Created by sebastien.popoff on 01/09/2020

Highlights

Spatio-temporal shaping of light through a scattering medium

[A. Boniface et al., arxiv, 2007.09050 (2020)]

Controlling the spatial and temporal properties of a short pulse is already difficult in free space, and require a well-calibrated and specific setup. When the pulse propagates through a scattering medium, its temporal and spatial properties are randomized, leading to a spatio-temporal speckle. However, the effect of the medium can be described by means of the multi-spectral transmission matrix. In this paper, A. Boniface and his colleagues show that by measuring previously this matrix, and by only controlling the spatial input field using a spatial light modulator, they can modulate at will the spatio-temporal properties of the point spread function of a pulse traveling through a complex medium.

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Created by sebastien.popoff on 17/07/2020

Highlights

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 22/06/2019

Talks Wavefront shaping

Wavefront Shaping in Complex Media for Linear Analog Computation

Sebastien M. Popoff

PR'19: Photorefractive Photonics and beyond (Gerardmer, France), June 21 2019

Abstract: Performing linear operations using optical devices is a crucial building block in many fields ranging from telecommunications to optical analog computation and machine learning. For many of these applications, key requirements are robustness to fabrication inaccuracies, reconfigurability, and scalability. Traditionally, the conformation or the structure of the medium is optimized in order to perform a given desired operation. Since the advent of wavefront shaping, we know that the complexity of a given operation can be shifted toward the engineering of the wavefront, allowing, for example, to use any random medium as a lens. We propose to use this approach to use complex optical media such as multimode fibers or scattering media as a computational platform driven by wavefront shaping to perform analog linear operations. Given a large random transmission matrix representing the light propagation in such a medium, we can extract any desired smaller linear operator by finding suitable input and output projectors. We demonstrate this concept by finding input wavefronts using a Spatial Light Modulator that causes the complex medium to act as a desired complex-valued linear operator on the optical field.

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Created by sebastien.popoff on 13/05/2019

Highlights

The speckle-correlation transmission matrix

[K. Lee and Y. Park, Nat. Commun, 7 (2016)]

[Y. Baek, K. Lee and Y. Park, Phys. Rev. Appl., 7 (2016)]

[L. Gong, Q. Zhao, H. Zhang, X.-Y. Hu, K. Huang, J.-M. Yang and Y.-M. Li, Light Sci. Appl., 8 (2019)]

Measuring the optical phase is a ubiquitous challenge in optics. Through a linear scattering medium, one can always link the output optical field to the input one using the transmission matrix. However, one still has to measure the phase of the complex output field. In [K. Lee and Y. Park, Nat. Commun, 7 (2016)] the authors introduce a technique to reconstruct a complex optical field using a thin diffuser. Once the matrix is calibrated, only an intensity measurement is required to reconstruct the amplitude and the phase of the complex optical field.

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