Created by sebastien.popoff on 25/08/2020

## Using prior information for speeding up the measurement of fiber transmission matrices

[S. Li et al., arxiv, 2007.15891, (2020)]

Due to disorder and dispersion, knowing the transmission matrix of a multimode fiber is usually required to reconstruct an input image for endoscopic applications. In the general case, its characterization for a fiber allowing $$N$$ guided modes requires at least $$N$$ complex measurements. However, we usually have additional information, the most common one being that the matrix is never totally random, and usually sparse, when expressed in the mode basis. In this study, the authors use such prior information to reduce drastically the number of measurements for the transmission matrix estimation using the framework of compressed sensing. They demonstrate the validity of such an approach for endoscopic imaging through multimode fibers.

Created by sebastien.popoff on 18/08/2020

## Taking advantage of imperfections to focus light in photonic crystals inside the stop gap

[R. Uppu et al., arxiv, 2007.11104v1 (2020)]

Photonic crystals have the ability to forbid the entrance of light for certain ranges of frequencies, that is even the usual reason why we build them. Within the spatial frequency range for which the stop band of a given photonic crystal exists, modulation of the input wavefront should not dramatically modify the penetration of light, which exhibits an exponential decay. In this paper, R. Uppu and collaborators from the University of Twente demonstrate that it is indeed possible to drastically change the penetration properties of light inside a photonic crystal by optimizing the wavefront taking advantage of unavoidable sources of disorder. They experimentally show the focusing of light inside such crystal beyond the expected maximal penetration length - the Bragg length.

Created by sebastien.popoff on 11/08/2020

## Postdoctoral position at the Langevin Institute

#### Wavefront shaping and study of light propagation in disordered multimode fibers

We are recruiting a postdoc for 1+ year(s) to work on the study of light propagation in multimode fibers for telecommunication applications using wavefront shaping. Join un in Paris!

Contact: Sébastien Popoff - sebastien.popoff(at)espci.fr