Learning and avoiding disorder in multimode fibers

[M.W. Matthès, arxiv, 2010.14813 (2020)]

In the past 10+ years, numerous advances were made for endoscopic imaging, micromanipulation, or telecommunication applications with multimode fiber. The main limitation to real-life applications is the sensitivity to perturbations that sometimes causes the transmission property of the fiber to change in real-time. To address this issue, the authors (we) show that, even in the presence of strong perturbations, there exists a set of channels that are almost insensitive to perturbations. Interestingly, these channels can be found using only measurements from small perturbation leveraging the so-called generalized Wigner-Smith operator. This requires the measurement of the transmission matrix, which is done thanks to a new technique based on deep learning frameworks that compensate automatically for misalignments and aberrations, allowing fast and easy acquisitions.

DMD diffraction tool

I presented in this tutorial the diffraction effects occurring in a DMD setup. It corresponds to a blazed grating effect and depends on the wavelength \(\lambda\), the pixel pitch \(d\), the incident angle \(\alpha\), and the angle of the micro-mirrors \(\theta\). Here is a simple app (see source code on Github) to calculate the criterion for optimal diffraction efficiency and the aspect of the diffraction pattern in the far-field when illuminating the DMD with a plane wave of incident angle \(\alpha\) with respect to the normal of the surface.

About mechanical stability using Vialux DMDs

We have been using DMDs from Vialux for a few years now, and I already published few posts about different effects that need to be taken into account when working with such devices (in particular aberrations and diffraction effects). One more trivial, but potentially troublesome, effect is due to vibrations, that come from the FPGA board and transmitted through the rigid flat cables. In this quick post, I show the damaging effect of vibrations and how to easily get rid of them, at least partially.

How to generate macropixel patterns for SLMs/DMDs with the Layout module

In many wavefront shaping experiments, such as for optimization experiments, like the seminal work by I. Vellkoop and A. Mosk, or for measuring the transmission matrix, one needs to control the amplitude and/or the phase of the field on a given number of macropixels (i.e. groups of pixels). Using DMDs, amplitude, and phase modulation can be achieved using the Lee hologram method and then sending the binary images to the device using the for ALP4lib in Python for Vialux DMDs. I released here a module written by M. W. Matthès and myself to easily and efficiently generate such patterns. The code can be found on my Github account here as well as an amplitude and phase modulation example: layout_amplitude_phase_modulation.ipynb.