Martin Lopez-Garcia

• PhD in Applied Physics
• Principal Investigator at International Iberian Nanotechnology Laboratory

Photonic band gap-based sensors can detect small variations in the refractive index of surrounding media, facilitating the precise detection of changes in their environment. In this proof-of-concept study, we demonstrate that biosilica produced by single-cell microalgae called diatoms can work as a photonic crystal slab sensor. We exploited the pse...

The discovery of natural slab photonic crystals in diatoms has sparked questions regarding their prevalence and functional role in nature. These advanced nanomaterials open so-called photonic stopbands in two dimensions, enabling precise light manipulation essential in technologies like quantum computing and photonics. However, the natural role of...

Slab photonic crystals, nanomaterials characterized by periodic pores for manipulating light, have applications in advanced optical technologies. Remarkably, similar materials have been identified in the silica shell of diatoms, in particular the girdle bands. Despite the potential applications and significance for diatom biology, their prevalence...

Plasmonic metasurfaces for structural color generation are typically built using the archetypal noble metals, gold, and silver. These possess plasmonic properties in the visible spectrum due to their inherent high free carrier densities. However, they are much more expensive compared to many other metals and exhibit several nanofabrication issues s...

Light-harvesting complexes in natural photosynthetic systems, such as those in purple bacteria, consist of photo-reactive chromophores embedded in densely packed “antenna” systems organized in well-defined nanostructures. In the case of purple bacteria, the chromophore antennas are composed of natural J-aggregates such as bacteriochlorophylls and c...

Optical Tamm states (OTS) are confined optical modes that can occur at the interface between two highly reflective structures. However, due to the strong reflectance required, their implementation with highly processable and metal-free flexible materials has proven challenging. Herein, we develop the first structure supporting OTS based only on org...

Light-harvesting complexes in natural photosynthetic systems, such as those in purple bacteria, consist of photo-reactive chromophores embedded in densely packed "antenna" systems organized in well-defined nanostructures. In the case of purple bacteria, the chromophore antennas are composed of natural J-aggregates such as bacteriochlorophylls and c...

Natural photonic structures are common across the biological kingdoms, serving a diversity of functionalities. The study of implications of photonic structures in plants and other phototrophic organisms is still hampered by missing methodologies for determining in situ photonic properties, particularly in the context of constantly adapting photosyn...

Optical Tamm States (OTS) are confined optical modes that can occur at the interface between two highly reflective structures. However, due to the strong reflectance required, their implemen-tation with highly processable and metal-free flexible materials has proven challenging. Herein, we develop the first structure supporting OTS based only on or...

Natural photosynthetic photonic nanostructures can show sophisticated light–matter interactions including enhanced light absorption by slow light even for highly pigmented systems. Beyond fundamental biology aspects, these natural nanostructures are very attractive as blueprints for advanced photonic devices. But the soft‐matter biomimetic implemen...

Natural photosynthetic photonic nanostructures can show sophisticated light matter-interactions including enhanced light absorption by slow light even for highly pigmented systems. Beyond fundamental biology aspects these natural nanostructures are very attractive as blueprints for advanced photonic devices. But the soft-matter biomimetic implement...

Nature has been a source of inspiration for the fabrication of new optical materials for centuries. During the last decades, the rapid developments in nanofabrication allowed mimicking the photonic properties of living organisms towards more efficient functional devices. But nanophotonics still relies on nanofabrication techniques and materials not...

Diatoms are microscopic algae found in all of Earths water courses. They produce frustules, porous silica exoskeletons, grown by precipitation of silicic acid from water. Frustule components, known as girdles, from some diatom species also feature highly periodic pore arrays with properties on the same scale and quality of ordering as manufactured...

Chloroplasts, the organelles responsible for photosynthesis in most plants and algae, exhibit a variety of morphological adaption strategies to changing light environments which can have important yet overlooked light scattering effects. This can be even more significant for iridoplasts, specialized chloroplasts whose tissue is arranged as a photon...

Photonics, the manipulation of light at nanoscale, is a key enabling technology with impact in health and energy applications, among others. In most cases photonics still relies on materials and fabrication methods inherited from other disciplines, usually requiring expensive, time consuming and environmentally-unfriendly processes. Recent experime...

Slab photonic crystals (PhCs) are photonic structures used in many modern optical technologies. Fabrication of these components is costly and usually involves eco-unfriendly methods, requiring modern nanofabrication techniques and cleanroom facilities. This work describes that diatom microalgae evolved elaborate and highly reproducible slab PhCs in...

Slab photonic crystals (PhCs) are photonic structures used in many modern optical technologies. Fabrication of these components is costly and usually involves eco‐unfriendly methods, requiring modern nanofabrication techniques and cleanroom facilities. This work describes that diatom microalgae evolved elaborate and highly reproducible slab PhCs in...

Iridescence in shade-dwelling plants has previously been described in only a few plant groups, and even fewer where the structural colour is produced by intracellular structures. In contrast with other Selaginella species, this work reports the first example in the genus of structural colour originating from modified chloroplasts. Characterization...

We show that micron-scale two-dimensional (2D) honeycomb microwells can significantly improve the stability of blue phase liquid crystals (BPLCs). Polymeric microwells made by direct laser writing improve various features of the blue phase (BP) including a dramatic extension of stable temperature range and a large increase both in reflectivity and...

Mass production of on-chip quantum photonic technologies requires low-cost integration of devices at the nanometer scale. Presently photonic components are made of ‘passive’ structures such as optical fibres and are limited in how small components can be made (several microns). More recently gold and silver photonic components have been proposed as...

The combination of chalcogenide phase-change materials with optical metamaterial arrays is exploited to create new forms of dynamic, tuneable and reconfigurable photonic devices including perfect absorbers, modulators, beam steerers and filters.

Natural photonic crystals are responsible for strong reflectance at selective wavelengths in different natural systems. We demonstrate that intracellular opal-like photonic crystals formed from lipids within photosynthetic cells produce vivid structural color in the alga Cystoseira tamariscifolia. The reflectance of the opaline vesicles is dynamica...

The development of flat, compact beam-steering devices with no bulky moving parts is opening up a new route to a variety of exciting applications, such as LIDAR scanning systems for autonomous vehicles, robotics and sensing, free-space, and even surface wave optical signal coupling. In this paper, the design, fabrication and characterization of inn...

The combination of chalcogenide phase-change materials with optical metamaterial arrays is exploited to create new forms of dynamic, tuneable and reconfigurable photonic devices including perfect absorbers, modulators, beam steerers and filters.

We simulate the coupling of light emitted by a solid state emitter into a structured polymer waveguide. The polymer waveguide is supported on a dielectric mirror making an easy to fabricate platform. This waveguide could be fabricated around a pre-selected and characterized atom like emitter such as a nitrogen vacancy center. We see near determinis...

We propose a method to directly visualize the photonic band-structure of micrometer-sized photonic crystals using wide-angle spectroscopy. By extending Fourier imaging spectroscopy sensitivity into the infrared range, we have obtained accurate measurements of the band structures along the high-symmetry directions (X-W-K-L-U) of polymeric three-dime...

We propose a method to directly visualize the photonic band-structure of micron size photonic crystals using wide angle spectroscopy. By extending Fourier Imaging Spectroscopy sensitivity into the infrared range we have obtained accurate measurements of the band-structures along the high-symmetry directions (X-W-K-L-U) of polymeric three-dimensiona...

Defect cavities in 3D photonic crystal can trap and store light in the smallest volumes allowable in dielectric materials, enhancing non-linearities and cavity QED effects. Here, we study inverse rod-connected diamond (RCD) crystals containing point defect cavities using plane-wave expansion and finite-difference time domain methods. By optimizing...

We present modelling results for efficient coupling of nanodiamonds containing single colour centres to polymer structures on distributed Bragg reflectors. We explain how hemispherical and super-spherical structures redirect the emission of light into small numerical apertures. Coupling efficiencies of up to 68.5% within a numerical aperture of 0.3...

Enhanced light harvesting is an area of interest for optimizing both natural photosynthesis and artificial solar energy capture1,2. Iridescence has been shown to exist widely and in diverse forms in plants and other photosynthetic organisms and symbioses3,4, but there has yet to be any direct link demonstrated between iridescence and photosynthesis...

Decades ago, molecular crystals shown metallic reflection associated with strong interactions between neighboring molecular excitons. [1] In these organic materials the individual molecules are spatially distributed in the crystal lattice and can be considered as small local dipoles that can be excited collectively under specific conditions. This b...

This paper presents fabrication, measurement and modelling results for a metal-dielectric-metal metasurface absorber for solar thermal applications. The structure uses amorphous carbon as an inter-layer between thin gold films with the upper film patterned with a 2D periodic array using focused ion beam etching. The patterned has been optimised to...

This paper presents fabrication, measurement and modelling results for a metal-dielectric-metal metasurface absorber for solar thermal applications. The structure uses amorphous carbon as an inter-layer between thin gold films with the upper film patterned with a 2D periodic array using focused ion beam etching. The patterned has been optimised to...

We report the first experimental observation of an excitonic optical Tamm state supported at the interface between a periodic multilayer dielectric structure and an organic dye-doped polymer layer. The existence of such states is enabled by the metal-like optical properties of the excitonic layer based on aggregated dye molecules. Experimentally de...

We report the first experimental observation of an Excitonic Optical Tamm State supported at the interface between a periodic multilayer dielectric structure and an organic dye-doped polymer layer. The existence of such states is enabled by the metal-like optical properties of the excitonic layer based on aggregated dye molecules. Experimentally de...

We present the simulation, fabrication, and optical characterization of low-index polymeric rod-connected diamond (RCD) structures. Such complex three-dimensional photonic crystal structures are created via direct laser writing by two-photon polymerization. To our knowledge, this is the first measurement at near-infrared wavelengths, showing partia...

We report the optical properties of single defects in inverse three-dimensional (3D) rod-connected diamond (RCD) photonic crystal (PhC) cavities by using plane-wave expansion (PWE) and finite-difference time domain (FDTD) methods. By optimizing the dimensions of a 3D inverse RCD PhC, wide photonic band gaps (PBG) are obtained. Optical cavities with...

We present a beam focusing flat lens for use in the mid-infrared wavelength range. The layer structure used is a 360 nm thick amorphous silicon layer on 200 nm thick aluminium on a 300 μm thick Borosilicate Glass Substrate. An aperture through the Al and a-Si layers is used to excite and enhance the coupling efficiency of a hybrid-surface plasmon p...

In this paper, we present direct measurement of the far field radiation pattern produced by a 62,500 element aluminum nanoantenna array. The 250 x 250 array consists of nanorod/monopole nanoantennas separated by a uniform 409 nm pitch. Using the Fourier Microscopy technique, angle resolved reflectance measurements revealed a 40 percent peak reflect...

Semiconductor and plasmonic nanostructures have attracted considerable attention during the last decade. Semiconductors are the basis of today's information technology because of the possibility of tailoring electrical and optical properties on a detailed level. An elementary optical excitation in semiconductors is the electron-hole pair (exciton)...

Fourier Microscopy offers several benefits as a characterisation tool for nanoantennas. It involves using the Back Focal Plane to obtain the spatial Fourier transform of all incident angles of light. Using this approach the resonant frequencies, reflectance/transmission, and far field radiation patterns for any given frequency can simultaneously be...

Electrical current switching of 100nm of Ge2Sb2Te5 on glass. Optical reflectance is measured in both amorphous and crystalline states and angular reflectance is shown for a FIB etched 1200nm period grating. Materials whose optical properties can be tuned or switched electrically are of considerable interest to a variety of industries and research...

Orbital angular momentum (OAM) represents an additional degree of freedom of a light beam, to be added to the standard ones (e.g. polarization, wavelength) [1-2]. Previously, we have demonstrated an integrated device for OAM generation, in which the Whispering Gallery mode (WGM) of the micro-ring resonator to a propagating OAM mode by using an angu...

Electrical switching of the orbital angular momentum (OAM) mode order emitted from an SOI microring resonator is reported. The integration of the microring with waveguide couplers is used to demonstrate modulation of the relative phase between pairs of OAM modes with opposite signs.

The capability of manipulating light at subwavelength scale has fostered the applications of flat metasurfaces in various fields. Compared to metallic structure, metasurfaces made of high permittivity low-loss dielectric resonators hold the promise of high efficiency by avoiding high conductive losses of metals at optical frequencies. This letter i...

The ability to rapidly switch between orbital angular momentum modes of light has important implications for future classical and quantum systems. In general, orbital angular momentum beams are generated using free-space bulk optical components where the fastest reconfiguration of such systems is around a millisecond using spatial light modulators....

We present a beam focusing flat lens for use in the mid-infrared wavelength range. An aperture and second-order grating structure in thin gold and silicon layers is used to excite and then scatter a propagating surface plasmon polariton (SPP) to constructively interfere in the far-field to produce a narrow beam. The silicon layer acts as a mechanis...

Self-assembled quantum dots (QDs), nanosized semiconductors, are often known as artificial atoms due to their atomic-like spectra. For this reason they have long been proposed as a means to mediate interactions between single photons, a useful capability for photonic quantum information technology. I will describe the role of QDs in the latest deve...

We present a stand-alone beam-focusing flat lens for use in the telecommunications wavelength range. Light incident on the back surface of the lens propagates through a subwavelength aperture and is heavily diffracted on exit and partially couples into a surface plasmon polariton and a surface wave propagating along the surface of the lens. Interfe...

We present evidence of optical Tamm states to surface plasmon polariton (SPP) coupling. We experimentally demonstrate that for a Bragg stack with a thin metal layer on the surface, hybrid Tamm-SPP modes may be excited when a grating on the air-metal interface is introduced. Out-coupling via the grating to free space propagation is shown to enhance...

Fast tuning of the Optical Angular Momentum (OAM) order of a vortex beam is demonstrated with 20μs switching times using a compact silicon photonic device.

This paper proposes guided-mode resonant GaN grating that are implemented on a GaN-on-silicon wafer structure. Numerical simulations based on rigorous coupled wave analysis (RCWA) are performed to model multiple resonances in thick GaN membranes. Back wafer etching of freestanding GaN membranes is used as a tuning mechanism to manipulate the optica...

This letter presents the fabrication and characterization of freestanding circular GaN gratings on a GaN-on-silicon platform. Optical modes propagate within the freestanding GaN membrane and their number decreases as the thickness of GaN membrane is reduced. Backside thinning of freestanding GaN membranes is used to obtain thinner GaN membranes tha...

In this paper, we describe the fabrication and the novel procedure for back thinning the GaN layer, which leads to improved optical performance. Angular-resolved reflectance measurements are then conducted to characterize the GaN gratings and show the dependence of resonant wavelength on grating period and membrane thickness. The measured results c...

Subwavelength $hbox{HfO}_{2}$ gratings are realized on a freestanding 200-nm-thick $hbox{HfO}_{2}$ membrane with air as the low refractive index materials on top and bottom. Strong coupling between the incident light and $hbox{HfO}_{2}$ grating is characterized by angular-resolved reflectivity measurement, and guided-mode resonances are experimenta...

This paper introduces the novel concept of a cross dipole nanoantenna for use in fluorescence based sensing applications. The dual-arm nature of the cross nanoantenna allows a dual resonant structure to be designed such that the shorter arm resonates with the pump wavelength and the longer arm with the emission wavelength. This is expected to furth...

This paper presents the fabrication, simulation and measurement of low refractive index micropilar/microcavity structures where the optical properties are retrieved by white light Fourier image spectroscopy. This paper aims to show with these results that organic micropillars and low refractive index cavities in 3D photonic crystals could be a suit...

Photonic crystals and plasmonic structures have become a key subject in the future of optical communications and optical computing. Therefore, the study of their optical properties has become challenging in the last few years since they present micro or nanometric dimensions which makes it difficult their proper optical characterization. In this ta...

We present a study on the ability of two-dimensional close-packed arrays of submicron dielectric spheres to confine electromagnetic radiation. Substrates having different nature, either dielectric or metallic, are considered, and the evolution of the strong spatial redistribution of the total field intensity is monitored by means of numerical simul...

Hybrid metallodielectric systems where dielectric components are combined with metals supporting surface plasmons are able to spatially redistribute the electromagnetic field intensity within its volume through hybrid photonic-plasmonic modes. While most of the work done recently in this kind of systems has been focused on the way such redistributi...

We present a study on the ability of two-dimensional close-packed arrays of submicron dielectric spheres to confine electromagnetic radiation. Substrates having different nature, either dielectric or metallic, are considered, and the evolution of the strong spatial redistribution of the total field intensity is monitored by means of numerical simul...

In this letter, we present both experimental and numerical studies of the magneto-optical (MO) properties of nickel infiltrated opals. Ni can show interesting MO properties that can be controlled by nanostructuration through colloidal crystals templating. Nanostructuration allows the coupling of light to surface plasmon modes of Ni, and a clear dep...

We report on an extremely fast and versatile synthetic approach, based on microwave assisted sol-gel chemistry, that allows a conformal nanometric coating of intricate three-dimensional structures. Using this methodology, we have achieved a conformal coverage of large areas of three-dimensional opals with a superparamagnetic manganese ferrite layer...

The light confinement properties of hybrid metallodielectric systems have been studied employing numerical simulations to obtain the optical response as well as the total field intensity associated with the different modes of the structure. The effect of intrinsic losses, absorption, and out-of-plane leakage on the quality factors (Q) of different...

Hybrid self-assembled metallodielectric structures have been recently explored as a means to strongly modify the spontaneous emission of internal sources. In this work we explore the role of losses on their optical response.

The emission properties of two-dimensional self-assembled photonic-plasmonic crystals are fine tuned by varying the filling fraction for a monolayer of dye-doped polystyrene spheres on gold substrate. A complete experimental and theoretical study is presented.

Three-dimensional magnetophotonic crystals (3D-MPCs) are being postulated as appropriate platforms to tailor the magneto-optical spectral response of magnetic materials and to incorporate this functionality in a new generation of optical devices. By infiltrating self-assembled inverse opal structures with monodisperse nickel nanoparticles we have f...

The optical properties of two-dimensional hybrid photonic-plasmonic crystals are fine-tuned by modifying the dielectric component of the system. The filling fraction of the dielectric component in monolayers of spheres deposited on gold substrates is controlled by means of oxygen-plasma etching. Doing so enables spectral tuning of the optical modes...

A hybrid photonic-plasmonic crystal structure comprising a close-packed monolayer of dielectric spheres deposited on plasmon-supporting gold substrate is investigated. The spontaneous emission of organic dyes embedded in the beads experiences a strong modification in intensity, polarization, and directionality. These facts are accounted for conside...

Monodisperse colloids have been prepared efficiently by copolymerization of methyl methacrylate and fluorescent first- and second-generation poly(phenylenevinylene) dendrons under surfactant-free emulsion polymerization conditions. The copolymers were characterized by UV–vis and fluorescence spectroscopy and size exclusion chromatography. Transmiss...

We report here on the fabrication and characterization of magnetophotonic crystals obtained by infiltrating magnetic nanoparticles (maghemite) into silica-based inverse opals. Good quality opals, with adjustable photonic and magnetic characteristics have been obtained by this method. Magnetic and magneto-optic measurements, performed by using SQUID...