Losses of plasmon surface waves on metallic grating

Abstract . Diffraction and absorption losses of plasmon surface waves (PSW) propagating along a metallic grating are investigated numerically as a function of groove depth . A periodicity of diffraction losses is found to exist . The energy flow distribution (EFD) above and inside the grooves is calculated and a similarity between the PSW on shallow and deep gratings is established above the grooves, while inside the grooves of deep gratings totally hidden curls in EFD are found to form . . Introduction Recently it has been discovered [1] that a close connection exists between different types of phenomena on metallic gratings : plasmon surface waves (PSW) excitation, non-Littrow perfect blazing It is well known that a pole of the scattering matrix corresponds to a solution of the homogeneous problem where nM is the complex refractive index of the substrate . For highly conducting metals Re (aP) > 1 and Im (aP) > 0, the latter corresponding to the energy absorbed in the metal as the PSW propagates along the interface . As the periodic modulation is introduced (h ;0), the PSW may be coupled to a propagating diffraction order(s) in the upper medium provided a suitable wavelength to period ratio 2/d is chosen . Radiation losses appear as a consequence of this and Im (aP) grows rather rapidly (for the results presented in figure 1 d=0. 5 µm and 2=0 . 6328 gm)

Organic solar cells as high-speed data detectors for visible light communication

Funding: Engineering and Physical Sciences Research Council (EPSRC) (EP/I00243X, EP/K00042X/1, EP/K008757/1).We show that solar cells, widely used in portable devices for power generation, can simultaneously extract a high-speed data signal in an optical wireless communication link. This Letter reports, to the best of our knowledge, the first use of an organic solar cell as an energy-harvesting receiver for visible light communications (VLCs). While generating maximum power in the cell, the communication link can deliver a data rate of 34.2 Mbps with a bit error rate of 4.08 x 10(-4) using an implementation of orthogonal frequency-division multiplexing. This approach could lead to printed optical data receivers in future eco-friendly VLC systems. Simultaneous functions of data communication and energy harvesting have great implications for the connectivity of future smart devices, many of which could become self-powered units as part of the "Internet of Things."PostprintPeer reviewe

Functional and structural leaf plasticity determine photosynthetic performances during drought stress and recovery in two platanus orientalis populations from contrasting habitats.

In the context of climatic change, more severe and long-lasting droughts will modify the fitness of plants, with potentially worse consequences on the relict trees. We have investigated the leaf phenotypic (anatomical, physiological and biochemical) plasticity in well-watered, drought- stressed and re-watered plants of two populations of Platanus orientalis, an endangered species in the west of the Mediterranean area. The two populations originated in contrasting climate (drier and warmer, Italy (IT) population; more humid and colder, Bulgaria (BG) population). The IT control plants had thicker leaves, enabling them to maintain higher leaf water content in the dry environment, and more spongy parenchyma, which could improve water conductivity of these plants and may result in easier CO2 diffusion than in BG plants. Control BG plants were also characterized by higher photorespiration and leaf antioxidants compared to IT plants. BG plants responded to drought with greater leaf thickness shrinkage. Drought also caused substantial reduction in photosynthetic parameters of both IT and BG plants. After re-watering, photosynthesis did not fully recover in either of the two populations. However, IT leaves became thicker, while photorespiration in BG plants further increased, perhaps indicating sustained activation of defensive mechanisms. Overall, our hypothesis, that plants with a fragmented habitat (i.e., the IT population) lose phenotypic plasticity but acquire traits allowing better resistance to the climate where they became adapted, remains confirmed

Visible light communication using InGaN optical sources with AlInGaP nanomembrane down-converters

We report free space visible light communication using InGaN sources, namely micro-LEDs and a laser diode, down-converted by a redemitting AlInGaP multi-quantum-well nanomembrane. In the case of microLEDs, the AlInGaP nanomembrane is capillary-bonded between the sapphire window of a micro-LED array and a hemispherical sapphire lens to provide an integrated optical source. The sapphire lens improves the extraction efficiency of the color-converted light. For the case of the downconverted laser diode, one side of the nanomembrane is bonded to a sapphire lens and the other side optionally onto a dielectric mirror; this nanomembrane-lens structure is remotely excited by the laser diode. Data transmission up to 870 Mb/s using pulse amplitude modulation (PAM) with fractionally spaced decision feedback equalizer is demonstrated for the micro-LED-integrated nanomembrane. A data rate of 1.2 Gb/s is achieved using orthogonal frequency division multiplexing (ODFM) with the laser diode pumped sample

Visible Light Communication Using a Blue GaN μLED and Fluorescent Polymer Color Converter

This letter presents a novel technique to achieve high-speed visible light communication (VLC) using white light generated by a blue GaN mu LED and a yellow fluorescent copolymer. We generated white light suitable for room illumination by optimizing the ratio between the blue electroluminescence of the mu LED and yellow photoluminescence of the copolymer color converter. Taking advantage of the components' high bandwidth, we demonstrated 1.68 Gb/s at a distance of 3 cm (at 240 lx illumination). To the best of our knowledge, this is the fastest white light VLC results using a single blue LED/color converter combination.PostprintPeer reviewe

A Multi-Gigabit/sec Integrated Multiple Input Multiple Output VLC Demonstrator

In this paper, we report the performance of an imaging multiple input multiple output (MIMO) visible light communication (VLC) system. The VLC transmitter consists of a two-dimensional, individually addressable Gallium Nitride micro light emitting diode (µLED) array. The receiver uses a two-dimensional avalanche photodiode (APD) array fabricated using complementary metal oxide semiconductor (CMOS). Using integrated CMOS-based LED drivers, a data rate greater than 1 Gbps was obtained at a link distance of 1 m with the system field of view (FOV) of 3.45 degree using four channels. At a reduced link distance of 0.5 m, a data rate of 7.48 Gbps was obtained using a nine channel MIMO system. This demonstrates the feasibility of compact MIMO systems which offer substantial data rates

LED Based Wavelength Division Multiplexed 10 Gb/s Visible Light Communications

LED based Visible Light Communications can provide high data rates to users. This can be further increased by the use of wavelength division multiplexing, using the different colours required to generate white light to transmit different data streams. In this paper a trichromatic approach is described, and the influence of colour combination on achievable data rate is analysed. A demonstration of LED based communications which achieves a data rate of >10 Gb/s by using a rate adaptive orthogonal-frequency-division-multiplexing scheme is also reported

High-Speed Integrated Visible Light Communication System: Device Constraints and Design Considerations

Visible light communications (VLC) has the potential to play a major part in future smart home and next generation communication networks. There is significant ongoing work to increase the achievable data rates using VLC, to standardize it and integrate it within existing network infrastructures. The future of VLC systems depends on the ability to fabricate low cost transceiver components and to realize the promise of high data rates. This paper reports the design and fabrication of integrated transmitter and receiver components. The transmitter uses a two dimensional individually addressable array of micro light emitting diodes (μLEDs) and the receiver uses an integrated photodiode array fabricated in a CMOS technology. A preliminary result of a MIMO system implementation operating at a data rate of 1 Gbps is demonstrated. This paper also highlights the challenges in achieving highly parallel data communication along with the possible bottlenecks in integrated approaches