diffraction and the presence of atmospheric turbulence. Alternatively, multimode optical fibers (MMF) can be used to transport information encoded in parallel across many modes over large distances, and with limited losses. However, the complex mode mixing process occurring during light propagation through the fiber scrambles the encoded information, making it unusable by the receiver. In their work, N. H. Valencia and co-workers demonstrate the transport of six-dimensional spatial-mode entanglement through a 2m-long commercial MMF, by compensating the random mode mixing effect using a transmission matrix-based wavefront-shaping technique. Such an ability to certify the presence of high-dimensional entanglement between two parties (Alice and Bob) is an essential step towards the implementation of practical HD-QKD protocols in optical fibers. |
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Created by sebastien.popoff on 03/08/2020
Parallelized STED microscopy using tailored speckles
[N. Bender et al., arxiv, 2007.15491 (2020)] Super-resolution fluorescence microscopy techniques, such as stimulated emission depletion (STED), rely on depleting fluorescence around a region smaller than the limit of diffraction. This can be achieved with a doughnut-shaped beam that is then scanned to produce an image. Such a process is time-consuming. Structured illumination techniques were proposed to parallelize the process by having multiple zeros of the field in the same image, for example with an array of doughnut beams. However, it typically limits optical sectioning as the field conserves its shape for quite large distances along the axial direction. One way to overcome this limitation is to use speckle patterns. Speckle exhibits numerous singularities, allowing parallelization of the technique, and they rapidly and non-repeatably change along the axial direction, guarantying the optical sectioning while being robust to aberrations. The issue is that speckle singularities (optical vortices) are not isotropic, leading to distortions of the image. In the present paper, N. Bender and co-authors use wavefront shaping to design ideal speckle patterns for non-linear microscopy to achieve isotropic and uniform super-resolution. |
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Created by sebastien.popoff on 17/07/2020
Noninvasive incoherent imaging through scattering media based on wavefront shaping
[T. Yeminy and O. Katz., arxiv, 2007.03956 (2020)] Wavefront shaping unlocked many exciting applications related to imaging through scattering media. However, they usually require to have some feedback from the object to observe, typically a guide-star generated by physically labeling the sample or by using ultrasound (that reduced the resolution). Other computer-based approaches recently developed relied on the memory-effect, which drastically limits the field of view, or requires a coherent illumination. In the present paper, T. Yeminy and O. Katz present a very simple approach that allows the reconstruction of an object hidden behind a scattering medium under incoherent illumination. It uses wavefront shaping of the scattered light together with an optimization procedure based on some assumptions about the object. |
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Created by sebastien.popoff on 04/07/2020
Endoscopy combining photoacoustic and fluorescence imaging with a small footprint
[S. Mezil et al., arxiv, 2006.10856 (2020)] Achieving optical-resolution photoacoustic imaging can currently only be obtained using endoscopy. It usually implies a quite bulky endoscope and/or a low signal-to-noise detection. In this paper, the authors present a technique that combines wavefront shaping through a multimode fiber, to scan the focus spot, with a single-mode fiber-based ultrasound sensor to achieve a high signal-to-noise with a small footprint (250 by 125 microns). |
