Tuning random lasing in photonic glasses

We present a detailed numerical investigation of the tunability of a diffusive random laser when Mie resonances are excited. We solve a multimode diffusion model and calculate multiple light scattering in presence of optical gain which includes dispersion in both scattering and gain, without any assumptions about the $\beta$ parameter. This allows us to investigate a realistic photonic glass made of latex spheres and rhodamine and to quantify both the lasing wavelength tunability range and the lasing threshold. Beyond what is expected by diffusive monochromatic models, the highest threshold is found when the competition between the lasing modes is strongest and not when the lasing wavelength is furthest from the maximum of the gain curve

Disordered Cellulose-based Nanostructures for Enhanced Light-scattering

Cellulose is the most abundant bio-polymer on earth. Cellulose fibres, such as the one extracted form cotton or woodpulp, have been used by humankind for hundreds of years to make textiles and paper. Here we show how, by engineering light matter-interaction, we can optimise light scattering using exclusively cellulose nanocrystals. The produced material is sustainable, biocompatible and, when compared to ordinary microfibre-based paper, it shows enhanced scattering strength (x4) yielding a transport mean free path as low as 3.5 um in the visible light range. The experimental results are in a good agreement with the theoretical predictions obtained with a diffusive model for light propagation

Integrated nano-plasmonics: reflecting a waveguide mode with a single nano-antenna

Integrated plasmonic systems have the potential to revolutionise telecom devices [1]. However, the large losses and poor efficiency of plasmonic systems [2] have limited the use of metallic systems as optical circuits. Here we present a hybrid silicon-metallic system in which a single nano-antenna embedded in a single-mode silicon waveguide acts as a tuneable and narrow-band switch. Nanoantennas interact very strongly with light [3], such that when the nano-antenna is at resonance with the waveguide mode up to 80% of the light is blocked by it. This drop in transmission is a consequence of scattering and interference between the dipole and the waveguide mode, which is efficient over the nano-rod resonance bandwidth. The high performance and simplicity of this hybrid device holds great promise for future optoelectronic circuits

A nanophotonic laser on a graph

Conventional nano-photonic schemes minimise multiple scattering to realise a miniaturised version of beam-splitters, interferometers and optical cavities for light propagation and lasing. Here instead, we introduce a nanophotonic network built from multiple paths and interference, to control and enhance light-matter interaction via light localisation. The network is built from a mesh of subwavelength waveguides, and can sustain localised modes and mirror-less light trapping stemming from interference over hundreds of nodes. With optical gain, these modes can easily lase, reaching $\sim$100 pm linewidths. We introduce a graph solution to the Maxwell's equation which describes light on the network, and predicts lasing action. In this framework, the network optical modes can be designed via the network connectivity and topology, and lasing can be tailored and enhanced by the network shape. Nanophotonic networks pave the way for new laser device architectures, which can be used for sensitive biosensing and on-chip optical information processing

Modal Coupling of Single Photon Emitters Within Nanofiber Waveguides

Nanoscale generation of individual photons in confined geometries is an exciting research field aiming at exploiting localized electromagnetic fields for light manipulation. One of the outstanding challenges of photonic systems combining emitters with nanostructured media is the selective channelling of photons emitted by embedded sources into specific optical modes and their transport at distant locations in integrated systems. Here, we show that soft-matter nanofibers, electrospun with embedded emitters, combine subwavelength field localization and large broadband near-field coupling with low propagation losses. By momentum spectroscopy, we quantify the modal coupling efficiency identifying the regime of single-mode coupling. These nanofibers do not rely on resonant interactions, making them ideal for room-temperature operation, and offer a scalable platform for future quantum information technology

Basic fibroblast growth factor mediates carotid plaque instability through metalloproteinase-2 and –9 expression

OBJECTIVE(S): We hypothesized that basic fibroblast growth factor (bFGF) may exert a role in carotid plaque instability by regulating the expression of matrix metalloproteinases (MMP). METHODS: Plaques obtained from 40 consecutive patients undergoing carotid endarterectomy were preoperatively classified as soft or hard. Serum bFGF was pre- and postoperatively measured. The release of MMP-2 and MMP-9 in the blood serum, and the activity, production and expression in the carotid specimens was analyzed. Specific anti-bFGF inhibition tests were performed in vitro on human umbilical artery smooth muscle cells (HUASMC) to evaluate the role of bFGF in the activity, production and expression of MMP-2 and -9. RESULTS: Twenty-one (53%) patients had a soft carotid plaque and 19 (48%) a hard plaque. Preoperative bFGF serum levels were higher in patients with soft plaques [soft=34 (28-39) pg/mL and hard=20 (17-22) pg/mL-p<0.001] and postoperatively returned to normal values (when compared to 10 healthy volunteers). The serum levels of MMP-2 in patients' with soft plaques were higher than those in patients' with hard plaques [soft=1222 (1190-1252) ng/mL and hard=748 (656-793)ng/mL-p<0.0001]. MMP-9 serum values were 26 (22-29) ng/mL for soft plaques and 18 (15-21) ng/mL for hard plaques (p<0.0001). We found increased activity, production and expression of MMP-2 and -9 in soft plaques compared to hard plaques (p<0.001). In vitro inhibition tests on HUASMC showed the direct influence of bFGF on the activity, production and expression of MMP-2 and -9 (p<0.001). CONCLUSIONS: bFGF seems to exert a key role in carotid plaque instability regulating the activity, production and expression of MMP thus altering the physiologic homeostasis of the carotid plaque

Simple Dynamics for Plurality Consensus

We study a \emph{Plurality-Consensus} process in which each of $n$ anonymous agents of a communication network initially supports an opinion (a color chosen from a finite set $[k]$). Then, in every (synchronous) round, each agent can revise his color according to the opinions currently held by a random sample of his neighbors. It is assumed that the initial color configuration exhibits a sufficiently large \emph{bias} $s$ towards a fixed plurality color, that is, the number of nodes supporting the plurality color exceeds the number of nodes supporting any other color by $s$ additional nodes. The goal is having the process to converge to the \emph{stable} configuration in which all nodes support the initial plurality. We consider a basic model in which the network is a clique and the update rule (called here the \emph{3-majority dynamics}) of the process is the following: each agent looks at the colors of three random neighbors and then applies the majority rule (breaking ties uniformly). We prove that the process converges in time $\mathcal{O}( \min\{ k, (n/\log n)^{1/3} \} \, \log n )$ with high probability, provided that $s \geqslant c \sqrt{ \min\{ 2k, (n/\log n)^{1/3} \}\, n \log n}$. We then prove that our upper bound above is tight as long as $k \leqslant (n/\log n)^{1/4}$. This fact implies an exponential time-gap between the plurality-consensus process and the \emph{median} process studied by Doerr et al. in [ACM SPAA'11]. A natural question is whether looking at more (than three) random neighbors can significantly speed up the process. We provide a negative answer to this question: In particular, we show that samples of polylogarithmic size can speed up the process by a polylogarithmic factor only.Comment: Preprint of journal versio

Biocompatible polymer and protein microspheres with inverse photonic glass structure for random micro-biolasers

This research was funded by Vietnam National Foundation for Science and Technology Development (NAFOSTED) under grant number 103.03-2017.318 and the the EPSRC Standard Grant EP/T027258/1.The miniaturization of random lasers to the micrometer scale is challenging but fundamental for the integration of lasers with photonic integrated circuits and biological tissues. Herein, it is demonstrated that random lasers with a diameter from 30 to 160 μm can be achieved by using a simple emulsion process and selective chemical etching. These tiny random laser sources are made of either dye-doped polyvinyl alcohol (PVA) or bovine serum albumin (BSA) and they are in the form of microporous spheres with monodisperse pores of 1.28 μm in diameter. Clear lasing action is observed when the microporous spheres are optically excited with powers larger than the lasing threshold, which is 154 μJ mm−2 for a 75 μm diameter PVA microporous sphere. The lasing wavelength redshifts 10 nm when the PVA microsphere diameter increases from 34 to 160 μm. For BSA microspheres, the lasing threshold is around 55 μJ mm−2 for a 70 μm diameter sphere and 104 μJ mm−2 for a 35 μm diameter sphere. The simple fabrication process reported allows for detail studies of morphology and size, important for fundamental studies of light–matter interaction in complex media, and applications in photonic integrated circuits, photonic barcoding, and optical biosensing.Publisher PDFPeer reviewe

Optical gain in DNA-DCM for lasing in photonic materials

We present a detailed study of the gain length in an active medium obtained by doping of DNA strands with DCM dye molecules. The superior thermal stability of the composite and its low quenching, permits to obtain optical gain coefficient larger than 300 cm^-1. We also show that such an active material is excellent for integration into photonic nano-structures, to achieve, for example, efficient random lasing emission, and fluorescent photonic crystals