Author Archives: spopoff

Simulation of multimode fiber modes: Straight and bent fibers [WP2]

We present a two part tutorial on how to numerically estimate the modes of straight or bent multimode fibers of arbitrary radial index profile. It allows calculating the mode profiles, the propagation constants and estimating the transmission matrix of a segment of a multimode fiber with a reasonable computationnal complexity.

Part 1: Straight fibers

Part 2: Bent fibers

Turning Optical Complex Media into Universal Reconfigurable Linear Operators by Wavefront Shaping [Paper, WP1]

Maxime W. Matthès, Philipp del Hougne, Julien de Rosny, Geoffroy Lerosey and Sébastien M. Popoff, Arxiv, (2018)

Performing linear operations using optical devices is a crucial building block in many fields ranging from telecommunication to optical analogue computation and machine learning. For many of these applications, key requirements are robustness to fabrication inaccuracies and reconfigurability. Current designs of custom-tailored photonic devices or coherent photonic circuits only partially satisfy these needs. Here, we propose a way to perform linear operations by using complex optical media such as multimode fibers or thin scattering layers as a computational platform driven by wavefront shaping. Given a large random transmission matrix (TM) representing light propagation in such a medium, we can extract a desired smaller linear operator by finding suitable input and output projectors. We discuss fundamental upper bounds on the size of the linear transformations our approach can achieve and provide an experimental demonstration. For the latter, first we retrieve the complex medium’s TM with a non-interferometric phase retrieval method. Then, we take advantage of the large number of degrees of freedom to find input wavefronts using a Spatial Light Modulator (SLM) that cause the system, composed of the SLM and the complex medium, to act as a desired complex-valued linear operator on the optical field. We experimentally build several 16×16 complex-valued operators, and are able to switch from one to another at will. Our technique offers the prospect of reconfigurable, robust and easy-to-fabricate linear optical analogue computation units.

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pyMMF: a Python module for multimode fibers simulations [WP2]

pyMMF is a simple module that allows finding the propagating modes of multimode fibers with arbitrary index profiles and simulates the transmission matrix for a given length. The solver can also take into account the curvature of the fiber (experimental). This code is not designed to compete with commercially available software in term of accuracy of the mode profiles/propagation constants or speed, it aims at quickly simulating realistic transmission matrices of short sections of fiber.


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Setting up a DMD: Diffraction effects [WP1]

DMDs are more complicated to use compared to liquid crystal SLMs due to the tilt of the pixels, making the system comparable to a blazed grating. The effect depends on the wavelength, the input angle and the pixel pitch and can significantly reduce the diffraction efficiency of the modulator. We present here a tutorial with simulations to understand and predict the diffraction effects when working with DMDs.

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ALP4lib: A open-source Python library for controlling DMDs [WP1]

Vialux provides Texas Instrument DMD (Digital MicroMirror Devices) chips with an electronic board to send and display image sequences at high speed (up to 30kHz).  We share here a simple module that wraps the C++ functions for Python developed for the MOLOTOF project. It allows to easily use the basic functions while providing the advanced features of the ALP API.


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Wavefront shaping in complex media: From the compensation to the harnessing of disorder [CLEO 2017]

Sébastien M. Popoff, CLEO, (2017)

In the past ten years, many techniques were developed to control light propagation in complex transmission media using spatial light modulators. It involved applications in numerous fields [1-2] including biomedical imaging and therapy, fiber endoscopy, cryptography, optical micromanipulation, optical spectroscopy, telecommunications and random lasers and also served as a tool for fundamental studies of light propagation in complex environments.

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