Tailoring ultrabroadband near-infrared luminescence in Bi-doped germanosilicate glasses.

Bi-doped glasses and optical fibers are extensively studied since they present broadband optical amplification in the near-infrared region (NIR), in which the optical telecommunication industry greatly depends for the transmission of optical signals. There are many scientific challenges about the NIR luminescent emissions from Bi ions, such as understanding its origin and further improving the associated optical amplification capacity. In this work, Bi-doped germanosilicate glass compositions with ultrabroadband NIR luminescence were fabricated, in the range of 925-1630 nm, which covers O, E, S, C, and L-telecommunication bands. An in-depth analysis of the impact of modifying excitation wavelengths, Bi content, and GeO2/SiO2 concentration ratio in the glass matrix demonstrates the possibility of considerably manipulating the Bi NIR luminescence, in terms of tuning emission parameters such as bandwidth, up to ~ 490 nm, and luminescence intensity. Based on theoretical and experimental luminescence data retrieved from the fabricated glasses, we demonstrate that the origin of broadband luminescence under all the considered excitation wavelengths can be ascribed to optical transitions of Bi0 ions. Therefore, an energy level diagram for Bi0 is proposed. We anticipate that our findings can provide clarifications to the existing uncertainty in the origin of Bi NIR emission, which will be useful to fabricate efficient future optical fiber amplifiers.

Towards REPO4 nanocrystal-doped optical fibers for distributed sensing applications.

Rayleigh scattering enhanced nanoparticle-doped optical fibers, for distributed sensing applications, is a new technology that offers unique advantages to optical fiber community. However, the existing fabrication technology, based on in situ grown alkaline earth nanoparticles, is restricted to few compositions and exhibit a great dependence on many experimental conditions. Moreover, there is still several uncertainties about the effect of drawing process on the nanoparticle characteristics and its influence on the scattering enhancement and the induced optical loss. In this work, we shed light on all these issues that prevent the progress in the field and demonstrate the suitability of doping optical fibers with YPO4 nanocrystals for developing tunable Rayleigh scattering enhanced nanoparticle-doped optical fibers. An exhaustive 3D microstructural study reveals that their features are closely linked to the fiber drawing process, which allow the size and shape engineering at the nanoscale. In particular, the YPO4 nanocrystals preserve their features to a large extent when the optical fibers are drawn below 1950 °C, which allows obtaining homogeneous nanocrystal features and optical performance. Fabricated fibers exhibit a tunable enhanced backscattering in the range of 15.3-54.3 dB, with respect to a SMF-28 fiber, and two-way optical losses in the range 0.3-160.7 dB/m, revealed by Optical Backscatter Reflectometry (OBR) measurements. This allows sensing lengths from 0.3 m up to more than 58 m. The present work suggests a bright future of YPO4 nanocrystals for distributed sensing field and open a new gate towards the incorporation of other rare-earth orthophosphate (REPO4) nanocrystals with pre-defined characteristics that will overcome the limitations of the current in situ grown alkaline earth-based technology.

Optimization & Characterization of Interdigitated Electrodes for Microbial Growth Monitoring.

This study optimally designed and implemented highly sensitive microscale interdigitated electrodes (IDEs) to monitor microorganisms' growth in diverse environments. Gold interdigitated electrodes (AuIDE) with 4 mm×4 mm effective sensing area and varying microscale interdigitate gaps were designed and fabricated. The electrodes were electrically characterized voltametrically. Electrochemical impedance spectroscopy (EIS) measurements were conducted to determine the optimal geometry by observing the impedance spectra of microelectrodes through varying pH and temperature. Furthermore, the sensors sensitivity was evaluated by measuring the impedance properties of a microscale volume of microorganism concentrations in growth media solution.

The EcoChip 2: An Autonomous Sensor Platform for Multimodal Bio-environmental Monitoring of the Northern Habitat.

This paper presents the EcoChip 2, an autonomous multimodal bio-environmental sensor platform for the monitoring of microorganisms in the northern habitat. The EcoChip 2 prototype includes an array of 96-wells for the continuous monitoring of microbiological growth through a multichannel electrochemical impedance analyzer circuit. In addition, the platform includes luminosity, humidity, temperature sensors and monitoring. The developed electronic board uses an ultra-low-power microcontroller unit, a custom power management unit, a low-power wireless ISM-2.45 GHz transceiver, and a flash memory to accumulate and store the sensor data over extended monitoring periods. When a wireless base station is placed within the transmission range of the EcoChip 2, an embedded low-power wireless transceiver transmits the 96-wells impedance data and the other sensor data stored in the flash memory to the user interface. We present the measured performance of the prototype, along with laboratory test results of bacterial growth measurements inside the 96 wells in parallel. We show that the EcoChip 2 can successfully measure the impedances associated with bacterial growth over several hours using an excitation frequency of 2 kHz with power consumption of 114.6 mW under operating mode.

Demonstration of an erbium-doped fiber with annular doping for low gain compression in cladding-pumped amplifiers.

We present the design and characterization of a cladding-pumped amplifier with erbium doping located in an annular region near the core. This erbium-doped fiber is proposed to reduce gain saturation, leading to smaller gain compression when compared to uniform core doping. Through numerical simulations, we first compare the performance of three fibers with different erbium doping profiles in the core or the cladding. When the doped fibers are operated at the optimum length, results show that the smaller overlap of the signal mode field with the annular erbium doping region leads to higher gain and lower saturation of the amplifier. A single-core erbium-doped fiber with an annular doping and a D-shaped cladding was fabricated. Measurements demonstrate less than 4 dB of gain compression over the C-band for input power ranging from -40 dBm to 3 dBm. Small gain compression EDFAs are of interest for applications that require input channel reconfiguration. Higher gain and saturation output power are also key issues in cladding-pumped multi-core amplifiers.

Co-doped Dy3+ and Pr3+ Ga5Ge20Sb10S65 fibers for mid-infrared broad emission.

Rare earth ion doped materials are means to obtain cost-effective infrared light sources, with enough brilliance for applications such as gas sensing. Within a sulfide matrix, the simultaneous luminescence of both Pr3+ and Dy3+ in the Ga5Ge20Sb10S65 glass is reported. The use of these two rare earths is giving rise to a broad continuous luminescence in the 2.2-5.5 µm wavelength range, which could be used as a mid-infrared light source for gas-sensing applications. The demonstration of CO2 and CH4 detection using a fiber drawn from these materials is reported.

Upconversion nanoparticle-decorated gold nanoshells for near-infrared induced heating and thermometry.

The present work involves the design of a multifunctional system based on gold nanoshells (AuNSs) decorated with lanthanide-based upconversion nanoparticles (UCNPs) intended as an optical heater and a temperature probe at the nanoscale. The synthesis of NaGdF4 UCNPs doped with ions Yb3+:Er3+ was performed via thermal decomposition of lanthanide fluoride precursors at high temperatures (>300 °C) in the presence of a coordinating ligand (oleic acid). UCNPs were synthesized at three different temperatures (310, 315 and 320 °C) and characterized in terms of morphological, structural and emission properties. In view of the intended biological applications, the surface of hydrophobic oleate-capped UCNPs was modified using a silica coating to achieve sufficient water dispersibility, through a modified Stöber process using a reverse micro-emulsion method. Monodisperse NaGdF4:Yb3+:Er3+ upconversion nanocrystals (∼25 nm dia.) were obtained in cubic (at 310, 315 °C) and hexagonal (at 320 °C) phases. The UCNPs in the hexagonal phase were shown to be more suitable as temperature sensors, due to their lower red-to-green emission ratios and higher thermal sensitivities. The emission spectrum of NaGdF4:Yb3+:Er3+ (oleate- or silica-coated) UCNPs was recorded at different temperatures in the vicinity of the physiological range (20-70 °C) and presented suitable properties for application as temperature sensors, such as excellent linearity (r2 > 0.99) and sensitivity (>3 × 10-3 K-1). The heating capacity of AuNSs@UCNPs was verified by monitoring the Er3+ emission, showing their potential for application as a hyperthermia agent controlled using a nanothermometer function.

A Microstructured Fiber with Defined Borosilicate Regions to Produce a Radial Micronozzle Array for Nanoelectrospray Ionization.

This work highlights the possibility of using microstructured fibres with predefined doped regions to produce functional microstructures at a fibre facet with differential chemical etching. A specially designed silica microstructured fibre (MSF) that possesses specific boron-doped silica regions was fabricated for the purpose of generating a radial micronozzle array. The MSF was drawn from a preform comprising pure silica capillaries surrounded by boron-doped silica rods. Different etching rates of the boron-doped and silica regions at the fiber facet produces raised nozzles where the silica capillaries were placed. Fabrication parameters were explored in relation to the fidelity and protrusion length of the nozzle. Using etching alone, the nozzle protrusion length was limited, and the inner diameter of the channels in the array is expanded. However with the addition of a protective water counter flow, nozzle protrusion is increased to 60 µm with a limited increase in hole diameter. The radial micronozzle array generated nine individual electrosprays which were characterized using spray current measurements and related to theoretical prediction. Signal enhancement for the higher charge state ions for two peptides showed a substantial signal enhancement compared to conventional emitter technology.

Tailoring the refractive index of Ge-S based glass for 3D embedded waveguides operating in the mid-IR region.

The photosensitivity of GeS(x) binary glasses in response to irradiation to femtosecond pulses at 800 nm is investigated. Samples with three different molecular compositions were irradiated under different exposure conditions. The material response to laser exposure was characterized by both refractometry and micro-Raman spectroscopy. It is shown that the relative content of sulfur in the glass matrix influences the photo-induced refractive index modification. At low sulfur content, both positive and negative index changes can be obtained while at high sulfur content, only a positive index change can be reached. These changes were correlated with variations in the Raman response of exposed glass which were interpreted in terms of structural modifications of the glass network. Under optimized exposure conditions, waveguides with positive index changes of up to 7.8 x 10(-3)and a controllable diameter from 14 to 25 µm can be obtained. Direct inscription of low insertion losses (IL = 3.1 - 3.9 dB) waveguides is demonstrated in a sample characterized by a S/Ge ratio of 4. The current results open a pathway towards the use of Ge-S binary glasses for the fabrication of integrated mid-infrared photonic components.

Control of the radiative properties via photon-plasmon interaction in Er3+ -Tm3+ -codoped tellurite glasses in the near infrared region.

The novelty of this paper is that it reports on the tuning of the spectral properties of Er3+ -Tm3+ ions in tellurite glasses in the near-infrared region through the incorporation of silver or gold nanoparticles. These noble metal nanoparticles can improve the emission intensity and expand the bandwidth of the luminescence spectrum centered at 1535 nm, covering practically all the optical telecommunication bands (S, C + L and U), and extended up to 2010 nm wavelength under excitation by a 976 nm laser diode. Both effects are obtained by the combined emission of Er3+ and Tm3+ ions due to efficient energy transfer processes promoted by the presence of silver or gold nanoparticles for the (Er3+)4I(11/2)→(Tm3+)3H5, (Er3+)4I(13/2)→(Tm3+)3H4 and (Er3+)4I(13/2)→(Tm3+)3F4 transitions. The interactions between the electronic transitions of Er3+ and Tm3+ ions that provide a tunable emission are associated with the dynamic coupling mechanism described by the variations generated by the Hamiltonian H DC in either the oscillator strength or the local crystal field, i.e. the line shape changes in the near-infrared emission band. The Hamiltonian is expressed as eigenmodes associated with the density of the conduction electron generated by the different nanoparticles through its collective free oscillations at each resonance frequency of the nanoparticle and their geometric dependence. A complete description of photon-plasmon interactions of noble metal nanoparticles with the Er3+ and Tm3+ ions is provided.

Few-mode fiber with inverse-parabolic graded-index profile for transmission of OAM-carrying modes.

A novel type of few-mode fiber, characterized by an inverse-parabolic graded-index profile, is proposed for the robust transmission of cylindrical vector modes as well as modes carrying quantized orbital angular momentum (OAM). Large effective index separations between vector modes (>2.1 × 10(-4)) are numerically calculated and experimentally confirmed in this fiber over the whole C-band, enabling transmission of OAM(+/-1,1) modes for distances up to 1.1 km. Simple design rules are provided for the optimization of the fiber parameters.

Characterization of OAM fibers using fiber Bragg gratings.

The reflectogram of a fiber grating is used to characterize vector modes of an optical fiber supporting orbital angular momentum states. All modes, with a minimal effective index separation around 10(-4), are simultaneously measured. OAM states are reflected by the FBG, along with a charge inversion, at the center wavelength of the Bragg reflection peak of the corresponding fiber vector mode.

Mid-infrared chalcogenide glass Raman fiber laser.

We report the first demonstration of a Raman fiber laser (RFL) emitting in the mid-infrared, above 3 µm. The operation of a single-mode As2S3 chalcogenide glass based RFL at 3.34 µm is demonstrated by using a low-loss Fabry-Pérot cavity formed by a pair of fiber Bragg gratings. A specially designed quasi-cw erbium-doped fluoride fiber laser emitting at 3.005 µm is used to pump the RFL. A laser output peak power of 0.6 W is obtained with a lasing efficiency of 39% with respect to the launched pump power.

Writing of Bragg gratings through the polymer jacket of low-loss As2S3 fibers using femtosecond pulses at 800 nm.

Fiber Bragg gratings (FBG) were written through the polymer jacket of low-loss single mode As(2)S(3) chalcogenide fibers by using femtosecond laser pulses at 800 nm and a phase-mask. Peak reflectivity in excess of 99% was obtained at 3440 nm after 5 min of exposure. The resulting FBG maintained a peak reflectivity of 90% after 64 min of thermal annealing at 100 °C. This demonstration paves the way to the development of all-fiber mid-infrared laser sources.

Study of the photosensitivity of GeS binary glasses to 800 nm femtosecond pulses.

We present the first study of the photosensitivity of GeS binary glasses in response to irradiation to femtosecond pulses at 800 nm. A maximum positive refractive index change of 3.5x10(-3) is demonstrated with the possibility to control the waveguide diameter from ~8 to ~50 µm by adjusting the input pulse energy. It is also demonstrated that under different exposure conditions, a maximum negative index change of -7.5x10(-3) can be reached. The present results clearly illustrate the potential of this family of glasses for the fabrication of mid-infrared waveguides.

Self-organized periodic structures on Ge-S based chalcogenide glass induced by femtosecond laser irradiation.

Self-organized periodic structures have been observed on the surface of the ablation craters of Ge-S based chalcogenide glass produced after irradiation by a focused beam of a femtosecond Ti:sapphire laser (1 kHz, 34 fs, 806 nm). Scanning electron microscopy and atomic force microscopy images of irradiated spots show a periodic structure of ripples with a spatial period of 720 nm (close to the wavelength of fs laser pulses) and an alignment parallel to the electric field of light. With an increasing number of pulses, from 5 to 50 pulses, a characteristic evolution of ripples was observed from a random structure to a series of generally aligned peaks-and-valleys self-organized periodic structures. Additionally, at the center of the ablated spot, micro-domains appear where the ripples are still regular but are assembled in a more complex fashion. The experimental observations are interpreted in terms of strong temperature gradients combined with interference of the incident laser irradiation and a scattered surface electromagnetic wave.

Bacterial cellulose-hydroxyapatite nanocomposites for bone regeneration.

The aim of this study was to develop and to evaluate the biological properties of bacterial cellulose-hydroxyapatite (BC-HA) nanocomposite membranes for bone regeneration. Nanocomposites were prepared from bacterial cellulose membranes sequentially incubated in solutions of CaCl(2) followed by Na(2)HPO(4). BC-HA membranes were evaluated in noncritical bone defects in rat tibiae at 1, 4, and 16 weeks. Thermogravimetric analyses showed that the amount of the mineral phase was 40%-50% of the total weight. Spectroscopy, electronic microscopy/energy dispersive X-ray analyses, and X-ray diffraction showed formation of HA crystals on BC nanofibres. Low crystallinity HA crystals presented Ca/P a molar ratio of 1.5 (calcium-deficient HA), similar to physiological bone. Fourier transformed infrared spectroscopy analysis showed bands assigned to phosphate and carbonate ions. In vivo tests showed no inflammatory reaction after 1 week. After 4 weeks, defects were observed to be completely filled in by new bone tissue. The BC-HA membranes were effective for bone regeneration.

Rare earth doped SnO2 nanoscaled powders and coatings: enhanced photoluminescence in water and waveguiding properties.

Luminescent Eu3+ and Er3+ doped SnO2 powders have been prepared by Sn4+ hydrolysis followed by a controlled growth reaction using a particle's surface modifier in order to avoid particles aggregation. The powders so obtained doped with up to 2 mol% rare earth ions are fully redispersable in water at pH > 8 and present the cassiterite structure. Particles size range from 3 to 10 nm as determined by Photon Correlation Spectroscopy. Rare earth ions were found to be essentially incorporated into the cassiterite structure, substituting for Sn4+, for doping concentration smaller than 0.05 mol%. For higher concentration they are also located at the particles surface. The presence of Eu3+ ions at the surface of the particles hinder their growth and has therefore allowed the preparation of new materials consisting of water redispersable powders coated with Eu(3+)-beta diketonate complexes. Enhanced UV excited photoluminescence was observed in water. SnO2 single layers with thickness up to 200 nm and multilayer coatings were spin coated on borosilicate glass substrates from the colloidal suspensions. Waveguiding properties were evaluated by the prism coupling technique. For a 0.3 microm planar waveguide single propagating mode was observed with attenuation coefficient of 3.5 dB/cm at 632.8 nm.

Localized surface plasmon resonance interaction with Er3+-doped tellurite glass.

We show the annealing effect on silver and Erbium-doped tellurite glasses in the formation of nanoparticles (NPs) of silver, produced by the reduction of silver (Ag+ → Ag0), aiming to an fluorescence enhancement. The absorption spectra show typical Localized Surface Plasmon Resonance (LSPR) band of Ag0 NP in addition to the distinctive absorption peaks of Er3+ ions. Both observations demonstrate that the photoluminescence enhancement is due to the coupling of dipoles formed by NPs with the Er3+ 4I(13/2) → 4I(15/2) transition. This plasmon energy transfer to the Er3+ ions was observed in the fluorescence spectrum with a blue-shift of the peaks.

Microstructured chalcogenide optical fibers from As(2)S(3) glass: towards new IR broadband sources.

The aim of this paper is to present an overview of the recent achievements of our group in the fabrication and optical characterizations of As(2)S(3) microstructured optical fibers (MOFs). Firstly, we study the synthesis of high purity arsenic sulfide glasses. Then we describe the use of a versatile process using mechanical drilling for the preparation of preforms and then the drawing of MOFs including suspended core fibers. Low losses MOFs are obtained by this way, with background level of losses reaching less than 0.5 dB/m. Optical characterizations of these fibers are then reported, especially dispersion measurements. The feasibility of all-optical regeneration based on a Mamyshev regenerator is investigated, and the generation of a broadband spectrum between 1 µm and 2.6 µm by femto second pumping around 1.5 µm is presented.