Materials and devices for green photonics

Resume : In this work, we report a simple synthesis and UV-visible photodetection application of monoclinic p-type MoO2 nanostructures (NSs) on Si platform for the first time. We have grown monoclinic MoO2 (?-MoO2) structures from previously grown ?-MoO3 structures/n-type Si via hydrogenation process at 450 °C. We have confirmed using XRD, XPS, and HRTEM that after hydrogenation ?-MoO3 NSs were completely converted into ?-MoO2 NSs without presence of any sub-oxidized phase of molybdenum oxide. As-grown nanostructured film exhibits very good p-type electrical conductivity of ? 2.015×103 S?cm?1 with hole mobility of ? 7.85±1.28 cm2?V?1?Sec?1 as evident from Hall measurements. To explore the photo-sensing properties of p-type MoO2 NSs, we have fabricated p-type MoO2/n-type Si heterojunction (as-grown) photodetector device with Au as top and Al as bottom contacts. The device exhibits peak photoresponsivity of 0.155 A/W with maximum detectivity 1.28 × 1011 cm-Hz1/2-W?1 and 44% external quantum efficiency (EQE) around ? 436 nm, at the reverse bias of 1.5 V. Importantly, this device also shows good self powered photodetection performance with peak responsivity and detectivity of ~45 mA/W and ~4 × 1010 cm-Hz1/2-W?1 respectively. This broad-band UV-visible light detection feature can be attributed to the synergistic effects of MoO2 band-edge absorption (E_g= 2.65 eV), interfacial defects states absorption and self absorption of Si. The photodetection behavior of the fabricated device has been understood by proposed band diagram with the help of experimentally derived work function of as-grown MoO2 nanostructured film using Kelvin probe force microscopy (KPFM). Keywords: ?-MoO2, hydrogenation, p-type semiconductor, photodetection and KPFM Reference: A. Ghosh et al., Under Review in J. Mater. Chem. C. C. Zhao et al., ACS Appl. Mater. Interfaces 2015, 7, 25981?25990. D. O. Scanlon et al., J. Phys. Chem. C 2010, 114, 4636?4645.

Resume : 　Optical excitation of a noble metal nanostructure can generate localized surface plasmons, resulting in a large electric field. Recently, semiconductors attract much attention as field-enhancement materials because of specific properties of and cost-effective material. Molybdenum disulphide (MoS2) is the one of the most promising two-dimensional semiconductor material in transition metal dichalcogenides for transistor, light emitting diode and so on because of its unique electronic and optical properties. If the field enhancement could be used for these devices, their efficiencies are significantly enhanced. Here, this is the first study that the field enhancement of MoS2 and its dependence of number of layers (10~3000 layers) are found. The enhancement effect was evaluated by the fluorescence and Raman intensity of dye molecules as well as two different theoretical calculations. As a result, a MoS2 flake with a specific thickness (~500 layers) shows the highest enhancement factor (EF) as 30 for fluorescence and 170 for Raman respectively, whereas EF becomes smaller over the thickness of 500 layers. Two theoretical calculations, based on Mie scattering theory and finite-difference time-domain method, are in good agreement with those of these experimental results. In addition, it was recognized that large and small enhancement effects are due to electric field and charge transfer effects, respectively, both of which depend on layer thickness.

Resume : We report in this work, the design, simulation, fabrication and experimental results for a enabling technology based on nanoscale engineering of the waveguide effective index by plasmonic resonance suited for implementation of on demand light roads in integrated optics applications in near infrared domain (1.3µm and/or 1.55µm). To this end, gold cut wires (CWs) deposited on the top of a Silicon on insulator waveguide are used to modify the local effective index by using plasmonic resonances of the gold nanoparticles interacting with the evanescent tail of the waveguide mode. The essential advantage of such an approach is the reduction of propagation losses since light is mainly confined in the Silicon slab. Specifically, two configurations of 2D hybrid waveguide based either on metasurface or metalines and targeting different optical functionalities are considered here. In contrast to photonic crystals the period of the CWs is much smaller than the Bragg period. Meanwhile localized plasmonic resonances allow a much higher degree of freedom for the control of effective index paving thus the way for their further use in miniaturized integrated optics applications. This considered approach is quite generic and has the merit of simplified technological implementation as compared with bulky metamaterials counterparts. It can be adapted to many other types of planar lightwave circuits platforms like GaN/AlN, InGaAsP/InP, doped silica glass etc.

Resume : Optical metamaterials offer the possibility of accessing extraordinary optical properties through the specific arrangement of their sub-wavelength structural units. A particularly interesting morphology is the gyroid due to its chiral, cubic, and triply-periodic geometry. Gyroid optical metamaterials with unit cell sizes of tens of nanometres can be conveniently fabricated via electrodeposition of gold into voided, self-assembled polymer templates. This self-assembly-based approach allows the fabrication of gold gyroids with different orientation and unit cell size. We here show that gyroid metamaterials exhibit a depressed effective plasma frequency as well as circular and linear dichroism, a surprising result given the underlying cubic symmetry. By combining electron microscopy and optical goniometry, we show that the reflection of light from gold gyroids is strongly polarisation-dependent, sensitive to the orientation of the gyroid and the terminations of its top surface. Our results highlight the influence of orientation and surface terminations of optical metamaterials, which has significant consequences for both their design and applications.

Resume : Metamaterials and metasurfaces rely on optically resonant nanostructures for the control and manipulation of light. Plasmons at metal/dielectrics interfaces provide strong resonances, which has encouraged, in the recent years, active research efforts towards the fabrication of nanostructured metal-dielectric materials and surfaces. Most nanoplasmonic metamaterials have been built by lithographic approaches using microelectronics technologies. This has enabled the fabrication of a large number of electromagnetic metamaterials operating at frequencies down to the ultraviolet. However these top-down approaches, though very precise in making ordered structures, are highly cost-, time- and energy-intensive, especially for sub-100nm resonator sizes (for visible wavelengths), so that materials are usually restricted to very small lateral dimensions and thicknesses. Alternative fabrication methodologies have been developed based on colloidal chemistry, self- and directed-assembly and soft matter physics. We will discuss some recent studies, which led to the fabrication of 3D dense assemblies of resonators presenting optical magnetism or hyperbolic permittivities. Self-assembly based methodologies present interesting perspectives both for the production of individual optically resonating colloids in large numbers, and for their assembly into large scale materials and surfaces.

Resume : Dielectric metasurfaces require the integration of materials with different dielectric constants, organized within precise nano-scale architectures. They are typically fabricated by the well-established lithographic or chemical processes, that remain difficult to scale to large-area and soft substrates. They are also costly and quite inefficient in terms of materials usage and resources. Here, we propose an alternative fabrication strategy based on the template dewetting of thin chalcogenide glass layers as a novel approach to self-organize a variety of large index contrast all-dielectric metasurfaces. Given the right dewetting time-temperature settings, initial film thickness and underlying pattern, the breakup of the film can occur at prescribed locations resulting in nano-objects of tunable position and sizes. The wide range of processing temperatures enables large-scale use of rigid but also flexible and stretchable substrates. We will show a variety of optical architectures that can be tailored to exhibit, with a minute amount of materials and no waste, high optical absorption, strong electromagnetic confinement or Fano resonances with characteristics better than structures built with electron beam lithography. This approach paves the way towards a simple and green fabrication route of advanced 2D and quasi 3D photonic devices for applications in sensing, light management and second harmonic generation.

Resume : When spinning photons propagate in inhomogeneous media or across an optical interface, spin-orbit interaction (SOI) may occur with an extra geometric phase. Metasurfaces, a new class of nanostructured interfaces composed of monolayers of artificial meta-atoms, can greatly enhance the photonic SOI in mesoscale and lead to many extraordinary phenomena (such as the spin-Hall effect and spin-to-vortex conversion) and important applications (such as the generation of complex optical fields). Metasurfaces are turning to be promising platforms for realizing various SOI effects and applications. Furthermore, the helicity and geometric phase are two key parameters of photonic SOI, representing the spin and orbital angular momenta of light, respectively. The characterization (especially the direction detection and measurement) of photonic SOI processes is highly demanded for the study of spin-orbit photonics. In this research, we first design and realize a Berry phase metasurface that can effectively manipulate the SOI and generate complex optical fields. As an example, a metasurface device generating vortex beam with topological charge of 3 is demonstrated. Then we develop a novel spin-selective and phase-resolved scanning near-field optical microscopic (SNOM) method and system utilizing the heterodyne interferometry and cross-polarization detection technique, which can directly probe and image the near-field SOI. The distribution and dynamic evolution of the geometric phase can be directly measured and intuitively illustrated. Moreover, we establish a convolution model based on the reciprocity of electromagnetism expanded in circular polarization bases to well interpret the detection mechanism and analyze the measurement data. Good agreement between the theoretical and experimental results has been obtained. Our work provides a versatile metasurface platform for efficient manipulation of photonic SOI in subwavelength scale and a powerful SNOM tool for experimental study of spin-orbit photonics.

Resume : Random lasing occurs within a system that contains a random assembly of elastic scatterers within an optical gain medium. Unlike a traditional laser, these multiple light scattering events can provide sufficient feedback as to generate lasing without a defined optical cavity, with the relationship between the gain feedback and the scattering determining the optical properties. Here we report random lasing from an organic dye-doped stretchable photocurable polymer. The polymer consisted of a mixture of a monofunctional monomer of epoxy aliphatic acrylate and a difunctional cross-linker consisting of an aliphatic urethane diacrylate combined with isoborynl acrylate. The lasing wavelength was determined primarily from the identity of the dye employed. However, mechanical stretching of the polymer was seen to impact the average wavelength of lasing. This likely results from alterations to the scattering pathway within the polymer upon mechanical stretching. The scattering nature of the polymer was also observed to be dependent on the ratio of the two polymer components, and showed both temporal and substrate dependence, with an increase in the randomness of the lasing wavelength observed after pressing the polymer on a glass substrate. Such mechanical stimuli responsiveness greatly increases the possible applications of random laser to include stress/strain sensing. The facile preparation of the cured polymer also lends itself to coating applications for novel optical devices.

Resume : All-inorganic perovskite quantum dots (PQDs), i.e., CsPbX3 (X = Cl, Br, I), have been widely investigated recently due to their marvelous luminescence properties. Appropriate amount of surface ligands cannot only stabilize PQDs in a colloidal solution but also improve the charge transport after they are fabricated as optoelectronic devices. In this research, the purification process was investigated by employing various solvents and with different polarities washing methods. Several characteristic methods have been used to analyze the surface chemical composition of the post-processed QDs, such as photoluminescence (PL), ultraviolet-visible spectroscopy (UV-vis), transmission electron microscopy (TEM), X-ray diffraction (XRD), thermogravimetric analysis (TGA), Fourier-transform infrared spectroscopy (FTIR), nuclear magnetic resonance spectroscopy (NMR), and X-ray photoelectron spectroscopy (XPS). Finally, a proper purification procedure using gentle washing process was demonstrated with illustration of the surface ligand binding structure.

Resume : White Organic Light-Emitting Diodes (WOLEDs) are known to be an ideal light source and they have been attracted an increasing interest because they offer many lighting applications; among them as illumination probe source in biosensors. The latter is reinforced by the fact that WOLED have no ultraviolet emission. In this work, novel copolymers bearing blue, yellow and red chromophores are used for the fabrication of WOLED systems. These systems provide easy tuning of white color by changing weight/weight ratios between the chromophores. In addition, they show higher efficiency and brightness than an individual device because of some additional pathways related to light production. The chromophores can be directly excited by capturing charge carriers or through energy transfer from the other chromophores. Incomplete energy transfer between the chromophores is necessary to get white light as combined emission from all of them. NIR-Vis-far UV Spectroscopic Ellipsometry, Photoluminescence, Electroluminescence and Atomic Force Microscopy characterization provide valuable information towards the optimization and functionalization of the WOLED devices in terms of CIE color coordinates, operational voltages, power efficiency and brightness.

Resume : A photonic jet is a jet of light that is produced at the sub-diffraction focus in the near field of a dielectric micro-object. The phenomenon has been obtained both in the near field of microspheres and of shaped optical fiber tips. It allows sub-wavelength focusing, high intensity concentration and high sensitivity backscattering measurements. Moreover, it illustrates the lens behavior of transparent microspheres, making possible super-resolved imaging. In this work, we show theoretically and experimentally how the photonic jet can be used in new green photonics techniques for micro-machining as well as for 3D optical characterization of materials and microsystems. With power lasers, photonic jets allow sub-micron processing without any chemical processing: marking, ablation, peak generation, etc. When used for imaging, microspheres can lead to 2D images with a resolution up to seven times smaller than the wavelength, consuming less energy than electron microscopy and requiring less time than AFM. In an interferometric configuration, the imaging process can also be used to reconstruct the 3D profile of micro-objects with a depth resolution of between 1 and 10 nm.

Resume : Silicon photonics is now available to enhance the bandwidth and efficiency of communication in computing systems. In this presentation, additional efficiency enhancements related to tight electro-optical integration at the chip- and system-level will be discussed. Corresponding technology advancements will be presented such as CMOS silicon photonics embedded lasers and the co-packaging of processors with such electro-optical silicon chips. Furthermore, novel applications of silicon photonics for the inference and training of neural networks will presented, building on the same III-V on silicon integrated optic platform as applied for optical communication subsystems on a chip.

Resume : In this work, we investigate an ultrafast transverse mode switches with low pump power and high conversion efficiency based on silicon on insulator (SOI) platform for the switching applications with preserving wavelength in the spatial division multiplexing(SDM) systems. The proposed ultrafast transverse mode switching is based multimode four-wave mixing (FWM) among four transverse modes of a silicon waveguide, i.e. quasi-TE0, TE1, TM0, and TM1 modes, and analyzed by modeling the conversion process with multi-mode coupled nonlinear Schrodinger equations. Two pumps at the TM0 and the TM1 mode form a transient index grating that travels along the pump waves through multimode interference and Kerr effect. The transient Kerr grating scatters the probe light at the TE0 mode to the idler light on the TE1 mode, or vice versa. Note that in contrast to static mode conversion realized by grating structures or tapered waveguides etc., such mode exchange is optically induced so that it can be inherently used as mode switches. By tailoring the geometry of the silicon nanowire, energy and momentum conservation, w_TE0-w_TE1=w_TM0-w_TM1 and ?_TE0-?_TE1=?_TM0-?_TM1 can be satisfied. The thickness of multimide waveguide is fixed as 220 nm, which is a common value available for SOI wafers. Cross section of an SOI waveguide of 220 nm × 1250 nm geometry with top silica cladding has been chosen for the rest of the study, which is possible to operate the inherent switch in the C-band wavelength region with THz bandwidth. Several works have been focused on ultrafast transverse mode switching with this schematic, including fiber and integrated Si3N4 waveguide with high peak power up to kW. Since silicon has even higher nonlinear-index coefficient n2 and smaller effective mode volume Aeff then those of the previous studied platforms, which may enable lower switching energy and a more compact on-chip structure. It should be noted that, the advantage of stronger mode confinement may come at the cost of increased group velocity mismatch which may limit the effective interaction length of the ultrafast transverse mode switching. Nonlinear absorption associated with silicon is also detrimental to nonlinear effects, but may be relieved by using reversed biased PIN structures. Therefore, a special focus is given to the group-velocity mismatch of the switch since four transverse modes are involved, which is degraded heavily from that of the single mode case. This is done by analyzing the four kinds of temporal profile of the switching window when four modes are assigned to the pump, probe as well as idler waves respectively. In order to better evaluate the performance of the switching windows, we introduce two parameters: 10% width of switching window and average ER estimated over the 10% window width. The 10% width of switching window is defined as the width at 10% of highest point of the switching window, which is used to guarantee a larger width at the bottom of the switching window. The average ER is the average of the extinction ratios in this 10% window width. Note that probe light is CW, while two pump lights are pulsed as well as the generated idler. Therefore, the switching window who owns smaller walk off variance among two pump and the idler waves performs the best. In addition, the peak power of the total pump pulses drops due to misalignment of the two pump pulse. Therefore, the maximum average ER is achieved at a length that is slightly longer than what are expected from coupled mode theory. Due to the walk-off effect among the pump light and probe light, the overall position of the switching window relative to the probe light will be misaligned, resulting in reduced overlap between the switching window and the probe pulses. By carefully optimize the temporal delay between the pump and probe pulses and probe pulse width, it is possible to achieve a conversion efficiency over 90% without resorting to the help of reducing the waveguide length, resulting in a switching energy of 120 pJ, which is more than seven fold smaller than that reported in Si3N4 waveguide [1]. The usage of the switch is further considered in a hybrid OTDM SDM switching scenario, where a high-speed 160 Gps OTDM signal is considered. A 160 Gps OTDM data stream is loaded on the TE1 mode (signal 1), and a 10 Gbps OTDM tributary (signal 2) is loaded on the TE0 mode. Signal 2 is aligned to a specific OTDM channel of signal 1. By launching 10GHz pump pulses on the TM1 and TM0 mode and make the pump pulses aligned with channel 1 of signal 1, it is possible to switch the data between channel 1 of signal 1 with signal 2. Wide open eye diagrams are shown to be possible using the optimized ultrafast transverse mode switch under an average switching power of 30.8 dBm, where the Si waveguides must be equipped with reverse biased PIN structures in order to remove the detrimental carrier effects. Note that Si waveguides without PIN structures may be used when the switching repetition rate is reduced. Since the SDM technology is widely explored to overcome the capacity crunch of single optical fibers, we expect this work offers guidelines for the design of ultrafast SDM switches based on the SOI platform. [1] T. Hellwig, J. P. Epping, M. Schnack, K.-J. Boller, and C. Fallnich, "Ultrafast, low-power, all-optical switching via birefringent phase-matched transverse mode conversion in integrated waveguides," Opt. Express 23, 19189-19201 (2015).

Resume : To further increase optical communication capacity, narrow linewidth laser sources and novel all-optical signal processing techniques are required to be developed. Stimulated Brillouin Scattering(SBS) owns several unique property including lower nonlinear threshold, ultra-narrow gain linewidth and easily to be realized in optical fibers, which can be exploited to satisfy requirements from the optical communication systems. Some experimental results will be presented about multiwavelength lasers, single longitudinal-mode fiber laser, optical microwave signal generation by optical heterodyne approach and single side modulated microwave signal with tunable carrier-to-sideband ratio based on SBS effect. The discussion and analyses are made for the experimental results, and the suggestion for the improvements are also given. But the Brillouin fiber devices suffer from their complexity and unstability. Integrated photonic components are desired for optical communications and signal process. Silicon-based phononic-photonic hybrid waveguide and silicon nanowire racetrack resonator are developed to implement forward stimulated Brillouin scattering(FSBS). These photonic components are fabricated using the CMOS compatible technology. The phononic-photonic hybrid waveguide consists of the suspended centered silicon photonic waveguide and bilateral silicon nitride phononic crystal waveguide which are utilized to confine the optical and acoustic fields respectively. The independent control of the optical and acoustic modes significantly increases the tunability of the whole structure. The silicon nanowire racetrack resonator is partly suspended by the tiny silica pillar. By nearly completely separating the silicon resonator from the silica substrate, the simultaneous acoustic and optical confinements in the silicon core are achieved to enhance the acousto-optic interaction. FSBS is demonstrated experimentally and the Brillouin amplification with 2.25dB is obtained. These proposed approaches furnishes an alternative way to extend the FSBS from bulk nonlinear optical media to chip-scale devices.

Resume : Graphene is an very interesting material with a lot of unique properties. In this talk, we review our recent work on graphene photonics on silicon platform, including silicon-graphene modulator, energy efficient graphene heater on silicon, graphene-plasmonic hybrid modulators, graphene-plasmonic photodetectors, showing promising of graphene in optical communication.

Resume : Controlling the optical field down to the nanometer scale is a key step in optoelectronic applications and light matter interaction at the nanoscale. Bowtie structures, rods and sharp tapers are commonly used to realize such optical properties, but their fabrication is challenging. In this context, the complementary structures, namely holes and cavities, are less explored. Herein, a simple system of two metallic nano-cavities milled in thin silver film is used to confine the electromagnetic (EM) field to an area of ~60nm^2. The field is confined onto a flat surface area and is either enhanced or suppressed by the polarization state of incident light. The energy of this spatially confined mode is determined by the distance between the two cavities and thus any color (wavelength) at the optical regime can be achieved. As a consequence, a dynamically controlled color is generated on an optical pixel size smaller than one micron square. Those results are supported both by transmission spectra and a Cathodoluminescence study.

Resume : Plasmonics can localize light in a sub-wavelength scale, which has the potential for integrating photonics and electronics on nanoscale. Comparing to numerous studies of noble metal, we firstly fabricated bismuth (Bi) quantum dots with diameters less than 60 nm on single crystalline yttrium iron garnet (YIG) using molecular beam epitaxy. YIG/Bi quantum dots hybrid systems exhibit a maximum 130% enhancement of magneto-optical Kerr rotation comparing to bare YIG, which is on account of localized surface plasmons resonance of Bi quantum dots. For a 3 μm thick magneto-optic material lutetium and bismuth co-doped YIG (LBIG) films, the introduction of surface Bi quantum dots in LBIG/Bi hybrids dramatically enhances Kerr rotation from 1626 mdeg to 2341 mdeg. High resolution transmission electron microscope demonstrated Bi quantum dots are amorphous and have no diffusion into YIG. The transmission-band valley in Fourier-transform infrared spectroscopy prove the resonant coupling of the light to surface plasmons excitations of YIG/Bi interface. Furthermore, giant fluorescence enhancement has been observed in YIG/Bi hybrid system. The results revealed an existence of Bi quantum dots plasmon resonances. Our experiments show the great ability in Kerr rotation regulation of Bi quantum dots, which could have applications in telecommunication, spintronics and magnetoplasmonic sensors.

Resume : Nanoporous metals are lack in nature, and therefore their properties are a direct result of the preparation strategy. Practically, all the current available preparation techniques are multistep, and the resulting nanoporous metal contains foreign additives which eventually govern their optoelectronic properties and may deteriorate their performance. The inner architecture of these networked metals consists of random sizes and shapes of both particles and holes. Consequently, these metallic architectures are able to interact with the entire solar spectrum through excitation of surface plasmons, collective oscillations of the metal’s free electrons. Herein, we demonstrate a simple scalable method to fabricate pure 3D metallic networks of nano-size building-blocks. Our strategy is based on physical vapor deposition (PVD) on an electrostatic silica aerogel substrate which initiates self-organization of the vapored metallic atoms into a nanoporous network. The resulting networks have distinct colors different from the corresponding bulks, as function of metal type, thickness and inner structural parameters of the networks. These large-scale networks are transparent, flexible, pure, and show indication for hot carriers generation and photo-catalytic activity upon white-light illumination. Silver networks present significant nonlinear optical behavior coming into expression by coherent and intense second harmonic generation (SHG) emission. The disordered inner architecture of the networks support electromagnetic field localization into hot-spots, and a broadband response. The large-scale lateral dimensions of the networks, together with the multiple intense localized hot-spots suggest that 3D metallic networks can outperform in a range of fields such as sensing, bio-imaging, quantum optics and photocatalysis.

Resume : We combined the electrospray method and closed space sublimation process to prepare the CH3NH3PbI3-xClx perovskite absorption film on the ITO (indium tin oxide)/PEDOT:PSS (polyethylene dioxythiophene doped with polystyrene-sulfonic acid) substrate. Through the adjustment of experimental parameters to obtain a uniform and pinhole-free film. The properties of CH3NH3PbI3-xClx thin film was analyzed by X-ray diffraction (XRD) and scanning electron microscopy (SEM). The thermal evaporation then used to deposit the fullerene (C60, 30 nm), bathocuproine (BCP, 10 nm), and Al (100 nm) onto the CH3NH3PbI3-xClx thin filmto fabrication the perovskite solar cell. The device structure is ITO/PEDOT:PSS/CH3NH3PbI3-xClx/C60/BCP/Al, the power conversion efficiency (PCE) of the perovskite solar cell is 8.23% measured under the typical AM 1.5G solar standard.

Resume : Advanced photovoltaic devices with a high performance/cost ratio is a major concern nowadays. In the present study, we investigate the energetic efficiency of a new concept based on an indirect (instead of direct) photovoltaic and thermoelectric coupling. Using state-of-the-art thermal transfer calculations, we have shown that such an indirect coupling is an interesting alternative to maximize solar energy exploitation. In our model, a concentrator is placed between photovoltaic and thermoelectric systems without any physical contact of the three components. Our major finding showed that the indirect coupling significantly improve the overall efficiency which is very promising for future photovoltaic developments.

Resume : We report recent progress towards the realization of optical integrated light sources based on the use of semiconductor single-wall carbon nanotube (s-SWNTs) emitters coupled with the localized modes of silicon on insulator nanobeam cavities. A carbon nanotube polymer matrix was prepared by highly purified PFO-wrapped HiPCO nanotubes, which resulted in highly purified (9,4) (8,6) (8,7) chirality carbon nanotubes in toluene solutions [1,2]. A thick of PFO-CNT layer (>500nm) was drop casted on top of the fabricated silicon photonic structures [2]. A specific effort to design optical nanocavities has been conducted to provide an efficient integration photonic host for SWNTs nanoemitters. Specifically, we undertook to design photonic resonators with small mode volumes (Vs < < (lambda/n)3) with large Q factors simultaneously (Qs>>103) and electromagnetic modes preferentially confined in the small index regions [3,4]. The silicon platform was chosen as the mainstream option for the realization of integrated optical sources for optical telecommunications and interconnects at telecom wavelengths (both around lambda=1.3µm and lambda=1.5µm). Silicon photonic structures were fabricated using electron beam lithography and inductively coupled plasma etching whole process. s-SWNTs were pumped in the 730nm-900nm wavelength range from the top of samples with a beam spot of around 1µm size that was scanned over the sample surface or along specific one dimensional cut-lines. Simultaneously the light polarization of the pump beam was controlled and continuously varied in order to investigate the polarization dependent excitation of s-SWNTs emitting in the near infrared. We monitored the ability of PL emitted waves to couple with the quasi-TE light polarization of the silicon photonic nanobeam cavitites. Since carbon nanotubes were essentially randomly distributed within the superficial cladding layer, the polarization dependence of the light collection, which had proved experimentally to be very strong, has been attributed to the modes? symmetries of the designed and fabricated nanocavities. A very clear reinforcement of the photoluminescence of carbon nanotubes by the effect of the resonators could be observed (> 100) in various configurations, proving the coupling of the luminescence of the nanotubes around 1.3 ?m and 1.55 ?m. The high quality factors associated with very low modal volumes led to active resonators working at Q/V> 500,000. All of these works make important contributions to the understanding of the mechanisms of coupling of carbon nanotube nanoemitters with silicon dielectric resonators fabricated in silicon photonics on SOI substrates. They contribute to advances towards the realization of on-chip integrated photon sources at telecom wavelengths. [1] E. Gaufres, N. Izard, X. Le Roux, D. Marris-Morini, S. Kazaoui, E. Cassan, and L. Vivien, "Photoluminescence enhancement of semiconducting-carbon-nanotubes-based thin films", P. L. Heremans, R. Coehoorn, and C. Adachi, eds. (2010), Vol. 7722, p. 77220Y. [2] E. Duran Valdeiglesias, W. Zhang, A. Noury, C. Alonso Ramos, S. Serna, X. Le Roux, E. Cassan, N. Izard, F. Sarti, U. Torrini, F. Biccari, A. Vinattieri, M. Balestrieri, A.-S. Keita, H. Yang, V. Bezugly, G. Cuniberti, A. Filoramo, M. Gurioli, L. Vivien, ?Integration of Carbon Nanotubes in Silicon Strip and Slot Waveguide Micro-Ring Resonators?, IEEE Transactions on Nanotechnology , vol. 15, no. 4, pp. 583-589, 2016. [3] T. H. C. Hoang, E. Durán-Valdeiglesias, C. Alonso-Ramos, S. Serna, W. Zhang, M. Balestrieri, A.-S. Keita, N. Caselli, F. Biccari, X. Le Roux, A. Filoramo, M. Gurioli, L. Vivien, E. Cassan, ?Narrow-linewidth carbon nanotube emission in silicon hollow-core photonic crystal cavity?, Optics Letters 42(11), 2228 (2017). DOI: 10.1364/OL.42.002228 [4] W. Zhang, S. Serna, X. Le Roux, L. Vivien, E. Cassan, ?Silicon nanobeam cavity for ultra-localized light-matter interaction?, Optics Letters 42 (17), 3323-3326 (2017).

Resume : Luminescent Solar Concentrators (LSCs) have experienced a renaissance with researchers realizing the possibility of creating power windows as a built-in photovoltaic option. These work by harvesting light, then re-emitting it into a waveguide, with a conventional photovoltaic device at the edge to generate electrical energy. In order to make these viable two major requirements are for transmitted light to be aesthetically pleasing and to have at least modest conversion efficiencies. Here we show a LSC system based on a BODIPY derivative, which has a broad transmission window across the majority of the visible spectrum, strong absorption at the red edge and high emission yield. This leads to optical efficiencies of ~4%. Beyond this, we investigate through a modelling approach, the possibilities of further enhancement with realistic developments in dye properties, thus helping to shape future research efforts.

Resume : Photodetection in the short-wave infrared (SWIR) spectrum is a challenging task achieved often by costly low-bandgap compound semiconductors involving highly toxic elements. In this work we report an alternative low-cost approach for SWIR sensors which relies on the plasmonic-induced photothermal effect of solution-processed colloidal gold nanorods (Au NRs). A series of uniform solution-processed Au NRs of various aspect-ratios were prepared exhibiting a strong and well-defined longitudinal LSPR maximum from 900 nm to 1.3 μm. A hybrid device structure was fabricated applying Au NRs on the surface of a thermistor. Under a monochromatic illumination, hybrid Au-NR/thermistor devices exhibit a clear photoresponse in the form of photo-induced resistance drop in the wavelength window from 1.0 μm to 1.8 μm. We characterize in detail the photo-responsivity of such hybrid devices over different wavelengths. Colloidal Au NRs, capable to perform fast conversion between photon absorption and thermal energy, thus open an interesting avenue for alternative low-cost SWIR photodetection.

Resume : A significant amount of energy is consumed to maintain thermal comfort in buildings, a huge portion of which is lost through windows. Thin films coating with spectrally selective properties on the surface of glass is an innovative solution to the problem. Thermochromic smart windows change their color and optical properties in response to temperature variations. Vanadium dioxide (VO2) is the most studied thermochromic material for the last decades in the infrared domain. Its main characteristic is to transit from a semiconductive state to a metallic state at a phase transition temperature (Tc) of 341 K which is closer to room temperature (300 K) than any other thermochromic material. This phase transition property allows a solar energy modulation with temperature and makes VO2 an attractive material for smart windows. Nevertheless, the fabrication of high-quality VO2 films requires a high deposition temperature over 400°C which limits its compatibility with temperature-sensitive substrates. In this work, we demonstrate the optimization of VO2 films using the magnetron sputtering technique reinforced by HiPIMS supply (High Power Impulse Magnetron Sputtering) and the effect of the annealing temperature on VO2 properties.

Resume : Polymer dispersed liquid crystal (PDLC)-based flexible windows have attracted great attention for various applications, such as privacy windows, energy-saving windows, optical shutters, and smart windows. In several components in flexible PDLC windows, flexible and transparent electrode mainly affects on the performance of flexible PDLC because electrical, optical, and mechanical properties of electrode are closely related the operation of the flexible PDLC windows. In this work, we report on thermally evaporated MoO3/Ag/MoO3 multilayer films as a flexible and transparent electrode for high performance flexible PDLC windows. By using thermal evaporation, we obtained high quality MoO3/Ag/MoO3 multilayer films without plasma damage, which is usually found in the sputtered electrodes. To optimize the thickness of MoO3 and Ag layer, we investigated electrical, optical, morphological and mechanical properties of MoO3/Ag/MoO3 multilayer as a function of MoO3 and Ag interlayer thickness in detail. Based on a figure of merit value, we obtained optimal MoO3/Ag/MoO3 electrode with a low sheet resistance of 10 Ohm/square, a high optical transmittance of 90% and critical bending radius of 2 mm, which are acceptable in fabrication of flexible PDLC windows. To show the feasibility of thermally evaporated MoO3/Ag/MoO3 electrode, we fabricated the MoO3/Ag/MoO3 multilayer-based flexible PDLC windows on PET substrate. The flexible PDLC windows showed 80% on-state transmittance at an applied voltage of 80V and 2% off-state transmittance at non-applied voltage. The curved PDLC windows also showed similar performance to the flat-state PDCL due to the outstanding mechanical properties of the MoO3/Ag/MoO3 electrode.Successful operation of the flexible PDLC window indicates that the thermal evaporated MoO3/Ag/MoO3 film is promising alternative transparent electrode substituting sputtered ITO films for highly transparent and flexible PDLC windows.

Resume : Plasmon-induced hot carriers have been considered as a new means of solar energy harvesting and conversion. Intensive researches focus on improving the light-triggered carrier generation and extraction efficiency, and thus the sub-bandgap photons can be utilized for overcoming the optical band-gap limitation in conventional semiconductor devices. Here we demonstrate that Au/TiO2 dumbbell nanostructures deposited on a thin Au film, forming plasmonic particle-on-film nanocavities, are an efficient optical absorber and hot carrier generator over the whole visible region. Here the optical excitation of collective localized surface plasmons in such coupled nanocavities efficiently generates energetic electrons in Au that can be emitted over the Au/TiO2 Schottky barrier to the TiO2 conduction band. Consequently, the energetic electrons participate in the chemical reaction occurring at the TiO2 surface. The coupled nanocavities therefore show a significant enhancement in both photocurrent generation and reaction rate compared to the same Au/TiO2 dumbbell nanostructures on an ITO film, which can be explained by the optical resonance enhancement and associated near-field amplification in the presence of the Au film. More interestingly, the coupled nanocavities has an extra hot carrier generation mechanism originating from the strong d-band optical transitions in the Au film itself, which is experimentally observed in this work.

Resume : Solid-state lighting based on phosphor converted white-emitting diodes has gained considerable attention as a replacement for conventional incandescent and fluorescent light sources due to their advantages compared with their conventional counterparts, such as luminous efficiency, lower energy consumption, diversity of packaging forms, long operating lifetime, and environmental safety. The YAG:Ce3+ can be applied in various forms such as phosphor in resins, the phosphor in silicone and phosphor in the glass, but these are not thermally stable. On the other hand, polycrystalline phosphors have an advantage of good thermal stability. Therefore, studies on polycrystalline phosphors are under way. YAG:Ce3+ ceramic phosphor plate (CPP) improved both yellow-ring phenomenon and the light-extraction efficiency Because of Al2O3 particle embedded in the cubic YAG:Ce3+ CPP as the second phase. Also, the Al2O3 particle has a birefringence effect due to its hexagonal structure, and its scattering of the light reduces the yellow-ring effect. In this study, we prepared YAG:Ce3+ CPP with various amounts of Al2O3. The characteristics were investigated according to the addition amount of Al2O3 and optimized. The luminous properties of the YAG:Ce3+ and Al2O3 are improved when compared to the YAG:Ce3+ alone, and hence, the luminous emittance, luminous flux, and conversion efficiency are improved. We suggest that CPP is a next-generation material for solid-state laser lighting in automotive applications.

Resume : All optical signal processing based on the high optical nonlinearity of antimonene is firstly demonstrated. Few-layer antimonene was fabricated and decorated on the microfiber as an optical device. The device can be applied as an optical Kerr switcher with extinction ratio up to ~12 dB and wavelength converting of modulated high speed signals at a frequency up to 15 GHz. Our findings indicate that antimonene-based photonics device is applicable in nonlinear fiber optics and could be potentially developed for the applications of next generation high-speed optical communication.

Resume : Organolead halide perovskite solar cells promise to accomplish a breakthrough on the energy market due to their solution processability, low-cost, and high efficiencies. However, serious concerns regarding to the use of toxic lead as well as the instability of these perovskites in humid conditions have triggered efforts towards developing non-toxic and stable organic–inorganic alternatives, which is critically important for the market. Organic–inorganic bismuth iodide based hybrid materials have attracted interest because of their potential semiconducting character, rich structural diversity, and interesting electronic and optical properties, for which the 6s2 lone pair of the Bi3+ plays an important role in the various material properties. Using 1,2-dimethylpyridinium iodide and BiI3 it is possible to create 2D bismuthates that have a great potential in photovoltaic sphere. Solar cells, produced on this material, shows the efficiency, that reached 0,1%. Varying different transport layers and different types of solar cells the PCE tend to rise up. Additionally, the properties of new designed material could be investigated in other types of devices. In particular, it is possible to use Bi-based complex halides as materials for lateral photodetectors, field-effect transistors and chemical sensors. The project investigation shows further prospects for the use of 2D bismuthates in photodetectors due to their response to light more than one order.

Resume : Over the past decades, silicon has been determined to be the most promising platform for onchip optical interconnect and nanophotonics. The technology for passive devices on the silicon-on-insulator (SOI) platform such as beam splitters, polarization rotators, resonators, gratings for wavelength division multiplexing (WDM), and active devices like Si/Germanium modulators and Raman laser has matured substantially. As the key components in on-chip optical integration, modulators, especially silicon optical modulators, have been improved dramatically in recent years, with notable improvement in bandwidth and signal-noise ratio. However, the rapidly increasing demands of optical interconnects draw unprecedented attention from the photonic communities and raise more and more challenging questions like ultralow power consumption and hundred-gigabit operation. Micro-resonators like micro rings/disks and photonic crystal cavities, which feature small footprint and relatively small driven signal for high extinction ratio, have been found to be a promising solution for on-chip silicon modulators. However, to ease the burden from the considerable photon lifetime in a high-quality factor (Q factor) cavity, the Q factors in high-rate modulators are limited to just few thousands that the photon decay rate can surpass the modulated bandwidth. This sacrifice on Q factors will result in a larger power consumption for required extinction ratio for which new and better solutions are under exploration. Fano resonance, which arises from the interference of a discrete resonant mode and continuum background, presents efficient transition between reflection and transmission compared to Lorentzian kind cavities. This extraordinary behavior of Fano resonance can be used to address the bandwidth-power trade-off of resonant modulator and potentially minimize the power consumption of silicon switching and modulation devices. Different types of Fano cavities have been proposed in previous works, including side-coupled one/two-dimension (1/2D) photonic crystal, spatial membrane structure and plasmonic resonators [1-4]. Excellent Fano performance has been achieved and optical pump source is applied to the side-coupled Fano structure for optical modulation [5, 6]. However, considering the discrete structure and width-sensitive coupling in the side-coupled nanobeam case, onchip electric-optic modulation relying on efficient control of free carrier concentration is difficult to and has not yet been demonstrated. Flexibility of P-N junctions [7] can be found on 2D photonic crystal cavities but the high insertion loss of such configurations overshadows their advantages, let alone the membrane photonic crystal and plasmonic resonator for which spatial light injection is usually needed. Therefore, novel, compact and efficient Fano structure is of interest to be explored for future photonic crystal Fano modulators. We propose here a method for Fano resonance generation in a standalone nanobeam cavity and investigate the fundamentals of our design. Leveraging the spatial-division multiplexing and smart control between transverse electric modes, we realize a sharp resonant mode and a flat background mode in the same physical silicon channel (eg in a single silicon waveguide). Unambiguous asymmetric spectrum light shape for the 1st and the 2nd cavity modes are then observed experimentally at the output port. These results obtained for a series of Fano cavities that have been compared with standard Fano configurations present extinction ratio around 15dB-25dB for wavelength resonance shifts of ~50pm, i.e. better properties than their classical Lorentzian counterparts with similar Q factors. Most importantly, all the elements needed are on the same physical silicon waveguide, without any side-coupled bus waveguide that is classically necessary in traditional Fano cavities [1,2]. This configuration gives huge convenience for further optical and especially electrical pumping work. To conclude, this Fano cavity scheme addresses the deadlock of Fano cavities for efficient optical modulation in single-waveguide geometries, explores the physics in Fano spectrum lineshape, and presents potential for low power consumption silicon optical modulators operating at high-data bit rates. [1] Shanhui Fan, “Sharp asymmetric line shapes in side-coupled waveguide-cavity systems,” Appl. Phys. Lett. 80, 908 (2002). [2] Mikkel Heuck, Philip Trøst Kristensen, Yuriy Elesin, Jesper Mørk, “Improved switching using Fano resonances in photonic crystal structures,” Opt. Lett. 38, 2466 (2013). [3] Weidong Zhoua,n, DeyinZhaoa, Yi-ChenShuaia, HongjunYanga, Santhad Chuwongina, ArvinderChadhaa, Jung-HunSeob, KenX.Wangc, Victor Liuc, ZhenqiangMab,nn, ShanhuiFan, “Progress in 2D photonic crystal Fano resonance photonics,” Progress in Quantum Electronics 38, 1 (2014). [4] Mikhail F. Limonov, Mikhail V. Rybin, Alexander N. Poddubny and Yuri S. Kivshar, “Fano resonance in photonics,” Nat. Photon. 11, 543 (2017). [5] Yi Yu, Hao Hu, Leif Katsuo Oxenløwe, Kresten Yvind, and Jesper Mork, “Ultrafast all-optical modulation using a photonic-crystal Fano structure with broken symmetry,” Opt. Lett. 40, 2357 (2015). [6] Yi Yu, Yaohui Chen, Hao Hu, Weiqi Xue, Kresten Yvind, and Jesper Mork, “Nonreciprocal transmission in a nonlinear photonic-crystal Fano structure with broken symmetry,” Laser & Photon. Rev. 9, 241 (2015).

Resume : Coupled mode theory (CMT) is an indispensable tool to analysis and design the photonic devices, such as waveguides and cavities, and has far-reaching implications and applications in many subfields of optics. Considering the recent development in metamaterial, man-made anisotropic medium can be created, leading to interesting applications in controlling the flow and polarization of light. Therefore, there is a large need to study waveguides that may contain anisotropy or bianisotropy. However in anisotropic or bianisotropic waveguides, the standard coupled mode theory fails due to the broken link between the forward and backward propagating modes, which together form the dual mode sets that are crucial in constructing couple mode equations. We generalize the coupled mode theory by treating the forward and backward propagating modes on the same footing in the modal expansion set. The waveguide problem is reformulated into a generalized eigenvalue problem as the original system. Then the adjoint system is introduced to supply the adjoint mode. Using the real inner product, the material tensors fulfilling the reciprocity conditions is equivalent to the self-adjoint property of differential operator, which is referred as waveguide reciprocity. Lorentz reciprocity, with source terms are set to be 0 in waveguide problem, lead to the bi-orthogonal relation between original field and adjoint field based on waveguide reciprocity. The two complementary systems together define the complete and orthogonal dual mode sets that are essential in constructing coupled mode equations. From the self-adjoint properties of original and adjoint differential operator, we establish the two relations between the dual mode sets, i.e., same-β argument and paring-β argument. The same-β argument means the original field and the adjoint field share the same β, while the paring-β argument means the two different eigen-solutions share the same absolute value of β but with different sign. With the two arguments, the dual mode sets can be simplified into the single mode set which contain forward backward propagating modes that are enough in constructing coupled mode equations. In a few special cases, the forward and backward propagating modes can indeed be transformed into each other via additional symmetries, such as, chiral symmetry, time reverse symmetry and parity symmetry. Once the symmetry relation between the forward and backward propagating modes is known, one is able to use the forward propagating modes as the complete mode set to expand the field of the perturbed waveguide, and the backward propagating modes as the test function to construct the couple mode equation. In Hau’s CMT, the time reversal operator is used to infer backward propagating mode from forward propagating mode, while the revised CMT in Xu’s work takes the advantage of the chiral symmetry to infer backward propagating mode from forward propagating mode. However, when the symmetry relation is broken, one need to combine forward mode and backward mode together to form the complete mode. Finally, by perturbation, the generalized coupled mode equation can be derived in a natural way. Importantly, the generalized coupled mode theory developed here handles the modal coupling in anisotropic and bianisotropic waveguides, where the existing coupled mode schemes fails. We illustrate the capability of our generalized coupled mode theory through three examples, i.e., anisotropic waveguides, bianisotropic waveguides, and bianisotropic waveguides with balanced gain and losses. The three examples unambiguously show the feasibility and the strength of our theory in studying the mode hybridization in waveguides with broken link between the forward and backward propagating modes.

Resume : Recently, detection of nitrogen oxides (NO and NO2) has become focus due to exposure to these toxic gases to the environment from the automotive and power plants combustion. A low quantity of exposure of these gases has a detrimental effect in the human body such as severe respiratory diseases, and irritation of the skin. Several ZnO nanostructures have been introduced to detect these toxic gases. It is found from the literature that most of the nitrogen oxide sensors are operated at high temperature. Therefore; widespread use of ZnO nanostructures for nitrogen oxide sensing has limitation due to high-energy consumption and explosive hazards at high temperature. However, light-driven gas sensing is a most promising approach for room temperature low power operated sensors. In order to enhance the light-driven gas sensing response, light trapping induced improvement of performances is a novel strategy in ordered ZnO nanostructures. We have fabricated ordered ZnO nanostructures using different sacrificial polystyrene colloid templates of diameters 300, 600, and 800 nm respectively. 300 nm colloids templated nanostructures have shown improved gas sensing response in the presence of white light than other sensors. The sensitivity of ordered sensors using 300 nm colloids is found to be enhanced 3 times at 10 ppm than the non-ordered ZnO nanorod sensors due to efficient light trapping within the structures. This observation suggests that the light trapping mechanism can be effectively used to design the sensors operated at room temperature with high sensing response. References [1] Gogurla N, Sinha A K, Santra S, Manna S and Ray S K 2015 Sci. Rep.4 6483.

Resume : Recently, stimuli-responsive photonic crystal hydrogel sensor is gaining a lot of attention. Hydrogel sensor differs from the complex electrochemical detection method by being able to easily sense the analyte materials with naked eyes through diffraction phenomenon without using any pigments. The volume of a hydrogel is changed by external stimulus like pH, temperature, chemical molecules, humidity, etc. Therefore, it works as the colorimetric sensor based on "Bragg's law". In this study, we developed “directed enhanced evaporation for colloidal assembly” (DEECA) as a rapid fabrication process for glucose sensor. Glucose and phenylboronic acid combine to form negative charge at pH9. The phenylboronic acid containing hydrogel swells due to repulsive force between the negative charges. However, at physiological pH, the swelling is weak due to low equilibrium constant for association reaction of glucose with phenylboronic acid. We fabricated the colorimetric glucose sensor by colloidal templating method, in which we copolymerized 2-hydroxymethyl methacrylate, phenylboronic acid, and 2-(methacryloyloxy)ethyltrimethyl-ammonium chloride to improve sensitivity at physiological pH by stabilizing anionic boronate. An increased glucose sensing response of inverse opal photonic gels was rigorously examined.

Resume : Recently, various photonic crystal hydrogel sensors having inverse opal structures have been studied. We fabricated an inverse opal hydrogel sensor that can detect CO2 gas in the open system as well as the closed system. In our system, the dissolved CO2 was converted to carbonate anion which reacts with amine functional group within the hydrogel to induce hydrogel swelling. The sensor was fabricated by DEECA (Directed Enhanced water Evaporation for Colloidal Assembly) method. On the hydrogel sensors in water, a steady flow of CO2/N2 mixed gas was applied at various ratios. The peak diffraction wavelength were obtained according to the concentration of CO2 gas. The physical phenomena of sensors were rigorously investigated with repeated changes CO2 and N2 flows. Also, the recovery of the sensor after CO2 sensing was investigated by temperature and pH controls

Resume : Use of non-reciprocal (NR) transmission in optical systems could considerably enrich possible architectures of integrated photonic circuits, mainly thanks to optical isolator or circulator functions. The development of optical guided structure with NR functionality requires simultaneous spatial and time-reversal symmetry breakings in the waveguide (WG). Especially the transverse magneto-optical (MO) Kerr effect (TMOKE) breaks time-reversal symmetry by NR dichroism and is easily implemented in planar waveguide configurations. Recent disruptive results have shown that the sign of the NR dichroism can be controlled by gold grating geometry on bismuth iron garnet (BIG) layer for a given magnetization direction, in non-guided configuration. It was theoretically and experimentally [1] shown that the amplitude and sign of the TMOKE is strongly affected by the interaction of resonant modes in the structure: the Fabry-Perot (FP) mode generated in the grating slits, and the SPP mode at the BIG/Au interface. The sign of the TMOKE can be switched by optimization of grating geometry without changing magnetization orientation. By varying the grating’s slit width, the interaction between SPP and FP modes can be tuned. This property is the starting point for a renewal of the integrated isolator design. In this paper we propose to extend it to the waveguide configuration with a 1D periodic Au grating on BIG waveguide. [1] L. Halagacka, M. Vanwolleghem, F. Vaurette, J. Ben-Youssef, P. Gogol, N. Yam, K. Postava, B. Dagens and J. Pistora, Experimental demonstration of anomalous nonreciprocal optical response of 1D periodic magnetoplasmonic nanostructures, Opt. Mat. Express 4, 1903 (2014)

Resume : Bismuth silver sulfide (AgBiS2) nanocrystals exhibits high absorption coefficient in visible to near Infrared (NIR) regions and are suitable for the optoelectronic devices such as solar cells and photodetectors. We report a facile method to prepare AgBiS2 nanocrystals in ambient environment by a modified hot injection method. The AgBiS2 nanocrystals are of high purity and crystallinity. The AgBiS2 nanocrystals based phototransistors were demonstrated with a high gain (about 105) for 895 nm at a low operation voltage of 0.1 V.

Resume : Light-matter momentum exchange is exploited in optical tweezing to trap small particles. In 1970, Arthur Ashkin demonstrated optical trapping and manipulation of micro-sized particles dispersed into a liquid system [1]. However, in optical systems, the tweezing action undergoes diffraction limit which prevents subwavelength objects to be trapped. A solution consists in using plasmonic structures able to concentrate light in subwavelength volumes thanks to surface plasmon polariton or localized surface plasmon. By taking advantage of plasmonic resonators inside tweezing systems, very deep and narrow potential energy well can be tailored to achieve stable optical tweezing down to subwavelength particles In this contribution, we demonstrate the possibility to trap beads having radius down to 50 nm, thanks to the high field enhancement offered by a gold dimer coupled with a SOI waveguide [2]. Furthermore, the amplitude modulation of the waveguide output power, arising from the environment modification due to the nanoparticle presence near the dimer gap can be used to read out the trapping event and the size of the trapped bead. [1] A. Ashkin, Phys. Rev. Lett. 24, 156, 1970. [2] A. Ecarnot, G. Magno, V. Yam, B. Dagens, Optics Letters, 2018.

Resume : The development of modern technologies and innovative solution for white light beam shaping allows new applications in different fields as photovoltaic science, illumination, automotive or lighting. We will present different optical components used for modifying irradiance maps with low cost large band white light source (in transmission or in reflective mode). The first elements are standard lightpipe and inverse tapered pipe. The second structure contains a matrix of different inclined facets allowing new light transformations. We make calculations to demonstrate and compare the irradiance map with different tools: Zemax OpticStudio 16 and Lightools from Synopsis, but also house made program linked to angular spectrum method. First, the idea was to study the dependence of different parameters like dimensions and material on the irradiance map. Second, the ultimate idea is also to optimize the irradiance map of white light source. In fact, in our case, the resolution is not the main crucial point in this work due to the searched goal. We manufacture also some structures with 3D Printing Technology using fused filament fabrication to verify the possibility of rapidly prototyping different optical elements.

Resume : The energy problems and environmental issues have become increasingly important in recent years. The plasmonic photocatalysis for hydrogen production provides a possible approach to convert solar energy into chemical fuels. The photocatalytic efficiency is increased due to plasmon-enhanced light absorption and photo-induced hot electrons, which are both caused by localized surface plasmon resonance (LSPR). In the present work, we focused on the hybrid photocatalysts of TiO2-Al structure, comparing with other plasmonic metals, such as Ag and Au. Aluminum is a potential plasmonic material especially for its abundance on the earth. Also notably, Al exhibits a promising property for the low optical losses from the visible light to UV regions. However, because of the high chemical activity, little is explored for photocatalysis with Al nanostructures. Here we fabricated several TiO2-metal structures, which includes single-crystal aluminum film growth by molecular beam epitaxy (MBE) and the deposition of TiO2 by atomic layer deposition (ALD). The LSPR properties of these hybrid structures have been investigated and these structures are employed as photocatalysts in an aqueous methanol solution. Under xeon lamp radiation, the hybrid TiO2-Al exhibited significant improvement in hydrogen producing efficiency, which is attributed to the plasmon-enhanced light absorption. The experimental results are in accordance with the simulation by finite difference time domain (FDTD) method.

Resume : Bimetallic nanoparticles (NPs) attract great attention in many research domains because of their interesting physicochemical properties [1]. In fact, those properties drastically evolve as a function of the structure, the composition, and the morphology of those NPs, parameters that can be tuned by different synthesis methods such as co-reduction, thermal decomposition and seeded-growth, among others [2, 3]. This versatility renders bimetallic NPs very efficient and useful in various applications that include plasmonics, biological sensing, and catalysis, which places them on the frontier of advanced materials chemistry [4]. In particular, in the case of core-shell (CS) bimetallic nanostructures like Au@Pd NPs, the improvement of their catalytic activity in low-temperature electrooxidation [5, 6] is due to both their sizes and the interactions between the Pd shells and Au cores [5, 7]. The work presented here is dedicated to the deep correlation between the optical properties of CS Au@Pd particles and their morphologies and sizes. Their preparation involves seed-assisted synthesis based on successive reduction steps that allow a better control of the morphology (size and shape) at the atomic scale [2, 4, 8]. The CS structure of the obtained NPs and their optical response are investigated respectively by transmission electron microscopy (TEM) and by UV-vis spectroscopy. Those experimental results are confirmed and predicted by optical simulations based on the DDA (Discrete Dipole Approximation) method, exhibiting the high optical sensitivity of CS nanostructures to their environment. [1] J. Phys. Chem. C 2015, 119, 9534−9542 [2]J. Phys. Chem. C 2014, 118, 22383−22388 [3]Adv. Mater. 2011, 23, 1044−1060 [4]Nano Lett.2007,Vol. 7, No. 6, 1701-1705 [5]Chromatographia ,2011, 74, 767–775 [6]J Am Chem Soc 126:15583–15591 [7]Electrochem Commun, 2007, 9,1725–1729 [8]Chem. Eur. J. 2012, 18, 8150–815

Resume : Photoluminescence (PL) and photoreflectance (PR) measurements have been used to determine the band gap energy of InGaAs and GaAsBi alloys. The temperature dependence of optical transitions in the temperature ranging from 12 to 300 K were investigated. Three theoretical models (Varshni, Viňa, and Pässler) were used to fit the experimental points. The results show that the temperature dependence of the fundamental gap energy is attributed to the sum of two contributions: the thermal expansion (TE) and the electron-phonon interaction (EPI). For InGaAs with different In concentration (x=0, 0.08, 0.16 and 0.37), the contribution to the EPI of the longitudinal optical phonon increases, relatively to the longitudinal acoustical phonon, with increasing In concentration. In the low temperature range, the small decrease in the optical transition energy is explicated by a competition between the two contributions (TE and EPI). At high temperature, the linear decrease of gap energy is explained essentially by the EPI. Additionally, we have estimated the thermal expansion coefficient of GaAsBi with different Bi concentration (x=0.013, 0.037 and 0.048). The results show a slowly decrease in the TE with temperature and Bi composition. This effect is considered to play an important role in the reduction of the temperature dependence of the band gap energy of GaAsBi alloys. GaAsBi alloys are important materials for the fabrication of temperature insensitive optical devices

Resume : Surface plasmon resonance biosensors have brought the analysis of biomolecular interactions to a new level of sensitivity without compromising the sample during the labelling process which can generate disturbance in molecular bindings if becomes time-consuming. The unmodified metal chips have a good sensitivity for a broad range of analytes, but for lower concentration of molecules the sensing property is diminished. To overcome this problem, coating the metal chip with different layers was proposed to enhance the sensitivity response of sensor by strong coupling of surface plasmons. The most exploit 2D material was graphene and it has been recently shown that modification of the gold substrate with a multilayer graphene structure determines a further improvement of the biosensing performances. In this context, for a deep insight of phenomena that led to the enhancement of sensitivity, we used both numerical and experimental approaches to investigate the influence of graphene and different graphene like 2D materials (MoS2, hBN and WS2) on the response of SPR sensor. The plasmonic modes in these types of heterostructures were characterized using finite element method (FEM) based algorithms with Comsol Multiphysics Radio Frequency Module and we showed that adding a new layer determines a significant improvement of the penetration depth that could explain the increase of chip sensitivity tested for DNA hybridization using Autolab Twingle SPR .

Resume : Intensive researches are currently conducted on the miniaturization of photonic devices and on the combination of photonics and electronics to decrease the power consumption and to create novel functionalities. For a wide range of applications including datacom, telecom, sensing and quantum optics, to name few, functional oxides have emerged as a promising material family thanks to their wide range of properties such as multiferroicity, piezoelectricity and optical nonlinearities. Among these materials, Yttria-Stabilized Zirconia (YSZ) is well known as a buffer layer for oxide-based thin films heterostructures, extensively used for LiNbO3, PbTiO3, Pb(Zr,Ti)O3 and YBa2Cu3O7 integration on silicon, but has not yet been studied for integrated optics. YSZ is also well known for its extraordinary thermal and chemical stability, as well as its hardness and mechanical durability. An increasing quantity of applications uses this material for the combination of its excellent mechanical and optical properties, such as its high refractive index, large optical band gap and transparency from the ultraviolet (UV) to the mid-infrared (mIR). The work has been mainly focused on the integration of YSZ functional oxide on sapphire substrates. Due to the refractive index contrast between sapphire (1.75) and YSZ (2.12) at a wavelength of 1300 nm, optical YSZ waveguides can be designed with good mode confinement. The study and optimization of growth parameters using Pulsed-Laser Deposition (PLD) technique allowed achieving high quality YSZ thin films on sapphire (0001) with remarkably sharp X-Ray diffraction rocking curve peaks in 10-3 degrees range for two different out-of-plane orientations. We have demonstrated that one or the other of these two orientations can be promoted with different atmosphere during the thermal annealing of sapphire substrate before the growth. Passive photonic structures such as grating couplers, single-mode waveguides and resonators have been then designed and fabricated thanks to electronic lithography and Ion-Beam Etching (IBE) techniques. Preliminary optical characterization results of integrated structures have been performed, revealing for instance propagation losses in YSZ waveguides as low as 2 dB/cm, showing ring and disk resonators with Q factors up to 12000, sub-wavelength Bragg filters with 16.2dB extinction ratio for 1.5 nm bandwidth. Finally, third-order nonlinear susceptibilities has been estimated with the absence of two photon absorption at telecom wavelengths YSZ waveguides. Our results demonstrate the fabrication of passive devices and basic building blocks, which combined with the outstanding nonlinear properties, provide a promising robust platform for functional oxides-based nonlinear on-chip applications. Furthermore, the first integration of YSZ on silicon photonics platform will also be reported.

Resume : Soft X-ray ultrashort pulses can be used to probe the ultrafast magnetization dynamics induced by a visible laser pump in alloyed ferromagnets with chemical selectivity. In this scope, several time resolved experiments such as High order Harmonics Generation (HHG) based Transverse Magneto Optical Kerr (T-MOKE) [1,2] or X-ray Magnetic Circular Dichroism (XMCD) [3] have been recently used. In this work, a time resolved IR-pump HH-probe with T-MOKE configuration will be used (Fig 1.a) to reconstruct the time evolution of magnetization at the M-edges of alloyed transitions metals [4]. The fundamental beam at 800 nm 25fs is delivered by a Ti:Sa femtosecond amplified laser at a 1kHz repetition rate. 10% of the incoming beam is used as a pump, 90% to drive HH up to 70 eV in a 200 mbar Ne gaseous target. Both beams are recombined and focused by using a toroidal mirror (TM) on the studied sample. As sketched in Fig. 1b, our experiment is used in a T-MOKE configuration at a =45° incidence angle in order to maximize the magnetic contrast. This work is part of UNION project (ANR-10-EQPX-52) in which chemical selectivity is used to evaluate the importance of exchange interaction between elements of ferromagnetic alloys in the damping processes of magnetization vector dynamics [5,6]. [1] C. La-O-Vorakiat et al. , Phys. Rev. Lett. 103, 257402 (2009). [2] S. Mathias et al. , PNAS 109 4792 (2016). [3] I. Radu et al. , SPIN 05, 1550004 (2015). [4] A. Maghraoui, PhD thesis « Génération d'harmoniques d'ordre élevé pour l'étude de la dynamique des charges et de l'aimantation de films de cobalt » [5] M. Barthelemy et al., invited talk at Ultrafast Magnetism Conference (2017) [6] D. Hinzke et al. , Phys. Rev. B 92, 054412 (2015).

Resume : Halide perovskite materials, such as CH3NH3PbI3 and CH3NH3PbBr3, form a new class of semiconductors with outstanding optoelectronics and photovoltaic properties. The present contribution deals with spin relaxation dynamics in these materials. The particular band structure of the conduction and valence bands of these materials allows theoretically to selectively create conduction band electrons with 100% spin polarisation if excited by circularly polarized light. First reports and a relatively high spin-orbit coupling (SOC) led to the expectation that the spin relaxation time be in the picosecond time range,. We studied the circular dichroism of the luminescence emitted from CH3NH3PbBr3 thin films at room temperature. The luminescence decay is bi-exponential, as often reported, with long decay times of 15-20 and 65-75 ns, attesting good sample quality. The relaxation time of the circular polarization defined is beyond the picosecond range, the exact value depending on experimental parameters. Indeed, we have evidence for the relaxation time being accelerated in the presence of larger carrier densities (stronger optical excitation) and by the presence of defects in the crystalline structure. These first observations were reproduced on many different CH3NH3PbBr3 samples but are in contradiction to other reports on CH3NH3PbI3. Therefore, complementary experiments are under way comparing these two material systems and the influence of parameters such as excitation wavelength.

Resume : Oxide layers bridging a graphene layer to n-silicon in GIS solar cells have been shown to reduce recombination at the cell junction. Under illumination, the built-in field at the Graphene-Silicon junction, forces minority photo-generated holes to the interface and ultimately to the G-side, while photoelectrons thermionically escape from the G-side to the semiconductor. Electrons from the graphene side may obtain sufficient energy to overcome the junction barrier by simultaneous thermionic emission (TE) and tunneling through the oxide layer to the semiconductor side. Graphene-based Schottky solar cells illuminated from the G-side respond to solar photons at energies above the semiconductor’s band gap, hence minority-hole photo-generation. Minority holes diffuse to the junction and aided by the built-in field tunnel through the junction to the graphene side. The interface is essentially a double barrier as a combination of junction Schottky barrier (qFB) and the Ox-layer. In this communication, we model the following currents crossing the GIS junction (a) thermionic current from the Graphene side to the semiconductor J(TE) by means of a modified Landauer transport mechanism and (b) hole-current JP from the n-Si side to the G-side. JTE thermionic current depends temperature T, Schottky barrier height qFb, and voltage V across the device; TE current in the GIS photodiode is a strong function of T^3/2 as J(TE)~(T^3/2)exp (-qFb/kT)exp(-kd) [exp(qV/kT)-1)]. The exp(-kd) exponential in the latter is the tunneling probability through the insulator of thickness d. Once thermo-electrons migrate to the n-region, they join the majority electron flow to the load under illumination. The electron tunneling probability exp (-kd) guarantees electron flow to the semiconductor (d = the oxide thickness). On the other hand, photo-generated hole-current is derived from standard techniques leading to Jp hole current, as a strong function of solar photon flux. These holes eventually will tunnel through the oxide to the graphene side. By neglecting recombination at the depletion region, we calculate the total current J = J(light) – J(dark), and deduce open-circuit voltage. Based on the two current expressions above, we deduce explicit (increased) open circuit voltage as a strong function of (a) photon flux (b) Schottky barrier height (c) T^3/2 (d) tunneling probability through the oxide and (e) mono-layer graphene properties embedded in a new Richardson's constant.

Resume : Inspired by electronic topological insulators, photonic topological structures (PTS) allow designers to exploit the new degrees of freedom arising from the topology that, so far, remains largely unexplored and unexploited. PTSs offers exotic unidirectional edge modes that can be exploited to conceive a novel type of waveguides, able to defeat backscattering and allowing a proper propagation of light around sharp corners and defects thanks to the topological protection against disorder. The big advantage of PTSs with respect to the electronic counterparts is that the metamaterial supporting these properties can be easily designed and fabricated. So far, the only way to attain an arbitrarily shaped waveguide relied on transformation optics in complex media, which requires a local tuning of the metamaterial properties that is difficult to implement at short wavelengths. The absence of backscattering enables PTSs to realise some of the promises of transformation optics even at telecom and visible spectral ranges. In this contribution we will show how to design arbitrarily shaped waveguides exploiting PSTs, giving an considerable freedom and flexibility in shaping waveguides and cavities. This can be vital to (i) optimise the circuitry topology, (ii) to improve the compactness of photonic circuitry and (iii) to increase the robustness against fabrication tolerances.

Resume : Photoinduced absorption spectroscopy, when used concurrently with transient photocurrent measurements, can be used to gain kinetic and mechanistic insight into the action of inorganic semiconductors as catalysts for water splitting. In this study we will be using the technique, along with hydrogen evolution measurements by a Clark electrode, to probe the action of known organic photovoltaic polymers as water-splitting agents.

Resume : The extra ordinary properties of Graphene (e.g. high electron mobility current density on SiO(2)/Si junctions, high mechanical strength, and high melting point) make it an excellent material for Graphene-based Schottky-Barrier diodes (G/SB). In such junctions, graphene mono-layers replace the metal forming G/semiconductor interfaces with several carrier transport mechanisms. In this talk we will be reviewing Schottky junctions and will be describing two carrier-transport mechanisms: tunneling and thermionic emission through potential barriers formed at the junction between graphene and n-type semiconductor. In the case of a typical G/SB diode, a thin layer of SiO(2) is grown between the graphene and the semiconductor. This layer allows carriers to reach either side of the junction via tunneling and thermionic emission. We model (a) the oxide layer as a tunneling barrier with a finite tunneling probability and (b) the Schottky barrier as a triangular potential barrier. We then calculate total current through the double barrier at the G/SB junction and express it as a strong function of temperature and the geometry of the device. The calculated current is the superposition of Tunneling and Thermionic components: J(Tu) ~ A*T^2 exp(-qVb/kT) [exp(qV/kT)-1] and J(Th) ~ A**T^2.5 exp(-qVb/kT) [exp(qV/kT)-1] respectively, where qVb is the Schottky junction barrier, V is the applied voltage, T is the temperature, and A*, A** are appropriate Richardson’s constants.