Master intership + PhD at the Langevin Institute

Invariant Properties in Multimode Fibers for Imaging Applications

We are recruiting a master student with the possibility to continue during a Ph.D (funded) to work on the study of light propagation in multimode fibers using wavefront shaping and numerical reconstruction algorithms (phase retrieval, deep learning). Join un in Paris!

Keywords: waveftont shaping, mutlimode fibers, mesoscopic physics, phase retrieval, deep learning

See our recent publication: 

• [Learning and avoiding disorder in multimode fibers, Phys. Rev. X, 2021]
• [Tailoring the Rotational Memory Effect in Multimode Fibers, arxiv, 2023]

TL;DR:
We will play with deep learning frameworks to develop new approaches for calibration-less imaging through multimode fibers based on the study of invariant properties in multimode fibers.

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

More information here.

Call for papers on Wavefront Shaping Tutorials:
JPhys Photonics Special Issue

Guest Editors

• Ivo Vellekoop - University of Twente, Netherlands
• Joshua Brake - Harvey Mudd College, United States
• Sébastien Popoff - CNRS - Institut Langevin - ESPCI, France

In the past 15 years, wavefront shaping has emerged as a preferred tool for controlling and studying light propagation in complex media. Thousands of papers have been published, many of which present new and potentially exciting applications. However, wavefront shaping is a tool that requires experience, custom codes, and most importantly, specific tricks, which are often not published or shared. This special issue provides an opportunity to disseminate this information, thereby ensuring the reproducibility of the results and promoting the spread of techniques in this field.

More information here

Here is a small experimental chatbot designed to answer questions about wavefront shaping.

The model is trained on the full text transcript of wavefrontshaping.net, as well as a collection of hundreds of transcripts of wavefront shaping-related articles and abstracts.

Compensating for phase drifts in holographic measurements

Digital holography allows measuring the complex amplitude of a given wavefront. We presented in detail the off-axis holography approach. However, it requires a separate reference arm. Due to air flow, vibrations, or other perturbations, the optical path length difference between the two arms can fluctuate in time, even in controlled lab experiments on a good optical table. This means that the phase of the measured wavefront is estimated up to a global phase that can randomly change over time. This is very detrimental for transmission matrix measurements as the relative phase between each column has to be precisely estimated. This is particularly true when the measurement time can take few minutes or more when using a liquid crystal spatial light modulator that has a limited frame rate. In [R. Mouthaan et al., Appl. Opt. (2022)], the authors propose a simple yet robust way to compensate for phase fluctuations, even when the phase changes completely between two frames.