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.

Dynamic structured illumination for confocal microscopy

Structured illumination enhances the resolution of a standard microscope by encoding the high spatial frequencies of an object's image into lower spatial frequencies through the use of a carefully selected pattern. In essence, it modifies the optical transfer function (OTF), which is the Fourier Transform of the point spread function (PSF), to increase sensitivity to high spatial frequencies. In [G. Noetinger et al, Arxiv 2306.14631 (2023)], the authors introduce a novel technique that further leverages time by incorporating a temporal periodic modulation, specifically through the use of a rotating mask, to encode multiple transfer functions within the temporal domain. This methodology is exemplified using a confocal microscope setup. At each scanning position, a temporal periodic signal is captured, enabling the construction of multiple images of the same object. The image carried by each harmonic is a convolution of the object with a phase vortex of topological charge, similar to the outcome when using a vortex phase plate as an illumination. This enables the collection of chosen high spatial frequencies from the sample, thereby enhancing the spatial resolution of the confocal microscope.

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

All-fiber Control of Entanglement:
Recovering Correlations via Mechanical Perturbations in a Multimode Fiber

In quantum optical communications, single photons can be used as a unit of quantum information. However, one can supercharge their capacity to carry information by encoding high-dimensional quantum dits, or qdits, into their transverse shape. They allow having more than two levels per unit of information as it is the case for bits. In fiber optical communications, it requires using multimode fibers to harness the spatial degrees of freedom to encode the qduts. However, when propagating through a real-life multimode fiber, the transverse shape of the photons gets scrambled because of mode mixing and modal interference. This scrambling of transverse shape is typically rectified using free-space spatial light modulators. But, this remedy prevents us from achieving a truly resilient all-fiber operation and requires a careful alignment and lab-graded stability hindering real-life implementation. In [R. Shekel et al., Arxiv 2306.02288 (2023)], the authors introduce an all-fiber method for controlling the shape of single photons and spatial correlations between entangled photon pairs. They do so by implementing carefully controlled mechanical perturbations to the fiber.