Liquid-core Fiber Research Articles

ICONE19-43639 A CHERENKOV THRESHOLD COUNTER USING LIQUID CORE FIBER FOR ESTIMATION OF RADIOACTIVE WASTE INVENTORY

Decommissioning of nuclear power plant will increase a number of radioactive wastes near future. In Japan, some of the radioactive wastes will show high intensity of radiation and must be disposed in underground that deep enough from human activities. Therefore, it is important to estimate the inventory of such intense radioactive wastes. But it is difficult to verify the inventory of such radioactive wastes directly by a radiation counter because its intensity is too high to estimate by conventional pulse counting method In order to verify the inventory of such radioactive wastes directly, we propose a threshold detector with liquid core fiber as a Cherenkov counter which is applicable to high intensity radiation field. As a result of the preliminary experiment using ^<137>Cs and ^<60>Co gamma sources, we have confirmed that the proposal counter worked as the threshold detector. In this paper, we present the principle of this detector and show a preliminary result of detector response to gamma-rays.

Hollow-Core Photonic Crystal Fibers for Surface-Enhanced Raman Scattering Probes

Photonic crystal fiber (PCF) sensors based on surface-enhanced Raman scattering (SERS) have become increasingly attractive in chemical and biological detections due to the molecular specificity, high sensitivity, and flexibility. In this paper, we review the development of PCF SERS sensors with emphasis on our recent work on SERS sensors utilizing hollow-core photonic crystal fibers (HCPCFs). Specifically, we discuss and compare various HCPCF SERS sensors, including the liquid-filled HCPCF and liquid-core photonic crystal fibers (LCPCFs). We experimentally demonstrate and theoretically analyze the high sensitivity of the HCPCF SERS sensors. Various molecules including Rhodamine B, Rhodamine 6G, human insulin, and tryptophan have been tested to show the excellent performance of these fiber sensors.

Supercontinuum generation in liquid-filled photonic crystal fiber with slow nonlinear response

We theoretically investigate the nonlinear propagation of femtosecond pulses in liquid-core photonic crystal fibers filled with CS2. The effect of slow nonlinearity due to reorientational contribution of liquid molecules on broadband supercontinuum generation in the femtosecond regime is studied using an appropriately modified nonlinear Schrodinger equation. To analyze the quality of the pulse, we perform the stability analysis and study coherence of supercontinuum pulse numerically. We show that the response of the slow nonlinearity not only enhances broadening of the pulse and changes the dynamics of the generated solitons, but also increases coherence of the pulse.

Modulational-instability-induced supercontinuum generation with saturable nonlinear response

We theoretically investigate the supercontinuum generation (SCG) on the basis of modulational instability (MI) in liquid-core photonic crystal fibers (LCPCF) with CS${}_{2}$-filled central core. The effect of saturable nonlinearity of LCPCF on SCG in the femtosecond regime is studied using an appropriately modified nonlinear Schr\odinger equation. We also compare the MI induced spectral broadening with SCG obtained by soliton fission. To analyze the quality of the pulse broadening, we study the coherence of the SC pulse numerically. It is evident from the numerical simulation that the response of the saturable nonlinearity suppresses the broadening of the pulse. We also observe that the MI induced SCG in the presence of saturable nonlinearity degrades the coherence of the SCG pulse when compared to unsaturated medium.

High-sensitivity molecular sensing using hollow-core photonic crystal fiber and surface-enhanced Raman scattering

A high-sensitivity molecular sensor using a hollow-core photonic crystal fiber (HCPCF) based on surface-enhanced Raman scattering (SERS) has been experimentally demonstrated and theoretically analyzed. A factor of 100 in sensitivity enhancement is shown in comparison to direct sampling under the same conditions. With a silver nanoparticle colloid as the SERS substrate and Rhodamine 6G as a test molecule, the lowest detectable concentration is 10(-10) M with a liquid-core photonic crystal fiber (LCPCF) probe, and 10(-8) M for direct sampling. The high sensitivity provided by the LCPCF SERS probe is promising for molecular detection in various sensing applications.

Evaluation of optical fiber microcell reactor for use in remote acid sensing

An optical fiber acid-sensor based on protonation of a porphyrin solution within a single-hole structured optical fiber is proposed and demonstrated. The liquid-core fiber acts as a microcell reactor, and changes in the spectral signature with acidification are detected. Challenges and limitations in the practical deployment of such sensors are evaluated. An effective chemical sensor is demonstrated, but issues such as diffusion limit its full utilization. Some solutions are discussed.

Tunable and low bending loss of liquid-core fiber

The liquid-core fiber with relatively high refractive index difference between the core and cladding is proven to be bending insensitive. The single mode condition and bending loss of the fiber with a mixture of toluene and chloroform as its core material are studied. The results show that the bending loss of this fiber is not only much smaller than the conventional silica single mode fiber but also can be tuned by the temperature and liquid mixture ratio. This kind of fiber may find its potential applications in all-optical network.

Enhanced and broadened SRS spectra of toluene mixed with chloroform in liquid-core fiber

Stimulated Raman scattering of toluene and its mixture with chloroform is studied in liquid-core optical fiber. The results show a remarkably broadened Raman line of the mixture from about 630 nm to 650 nm by a pumping wavelength at 532 nm, which is assigned to the interaction of CH vibrations of the two liquids. The results suggest that interactions between adjacent vibrations can produce strong and wide Raman spectra in liquid-core fiber which may prove a new simple way for supercontinuum generation.

Liquid-filled microstructured polymer fibers as monolithic liquid-core array fibers

Liquid-filled microstructured polymer optical fibers (MPOFs) as monolithic liquid-core array fiber are proposed and prepared by injecting high-refractive-index liquid into the holes array of the MPOFs. One example for potential applications is demonstrated as a new kind of coherent imaging fiber. It provides great potential for applications in chemical sensing, biosensors, and endoscopy, particularly in bifunctional detection.

Bandgaps and antiresonances in integrated-ARROWs and Bragg fibers; a simple model

We consider the spectral properties of dielectric waveguides with low refractive index cores and binary layered claddings, such as Bragg fibers and integrated-ARROWs. We show that the full, nontrivial, 2-D spectrum of Bloch bands (hence bandgaps) of such claddings correspond, in structure and topology, to the dispersion properties of both constituent layer types; quantitatively demonstrating an intimate relationship between the bandgap and antiresonance guidance mechanisms. The dispersion functions of these layers, and the interactions thereof, thus form what we coin the Stratified Planar Anti-Resonant Reflecting OpticalWaveguide (SPARROW) model, capable of quantitative, analytic, descriptions of many nontrivial bandgap and antiresonance properties. The SPARROW model is useful for the spectral analysis and design of Bragg fibers and integrated-ARROWs with cores of arbitrary refractive index (equal to or less than the lowest cladding index). Both waveguide types are of interest for sensing and microfluidic applications due to their natural ability to guide light within low-index cores, permitting low-loss guidance within a large range of gases and liquids. A liquid-core Bragg fiber is discussed as an example, demonstrating the applicability of the SPARROW model to realistic and important waveguide designs.

Liquid-core liquid-cladding optical fibers sustained by light radiation pressure: Electromagnetic model and geometrical analog

We present an electromagnetic model describing liquid-core liquid-cladding optical fibers sustained by light radiation pressure that encompass the contribution of all the allowed propagating modes. Various sequences of unstable and stable equilibrium liquid column diameters are found above a threshold power. The nontrivial relationship between a single-valued or multivalued column diameter with a mono- or multimodal structure of the electromagnetic field is analyzed, and the influence of the light-matter interaction geometry is estimated. Moreover, we propose a geometrical interpretation based on a ray optics approach that brings an intuitive understanding of the role played by the higher-order propagation mode in the occurrence of a multistable liquid-core behavior.

Liquid Optical Fibers with a Multistable Core Actuated by Light Radiation Pressure

We report on spatiotemporal behavior of self-adapted dielectric liquid columns generated and sustained by light radiation pressure. We show that single- or multivalued liquid column diameter depends on the excitation light beam. When the beam diameter is sufficiently small, we observe a well-defined stationary column diameter. In contrast, at a larger beam diameter, the liquid column experiences complex spatiotemporal dynamics whose statistical analysis evidences an underlying multistable structure. Experimental observations are all supported by a full electromagnetic model that accounts for the wave guiding properties of the liquid column viewed as a step-index liquid-core liquid-cladding optical fiber having an optically tunable core diameter.

Index-guiding liquid-core photonic crystal fiber for solution measurement using normal and surface-enhanced Raman scattering

We have explored the use of index-guiding liquid-core (LC) photonic crystal fiber (PCF) as a robust platform for measurements of solutions of trace volume using normal and surface-enhanced Raman scattering (SERS). The LC PCF was fabricated by selectively sealing the cladding air channels at the distal ends of a hollow-core PCF while leaving the center core open, using a fusion splicer. Utilizing a 30-cm-long LC PCF with the entire center core filled with the ~0.1-µL solution of interest, we have obtained normal Raman spectra of water, ethanol, and 1 vol% ethanol in water. Sensitive and reproducible SERS detection of 1.7×10−7 M thiocyanate anions (14 ppb of NaSCN) in water has also been achieved.

High Sensitive Temperature Sensor Using a Liquid-core Optical Fiber with Small Refractive Index Difference Between Core and Cladding Materials.

An intensive temperature sensor based on a liquid-core optical fiber has been demonstrated for the measuring the temperature of the environment. The core of fiber is filled with a mixture of toluene and chloroform in order to make the refractive index of the liquid-core and the cladding of the fiber close. The experiment shows that a temperature sensitivity of about 5 dB/K and a tunable temperature range (from 20 oC to 60 oC) can be achieved. Based on the dielectric-clad liquid core fiber model, a simulation was carried out and the calculated results were in good accord with the experimental measurement.

Towards practical liquid and gas sensing with photonic crystal fibres: side access to the fibre microstructure and single-mode liquid-core fibre

Photonic crystal fibres (PCFs) have important applications in sensing the optical properties of fluids. To this end, the material should be inserted into the fibre holes in order to interact with the propagating field. When dealing with liquids, it is particularly interesting to exclusively insert the sample into the core of a hollow-core PCF, which then guides light through the liquid via total internal reflection. Nevertheless, there is still a series of issues to be addressed before fluid sensing with PCFs becomes practical. The work described here proposes and demonstrates possible solutions for two of these issues: (a) how to insert the sample through a lateral access to the fibre longitudinal holes so that the fibre tips are free for optical handling and accessing and (b) in the case of a liquid-core PCF, how to reduce the number of propagating modes.

High sensitivity autocorrelator based on a fluorescent liquid core fiber

The hollow core of an air-silica microstructured fiber was selectively filled with an alcoholic solution containing a laser dye (coumarin 515). This innovative liquid core fiber was used to build an efficient intensity autocorrelator operating by transverse imaging of the nonlinear fluorescence. Accurate measurement of pulse duration in the picosecond regime with submilliwatt average power has been demonstrated in the near infrared.

Theoretical design of a liquid-core photonic crystal fiber for supercontinuum generation

We have numerically studied a hollow-core photonic crystal fiber, with its core filled with highly nonlinear liquids such as carbon disulfide and nitrobenzene. Calculations show that the fiber has an extremely high nonlinear parameter gamma on the order of 2.4/W/m at 1.55 mum. The group velocity dispersion of this fiber exhibits an anomalous region in the near-infrared, and its zero-dispersion wavelength is around 1.55 mum. This leads to potentially significant improvements and a large bandwidth in supercontinuum generation. The spectral properties of the supercontinuum generation in liquid-core photonic crystal fibers are simulated by solving the generalized nonlinear Schrödinger equation. The results demonstrate that the liquid-core PCF is capable to generate dramatically broadened supercontinua in a range from 700 nm to more than 2500 nm when pumping at 1.55 mum with subpicosecond pulses.

Ultrasensitive detection of 1,4-Bis(4-vinylpyridyl)phenylene in a small volume of low refractive index liquid by surface-enhanced Raman scattering-active light waveguide.

This paper reports a novel surface-enhanced Raman scattering (SERS)-active light waveguide method for ultrasensitive detection of a sample dissolved in a small volume of low refractive index liquid. The SERS-active light waveguide demonstrated in this study was constructed via the light-guiding silica capillary. The surface of its inner wall was modified with SERS-active silver nanoparticles that can remarkably enhance Raman signals. The capillary with SERS-active modified layer was filled with the sample solution to form the SERS-active liquid core (LC) fiber. The incident laser beam travels through the waveguide in a totally reflective mode within the fiber wall and penetrates a small distance into the sample solution by the evanescent wave field. The Raman scattering of the analytes adsorbed onto the surface of the SERS-active modified layer can be excited by the laser beam and refracted into the fiber wall. Thus, a sample dissolved in low index liquid, e.g., methanol, can be quantitatively monitored by Raman spectroscopy and detection limit of its concentration is lower than 10(-9) mol/L.

Photochromic liquid-core fibers with nonlinear input~output characteristics

Photochromic liquid-core fibers were fabricated by using benzene or 2-propanol solution of spirobenzopyran. The fiber element consisting of a benzene-solution core and a silica-glass cladding exhibited variable transmittance that was controlled by ultraviolet irradiation. When a visible laser beam (532-nm wavelength) was used as input signal, output signal power increased nonlinearly with input power due to reversed photochromism. This nonlinear input-output characteristic was observed without ultraviolet light, when a fiber was constructed with 2-propanol solution and a polymer-coated glass tube. These experimental results agreed with the theoretical prediction that was based on a simple photochromic fiber model.

High-resolution tracking using large capillary bundles filled with liquid scintillator

We have developed large high-resolution tracking detectors based on glass capillaries filled with organic liquid scintillator of high refractive index. These liquid-core scintillating optical fibres act simultaneously as detectors of charged particles and as image guides. Track images projected onto the readout end of a capillary bundle are visualized by an optoelectronic chain consisting of a set of image-intensifier tubes followed by a photosensitive CCD or by an EBCCD camera. Two prototype detectors, each composed of ≈10 6 capillaries with 20– 25 μm diameter and 0.9–1.8 m length, have been tested, and a spatial resolution of the order of 20– 40 μm has been attained. A high scintillation efficiency and a large light-attenuation length, in excess of 3 m, was achieved through special purification of the liquid scintillator. Along the tracks of minimum-ionizing particles, the hit densities obtained were ∼8 hits/ mm at the readout window, and ∼3 hits/ mm at ∼1 m away. The level of radiation resistance of the prototype detectors is at least an order of magnitude higher than that of other tracking devices of comparable performance.