Laser printing with structural colors arising from nanostructure-light interaction is emerging as a promising technology to address the problem of toxic compounds in conventional coloration methods. Up to date, the best-performing laser coloration techniques rely on ultrafast pulsed lasers. In this work, we introduce an approach for low-power, wide-gamut laser coloration on a pre-processed metamaterial of self-assembled nanoparticles. The metamaterial, with aluminum-coated polystyrene nanospheres, changes color through oxidation layer and deformation shape control, achieved using a focused CW laser with an average power of 10 mW. This approach achieves a 33k DPI resolution on a flexible substrate with the broadest color gamut reported.
KEYWORDS: Water splitting, Alloys, Solar energy, Oxidation, X-ray photoelectron spectroscopy, Scanning transmission electron microscopy, Sustainability, Solar processes, Nitrogen, Nanofilms
We report a light-induced oxyhydroxides-alloy heterostructure reconfigured from a nickel-iron alloy film as a highly catalytic and protective layer on photoanodes for solar water oxidation. The optimized photoanodes exhibit a high applied bias photon-to-current efficiency of 4.24% and long-term stability beyond 250 hours, outperforming the closest competitors by 330% in efficiency and 408% in stability, respectively. This self-generated catalytic-protective oxyhydroxides-alloy layer coating strategy opens the way to implementing large scalable photoelectrochemical devices for solar fuel production with high efficiency and device lifetime.
In this work, we propose a novel framework for large-scale aperiodic nanophotonic inverse design utilizing an experimental machine-learning technique. With this technique, we create an extensive dataset of 10 million experimental structures for enhanced flat-optics design. This largest publicly available inverse design dataset, achieved through electron beam lithography, bypasses the extensive computational demand of first-principle simulations. Experimental acquisition ensures the dataset embodies real-world variances, leading to ML models with a ten-fold improved prediction accuracy in optical responses, drastically reducing validation RMSE from 0.012 to 0.0018. With this dataset, we developed a framework for large-scale aperiodic photonics design capable of designing tens of structures per second. We demonstrate the efficiency of the proposed technique by creating a large (3x3mm) aperiodic photonic structure composed of >10000 individual structures with pre-defined transmission/reflection responses.
This work proposed a universal platform for ultra-sensitive detection, which integrates sensory data acquisition and spectral feature extraction into a single machine learning (ML) hardware.We fabricated and tested the sensing platform in glucose detection tasks, reaching 5 orders of magnitude higher sensitivity compared to the state-of-the-art. This technology requires no bulky spectral measuring devices such as a spectrum analyzer but a standard off-the-shelf camera to achieve real-time detection of the glucose concentration.
We present a framework for optical metrology in which, through the hardware implementation of artificial intelligence via metasurfaces, a conventional camera becomes a metrology system capable of retrieving observables from a light beam. We show the experimental realization of a prototype of this system and the results of its use for measuring the properties of thin films.
While current nanofabrication techniques for manipulating light at the nanoscale focus on specific geometrical patterns using nanopatterning, nanomanufacturing, and lithography, exploring phase-changing media for these purposes remains limited. Our study presents a nanostructuring platform that utilizes nonlinear light-matter interactions to achieve controllable alterations in material geometry and phase. The base material for the platform is an oxide-polymer heterostructure. Laser-induced passivation and reshaping of 2D monolayers of such structures enable gradual phase transitions with resonant optical behavior. This platform shows promise in low-power inkless laser color printing, achieving high-resolution printing with a broad color gamut.
Hyperspectral imaging has attracted significant attention to identify spectral signatures for image classification and automated pattern recognition in computer vision. State-of-the-art implementations of snapshot hyperspectral imaging rely on bulky, non-integrated, and expensive optical elements, which do not allow fast data processing, e.g., real-time and high-resolution videos. This work introduces Hyplextm, a CMOS-compatible, fast hyperspectral camera that replaces bulk optics with suitably designed artificial intelligent optical hardware components. Hyplextm does not require spectrometers but uses conventional monochrome cameras, allowing real-time and high-resolution hyperspectral imaging at inexpensive costs. In this invited talk, we discuss the design, implementation, and real-world applications of Hyplextm.
In this work we make use of an inverse design methodology for the design of high efficiency deformation robust flat optics. Our approach leverages neural network predictors trained to quickly estimate the results of finite difference time domain (FDTD) simulations. By rapidly exploring the solution space, we find geometries that exhibit an optical response tolerant to dimensional errors. We validate our approach by fabricating and characterizing flat optics polarizers on top of polyamide tape. The devices exhibit a polarization efficiency of 85% over a 200 nm bandwidth and retain high performance when subjected to large deformations, in contrast to a control non-robust design.
In this invited talk, I will review our recent theoretical, and experimental results in the field of artificial intelligence (AI) assisted inverse design of a new class of flexible ultra-flat optics (thickness < 100nm) for high efficiency (close to unitary) vectorial control of light. These devices are supported by a layer of “physical” neural network units in suitably engineered optical nanoresonators. These systems act as universal approximators of arbitrary defined input-output responses, processing information at the speed of light.
I will discuss basic optical components and new integrated systems for processing high-dimensional visual information in real-time and a new concept of universal integrated, ultra-flat equipment for metrology applications based on data-driven science. Finally, I will also discuss some recent challenges in manufacturing high-resolution, large-scale samples up to 3-inches in size.
Over the past twenty years flat-optics and metasurfaces emerged as a promising light manipulation technology. One of the challenges is obtaining scalable and highly efficient designs that can withstand the fabrication errors associated with nanoscale manufacturing. This problem becomes more severe in flexible structures. In this work, we present an inverse design platform that enables the fast design of flexible metasurfaces that maintain high performance under deformations. We validate this method by a series of experiments in which we realize broadband flexible light polarizers efficiency of 80% over 200 nm bandwidths.
This work presents an AI-driven framework to extract the biological tissue's refractive index and thickness maps from a single RGB image. This approach is based on a physical light-trapping surface and an unsupervised inverse search projector which projects given RGB pixel to the sample's refractive index and thickness at the corresponding coordinate.
We introduce a universal design platform for the development of highly-efficient wavefront engineering structures. To validate this methodology, we fabricated many different optical devices with an experimental efficiency exceeding 99%.
Flat optics allow the production of integrated, lightweight, portable and wearable optical devices. In this work we propose a flat optics design platform that employs concepts from evolutionary algorithms to deep learning with convolutional neural networks, and demonstrate a general design framework that can furnish an arbitrarily designed system response in as little as 50nm of silicon. The proposed framework is fundamental for our most recent experimental paper, in which we present a plethora of high efficiency devices, including, but not limited to: polarizing beam splitters, dichroic mirrors and metasurfaces for a novel 2-pixel display technology.
In this work, we introduce a technique capable of recovering both the refractive index and thickness maps of a cell using a single measurement in the form of a color photograph of the sample. Our method exploits the appearance of thin-film interference colors on a cell when placed on top of a suitable surface. An inverse search algorithm is used to map these colors to the refractive index and thickness values of each pixel in the image. Experimentally, we show the technique can achieve a 10-2 RIU sensitivity, sufficient to differentiate between cellular organelles.
We engineered an epsilon-near-zero (ENZ) material from suitably disordered metallic nanostructures. We create a new class of dispersionless composite materials that efficiently harnesses white light. By means of Atomic Force Microscopy (AFM) and Photoluminescence (PLE) measurements we experimentally demonstrate that this nanomaterial increases up to a record value the absorption of ultra-thin light harvesting films at visible and infrared wavelengths. Moreover, we obtained a 170% broadband increase of the external quantum efficiency (EQE) when these ENZ materials are inserted in an energy-harvesting module. We developed an inexpensive electrochemical deposition process that enables large-scale production of this material for energy-harvesting applications.
In this invited talk I will review our research activity on near-field Anapole nanolasers. Anapoles are radiationless light states that do not possess far field emission. Thanks to their unique nature, these states enable a new concept of laser source, whose emission is totally confined in the near field. We will discuss applications of this concept for ultra-fast (100 fs), mode-locking pulse generation in integrated optical structures with GaAs semiconductors.
Developing secure communications is a research area of growing interest. During the past years, several cryptographic schemes have been developed, with
Quantum cryptography being a promising scheme due to the use of quantum effects, which make very difficult for an eavesdropper to intercept the communication. However, practical quantum key distribution methods have encountered several limitations; current experimental realizations, in fact, fail to scale up on long distances, as well as in providing unconditional security and speed comparable to classical optical communications channels.
Here we propose a new, low cost and ultra-fast cryptographic system based on a fully classical optical channel. Our cryptographic scheme exploits the complex synchronization of two different random systems (one on the side of the sender and another on the side of the receiver) to realize a “physical” one paid system.
The random medium is created by an optical chip fabricated through electron beam lithography on a Silicon On Insulator (SOI) substrate.
We present experiments with ps lasers and commercial fibers, showing the ultrafast distribution of a random key between two users (Alice and Bob), with absolute no possibility for a passive/active eavesdropper to intercept the communication. Remarkably, this system enables the same security of quantum cryptography, but with the use of a classical communication channel.
Our system exploits a unique synchronization that exists between two different random systems, and at such is extremely versatile and can enable safe communications among different users in standards telecommunications channels.
Structural colours represents a research area of great interest, due to a wide field of application ranging from micro-security to biomimetic materials. At present metallic substrate are heavily employed and only a partial spectra of colours can be realised. We propose a novel, metal-free technology that exploits the complex scattering from a disordered three-dimensional dielectric material on a silicon substrate. We reproduce experimentally the full spectrum of CMYK colours, including variations in intensity. Our resolution lies in the nm range, limited only by the electron beam lithography fabrication process. We demonstrate that this technique is extremely robust, suitable for flexible and reusable substrates. Full of these notable proprieties these nano-structures fits perfectly with the requirements of a real-world technology.
In this invited contribution I will review recent results of our research in the field of complex nanolasers. I will begin by discussing recent experimental results from a new type of ultra-dark nanoparticles, which behave as an ideal black-body and spontaneously produce single color pulses thanks to an equivalent Bose-Einstein Condensation of light.1 I will then discuss new quantum information sources from core-shell spaser nanoparticles.2 Finally, I will illustrate a new type of laser source that emits only in the near field, discussing applications in integrated optical circuits.
Integrating coherent light sources at the nanoscale with spasers is one of the most promising applications of plasmonics. A spaser is a nano-plasmonic counterpart of a laser, with photons replaced by surface plasmon polaritons and the resonant cavity replaced by a nanoparticle supporting localized plasmonic modes. Despite the large body of experimental and theoretical studies, the understanding of the fundamental properties of the spaser emission is still challenging. In this work, we investigated the ultrafast dynamics of the emission from a core-shell spaser by developing a rigorous first-principle numerical model. Our results show that the spaser is a highly nonlinear system with many interacting degrees of freedom, whose emission sustain a rich manifold of different spatial phases. In the regime of strong interaction we observed that the spaser emission manifests an irreversible ergodic evolution, where energy is equally shared among all the available degrees of freedom. Under this condition, the spaser generates ultrafast vortex lasing modes that are spinning on the femtosecond scale, acquiring the character of a nanoparticle with an effective spin. Interestingly, the spin orientation is defined by spontaneous symmetry breaking induced by quantum noise, which is a fundamental component of our ab-initio model. This opens up interesting possibilities of achieving unidirectional emission from a perfectly spherical nanoparticle, stimulating a broad range of applications for nano-plasmonic lasers as unidirectional couplers, random information sources and novel form of photonics neural-networks.
We report on the all-optical control of chaotic optical resonators based on silicon on insulator (SOI) platform. We show that simple non-chaotic cavities can be tuned to exhibit chaotic behavior via intense optical pump- ing, inducing a local change of refractive index. To this extent we have fabricated a number of devices and demonstrated experimentally and theoretically that chaos can be triggered on demand on an optical chip.
We show here theoretically and experimentally how chaotic Photonic Crystal resonators can be used for en-
ergy harvesting applications and the demonstration of fundamental theories, like the onset of superradiance in
quantum systems.
We discuss Bloch oscillations in waveguide arrays created in a nematic liquid crystalline layer. Bloch oscillations can originate from the specific distribution of refractive index, where a linear gradient is added to the transverse periodicity. Light can oscillate periodically in the transverse direction as it propagates, returning to its initial spatial position and profile after each full cycle. To introduce a spatially periodic refractive index modulation in nematic liquid crystalline waveguides a set of comb-shaped transparent ITO electrodes is placed on one of the glass surfaces. The applied bias allows tuning the structure from light confinement in one dimension, i.e. planar waveguiding, to bidimensional confinement. In the proposed geometry, the thickness of the liquid crystal layer changes linearly as a function of the transverse coordinate. In this way, both linear and nonlinear effective index changes are introduced in each waveguide.
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