arXiv subjects

Miguel A. Bandres

Publications and source records attributed to Miguel A. Bandres.

16 recordsLinked to original sources

arXiv2026

Wavelength-Dependent Evolution of Full-Field Transfer Matrices in Photonic Lanterns

A fiber-based photonic lantern can couple an array of single-mode optical fibers to the guided modes of a multimode fiber, with the mapping between the single-mode fibers and guided modes fully described by a complex-valued transfer matrix. Recent experimental studies have reported strong wavelength-dependent evolution of this matrix in non-mode-selective photonic lanterns, yet a quantitative physical explanation for this behavior has not previously been demonstrated. Here, we present direct measurements of the wavelength-dependent encoding transfer matrix of a photonic lantern across the range 1525 nm to 1575 nm using off-axis holographic imaging, enabling high-fidelity recovery of both amplitude and phase. Beyond measurement, we introduce a physically grounded propagation model and numerical simulation that quantitatively reproduces the observed wavelength evolution and provides a unified physical explanation for behavior reported in prior experimental work. The model identifies differential modal phase accumulation in the multimode section as the dominant mechanism governing spectral evolution and shows that increasing the length of the multimode end systematically accelerates the phase evolution of the transfer matrix with wavelength. These results establish a direct and predictive link between photonic lantern geometry and spectral response, providing a design framework for tailoring lanterns either to enhance sensitivity to closely spaced wavelengths or to enforce uniform response over broad bandwidths for spectroscopic and imaging applications.

physics.optics↗

arXiv2024

Spatiotemporal Control of Ultrafast Pulses in Multimode Optical Fibers

Multimode optical fibers represent the ideal platform for transferring multidimensional light states. However, dispersion degrades the correlations between the light's degrees of freedom, thus limiting the effective transport of ultrashort pulses between distant nodes of optical networks. Here, we demonstrate that tailoring the spatiotemporal structure of ultrashort light pulses can overcome the physical limitations imposed by both chromatic and modal dispersion in multimode optical fibers. We synthesize these light states with predefined spatial and chromatic dynamics through applying a sequence of transformations to shape the optical field in all its dimensions. Similar methods can also be used to overcome dispersion processes in other physical settings like acoustics and electron optics. Our results will enable advancements in laser-based technologies, including multimode optical communications, imaging, ultrafast light-matter interactions, and high brightness fiber sources.

physics.optics↗

arXiv2021

Mode-Locked Topological Insulator Laser Utilizing Synthetic Dimensions

We propose a system that exploits the fundamental features of topological photonics and synthetic dimensions to force many semiconductor laser resonators to synchronize, mutually lock, and under suitable modulation emit a train of transform-limited mode-locked pulses. These lasers exploit the Floquet topological edge states in a 1D array of ring resonators, which corresponds to a 2D topological system with one spatial dimension and one synthetic frequency dimension. We show that the lasing state of the multi-element laser system possesses the distinct characteristics of spatial topological edge states while exhibiting topologically protected transport. The topological synthetic-space edge mode imposes a constant-phase difference between the multi-frequency modes on the edges, and together with modulation of the individual elements forces the ensemble of resonators to mode-lock and emit short pulses, robust to disorder in the multi-resonator system. Our results offer a proof-of-concept mechanism to actively mode-lock a laser diode array of many lasing elements, which is otherwise extremely difficult due to the presence of many spatial modes of the array. The topological synthetic-space concepts proposed here offer an avenue to overcome this major technological challenge, and open new opportunities in laser physics.

physics.optics↗

arXiv2020

Two-photon edge states in photonic topological insulators: topological protection versus degree of entanglement

Topological insulators combine insulating properties in the bulk with scattering-free transport along edges, supporting dissipationless unidirectional energy and information flow even in the presence of defects and disorder. The feasibility of engineering quantum Hamiltonians with photonic tools, combined with the availability of entangled photons, raises the intriguing possibility of employing topologically protected entangled states in optical quantum computing and information processing. However, while two-photon states built as a product of two topologically protected single-photon states inherit full protection from their single-photon "parents", high degree of non-separability may lead to rapid deterioration of the two-photon states after propagation through disorder. We identify physical mechanisms which contribute to the vulnerability of entangled states in topological photonic lattices and present clear guidelines for maximizing entanglement without sacrificing topological protection.

quant-ph↗

arXiv2018

Observation of Light Guiding by Artificial Gauge Fields

The use of artificial gauge fields enables systems of uncharged particles to behave as if affected by external fields. Generated by geometry or external modulation, artificial gauge fields have been instrumental in demonstrating topological phenomena in many physical systems, including photonics, cold atoms and acoustic waves. Here, we demonstrate experimentally for the first time waveguiding by means of artificial gauge fields. To this end, we construct artificial gauge fields in a photonic waveguide array, by using waveguides with nontrivial trajectories. First, we show that tilting the waveguide arrays gives rise to gauge fields that are different in the core and the cladding, shifting their respective dispersion curves, and in turn confining the light to the core. In a more advanced setting, we demonstrate waveguiding in a medium with the same artificial gauge field and the same dispersion everywhere, but with a phase-shift in the gauge as the only difference between the core and the cladding. The phase-shifted sinusoidal trajectories of the waveguides give rise to waveguiding via bound states in the continuum. Creating waveguiding and bound states in the continuum by means of artificial gauge fields is relevant to a wide range of physical systems, ranging from photonics and microwaves to cold atoms and acoustics.

physics.optics↗

arXiv2018

Photonic Topological Insulator in Synthetic Dimensions

Topological phases enable protected transport along the edges of materials, offering immunity against scattering from disorder and imperfections. These phases were suggested and demonstrated not only for electronic systems, but also for electromagnetic waves, cold atoms, acoustics, and even mechanics. Their potential applications range from spintronics and quantum computing to highly efficient lasers. Traditionally, the underlying model of these systems is a spatial lattice in two or three dimensions. However, it recently became clear that many lattice systems can exist also in synthetic dimensions which are not spatial but extend over a different degree of freedom. Thus far, topological insulators in synthetic dimensions were demonstrated only in cold atoms, where synthetic dimensions have now become a useful tool for demonstrating a variety of lattice models that are not available in spatial lattices. Subsequently, efforts have been directed towards realizing topological lattices with synthetic dimensions in photonics, where they are connected to physical phenomena in high-dimensions, interacting photons, and more. Here we demonstrate experimentally the first photonic topological insulator in synthetic dimensions. The ability to study experimentally photonic systems in synthetic dimensions opens the door for a plethora of unexplored physical phenomena ranging from PT-symmetry, exceptional points and unidirectional invisibility to Anderson localization in high dimensions and high-dimensional lattice solitons, topological insulator lasers in synthetic dimensions and more. Our study here paves the way to these exciting phenomena, which are extremely hard (if not impossible) to observe in other physical systems.

physics.optics↗

arXiv2018

Observation of Accelerating Wave Packets in Curved Space

We present the first experimental observation of accelerating beams in curved space. More specifically, we demonstrate, experimentally and theoretically, shape-preserving accelerating beams propagating on spherical surfaces: closed-form solutions of the wave equation manifesting nongeodesic self-similar evolution. Unlike accelerating beams in flat space, these wave packets change their acceleration trajectory due to the interplay between interference effects and the space curvature, and they focus and defocus periodically due to the spatial curvature of the medium in which they propagate.

physics.optics↗

arXiv2017

Complex Edge-State Phase Transitions in 1D Topological Laser Arrays

We report the first observation of lasing in topological edge states in a 1D Su-Schrieffer-Heeger active array of resonators. We show that in the presence of chiral-time ($\mathcal{CT}$) symmetry, this non-Hermitian topological structure can experience complex phase transitions that alter the emission spectra as well as the ensued mode competition between edge and bulk states. The onset of these phase transitions is found to occur at the boundaries associated with the complex geometric phase- a generalized version of the Berry phase in Hermitian settings. Our experiments and theoretical analysis demonstrate that the topology of the system plays a key role in determining its operation when it lases: topologically controlled lasing.

physics.optics↗

arXiv2017

Topological Photonic Quasicrystals: Fractal Topological Spectrum and Protected Transport

We show that it is possible to have a topological phase in two-dimensional quasicrystals without any magnetic field applied, but instead introducing an artificial gauge field via dynamic modulation. This topological quasicrystal exhibits scatter-free unidirectional edge states that are extended along the system's perimeter, contrary to the states of an ordinary quasicrystal system, which are characterized by power-law decay. We find that the spectrum of this Floquet topological quasicrystal exhibits a rich fractal (self-similar) structure of topological "minigaps," manifesting an entirely new phenomenon: fractal topological systems. These topological minigaps form only when the system size is sufficiently large because their gapless edge states penetrate deep into the bulk. Hence, the topological structure emerges as a function of the system size, contrary to periodic systems where the topological phase can be completely characterized by the unit cell. We demonstrate the existence of this topological phase both by using a topological index (Bott index) and by studying the unidirectional transport of the gapless edge states and its robustness in the presence of defects. Our specific model is a Penrose lattice of helical optical waveguides - a photonic Floquet quasicrystal; however, we expect this new topological quasicrystal phase to be universal.

cond-mat.mes-hall↗

arXiv2013

Three-dimensional Accelerating Electromagnetic Waves

We present a general theory of three-dimensional nonparaxial spatially-accelerating waves of the Maxwell equations. These waves constitute a two-dimensional structure exhibiting shape-invariant propagation along semicircular trajectories. We provide classification and characterization of possible shapes of such beams, expressed through the angular spectra of parabolic, oblate and prolate spheroidal fields. Our results facilitate the design of accelerating beams with novel structures, broadening scope and potential applications of accelerating beams.

physics.optics↗

arXiv2013

Nondiffracting Accelerating Waves: Weber waves and parabolic momentum

Diffraction is one of the universal phenomena of physics, and a way to overcome it has always represented a challenge for physicists. In order to control diffraction, the study of structured waves has become decisive. Here, we present a specific class of nondiffracting spatially accelerating solutions of the Maxwell equations: the Weber waves. These nonparaxial waves propagate along parabolic trajectories while approximately preserving their shape. They are expressed in an analytic closed form and naturally separate in forward and backward propagation. We show that the Weber waves are self-healing, can form periodic breather waves and have a well-defined conserved quantity: the parabolic momentum. We find that our Weber waves for moderate to large values of the parabolic momenta can be described by a modulated Airy function. Because the Weber waves are exact time-harmonic solutions of the wave equation, they have implications for many linear wave systems in nature, ranging from acoustic, electromagnetic and elastic waves to surface waves in fluids and membranes.

physics.optics↗

arXiv2012

Spherical fields as nonparaxial accelerating waves

We introduce nonparaxial spatially accelerating waves whose two-dimensional transverse profiles propagate along semicircular trajectories while approximately preserving their shape. We derive these waves by considering imaginary displacements on spherical fields, leading to simple closed-form expressions. The structure of these waves also allows the closed-form description of pulses.

physics.optics↗

arXiv2010

One-Loop Corrections to Type IIA String Theory in AdS4 x CP3

We study various methods for computing the one-loop correction to the energy of classical solutions to type IIA string theory in AdS4 x CP3. This involves computing the spectrum of fluctuations and then adding up the fluctuation frequencies. We focus on two classical solutions with support in CP3: a rotating point-particle and a circular spinning string with two angular momenta equal to J. For each of these solutions, we compute the spectrum of fluctuations using two techniques, known as the algebraic curve approach and the world-sheet approach. If we use the same prescription for adding fluctuation frequencies that was used for type IIB string theory in AdS5 x S5, then we find that the world-sheet spectrum gives convergent one-loop corrections but the algebraic curve spectrum gives divergent ones. On the other hand, we find a new summation prescription which gives finite results when applied to both the algebraic curve and world-sheet spectra. Naively, this gives three predictions for the one-loop correction to the spinning string energy (one from the algebraic curve and two from the world-sheet), however we find that in the large-j limit (where j=J/sqrt(2pi^2 lambda)), the j^(-2n) terms in all three cases agree. We therefore obtain a unique prediction for the one-loop correction to the spinning string energy.

hep-th↗

arXiv2008

Studies of the ABJM Theory in a Formulation with Manifest SU(4) R-Symmetry

We examine the three-dimensional N = 6 superconformal Chern--Simons theory with U(N) X U(N) gauge symmetry, which was recently constructed by Aharony, Bergman, Jafferis, and Maldacena (ABJM). Using a formulation with manifest SU(4) R-symmetry and no auxiliary fields, we verify in complete detail both the Poincare supersymmetry and the conformal supersymmetry of the action. Together, these imply the complete OSp(6|4) superconformal symmetry of the theory. The potential, which is sixth order in scalar fields, is recast as a sum of squares.

hep-th↗

arXiv2008

Ghost-Free Superconformal Action for Multiple M2-Branes

The Bagger--Lambert construction of N = 8 superconformal field theories (SCFT) in three dimensions is based on 3-algebras. Three groups of researchers recently realized that an arbitrary semisimple Lie algebra can be incorporated by using a suitable Lorentzian signature 3-algebra. The SU(N) case is a candidate for the SCFT describing coincident M2-branes. However, these theories contain ghost degrees of freedom, which is unsatisfactory. We modify them by gauging certain global symmetries. This eliminates the ghosts from these theories while preserving all of their desirable properties. The resulting theories turn out to be precisely equivalent to N = 8 super Yang--Mills theories.

hep-th↗

arXiv2008

N = 8 Superconformal Chern--Simons Theories

A Lagrangian description of a maximally supersymmetric conformal field theory in three dimensions was constructed recently by Bagger and Lambert (BL). The BL theory has SO(4) gauge symmetry and contains scalar and spinor fields that transform as 4-vectors. We verify that this theory has OSp(8|4) superconformal symmetry and that it is parity conserving despite the fact that it contains a Chern--Simons term. We describe several unsuccessful attempts to construct theories of this type for other gauge groups and representations. This experience leads us to conjecture the uniqueness of the BL theory. Given its large symmetry, we expect this theory to play a significant role in the future development of string theory and M-theory.

hep-th↗