Juliano G. Hayashi

Ultrahigh-sensitivity temperature fiber sensor based on multimode interference

The proposed sensing device relies on the self-imaging effect that occurs in a pure silica multimode fiber (coreless MMF) section of a single-mode-multimode-single-mode (SMS)-based fiber structure. The influence of the coreless-MMF diameter on the external refractive index (RI) variation permitted the sensing head with the lowest MMF diameter (i.e., 55 μm) to exhibit the maximum sensitivity (2800  nm/RIU). This approach also implied an ultrahigh sensitivity of this fiber device to temperature variations in the liquid RI of 1.43: a maximum sensitivity of -1880  pm/°C was indeed attained. Therefore, the results produced were over 100-fold those of the typical value of approximately 13  pm/°C achieved in air using a similar device. Numerical analysis of an evanescent wave absorption sensor was performed, in order to extend the range of liquids with a detectable RI to above 1.43. The suggested model is an SMS fiber device where a polymer coating, with an RI as low as 1.3, is deposited over the coreless MMF; numerical results are presented pertaining to several polymer thicknesses in terms of external RI variation.

Surface-Enhanced Resonance Raman Scattering (SERRS) Using Au Nanohole Arrays on Optical Fiber Tips

AbstractCircular and bow tie-shaped Au nanoholes arrays were fabricated on gold films deposited on the tips of single-mode optical fibers. The nanostructures were milled using focused ion beam with a high quality control of their shapes and sizes. The optical fiber devices were used for surface-enhanced resonance Raman scattering (SERRS) measurements in both back- and forward-scattering geometries, yielding promising performance in both detection arrangements. The effect of the hole shape on the SERRS performance was explored with the bow tie nanostructures presenting a better SERRS performance than the circular holes arrays. The results present here are another step towards the development of optical fiber tips modified with plasmonic nanostructures for SERRS applications. FigureCircular and bow tie-shaped nanohole arrays were milled on gold films deposited on the tips of single-mode optical fibers. The arrays were fabricated by focused ion beam milling, which allowed good control over the sizes and the shapes of the nanostructures. The optical fiber devices were used for surface-enhanced resonance Raman scattering (SERRS) measurements in both back- and forward-scattering geometries. This work represents another step towards the development of optical fiber tips modified with plasmonic nanostructures for SERRS applications

Photonic-crystal fiber-based pressure sensor for dual environment monitoring.

In this paper the development of a side-hole photonic-crystal fiber (SH-PCF) pressure sensor for dual environment monitoring is reported. SH-PCF properties (phase and group birefringence, sensitivity to pressure variations) are measured and compared to simulated data. In order to probe two environments, two sections of the SH-PCF with different lengths are spliced and set in a Solc filter-like configuration. This setup allows obtaining the individual responses of the first and second fiber independently, which is useful for a space-multiplexed measurement. As the employed fiber is sensitive to pressure variations, we report the use of this configuration for dual environment pressure sensing.

High sensitivity LPG Mach–Zehnder sensor for real-time fuel conformity analysis

A high sensitivity refractive index sensor based on the combination of mechanically induced long period gratings (LPG) and fiber tapers was developed for real-time fuel quality analysis. The sensor was built in a Mach–Zehnder configuration by employing a pair of in-series gratings. In order to enhance sensor sensitivity, the region between both LPGs was tapered down from 125 to 10 µm. The system was tested by measuring water concentration in ethanol and ethanol concentration in commercial gasoline. The tapered sensor has shown an average sensitivity of 930 nm/RIU, 18 times higher than the non-tapered version. The resolution limit of the system using spectral interrogation was estimated to be 0.06% of ethanol dissolved in gasoline. For the purpose of real-time monitoring, an interrogation system based on white light interferometry (WLI) and virtual instrumentation was employed to evaluate ethanol evaporation in water, avoiding the use of spectral analysis. The WLI system, using phase tracking techniques, enabled us to record the evolution of the ethanol concentration in water with a resolution of 0.005% (v/v).

Numerical and Experimental Studies for a High Pressure Photonic Crystal Fiber Based Sensor

We report a study of using photonic crystal fibers (PCFs) for high pressure applications. An opto‐mechanical analysis was realized in regular PCFs and suspended‐core microstructured optical fibers for different fiber geometrical parameters. It was found that the pressure sensitivity is highly dependent on the fiber structure. It was also experimentally shown that even small core PCFs with high air filling fraction can deal with pressures as high as 500 bar (7350 psi) without any noticeable problem.

Refractometric sensor based on all-fiber coaxial Michelson and Mach-Zehnder interferometers for ethanol detection in fuel

A refractometric sensor based on mechanically induced interferometers formed with long period gratings is reported. It is also shown two different setups based on a Michelson and Mach-Zender interferometer and its application to measure ethanol concentration in gasoline.

Side-hole photonic crystal fibers

A new class of photonic crystal fiber, namely side-hole PCF, is analyzed and demonstrated. The presence of massive holes surrounding a microstructured cladding allows the realization of devices based on PCFs with integrated electrodes and fibers with high pressure sensitivity. The side holes can also be used to produce ultrahigh birefringence fibers based on squeezed-lattice structures and tunable single-polarization single-mode polymeric microstructured fibers.

Characterizing Slow Photochemical Reaction Kinetics by Enhanced Sampling of Rare Events with Capillary Optical Fibers and Kramers’ Theory

Characterization of slow chemical reactions is essential for assessing catalytic efficiency in chemistry and biology. Traditionally, chemical reaction rates are obtained from population relaxation kinetics measurements and the Arrhenius equation. Unfortunately, it is difficult to use this approach to characterize reactions wherein concentrations change slowly. Thus, it is interesting to see whether a dynamical view of chemical reactions may be used to obtain the reaction rates of slow processes. In the present work, we perform Brownian dynamics simulations of an asymmetric double-well potential to investigate how enhanced sampling of barrier crossing at transition states improves the characterization of reaction rate constants. We then present the design of a liquid-filled capillary optical fiber-based fluorescence spectrometer, which, like rare events, is also based on Poissonian statistics. We use the instrument to characterize the slow photochemical degradation kinetics of poly[2-methoxy-5-(2-ethylhexyloxy)-1,4-phenylenevinylene] (MEH-PPV) in o-dichlorobenzene. We have employed in situ optical microscopy measurements and electrodynamics simulations to characterize the excitation beam profile inside a liquid-filled capillary fiber. We compare the cuvette and capillary fiber sample holders and show that the MEH-PPV fluorescence line shape is independent of the sample holder, as expected. We characterize the photochemical degradation kinetics of MEH-PPV in o-dichlorobenzene solutions placed in the cuvette versus that in the capillary fiber. We observe small and slow changes in the time-dependent fluorescence spectra when the degradation reaction is performed in the cuvette. On the other hand, we are able to characterize reactant-concentration decay and product-concentration buildup from the time-dependent fluorescence spectra recorded during photochemical degradation of MEH-PPV performed inside the capillary optical fiber. Ultrafast optically heterodyne-detected optical Kerr effect spectroscopy and multimode Brownian oscillator analysis provide further insights into the role of bath oscillator modes of friction in the mechanism of MEH-PPV photochemical degradation. Overall, the work presented herein shows that slow photochemical degradation kinetics of MEH-PPV can be successfully and efficiently assessed in the capillary fiber fluorescence spectrometer.

Dual-environment pressure sensor using a photonic-crystal fiber

In this paper, we report the development of a side-hole photonic-crystal fiber (SH-PCF) based dual-environment pressure sensor. SH-PCF sensitivity to pressure variations was measured and compared to simulated data. SH-PCF sensitivity was found to be 2.8 times higher than the one presented by the commercial PM-1550-01 fiber. For probing two environments, one spliced two sections of the studied SH-PCF with different lengths in a solc-filter-like configuration. Individual responses of the first and second fiber can be independently obtained in this setup. Therefore, making use of SH-PCF sensitivity to pressure variations, a pressure sensor for dual environment monitoring is build up.

Fabrication and characterization of spun HiBi PCF fibers for current sensing applications

In this paper three highly birefringent (HiBi) spun photonic crystal fibers (PCF) are fabricated and their performance are characterized for electrical current measurement. These fibers are tested by coiling them around an electric conductor using three distinct winding diameters with different turns. The results present a very good linear relation with the current and its sensitivity depends on the winding diameter and on the number of turns. For the larger winding diameter, the fiber with lower circular pitch had higher sensitivity and for the smaller winding diameter the best sensitivity result was for the fiber with higher circular pitch.