Specialty Fibers Research Articles

Characterization of the microstructures of specialty optical fibers for electric-field sensing by propagation-based x-ray phase-contrast microtomography

In this work, we present a quantitative (statistical) 3D morphological characterization of optical fibers used in electric-field sensing. The characterization technique employs propagation-based x-ray phase-contrast microcomputed tomography (micro-CT). In particular, we investigate specialty optical fibers that contain microstructured holes that are electro-optically modified by thermal poling to induce second-order nonlinear effects (SONE). The efficiency of the SONE is reflected in the characterization parameter, Vπ , which is highly dependent on the dimensions of the fiber. The fiber microstructures must be uniform to support the fabrication of reproducible devices. The results obtained using the micro-CT technique show that uncertainty of ±1.7% arises in the determination of the expected value of the voltage that causes a change in the phase of the electromagnetic wave equal to π rad (Vπ ), demonstrating a great advantage, compared with other techniques e.g. SEM, which would need at least 1000 images of the cross-section of an optical fiber, taken at different points, making the process more expensive and time-consuming.

Effects of Reflow Soldering Process Conditions on the Reliability of Specialty Optical Fibers

We will present our recent work on the reliability of specialty optical fibers designed for use in silicon photonics, subjected to reflow soldering process conditions. Coating thermal stability, fiber mechanical properties, and induced optical loss after reflow soldering will be discussed. Performances of post-reflow fibers under temperature cycling and damp heat aging environmental tests will also be discussed.

Distributed X-Ray Dosimetry With Optical Fibers by Optical Frequency Domain Interferometry

This article reports on the first demonstration of in situ , real-time dosimetry realized with an enhanced backscattering optical fiber, and a high-resolution optical backscattering reflectometry measurement. This work is devised to overcome the current problems in monitoring radiotherapy treatments, in particular, the difficult evaluation of not only the actual X-ray dose that is accumulated on the target volume but also the distribution profile of the ionizing radiation beam. Overall, the research aims at developing a dose sensor with the most demanding features of small form factor, spatial profiling, and remote interrogation. The experiments have been conducted by evaluating the spatial profile of radiation-induced spectral shift of the Rayleigh backscattering along an optical fiber exposed to X-rays. The sensing element is a section of specialty optical fiber whose Rayleigh backscattering signature changes under ionizing radiation. The specialty fiber is designed to exhibit an enhanced backscattering, in order to overcome the poor sensitivity to radiation of standard optical fibers that are normally, used in telecommunications. The enhanced sensitivity is achieved by doping the core with either aluminum or magnesium nanoparticles, and two different fibers have been fabricated and tested. The experimental results show the capability of real time detection of the radiation profile from high-dose rates (700 Gy/min) to low-dose rates (2 Gy/min). Moreover, different sensing mechanisms and responses to high- and low-dose rates are evidenced. A comparison with a quasi-distributed sensing system based on an array of fiber Bragg gratings (FBGs) is discussed, highlighting the superior performance of the backscattering approach in terms of sensitivity and spatial resolution, whereas the array of FBGs exhibits an advantage in terms of sampling speed.

Diaphragm-Embedded Optical Fiber Sensors: A Review and Tutorial

In this article, we thoroughly discuss many aspects of diaphragm-embedded optical fiber sensors covering industrial, robotics and medical applications: from the modeling to field applications, which also include sensor fabrication (such as interferometers, grating-based sensors, intensity variation sensors) in standard and specialty optical fibers, diaphragm and optical fiber materials thermal and mechanical characterizations. The operation limits of the sensors, interrogation techniques and the measurement possibilities that such sensors provide are also discussed. We expect that this review and tutorial provide valuable information regarding the optical fiber sensor approach, material selection and sensor assembly for the development of diaphragm-embedded optical fiber sensors.

Bidirectional Interferometric Flowmeter With Linear Sensitivity and Large Dynamic Range

We propose a bidirectional flowmeter based on specialty fiber interferometry by controlled mode excitation for measuring the frequency of the vortices induced by a bluff body. The proposed arrangement of the cylindrical bluff body with a slit and the interferometric system based on modal excitation allows the bidirectional flowmeter to determine the flow velocities in either direction precisely and effectively. We have encapsulated the specialty fiber interferometer in a protective metal casing, which not only allows the interferometer to respond to the vortex frequency but also provides mechanical stability to the whole flowmeter so at to operate in a harsh environment. Experiments are conducted by introducing the modal interferometer in the slit of the cylindrical bluff body at various flow rates ranging from Reynolds number (Re) = 7200 to 56 600. A linear response is observed between the flow velocity and the vortex frequency from both directions. Thus, this work provides a reconfigurable bidirectional flowmeter, which is sensitive even at low flow rates and demonstrates a large operating range.

All-Fiber Measurement of Surface Tension Using a Two-Hole Fiber.

An all-fiber approach is presented to measure surface tension. The experimental realization relies on the use of a specialty fiber, a so-called two-hole fiber (THF), which serves a two-fold purpose: providing a capillary channel to produce bubbles while having the means to measure the power reflected at the end facet of the fiber core. We demonstrate that provided a controlled injection of gas into the hollow channels of the THF, surface tension measurements are possible by simply tracking the Fresnel reflection at the distal end of the THF. Our results show that the characteristic times involved in the bubble formation process, from where the surface tension of the liquids under test is retrieved, can be measured from the train of pulses generated by the continuous formation and detachment of bubbles.

Fire safe, sustainable loose furnishing

SummaryThe aim of this exploratory study has been to investigate the fire properties and environmental aspects of different upholstery material combinations, mainly for domestic applications. An analysis of the sustainability and circularity of selected textiles, along with lifecycle assessment, is used to qualitatively evaluate materials from an environmental perspective. The cone calorimeter was the primary tool used to screen 20 different material combinations from a fire performance perspective. It was found that textile covers of conventional fibres such as wool, cotton and polyester, can be improved by blending them with fire resistant speciality fibres. A new three‐dimensional web structure has been examined as an alternative padding material, showing preliminary promising fire properties with regard to ignition time, heat release rates and smoke production.

Overview of Recent Advances in the Design of Plasmonic Fiber-Optic Biosensors.

Plasmonic fiber-optic biosensors combine the flexibility and compactness of optical fibers and high sensitivity of nanomaterials to their surrounding medium, to detect biological species such as cells, proteins, and DNA. Due to their small size, accuracy, low cost, and possibility of remote and distributed sensing, plasmonic fiber-optic biosensors are promising alternatives to traditional methods for biomolecule detection, and can result in significant advances in clinical diagnostics, drug discovery, food process control, disease, and environmental monitoring. In this review article, we overview the key plasmonic fiber-optic biosensing design concepts, including geometries based on conventional optical fibers like unclad, side-polished, tapered, and U-shaped fiber designs, and geometries based on specialty optical fibers, such as photonic crystal fibers and tilted fiber Bragg gratings. The review will be of benefit to both engineers in the field of optical fiber technology and scientists in the fields of biosensing.

Introduction to the JSTQE Special Issue on Emerging Applications of Multimode, Multicore and Specialty Fibers

The papers in this special section focus on emerging applications of multimode, multicore, and specialty optical fibers. The papers cover a broad range of advanced optical fiber technologies and applications.

Cylindrical vector beam generation based on arc-induced long-period gratings in few-mode fiber

We propose and demonstrate the use of the cost-effective electric arc writing method for the all-fiber cylindrical vector beam (CVB) and orbital angular momentum (OAM) beam generation in few-mode fibers (FMFs) for the first time to the best of our knowledge. We show that this technique enables the writing of long-period fiber gratings (LPFGs) with pitch values as small as 238 μm, which is required in some high-index contrast specialty fibers tailored for the stable guiding of CVB and OAM modes. Conversion efficiencies around 81% are measured for three different symmetric CVBs. The polarization-dependent properties of the fabricated gratings are elucidated, and we report a polarization-dependent loss of about 2.5 dB across the different CVBs. By means of a fabricated LPFG, we further demonstrated the all-fiber generation of the OAM states with topological charge (±1) at the output of the FMF. The results are relevant to the fields of space-division multiplexing, optical sensors, and optical tweezers that would benefit from a compact source of quality CVB and OAM beams of high average optical power.

Hollow-Core Photonic Crystal Fiber Gas Sensing.

Fiber gas sensing techniques have been applied for a wide range of industrial applications. In this paper, the basic fiber gas sensing principles and the development of different fibers have been introduced. In various specialty fibers, hollow-core photonic crystal fibers (HC-PCFs) can overcome the fundamental limits of solid fibers and have attracted intense interest recently. Here, we focus on the review of HC-PCF gas sensing, including the light-guiding mechanisms of HC-PCFs, various sensing configurations, microfabrication approaches, and recent research advances including the mid-infrared gas sensors via hollow core anti-resonant fibers. This review gives a detailed and deep understanding of HC-PCF gas sensors and will promote more practical applications of HC-PCFs in the near future.

Mode-field Matching Down-Tapers on Single-Mode Optical Fibers for Edge Coupling Towards Generic Photonic Integrated Circuit Platforms

Connections between standard single-mode fibers and waveguides in photonic integrated circuits tend to have relatively high coupling losses due to a difference in mode size and mode profile between both light guiding media. Edge coupling strategies involving specialty fibers are frequently used to obtain the best performance in terms of coupling efficiency, bandwidth and polarization independence. We propose the fabrication of free-standing down-taper structures on top of cleaved fiber facets by two-photon direct laser writing and show their performance for silicon, silicon nitride and indium phosphide generic chip platforms. We present a comprehensive analysis of the design of such taper structures that show unprecedented flexibility. We demonstrate their fabrication and fully characterize them in terms of output modal fields and coupling efficiencies. Furthermore, we experimentally compare the fabricated down-tapers with commercially available lensed fibers and demonstrate equal or better coupling efficiency for four out of the five investigated photonic integrated circuit platforms, with a measured improvement in coupling efficiency up to 1.43 dB.

Laboratory tests for MIR light detection and transport with specialty optical fibres

The FAMU (Fisica degli Atomi Muonici) experiment at the RIKEN RAL pulsed muon facility will measure the proton Zemach radius with high precision, thus contributing to the solution of the so-called “proton radius puzzle”. The situation is now confused and new measurements will help reduce the discrepancy as measured with electrons or muons. To this aim, FAMU will make use of a high-intensity pulsed muon beam at RIKEN-RAL impinging on a cryogenic hydrogen target and a tunable Mid-infrared (MIR) laser emitting at about 6.78 μm, to measure the hyperfine (HFS) splitting of the 1S state of muonic hydrogen. The injection of light into the cryogenic target and its monitoring via dedicated MIR sensors is an asset for the experiment. A possible solution is via specialty MIR fibres based on hollow core waveguides or polycrystalline fibres. Two dedicated setups based on pulsed QCL lasers, from Alpes Laser, emitting around 6.78 μm have been used to study the fibre attenuation while the high energy laser specifically developed for the FAMU project has been used to study the damage threshold at high energies. The alignment of MIR laser radiation into an optical cavity presents criticalities due to geometrical constraints. Its control requires the use of small and sensitive detectors. The results obtained with a quantum IR sensor with an integrated circuit for signal processing are reported.

Comparison of cross specialty fibre optic airway competence in the south east of England.

Comparison of cross specialty fibre optic airway competence in the south east of England.

Zeolite 法による機能性シリカガラスの可能性と特殊ファイバ素子開発

Zeolite 法による機能性シリカガラスの可能性と特殊ファイバ素子開発

Splicing of silica-based MOF and standard SMF: Loss evaluation using an enhanced field model

Abstract Splice losses between the transmission optical fibers and the fiber-based devices have been considered as one of the bottlenecks in accomplishing the optical networks. Consequently, the practical utilization of specialty optical fibers such as triangular solid-core microstructured optical fibers (T-MOFs) in conjunction with splicing to dissimilar standard single-mode fiber (SMF) prerequisite a trustworthy, repeatable and robust low-loss splicing. Utilizing an enhanced field model, we appraised the splice losses between two similar T-MOFs without considering collapsing of air-holes at the joint interface with azimuthal and transverse offsets, and the splice loses between T-MOF and classical SMF are also explored. Collapsing of air-holes can facilitate to minimize the mode-profile inconsistency at splicing interface and hence, lowering the losses; therefore, we evaluated the mode-field diameter (MFD) as a function of collapse ratio. We reported splice losses of ~0.378 dB and ~5.032 dB at 1.55 µm between two identical T-MOFs with Λ = 4.0 µm, for the case of azimuthal and transverse offset, respectively. Also, we examined the consistency of our results by evaluating the relative errors, and the comparisons have been incorporated with those as reported in the literature.

PANDA Type Four-Core Fiber With the Efficient Use of Stress Rods

We design a panda type four-core fiber with a comparable optical property of the polarization maintenance single mode fiber (PM-SMF) and can support 8 non-polarization-degenerate eigenmodes with a birefringence of approximate 3.24 × 10 -4 over the wavelength range from 1288 to 1630 nm. In particular, only four stress rods are efficiently used to achieve the PM characteristics for each core, in comparison with traditional design of panda type PM-SMF. Meanwhile, we identify that the optimal configuration of stress rods can not only enhance the birefringence, but also further suppress the crosstalk (XT) between two primary eigenstate of polarization (ESOP) arising in adjacent cores, although the corresponding XT at secondary ESOP remains unchanged. Moreover, our numerical results show that both chromatic dispersion (CD) together with mode field diameter (MFD) and the bending sensitivity are consistent among four cores. We believe that such specialty multi-core fiber is ideal for compact and cost-effective fiber-optic gyroscope (FOG) application, besides the potential in the MIMO-free spatial division multiplexing (SDM) interconnection.

Generalized Method to Describe the Propagation of Pulses in Classical and Specialty Optical Fibers

The comprehension of pulsed light propagation is of paramount importance in fiber optics. Here, we present a general method to describe the propagation of pulses in any kind of optical fiber, regardless of its fabrication process or constituent materials. As a result, we obtain a rich toolbox for the analysis and synthesis of optical fibers, which allows us to circumvent the resolution of Maxwell's equations by using heavy-computational numerical methods. To illustrate this, we analyze the pulse propagation problem in non-paraxial anisotropic single-core and multi-core fibers that cover a large variety of optical fibers including classical weakly guiding fibers, optical gain fibers, polarization-maintaining fibers, highly nonlinear fibers, and photonic crystal fibers. Moreover, it is shown that our method can be applied to any kind of guided and unguided medium undergoing spatial and temporal perturbations, provided that the distance and temporal width between different consecutive spatial and temporal medium perturbations are respectively higher than the spatial and temporal width of the optical pulses.

Fiber-based early diagnosis of venous thromboembolic disease by label-free D-dimer detection

D-dimer is a useful diagnostic biomarker for deep vein thrombosis or pulmonary embolism, collectively referred to as venous thromboembolism (VTE). The ability to detect in real-time the amount of D-dimer with a fast and reliable method is a key step to anticipate the appearance of these diseases. Here, the results of a highly specific and sensitive biosensor for the detection of D-dimer based on lossy mode resonance in fiber optics are presented. The unique features of specialty fibers in light management integrated with microfluidics allow detecting D-dimer in human serum with a detection limit of 100 ng/mL, a value 5-fold below the clinical cutoff value. Comparison of the results achieved with mass-spectrometry-based proteomics, which allows for the identification of beta- and gamma-chains of fibrinogen, demonstrates the ability of our platform to specifically (>90%) recognize D-dimer. Therefore, this technology potentially represents a paradigm shift in the development of a simple, high-specificity and label-free biosensing platform, which can be applied to speed up diagnostic healthcare processes of venous thromboembolism toward an early diagnostic and personalized treatment system.

Emerging Applications of Multimode, Multicore and Specialty Fibers

Emerging Applications of Multimode, Multicore and Specialty Fibers