Side-detection of out-coupled core light from a microfluidic fiber microslit

The interactions of the core-propagating light with an intersecting microslit within a conventional single-mode fiber are investigated. Orientation-dependent out-coupling of core light was utilized to create side-detection, miniature fiber rotation sensors.

Optical sensor interrogation with a blazed fiber Bragg grating and a charge-coupled device linear array

We present what is to our knowledge the first comprehensive investigation of the use of blazed fiber Bragg gratings (BFBGs) to interrogate wavelength division multiplexed (WDM) in-fiber optical sensor arrays. We show that the light outcoupled from the core of these BFBGs is radiated with sufficient optical power that it may be detected with a low-cost charge-coupled device (CCD) array. We present thorough system performance analysis that shows sufficient spectral-spatial resolution to decode sensors with a WDM separation of 75 ρm, signal-to-noise ratio greater than 45-dB bandwidth of 70 nm, and drift of only 0.1 ρm. We show the system to be polarization-state insensitive, making the BFBG-CCD spectral analysis technique a practical, extremely low-cost, alternative to traditional tunable filter approaches.

Blocked diisocyanates as reactive coupling agents: Application to pine fiber-polypropylene composites

In this paper, composites from polypropylene and Kraft pulp (from Pinus radiata) were prepared. Phenyl isocyanate, unblocked and phenol blocked derivatives of 4,4`-methylenebis (phenyl isocyanate) (MDI) were used as coupling agents and the mechanical properties of the obtained composites analyzed. The results showed that the addition of such compatibilizers readily improved the tensile and flexural strengths of the composites. However, no significant variation in the mechanical properties was observed for composite formulations comprising different isocyanate compounds. Accordingly, the chemical structure of isocyanate derivatives did not affect extensively the mechanical properties of MDI-coupled pine fiber reinforced composites. These results were similar to those obtained in previous studies regarding the efficiency of organosilane coupling agents. In comparison to monoreactive isocyanates, the addition of MIDI increased considerably the mechanical properties of pine fiber-polypropylene composites. The mechanical anchoring of polymeric PP chains onto the irregular reinforcement surface supported this result. Non-isothermal DSC analysis showed a slowing effect of MDI on the crystallization kinetics of the coupled composites. This may have been the result of diminished polymer chain mobility in the matrix due to mechanical anchoring onto the fiber surface. Considering these results, the occurrence of strong bonds between the composite components was stated, rather than the unique existence of Van der Waals interactions among the non-polar structures. (c) 2008 Elsevier Ltd. All rights reserved.

Impairment of mossy fiber long-term potentiation and associative learning in pituitary adenylate cyclase activating polypeptide type I receptor-deficient Mice

The pituitary adenylate cyclase activating polypeptide (PACAP) type I receptor (PAC1) is a G-protein-coupled receptor binding the strongly conserved neuropeptide PACAP with 1000-fold higher affinity than the related peptide vasoactive intestinal peptide. PAC1-mediated signaling has been implicated in neuronal differentiation and synaptic plasticity. To gain further insight into the biological significance of PAC1-mediated signaling in vivo, we generated two different mutant mouse strains, harboring either a complete or a forebrain-specific inactivation of PAC1. Mutants from both strains show a deficit in contextual fear conditioning, a hippocampus-dependent associative learning paradigm. In sharp contrast, amygdala-dependent cued fear conditioning remains intact. Interestingly, no deficits in other hippocampus-dependent tasks modeling declarative learning such as the Morris water maze or the social transmission of food preference are observed. At the cellular level, the deficit in hippocampus-dependent associative learning is accompanied by an impairment of mossy fiber long-term potentiation (LTP). Because the hippocampal expression of PAC1 is restricted to mossy fiber terminals, we conclude that presynaptic PAC1-mediated signaling at the mossy fiber synapse is involved in both LTP and hippocampus-dependent associative learning.

Gut microbiota metabolism of dietary fiber influences allergic airway disease and hematopoiesis.

Metabolites from intestinal microbiota are key determinants of host-microbe mutualism and, consequently, the health or disease of the intestinal tract. However, whether such host-microbe crosstalk influences inflammation in peripheral tissues, such as the lung, is poorly understood. We found that dietary fermentable fiber content changed the composition of the gut and lung microbiota, in particular by altering the ratio of Firmicutes to Bacteroidetes. The gut microbiota metabolized the fiber, consequently increasing the concentration of circulating short-chain fatty acids (SCFAs). Mice fed a high-fiber diet had increased circulating levels of SCFAs and were protected against allergic inflammation in the lung, whereas a low-fiber diet decreased levels of SCFAs and increased allergic airway disease. Treatment of mice with the SCFA propionate led to alterations in bone marrow hematopoiesis that were characterized by enhanced generation of macrophage and dendritic cell (DC) precursors and subsequent seeding of the lungs by DCs with high phagocytic capacity but an impaired ability to promote T helper type 2 (TH2) cell effector function. The effects of propionate on allergic inflammation were dependent on G protein-coupled receptor 41 (GPR41, also called free fatty acid receptor 3 or FFAR3), but not GPR43 (also called free fatty acid receptor 2 or FFAR2). Our results show that dietary fermentable fiber and SCFAs can shape the immunological environment in the lung and influence the severity of allergic inflammation.

(E)-2-Nonenal determination in brazilian beers using headspace solid-phase microextraction and gas chromatographic coupled mass spectrometry (HS-SPME-GC-MS)

(E)-2-nonenal is considered an important off-flavor of beer, related to the flavor of beer staling. In this study, a new method for determination of (E)-2-nonenal in beer using headspace solid-phase microextraction and gas chromatographic coupled mass spectrometry (HS-SPME-GC-MS) was developed and applied in Brazilian beer samples. The extractions were carried out in CAR-PDMS (carboxen-polydimethylsiloxane) fiber and the best results were found with 15 minutes of equilibrium and 90 minutes of extraction at 50 °C. The method was linear in the range from 0.02 to 4.0 μg.L-1 with correlation coefficient of 0.9994. The limits of detection and quantification were 0.01 and 0.02 μg.L-1, respectively. 96.5% of recovery and 4% precision (RSD) were obtained in the fortification of beer samples with 2.0 μg.L-1 of (E)-2-nonenal. The developed method proved to be simple, efficient and highly sensitive to the determination of this analyte being easily applied in the quality control of the brewery. (E)-2-nonenal was found in all beer samples analyzed with levels between 0.17 and 0.42 μg.L-1.

Determination of anticonvulsants in human plasma using SPME in a heated interface coupled online to liquid chromatography (SPME-LC)

A simple and sensitive method using solid phase microextraction (SPME) and liquid chromatography (LC) with heated online desorption (SPME-LC) was developed and validated to analyze anticonvulsants (AEDs) in human plasma samples. A heated lab-made interface chamber was used in the desorption procedure, which allowed the transference of the whole extracted sample. The SPME conditions were optimized by applying an experimental design. Important factors are discussed such as fiber coating types, pH, extraction time and desorption conditions. The drugs were analyzed by LC, using a C18 column (150 mm 4.6 mm 5 mm); and 50 mmol L1 , pH ¼ 5.50 ammonium acetate buffer : acetonitrile : methanol (55 : 22 : 23 v/v) as the mobile phase with a flow rate of 0.8 mL min1 . The suggested method presented precision (intra-assay and inter-assay), linearity and limit of quantification (LOQ) all adequate for the therapeutic drug monitoring (TDM) of AEDs in plasma.

Determination of anticonvulsants in human plasma using SPME in a heated interface coupled online to liquid chromatography (SPME-LC)

A simple and sensitive method using solid phase microextraction (SPME) and liquid chromatography (LC) with heated online desorption (SPME-LC) was developed and validated to analyze anticonvulsants (AEDs) in human plasma samples. A heated lab-made interface chamber was used in the desorption procedure, which allowed the transference of the whole extracted sample. The SPME conditions were optimized by applying an experimental design. Important factors are discussed such as fiber coating types, pH, extraction time and desorption conditions. The drugs were analyzed by LC, using a C18 column (150 mm x 4.6 mm x 5 mm); and 50 mmol L-1, pH 5.50 ammonium acetate buffer : acetonitrile : methanol (55 : 22 : 23 v/v) as the mobile phase with a flow rate of 0.8 mL min(-1). The suggested method presented precision (intra-assay and inter-assay), linearity and limit of quantification (LOQ) all adequate for the therapeutic drug monitoring (TDM) of AEDs in plasma.

Thermal excitations of optical nanofibers measured with a fiber-integrated Fabry-Pérot cavity

Efficient coupling of light to quantum emitters, such as atoms, molecules or quantum dots, is one of the great challenges in current research. The interaction can be strongly enhanced by coupling the emitter to the eva-nescent field of subwavelength dielectric waveguides that offer strong lateral confinement of the guided light. In this context subwavelength diameter optical nanofibers as part of a tapered optical fiber (TOF) have proven to be powerful tool which also provide an efficient transfer of the light from the interaction region to an optical bus, that is to say, from the nanofiber to an optical fiber. rnAnother approach towards enhancing light–matter interaction is to employ an optical resonator in which the light is circulating and thus passes the emitters many times. Here, both approaches are combined by experi-mentally realizing a microresonator with an integrated nanofiber waist. This is achieved by building a fiber-integrated Fabry-Pérot type resonator from two fiber Bragg grating mirrors with a stop-band near the cesium D2-line wavelength. The characteristics of this resonator fulfill the requirements of nonlinear optics, optical sensing, and cavity quantum electrodynamics in the strong-coupling regime. Together with its advantageous features, such as a constant high coupling strength over a large volume, tunability, high transmission outside the mirror stop band, and a monolithic design, this resonator is a promising tool for experiments with nanofiber-coupled atomic ensembles in the strong-coupling regime. rnThe resonator's high sensitivity to the optical properties of the nanofiber provides a probe for changes of phys-ical parameters that affect the guided optical mode, e.g., the temperature via the thermo-optic effect of silica. Utilizing this detection scheme, the thermalization dynamics due to far-field heat radiation of a nanofiber is studied over a large temperature range. This investigation provides, for the first time, a measurement of the total radiated power of an object with a diameter smaller than all absorption lengths in the thermal spectrum at the level of a single object of deterministic shape and material. The results show excellent agreement with an ab initio thermodynamic model that considers heat radiation as a volumetric effect and that takes the emitter shape and size relative to the emission wavelength into account. Modeling and investigating the thermalization of microscopic objects with arbitrary shape from first principles is of fundamental interest and has important applications, such as heat management in nano-devices or radiative forcing of aerosols in Earth's climate system. rnUsing a similar method, the effect of the TOF's mechanical modes on the polarization and phase of the fiber-guided light is studied. The measurement results show that in typical TOFs these quantities exhibit high-frequency thermal fluctuations. They originate from high-Q torsional oscillations that couple to the nanofiber-guided light via the strain-optic effect. An ab-initio opto-mechanical model of the TOF is developed that provides an accurate quantitative prediction for the mode spectrum and the mechanically induced polarization and phase fluctuations. These high-frequency fluctuations may limit the ultimate ideality of fiber-coupling into photonic structures. Furthermore, first estimations show that they may currently limit the storage time of nanofiber-based atom traps. The model, on the other hand, provides a method to design TOFs with tailored mechanical properties in order to meet experimental requirements. rn

Design and optimization of optical, fiber based PSK demodulators for high-bit-rate optical networks

El objetivo principal de esta tesis ha sido el diseño y la optimización de receptores implementados con fibra óptica, para ser usados en redes ópticas de alta velocidad que empleen formatos de modulación de fase. En los últimos años, los formatos de modulación de fase (Phase Shift keying, PSK) han captado gran atención debido a la mejora de sus prestaciones respecto a los formatos de modulación convencionales. Principalmente, presentan una mejora de la eficiencia espectral y una mayor tolerancia a la degradación de la señal causada por la dispersión cromática, la dispersión por modo de polarización y los efectos no-lineales en la fibra óptica. En este trabajo, se analizan en detalle los formatos PSK, incluyendo sus variantes de modulación de fase diferencial (Differential Phase Shift Keying, DPSK), en cuadratura (Differential Quadrature Phase Shift Keying, DQPSK) y multiplexación en polarización (Polarization Multiplexing Differential Quadrature Phase Shift Keying, PM-DQPSK), con la finalidad de diseñar y optimizar los receptores que permita su demodulación. Para ello, se han analizado y desarrollado nuevas estructuras que ofrecen una mejora en las prestaciones del receptor y una reducción de coste comparadas con las actualmente disponibles. Para la demodulación de señales DPSK, en esta tesis, se proponen dos nuevos receptores basados en un interferómetro en línea Mach-Zehnder (MZI) implementado con tecnología todo-fibra. El principio de funcionamiento de los MZI todo-fibra propuestos se asienta en la interferencia modal que se produce en una fibra multimodo (MMF) cuando se situada entre dos monomodo (SMF). Este tipo de configuración (monomodo-multimodo-monomodo, SMS) presenta un buen ratio de extinción interferente si la potencia acoplada en la fibra multimodo se reparte, principal y equitativamente, entre dos modos dominantes. Con este objetivo, se han estudiado y demostrado tanto teórica como experimentalmente dos nuevas estructuras SMS que mejoran el ratio de extinción. Una de las propuestas se basa en emplear una fibra multimodo de índice gradual cuyo perfil del índice de refracción presenta un hundimiento en su zona central. La otra consiste en una estructura SMS con las fibras desalineadas y donde la fibra multimodo es una fibra de índice gradual convencional. Para las dos estructuras, mediante el análisis teórico desarrollado, se ha demostrado que el 80 – 90% de la potencia de entrada se acopla a los dos modos dominantes de la fibra multimodo y se consigue una diferencia inferior al 10% entre ellos. También se ha demostrado experimentalmente que se puede obtener un ratio de extinción de al menos 12 dB. Con el objeto de demostrar la capacidad de estas estructuras para ser empleadas como demoduladores de señales DPSK, se han realizado numerosas simulaciones de un sistema de transmisión óptico completo y se ha analizado la calidad del receptor bajo diferentes perspectivas, tales como la sensibilidad, la tolerancia a un filtrado óptico severo o la tolerancia a las dispersiones cromática y por modo de polarización. En todos los casos se ha concluido que los receptores propuestos presentan rendimientos comparables a los obtenidos con receptores convencionales. En esta tesis, también se presenta un diseño alternativo para la implementación de un receptor DQPSK, basado en el uso de una fibra mantenedora de la polarización (PMF). A través del análisi teórico y del desarrollo de simulaciones numéricas, se ha demostrado que el receptor DQPSK propuesto presenta prestaciones similares a los convencionales. Para complementar el trabajo realizado sobre el receptor DQPSK basado en PMF, se ha extendido el estudio de su principio de demodulación con el objeto de demodular señales PM-DQPSK, obteniendo como resultado la propuesta de una nueva estructura de demodulación. El receptor PM-DQPSK propuesto se basa en la estructura conjunta de una única línea de retardo junto con un rotador de polarización. Se ha analizado la calidad de los receptores DQPSK y PM-DQPSK bajo diferentes perspectivas, tales como la sensibilidad, la tolerancia a un filtrado óptico severo, la tolerancia a las dispersiones cromática y por modo de polarización o su comportamiento bajo condiciones no-ideales. En comparación con los receptores convencionales, nuestra propuesta exhibe prestaciones similares y además permite un diseño más simple que redunda en un coste potencialmente menor. En las redes de comunicaciones ópticas actuales se utiliza la tecnología de multimplexación en longitud de onda (WDM) que obliga al uso de filtros ópticos con bandas de paso lo más estrechas posibles y a emplear una serie de dispositivos que incorporan filtros en su arquitectura, tales como los multiplexores, demultiplexores, ROADMs, conmutadores y OXCs. Todos estos dispositivos conectados entre sí son equivalentes a una cadena de filtros cuyo ancho de banda se va haciendo cada vez más estrecho, llegando a distorsionar la forma de onda de las señales. Por esto, además de analizar el impacto del filtrado óptico en las señales de 40 Gbps DQPSK y 100 Gbps PM-DQPSK, este trabajo de tesis se completa estudiando qué tipo de filtro óptico minimiza las degradaciones causadas en la señal y analizando el número máximo de filtros concatenados que permiten mantener la calidad requerida al sistema. Se han estudiado y simulado cuatro tipos de filtros ópticos;Butterworth, Bessel, FBG y F-P. ABSTRACT The objective of this thesis is the design and optimization of optical fiber-based phase shift keying (PSK) demodulators for high-bit-rate optical networks. PSK modulation formats have attracted significant attention in recent years, because of the better performance with respect to conventional modulation formats. Principally, PSK signals can improve spectrum efficiency and tolerate more signal degradation caused by chromatic dispersion, polarization mode dispersion and nonlinearities in the fiber. In this work, many PSK formats were analyzed in detail, including the variants of differential phase modulation (Differential Phase Shift Keying, DPSK), in quadrature (Differential Quadrature Phase Shift Keying, DQPSK) and polarization multiplexing (Polarization Multiplexing Differential Quadrature Phase Shift Keying, PM-DQPSK), in order to design and optimize receivers enabling demodulations. Therefore, novel structures, which offer good receiver performances and a reduction in cost compared to the current structures, have been analyzed and developed. Two novel receivers based on an all-fiber in-line Mach-Zehnder interferometer (MZI) were proposed for DPSK signal demodulation in this thesis. The operating principle of the all-fiber MZI is based on the modal interference that occurs in a multimode fiber (MMF) when it is located between two single-mode fibers (SMFs). This type of configuration (Single-mode-multimode-single-mode, SMS) can provide a good extinction ratio if the incoming power from the SMF could be coupled equally into two dominant modes excited in the MMF. In order to improve the interference extinction ratio, two novel SMS structures have been studied and demonstrated, theoretically and experimentally. One of the two proposed MZIs is based on a graded-index multimode fiber (MMF) with a central dip in the index profile, located between two single-mode fibers (SMFs). The other one is based on a conventional graded-index MMF mismatch spliced between two SMFs. Theoretical analysis has shown that, in these two schemes, 80 – 90% of the incoming power can be coupled into the two dominant modes exited in the MMF, and the power difference between them is only ~10%. Experimental results show that interference extinction ratio of 12 dB could be obtained. In order to demonstrate the capacity of these two structures for use as DPSK signal demodulators, numerical simulations in a completed optical transmission system have been carried out, and the receiver quality has been analyzed under different perspectives, such as sensitivity, tolerance to severe optical filtering or tolerance to chromatic and polarization mode dispersion. In all cases, from the simulation results we can conclude that the two proposed receivers can provide performances comparable to conventional ones. In this thesis, an alternative design for the implementation of a DQPSK receiver, which is based on a polarization maintaining fiber (PMF), was also presented. To complement the work made for the PMF-based DQPSK receiver, the study of the demodulation principle has been extended to demodulate PM-DQPSK signals, resulting in the proposal of a novel demodulation structure. The proposed PM-DQPSK receiver is based on only one delay line and a polarization rotator. The quality of the proposed DQPSK and PM-DQPSK receivers under different perspectives, such as sensitivity, tolerance to severe optical filtering, tolerance to chromatic dispersion and polarization mode dispersion, or behavior under non-ideal conditions. Compared with the conventional receivers, our proposals exhibit similar performances but allow a simpler design which can potentially reduce the cost. The wavelength division multiplexing (WDM) technology used in current optical communications networks requires the use of optical filters with a passband as narrow as possible, and the use of a series of devices that incorporate filters in their architecture, such as multiplexers, demultiplexers, switches, reconfigurable add-drop multiplexers (ROADMs) and optical cross-connects (OXCs). All these devices connected together are equivalent to a chain of filters whose bandwidth becomes increasingly narrow, resulting in distortion to the waveform of the signals. Therefore, in addition to analyzing the impact of optical filtering on signal of 40 Gbps DQPSK and 100 Gbps PM-DQPSK, we study which kind of optical filter minimizes the signal degradation and analyze the maximum number of concatenated filters for maintaining the required quality of the system. Four types of optical filters, including Butterworth, Bessel, FBG and FP, have studied and simulated.

Fiber Bragg grating sensor interrogation system using a CCD side detection method with Superimposed blazed gratings

We present, for the first time to our knowledge, experimental evidence showing that superimposed blazed fiber Bragg gratings may be fabricated and used to extend the dynamic range of a grating-based spectrometer. Blazed gratings of 4° and 8° were superimposed in germanosilicate fiber by ultraviolet inscription and used in conjunction with a coated charged-coupled device array to interrogate a wavelength-division-multiplexing sensor array. We show that the system can be used to monitor strain and temperature sensors simultaneously with an employable bandwidth which is extendable to 70 nm.

Dual-peak long-period fiber gratings with enhanced refractive index sensitivity by finely tailored mode dispersion that uses the light cladding etching technique

We have experimentally investigated the mode dispersion property and refractive index sensitivity of dual-peak long-period fiber gratings (LPGs) that were sensitized by hydrofluoric acid (HF) etching. The nature of the coupled cladding modes close to the dispersion turning point makes the dual-peak LPGs ultrasensitive to cladding property, permitting a fine tailoring of the mode dispersion and index sensitivity by the light cladding etching method using HF acid of only 1% concentration. As an implementation of an optical biosensor, the etched device was used to detect the concentration of hemoglobin protein in a sugar solution, showing a sensitivity as high as 20 nm/1%.

Fiber Bragg grating sensor interrogation system using a CCD side detection method with superimposed blazed gratings

We present, for the first time to our knowledge, experimental evidence showing that superimposed blazed fiber Bragg gratings may be fabricated and used to extend the dynamic range of a grating-based spectrometer. Blazed gratings of 4° and 8° were superimposed in germanosilicate fiber by ultraviolet inscription and used in conjunction with a coated charged-coupled device array to interrogate a wavelength-division-multiplexing sensor array. We show that the system can be used to monitor strain and temperature sensors simultaneously with an employable bandwidth which is extendedable to 70 nm.

Dual-peak long-period fiber gratings with enhanced refractive index sensitivity by finely tailored mode dispersion that uses the light cladding etching technique

We have experimentally investigated the mode dispersion property and refractive index sensitivity of dual-peak long-period fiber gratings (LPGs) that were sensitized by hydrofluoric acid (HF) etching. The nature of the coupled cladding modes close to the dispersion turning point makes the dual-peak LPGs ultrasensitive to cladding property, permitting a fine tailoring of the mode dispersion and index sensitivity by the light cladding etching method using HF acid of only 1% concentration. As an implementation of an optical biosensor, the etched device was used to detect the concentration of hemoglobin protein in a sugar solution, showing a sensitivity as high as 20 nm/1%. © 2007 Optical Society of America.

Physical characteristics of localized surface plasmons resulting from nano-scale structured multi-layer thin films deposited on D-shaped optical fiber

Novel surface plasmonic optical fiber sensors have been fabricated using multiple coatings deposited on a lapped section of a single mode fiber. UV laser irradiation processing with a phase mask produces a nano-scaled surface relief grating structure resembling nano-wires. The resulting individual corrugations produced by material compaction are approximately 20 μm long with an average width at half maximum of 100 nm and generate localized surface plasmons. Experimental data are presented that show changes in the spectral characteristics after UV processing, coupled with an overall increase in the sensitivity of the devices to surrounding refractive index. Evidence is presented that there is an optimum UV dosage (48 joules) over which no significant additional optical change is observed. The devices are characterized with regards to change in refractive index, where significantly high spectral sensitivities in the aqueous index regime are found, ranging up to 4000 nm/RIU for wavelength and 800 dB/RIU for intensity. © 2013 Optical Society of America.