arXiv subjects

Sébastien M. Popoff

Publications and source records attributed to Sébastien M. Popoff.

15 recordsLinked to original sources

arXiv2026

Phase retrieval based on intensity-only spatiotemporal wavefront shaping

We introduce a phase retrieval method based on harmonic field representations generated by intensity-only spatiotemporal modulation. A periodic amplitude angular modulation encodes phase information into temporal intensity harmonics, enabling wavefront reconstruction without interferometry, reference beams, or a calibrated phase modulator. We consider a disordered system that can be modeled as a phase plate and measure the intensity pattern in the far field for a rotating excitation pattern generated by a digital micromirror device (DMD). We extract the harmonic components of the spatiotemporal speckle and exploit a gradient-based optimization algorithm to retrieve both the optical phase in the plane of the camera corresponding to a plane-wave illumination and the effective phase plate that represents the disordered system. We demonstrate experimentally the accuracy of the approach in quantitatively estimating and compensating for phase distortion ranging from low-spatial-frequency aberrations to high-frequency distortions of a ground-glass diffuser. The proposed approach establishes a new route toward calibration-free phase retrieval using intensity-only measurements.

physics.optics↗

arXiv2026

A practical guide to Digital Micro-mirror Devices (DMDs) for wavefront shaping

Digital micromirror devices have gained popularity in wavefront shaping, offering a high frame rate alternative to liquid crystal spatial light modulators. They are relatively inexpensive, offer high resolution, are easy to operate, and a single device can be used in a broad optical bandwidth. However, some technical drawbacks must be considered to achieve optimal performance. These issues, often undocumented by manufacturers, mostly stem from the device's original design for video projection applications. Herein, we present a guide to characterize and mitigate these effects. Our focus is on providing simple and practical solutions that can be easily incorporated into a typical wavefront shaping setup.

physics.optics↗

arXiv2025

Two-Photon Bandwidth of Hyper-Entangled Photons in Complex Media

When light propagates through complex media, its output spatial distribution is highly sensitive to its wavelength. This fundamentally limits the bandwidth of applications ranging from imaging to communication. Here, we demonstrate analytically and numerically that the spatial correlations of hyper-entangled photon pairs, simultaneously entangled spatially and spectrally, remain stable across a broad bandwidth: The chromatic modal dispersion experienced by one photon is canceled to first order by its spectrally anti-correlated twin, defining a "two-photon bandwidth" that can far exceed its classical counterpart. We illustrate this modal dispersion cancellation in multimode fibers, thin diffusers and blazed gratings, and demonstrate its utility for broadband wavefront shaping of quantum states. These findings advance our fundamental understanding of quantum light in complex media with applications in quantum imaging, communication, and sensing.

quant-ph↗

arXiv2025

Fundamental Bounds of Wavefront Shaping of Spatially Entangled Photons

Wavefront shaping enables control of classical light through scattering media. Extending these techniques to spatially entangled photons promises new quantum applications, but their fundamental limits, especially when both photons scatter, remain unclear. Here, we theoretically and numerically investigate the enhancement of two-photon correlations through thick scattering media. We analyze configurations where a spatial light modulator shapes one or both photons, either before or after the medium, and show that the optimal enhancement differs fundamentally from classical expectations. For a system with $N$ modes, we show that shaping one photon yields the classical enhancement $η\approx (π/4)N$, while shaping both photons before the medium reduces it to $η\approx (π/4)^2N$. However, in some symmetric detection schemes, when both photons are measured at the same mode, perfect correlations are restored with $η\approx N$, resembling digital optical phase conjugation. Conversely, shaping both photons after the medium leads to a complex, NP-hard-like optimization problem, yet achieves superior enhancements, up to $η\approx 4.6N$. These results reveal unique quantum effects in complex media and identify strategies for quantum imaging and communication through scattering environments.

quant-ph↗

arXiv2025

Wavefront shaping enhanced nano-optomechanics down to the quantum precision limit

We introduce wavefront shaping as a tool for optimizing the sensitivity in nano-optomechanical measurement schemes. We perform multimode output analysis of an optomechanical system consisting of a focused laser beam coupled to the transverse motion of a tapered cantilever, and demonstrate that wavefront shaping enables a 350-fold enhancement of the measurement signal-to-noise (+25.5 dB) compared to standard split-detection, close to the quantum precision limit. Our results open new perspectives in terms of sensitivity and control of the optomechanical interaction.

quant-ph↗

arXiv2025

Open transmission channels in multimode fiber cavities with random mode mixing

The transport of light in disordered media is governed by open transmission channels, which enable nearly complete transmission of the incident power, despite low average transmission. Extensively studied in diffusive media and chaotic cavities, open channels exhibit unique properties such as universal spatial structure and extended dwell times. However, their experimental study is challenging due to the large number of modes required for control and measurement. We propose a multimode fiber cavity (MMFC) as a platform to explore open channels. Leveraging mode confinement and finite angular spread, MMFCs enable a full control over all channels. This allowed us to achieve an 18-fold power enhancement by selectively exciting an open channel with a transmission rate of $0.90 \pm 0.04$. By analyzing 100 transmission matrices of MMFC realizations, we observed a bimodal transmission eigenvalue distribution, indicating high channel control and low losses. The scalability of MMFCs, combined with long dwell times and potential for nonlinear phenomena, offers new opportunities for studying complex wave transport.

physics.optics↗

arXiv2024

Tutorial: How to build and control an all-fiber wavefront modulator using mechanical perturbations

Multimode optical fibers support the dense, low-loss transmission of many spatial modes, making them attractive for technologies such as communications and imaging. However, information propagating through multimode fibers is scrambled, due to modal dispersion and mode mixing. This is usually rectified using wavefront shaping techniques with devices such as spatial light modulators. Recently, we demonstrated an all-fiber system for controlling light propagation inside multimode fibers using mechanical perturbations, called the fiber piano. In this tutorial we explain the design considerations and experimental methods needed to build a fiber piano, and review applications where fiber pianos have been used.

physics.optics↗

arXiv2024

Characterization and Exploitation of the Rotational Memory Effect in Multimode Fibers

In an ideal perfectly straight multimode fiber with a circular-core, the symmetry ensures that rotating the input wavefront leads to a corresponding rotation of the output wavefront. This invariant property, known as the rotational memory effect (RME), remains independent of the typically unknown output profile. The RME thus offers significant potential for imaging and telecommunication applications. However, in real-life fibers, this effect is degraded by intrinsic imperfections and external perturbations, and is challenging to observe because of its acute sensitivity to misalignments and aberrations in the optical setup. Thanks to processing involving a spatial light modulator, we efficiently overcome these measurement biases, allowing for precise quantification of the RME. We establish an experimental and theoretical framework for studying and manipulating the RME in multimode fibers. Theoretical predictions are consistent with experimental data and simulations, connecting the shape of the angular-dependent correlation of the RME to the geometrical properties of the core deformation. This work opens the road for accurate characterization of the distributed disorder originating from the fabrication process and calibration-less imaging in multimode fibers.

physics.optics↗

arXiv2023

Crashing with disorder: Reaching the precision limit with tensor-based wavefront shaping

Perturbations in complex media, due to their own dynamical evolution or to external effects, are often seen as detrimental. Therefore, a common strategy, especially for telecommunication and imaging applications, is to limit the sensitivity to those perturbations in order to avoid them. Here, we instead consider crashing straight into them in order to maximize the interaction between light and the perturbations and thus produce the largest change in output intensity. Our work hinges on the innovative use of tensor-based techniques, presently at the forefront of machine learning explorations, to study intensity-based measurements where its quadratic relationship to the field prevents the use of standard matrix methods. With this tensor-based framework, we are able to identify the optimal crashing channel which maximizes the change in its output intensity distribution and the Fisher information encoded in it about a given perturbation. We further demonstrate experimentally its superiority for robust and precise sensing applications. Additionally, we derive the appropriate strategy to reach the precision limit for intensity-based measurements leading to an increase in Fisher information by more than four orders of magnitude with respect to the mean for random wavefronts when measured with the pixels of a camera.

physics.optics↗

arXiv2023

Dynamic structured illumination for confocal microscopy

Structured illumination enables the tailoring of an imaging device's optical transfer function to enhance resolution. We propose the incorporation of a temporal periodic modulation, specifically a rotating mask, to encode multiple transfer functions in the temporal domain. This approach is demonstrated using a confocal microscope configuration. At each scanning position, a temporal periodic signal is recorded. By filtering around each harmonic of the rotation frequency, multiple images of the same object can be constructed. The image carried by the $n{\mathrm{th}}$ harmonic is a convolution of the object with a phase vortex of topological charge $n$, 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.

physics.optics↗

arXiv2023

Shaping Single Photons through Multimode Optical Fibers using Mechanical Perturbations

The capacity of information delivered by single photons is boosted by encoding high-dimensional quantum dits in their transverse shape. Transporting such high-dimensional quantum dits in optical networks may be accomplished using multimode optical fibers, which support the low-loss transmission of multiple spatial modes over existing infrastructure. However, when photons propagate through a multimode fiber their transverse shape gets scrambled because of mode mixing and modal interference. This is usually corrected using free-space spatial light modulators, inhibiting a robust all-fiber operation. In this work, we demonstrate an all-fiber approach for controlling the shape of single photons and the spatial correlations between entangled photon pairs, using carefully controlled mechanical perturbations of the fiber. We optimize these perturbations to localize the spatial distribution of a single photon or the spatial correlations of photon pairs in a single spot, enhancing the signal in the optimized spot by over an order of magnitude. Using the same approach we show a similar enhancement for coupling light from a multimode fiber into a single-mode fiber.

quant-ph↗

arXiv2022

Super-resolved imaging based on spatiotemporal wavefront shaping

A novel approach to improving the performances of confocal scanning imaging is proposed. We experimentally demonstrate its feasibility using acoustic waves. It relies on a new way to encode spatial information using the temporal dimension. By moving an emitter, used to insonify an object, along a circular path, we create a temporally modulated wavefield. Due to the cylindrical symmetry of the problem and its temporal periodicity, the spatiotemporal input field can be decomposed into harmonics corresponding to different spatial vortices, or topological charges. Acquiring the back-reflected waves with receivers which are also rotating, multiple images of the same object with different Point Spread Functions (PSFs) are obtained. Not only is the resolution improved compared to a standard confocal configuration, but the accumulation of information also allows building images beating the diffraction limit. The topological robustness of the approach promises good performances in real life conditions.

physics.optics↗

arXiv2022

Restoring and tailoring very high dimensional spatial entanglement of a biphoton state transmitted through a scattering medium

We report experimental results where a momentum entangled biphoton state with a giant dimensionality of 8000 is retrieved and manipulated when only one photon of the pair is transmitted through a thin scattering medium. For this purpose, the transmission matrix of the complex medium is first measured with a phase-shifting interferometry measurement method using a spatial light modulator (SLM) illuminated with a laser source. From this matrix, different phase masks are calculated and addressed on the SLM to spatially control the focusing of the laser through the complex medium. These same masks are used to manipulate the phase of the biphoton wave function transmitted by the thin diffuser in order to restore and control in the same way the momentum correlations between the far-field images of twin beams issued from strongly spatial-multi-mode spontaneous parametric down conversion.

quant-ph↗

arXiv2021

Learning and avoiding disorder in multimode fibers

Multimode optical fibers (MMFs) have gained renewed interest in the past decade, emerging as a way to boost optical communication data-rates in the context of an expected saturation of current single-mode fiber-based networks. They are also attractive for endoscopic applications, offering the possibility to achieve a similar information content as multicore fibers, but with a much smaller footprint, thus reducing the invasiveness of endoscopic procedures. However, these advances are hindered by the unavoidable presence of disorder that affects the propagation of light in MMFs and limits their practical applications. We introduce here a general framework to study and avoid the effect of disorder. We experimentally find an almost complete set of optical channels that are resilient to disorder induced by strong deformations. These deformation principle modes are obtained by only exploiting measurements for weak perturbations. We explain this effect by demonstrating that, even for a high level of disorder, the propagation of light in MMFs can be characterized by just a few key properties. These results are made possible thanks to a precise and fast estimation of the modal transmission matrix of the fiber which relies on a model-based optimization using deep learning frameworks.

physics.optics↗

arXiv2018

Turning Optical Complex Media into Universal Reconfigurable Linear Operators by Wavefront Shaping

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 $16\times16$ 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.

physics.optics↗