CyberSec Research

We exploit the optical lever principle to detect minute fluctuations of a liquid-air interface. Waves propagating on the interface deflect a specularly reflected laser beam, inducing angular deviations captured by a dual-element photodiode. We realise this principle in a compact set-up including a temperature-controlled fluid sample. Deflection angle fluctuations span five orders of magnitude in frequency, enabling detection of both low-frequency eigenmodes and high-frequency capillary waves driven by thermal effects. These results demonstrate the broad dynamical range and versatility of specular reflection spectroscopy as a minimally-invasive tool for probing interfacial dynamics in fluid and soft matter systems.

Recent progress in large-scale metasurfaces requires phase profiles beyond traditional hyperbolic designs. We show hyperbolic phase distributions cause spherical aberration from mismatched light propagation geometry and unrealistic phase assumptions. By analyzing metalens fundamentals via isophase surfaces, we develop a spherical phase profile based on spherical wavefront theory. This method prevents spherical aberration, essential for wide-aperture metalenses. Simulations prove superior focusing: spherical phase reduces FWHM by 7.3% and increases peak intensity by 20.4% versus hyperbolic designs at 31.46 micron radius. Spherical phase maintains consistent focusing across radii, while hyperbolic phase shows strong correlation (R squared = 0.95) with aberration. We also propose a normal vector tracing metric to measure design aberrations. This work establishes a scalable framework for diffraction-limited metalenses.

We construct a semiclassical theory for electrons in a non-Hermitian periodic system subject to perturbations varying slowly in space and time. We derive the energy of the wavepacket to first order in the gradients of the perturbations. Applying the theory to the specific case of a uniform external magnetic field, we obtain an expression for the orbital magnetization energy. Using the principles of non-Hermitian dynamics, we define a physically meaningful non-Hermitian generalization of the angular momentum operator and show that it is compatible with the real part of the orbital magnetic moment. The imaginary part of the orbital magnetic moment is also discussed and shown to originate from an imaginary counterpart to the angular momentum that gives rise to a non-Hermitian generalization of the Aharonov-Bohm effect.

We investigate the focusing characteristics of scalar and vector beams within an atomic medium. An active-Raman-gain configuration is employed to achieve significant Kerr nonlinearity in a four-state atomic system. The probe beams can attain focusing within the medium through careful selection of input beam intensities and the spatial profile of the control field. We analytically derive the linear and third-order nonlinear susceptibilities for both scalar and vector probe beams. Our observations indicate that, in addition to the energy transfer from the control beam to the probe beam, the giant cross-Kerr nonlinearity facilitates the focusing of the scalar probe beam into a significantly smaller spot size. Conversely, the vector probe beams exhibit gain-induced narrowing. Furthermore, we evaluate the state of polarization for the vector beam at the minimum beam waist, observing a polarization rotation and a change in ellipticity during propagation. Through the mechanism of focusing, we achieve a reduced spot size for the probe beam, which may have substantial implications for resolution enhancement in microscopy applications.

Polaritons in nanophotonic structures have attracted long-standing interest owing to their fundamental importance and potential for applications in nonlinear and quantum optics. Nanoantennas (NAs) made from high refractive index dielectrics offer a suitable platform for polariton physics thanks to the strongly confined optical Mie resonances and low optical losses in contrast to metallic NAs. However, Mie modes are mainly confined within the NA, making inefficient their coupling with excitons in materials deposited externally. Here, we overcome this limitation by using a high-refractive index van der Waals material WS$_2$, which allows straightforward fabrication of NAs on gold. The combination of a 27 nm tall WS$_2$ NA and a gold substrate enables strong modification of the Mie mode distribution and field enhancement inside and in the vicinity of the NA. This allows observation of room-temperature Mie-polaritons (with a Rabi splitting above 80 meV) arising from the strong coupling between Mie modes and the exciton in a monolayer WSe$_2$ placed on WS$_2$/gold NAs. We demonstrate strong nonlinearity of Mie-polaritons, one order of magnitude higher than for excitons in monolayer WSe$_2$ on gold. Our results highlight applicability of van der Waals materials for the realisation of hybrid dielectric-metallic nanophotonics for the study of the strong light-matter interaction.

High-intensity laser systems present unique measurement and optimization challenges due to their high complexity, low repetition rates, and shot-to-shot variations. We discuss recent developments towards a unified framework based on information theory and Bayesian inference that addresses these challenges. Starting from fundamental constraints on the physical field structure, we recently demonstrated how to capture complete spatio-temporal information about individual petawatt laser pulses. Building on this foundation, we demonstrate how Bayesian frameworks can leverage temporal correlations between consecutive pulses to improve measurement precision. We then extend these concepts to active sensing strategies that adaptively select measurements to maximize information gain, exemplified through Bayesian autocorrelation spectroscopy. Finally, we show how these information-optimal measurement principles naturally extend to Bayesian optimization. This progression represents a paradigm shift where measurement devices transition from passive data collectors to active participants in complex experiments.

We achieve a record spectral efficiency of 1935.6 bit/s/Hz in the C+L bands in a 10-km 19-ring-core fiber supporting 266 OAM modes. GMI-estimated capacity of 25.24 Pb/s are transmitted using low-complexity 4x4 MIMO.

Organic crystal waveguides, known for excellent light-guiding and photonic versatility, present a promising alternative to conventional optical media in visible light communication (VLC) systems. In a novel approach, the high photoluminescence quantum yield organic crystal 2,2dash-((1E,1Edash)-hydrazine-1,2-diylidenebis(methaneylylidene))diphenol (SAA) is used as an optical waveguide medium for real-time data communication in the visible range, employing a microcontroller unit with on off keying modulation. Leveraging its spectral properties, the SAA crystal demonstrates dual active and passive waveguiding capabilities for signal modulation. Error-free signal detection is achieved thanks to the smooth, defect-free surface morphology of the crystal. The relationship between incident angle and light intensity reveals stable fluorescence under narrow angle excitation, positioning the crystal as an all-angle signal receiver that surpasses conventional optical fibers. A real time data transfer setup is demonstrated, enabling direct transmission from a serial interface and accurate reconstruction of grayscale images. This represents the first implementation of a fully organic crystal-based VLC platform, integrating wavelength conversion, omnidirectional waveguiding, and real time signal processing. The results establish a foundation for compact, efficient, and integrable photonic communication technologies.

Increasing datacenter demands require power-efficient optical interconnects. However, a conventional standard transmitter using a silicon rib-waveguide Mach-Zehnder modulator and voltage-mode driver has low efficiency and consumes watt-class high power and occupies a several-square-millimeter footprint, which limits large-scale integration for parallel transmission. This paper presents a transmitter consisting of a compact photonic crystal waveguide (PCW) modulator and a current-mode open-collector driver. The PCW modulator is designed to have high impedance in addition to the slow-light effect. The driver connected to the modulator without termination resistors is optimized based on electronics-photonics co-simulations using a standard electronic circuit simulator with an in-house photonic model library. Co-packaging these dramatically reduces the power consumption to 50 mW and a bit energy to 0.78 pJ/bit at 64-Gbaud, and the footprint to 0.66 mm2. This result represents a significant advancement toward the integration of a large number of transmission channels with no temperature control.

We analytically derive an expression for a speckle field's intensity probability density function (PDF) in a nonlinear medium. The analytically driven results are in good agreement with the numerical outcomes. In a focusing nonlinear medium, the local intensity of the speckle is enhanced as manifested through the longer tail of the PDF. In contrast, the local intensity of speckle is reduced in the presence of a defocusing nonlinearity, and the tail of the probability density function also reduces. This change in local intensity of the speckles arises due to the cubic Kerr nonlinearity, which eventually modifies the second-order statistics. Hence, the intensity correlation is altered as per the nature of the associated nonlinearity while the field correlation remains invariant of both types of the nonlinear conditions.

Excitons in biased bilayer graphene are electrically tunable optical excitations residing in the mid-infrared (MIR) spectral range, where intrinsic optical transitions are typically scarce. Such a tunable material system with an excitonic response offer a rare platform for exploring light-matter interactions and optical hybridization of quasiparticles residing in the long wavelength spectrum. In this work, we demonstrate that when the bilayer is encapsulated in hexagonal-boron-nitride (hBN)-a material supporting optical phonons and hyperbolic-phonon-polaritons (HPhPs) in the MIR-the excitons can be tuned into resonance with the HPhP modes. We find that the overlap in energy and momentum of the two MIR quasiparticles facilitate the formation of multiple strongly coupled hybridized exciton-HPhP states. Using an electromagnetic transmission line model, we derive the dispersion relations of the hybridized states and show that they are highly affected and can be manipulated by the symmetry of the system, determining the hybridization selection rules. Our results establish a general tunable MIR platform for engineering strongly coupled quasiparticle states in biased graphene systems, opening new directions for studying and controlling light-matter interactions in the long-wavelength regime.

We report optical trapping and transport at atmospheric pressure of nanoparticles in a moving interference pattern in hollow-core photonic crystal fiber. Unlike in previous work at low pressure, when the viscous drag forces are weak and the particles travel at the fringe velocity, competition between trapping and drag forces causes the particle velocity to oscillate as it is momentarily captured and accelerated by each passing fringe, followed by release and deceleration by viscous forces. As a result the average particle velocity is lower than the fringe velocity. An analytical model of the resulting motion shows excellent agreement with experiment. We predict that nanoparticles can be trapped at field nodes if the fringes are rocked to and fro sinusoidally-potentially useful for reducing the exposure of sensitive particles to trapping radiation. The high precision of this new technique makes it of interest for example in characterizing nanoparticles, exploring viscous drag forces in different gases and liquids, and temperature sensing.

Precise control over the spatial and polarization properties of light is foundational for advanced photonic systems, yet most conventional approaches are constrained to local, contact-based manipulation at physical interfaces. To overcome these constraints, here we introduce a fundamentally new framework for action-at-a-distance polarization control using virtual polarization elements (VPEs). VPEs apply prescribed local Jones matrix transformations between an input field at the modulation plane and an output field at a remote, contactless free-space plane, enabling polarization transformations without physical interaction at the target. We demonstrate VPEs, in metasurface platform, realizing diverse polarization functionalities, including single-function VPEs for circular polarizer, linear polarizer, half-wave plate, and quarter-wave plate operations; a multifunction VPE simultaneously implementing distinct polarization functions with arbitrary phase difference across spatial regions; and vortex waveplate configurations generating structured vector vortex beams. By decoupling the modulation and target planes, VPEs open new opportunities for remote polarization shaping, non-invasive beam engineering, and contactless polarization manipulation in challenging optical environments.

A new design of a microwave-range ENZ metamaterial consisting of rods with an obround cross-section is proposed. The plasma frequency of the metamaterial can be tuned by rotating the constituent meta-atoms. Tunability of the plasma frequency by 26% is demonstrated both experimentally and numerically. The observed tuning range is dramatically higher than in the one observed in natural materials at optical range.

The optical reflection coefficient of a dielectric medium moving uniformly in the plane spanned by its surface is rigorously calculated using classical electrodynamics and special relativity, and expressed in the Fourier domain, as a function of the incident frequency and wavevector, valid in both the far- and near-field regimes. It is found that cross-polarisation appears as a consequence of the motion, except when it is directed along the plane of incidence. As an example, using a Drude model for the permittivity of the surface at rest, the dispersion relation of its surface modes is calculated. A tilting of the dispersion relation is observed, leading to movement-induced surface plasmon unidirectionality and non-reciprocity.

We demonstrate the general failure of the famous concept of tight binding and mode hybridization underlying modern theories of coupled open resonators. In spite of sophisticated examples in the literature, successfully illustrating these theories, the latter fail to describe any planar systems. This includes the simplest possible case of two dielectric slabs placed next to each other or separated by a distance, which is straightforward for verification, due to its analytical solvability. We present a rigorous theory capable of calculating correctly the eigenmodes of arbitrary three-dimensional dispersive coupled resonators in terms of their individual modes, providing insight into the proper mode hybridization and formation of bonding and antibonding supermodes. Planar optical resonators, such as coupled slabs and Bragg-mirror microcavities, are used for illustrative purposes as they allow precise and reliable verification of the theory.

The applicability ranges of macroscopic and microscopic electromagnetisms are opposite. While microscopic electromagnetism deals with point sources, singular fields, and discrete atomistic materials, macroscopic electromagnetism concerns smooth average distributions of sources, fields, and homogenized effective metamaterials. Greens function method - GFM - involves finding fields of point sources and applying superposition principle to find fields of distributed sources. When utilized to solve microscopic problems GFM is perfectly within the applicability range. Extension of GFM to simple macroscopic problems is convenient, but not fully logically sound, since point sources and singular fields are technically not a subject of macroscopic electromagnetism. This explains the difficulty of both finding the Greens functions and applying superposition principle in complex isotropy-broken media, which are very different from microscopic environments. In this manuscript, we lay out a path to solution of macroscopic Maxwells equations for distributed sources bypassing GFM, by introducing inverse approach and a method based on Om-potential which we describe here. To the researchers of electromagnetism this provides access to powerful analytical tools and a broad new space of solutions for Maxwells equations.

Thermal signatures represent ubiquitous infrared appearances of objects, carrying their unique spectral fingerprints. Despite extensive efforts to decipher and manipulate thermal-infrared signals, the ability to fully control them across spatial, temporal and spectral domains remains a significant challenge due to the slow speed, diffuse and broadband emitting nature of thermal emission in most materials. Here, we demonstrate a reconfigurable ultrafast thermal metamaterial pixel array that integrates active metasurfaces with dual-gate graphene transistors (Gr-FETs). The Gr-FETs with dual-gate control in each pixel achieve the heater-switch dual functionalities. As broadband transparent microheaters, Gr-FETs support the arbitrary design of integrated metasurfaces to achieve multi-color, narrowband infrared emission and operate at ultrafast modulation speeds. Concurrently as electrical switches, they enable a unified control scheme for pixel arrays of various sizes over large areas without compromising emission intensity. By decoupling the thermal generation and emission design processes, our approach provides an unprecedented degree of flexibility in programming thermal output across space, time, and wavelength. Our fabricated thermal pixel array experimentally demonstrated 26 alphabetical letters by applying progressive scanning, thus paving the way for practical realization of universal thermal signature controls for advanced thermal-infrared applications.