Suspended-core Optical Fibers Research Articles

Spectral tailoring of photon pairs from microstructured suspended-core optical fibers with liquid-filled nanochannels.

We theoretically study the generation of photon pairs via spontaneous four-wave mixing (SFWM) in a liquid-filled microstructured suspended-core optical fiber. We show that it is possible to control the wavelength, group velocity, and bandwidths of the two-photon states. Our proposed fiber structure shows a large number of degrees of freedom to engineer the two-photon state. Here, we focus on the factorable state, which shows no spectral correlation in the two-photon components of the state, and allows the heralding of a single-photon pure state without the need for spectral post-filtering.

Single-peak fiber Bragg gratings in suspended-core optical fibers.

Femtosecond laser inscribed fiber Bragg gratings in pure-silica suspended-core optical fibers have previously been demonstrated as a promising platform for high temperature sensing. However, the density of gratings that could be written on a single fiber was limited by undesired reflections associated with higher order modes in these high numerical aperture fibers. This resulted in a complex, broadband reflection spectrum with limited multiplexing capability. In this work we utilize modifications to the fine structure of the suspended core optical fibers to fine tune the relative confinement loss of the optical fiber modes, thus reducing the contribution from such higher order modes. The effects of these changes on mode propagation are modeled, giving a range of fibers with different confinement loss properties which can be tailored to the specific length scale of a desired application. We achieve single-peak reflections from individual fiber Bragg gratings, significantly improving performance for multipoint sensing and demonstrate this technique by writing 20 gratings onto a single fiber.

Simulation Study of Mid-infrared Supercontinuum Generation at Normal Dispersion Regime in Chalcogenide Suspended-core Fiber Infiltrated with Water

We report simulation results of supercontinuum generation in the suspended-core optical fibers made of chalcogenide (As2S3) infiltrated with water at mid-infrared wavelength range. Applying water-hole instead of the air-hole in fibers allows improving the dispersion characteristics, hence, contributing to supercontinuum generations. As a result, the broadband supercontinuum generation ranging from 1177 nm to 2629 nm was achieved in a 10 cm fiber by utilizing very low input pulse energy of 0.01 nJ and pulse duration of 100 fs at 1920 nm wavelength.

Tip Packaged High-Temperature Miniature Sensor Based on Suspended Core Optical Fiber

A tip packaged high-temperature miniature sensor constructed by a suspended-core optical fiber (SCF) is presented and experimentally demonstrated. An SCF with a short length spliced to the single-mode fiber (SMF) is utilized to build the Fabry-Perot interferometer (FPI). A section of SMF acting as a tip package is spliced to the end of the SCF, which gives the sensor immunity of the external refractive index (RI). The test processes of heating up and cooling down are repeated three times to evaluate the repeatability and hysteresis. The arithmetic means temperature sensitivity increases from 9.42 pm/ °C to 12.51 pm/ °C over the temperature range of 50–800 °C. Moreover, the maximum stability error is 5 °C within the high-temperature 800 °C duration period. This tip packaged sensor with simple fabrication, good repeatability, and good stability within a large dynamic range is advantageous to practical temperature measurement and massive production.

Experimentally and analytically derived generalized model for the detection of liquids with suspended-core optical fibers

Abstract A generalized model for the detection of liquids within suspended-core microstructured optical fibers has been experimentally and theoretically derived. The sensor detection is based on the refractometric principle of transmission losses due to the overlap of the evanescent field with the liquid analyte. A number of parameters, including fiber core diameter and filling length, have been included in the general model. Specially tailored suspended-core fibers were manufactured with the core diameters within the range of 2.4 μ m to 4.0 μ m. Five selected liquid analytes were used to cover the refractive index range of 1.35 to 1.42. Based on experiments, the characteristics of the parameters of the semi-empirical model have been determined by a genetic algorithm using 283 measurement data sets. The model can be used to design sensors for the detection of liquid analytes as it provides a set of parameters allowing to optimize the sensor’s sensitivity for a wide scale of applications. Finally, numerical simulations of the system were carried out by an eigenmode routine to support the results of the generalized model.

Microstructured optical fiber based chloride ion sensing method for concrete health monitoring

Chloride erosion is the main factor to decrease durability of concrete, it is fairly important to control and monitor chloride in concrete structure. A new sensor based on a suspended core optical fiber was developed to detect the chloride in concrete, in which lucigenin is selected as a fluorescence sensitive material for chloride. A novel type of the sol-gel membrane was introduced to immobilize lucigenin onto the inner wall of the suspended core optical fiber with dip-coating method. The properties of the sol-gel membrane were characterized by scanning electron microscope (SEM) and Fourier transforming infrared (FT-IR), and energy of evanescent field the suspended core optical fiber was calculated by using COMSOL. The fluorescence fluctuations of the optic fiber sensor are chloride concentration-dependent and the relationship between relative fluorescence intensity and chloride concentration follows the Stern–Volmer equation. The linear calibration formulas I0/I = 1 + 1.463[Cl−] (R2 = 0.973) and I0/I = 1 + 1.982[Cl−] (R2 = 0.984) with the detection limit of 0.02 M are obtained through detecting standard KCl solution and concrete simulated pore solution of KCl (pH = 13.5), respectively. Besides, specificity of the sensor is also tested.

Dispersion characteristics of a suspended-core optical fiber infiltrated with water.

In this paper we present a study on the dispersion characteristics in the suspended-core optical fibers made of borosilicate of NC21A glass infiltrated with water. Replacement of air with water results in dramatic improvement of the dispersion characteristics in the fibers, valuable in the process of supercontinuum generation. A near-zero flat dispersion can be achieved in the anomalous or normal dispersion range for various diameters of the core.

Detailed numerical investigation of the interaction of longitudinal acoustic waves with fiber Bragg gratings in suspended-core fibers

The interaction between longitudinal acoustic waves and fiber Bragg gratings in suspended-core optical fibers is numerically investigated. The fiber core size and the air hole size are varied, and the mechanical and grating properties are simulated by means of the finite element method and the transfer matrix method, respectively. Changes of the effective index, confinement factor, silica area, strain and wavelength shift induced by the acoustic wave are evaluated, and the resultant side lobe reflectivity is estimated. A side lobe reflectivity increase of 66% compared to standard fibers is estimated, which allows reducing the modulation index or the grating length in as much as 75%. Besides, the larger reduction of the required acoustic power for achieving the acousto-optic modulation points out to more efficient modulator devices in suspended-core fibers.

X-ray tomography for structural analysis of microstructured and multimaterial optical fibers and preforms.

Specialty optical fibers, in particular microstructured and multi-material optical fibers, have complex geometry in terms of structure and/or material composition. Their fabrication, although rapidly developing, is still at a very early stage of development compared with conventional optical fibers. Structural characterization of these fibers during every step of their multi-stage fabrication process is paramount to optimize the fiber-drawing process. The complexity of these fibers restricts the use of conventional refractometry and microscopy techniques to determine their structural and material composition. Here we present, to the best of our knowledge, the first nondestructive structural and material investigation of specialty optical fibers using X-ray computed tomography (CT) methods, not achievable using other techniques. Recent advances in X-ray CT techniques allow the examination of optical fibers and their preforms with sub-micron resolution while preserving the specimen for onward processing and use. In this work, we study some of the most challenging specialty optical fibers and their preforms. We analyze a hollow core photonic band gap fiber and its preforms, and bond quality at the joint between two fusion-spliced hollow core fibers. Additionally, we studied a multi-element optical fiber and a metal incorporated dual suspended-core optical fiber. The application of X-ray CT can be extended to almost all optical fiber types, preforms and devices.

Genotyping single nucleotide polymorphisms using different molecular beacon multiplexed within a suspended core optical fiber.

We report a novel approach to genotyping single nucleotide polymorphisms (SNPs) using molecular beacons in conjunction with a suspended core optical fiber (SCF). Target DNA sequences corresponding to the wild- or mutant-type have been accurately recognized by immobilizing two different molecular beacons on the core of a SCF. The two molecular beacons differ by one base in the loop-probe and utilize different fluorescent indicators. Single-color fluorescence enhancement was obtained when the immobilized SCFs were filled with a solution containing either wild-type or mutant-type sequence (homozygous sample), while filling the immobilized SCF with solution containing both wild- and mutant-type sequences resulted in dual-color fluorescence enhancement, indicating a heterozygous sample. The genotyping was realized amplification-free and with ultra low-volume for the required DNA solution (nano-liter). This is, to our knowledge, the first genotyping device based on the combination of optical fiber and molecular beacons.

Fabrication of multiple parallel suspended-core optical fibers by sheet-stacking

We demonstrate the fabrication of a novel type of optical fibers with multiple parallel air-suspended cores by the sheet-stacking method. Using this technique we have constructed optical fibers with up to 10 parallel micron-size suspended cores. No extra scattering loss from the fabrication process was observed in a fabricated dual air-suspended core fiber. The sheet-stacking method opens the way towards using a wide range of optical glasses for manufacturing multiple parallel suspended-core specialty optical fibers with novel optical functionalities such as dispersion tunability. Fusion splicing has also been successfully used to connect such a multiple core fiber with a conventional silica fiber.

Explosives detection by fluorescence quenching of conjugated polymers in suspended core optical fibers

In this work we demonstrate a suspended core microstructured optical fiber-based sensor platform for explosives detection based on the fluorescence quenching of a surface-attached conjugated polymer poly[2-methoxy-5-(2-ethylhexyloxy)-1,4-phenylenevinylene] (MEH-PPV). These fibers allow for strong evanescent field interactions with the surrounding media because of their small core size, and can sample minute liquid volumes. This is the first demonstration of a fluorescent conjugated polymer sensor capable of measuring liquid explosives samples loaded within an optical fiber. This technique is used to identify 1,4-dinitrobenzene (DNB), a member of the nitroaromatics family of explosives, in acetone for concentrations as low as 6.3ppm in a total sampling volume of 27nl and to quantify its concentration using the fluorescence decay lifetime, requiring an analysis time of only a few minutes.

Identification and Quantification of Explosives in Nanolitre Solution Volumes by Raman Spectroscopy in Suspended Core Optical Fibers

A novel approach for identifying explosive species is reported, using Raman spectroscopy in suspended core optical fibers. Numerical simulations are presented that predict the strength of the observed signal as a function of fiber geometry, with the calculated trends verified experimentally and used to optimize the sensors. This technique is used to identify hydrogen peroxide in water solutions at volumes less than 60 nL and to quantify microgram amounts of material using the solvent's Raman signature as an internal calibration standard. The same system, without further modifications, is also used to detect 1,4-dinitrobenzene, a model molecule for nitrobenzene-based explosives such as 2,4,6-trinitrotoluene (TNT).

Molecular beacons immobilized within suspended core optical fiber for specific DNA detection

We propose and experimentally demonstrate a new class of sensor for specific DNA sequences based on molecular beacons (MB) immobilized on the internal surfaces of suspended core optical fibers (SCF). MBs, a type of hairpin structured DNA probe, are attached on the surface of the SCF core using a fuzzy nanoassembly process used in conjunction with a biotin-streptavidin-biotin surface attachment strategy. The proposed DNA sensor detects complementary DNA sequences (cDNA) while discriminating sequences differing from the target by just one base. This enables the detection of DNA in unprecedentedly small sample volumes (nL scale) and is, to the best of our knowledge, the first specific DNA detection using a DNA probe immobilized within a microstructured optical fiber.

Sensing Free Sulfur Dioxide in Wine

Sulfur dioxide (SO2) is important in the winemaking process as it aids in preventing microbial growth and the oxidation of wine. These processes and others consume the SO2 over time, resulting in wines with little SO2 protection. Furthermore, SO2 and sulfiting agents are known to be allergens to many individuals and for that reason their levels need to be monitored and regulated in final wine products. Many of the current techniques for monitoring SO2 in wine require the SO2 to be separated from the wine prior to analysis. This investigation demonstrates a technique capable of measuring free sulfite concentrations in low volume liquid samples in white wine. This approach adapts a known colorimetric reaction to a suspended core optical fiber sensing platform, and exploits the interaction between guided light located within the fiber voids and a mixture of the wine sample and a colorimetric analyte. We have shown that this technique enables measurements to be made without dilution of the wine samples, thus paving the way towards real time in situ wine monitoring.

Nanoscale all-normal dispersion optical fibers for coherent supercontinuum generation at ultraviolet wavelengths

We report on the possibilities of nanoscale optical fibers with all-normal dispersion behavior for pulse-preserving and coherent supercontinuum generation at deep ultraviolet wavelengths. We discuss the influence of important parameters such as pump wavelength and fiber diameter, for both optical nanofibers and nanoscale suspended-core optical fibers. Simulations reveal that by appropriate combination of fiber geometry and input pulse parameters, intensive spectral components well below 300 nm are generated. In addition, the impact of preceding taper transitions used for input coupling purposes is discussed in detail.

Bending insensitivity of fiber Bragg gratings in suspended-core optical fibers

This Letter presents simulation and experimental results that explore bending insensitivity of fiber Bragg gratings in suspended-core optical fibers. The implementation of thin silica bridge in the fibers enhances index contrast of the fiber core and reduces bending-induced strain transfer to the fiber core. This fiber design lead to a reduction of over 7 times in strain-induced fiber Bragg grating resonant peak shifts in the suspended-core fiber compared with that in standard telecommunication fiber, and an 0.14 dB bending loss at a bending radius of 6.35 mm.

Suspended core tellurite glass optical fibers for infrared supercontinuum generation

We report the fabrication and characterization of tellurite TeO 2–ZnO–Na 2O (TZN) microstructured suspended core optical fibers (MOFs). These fibers are designed for infrared supercontinuum generation with zero dispersion wavelength (ZDW) at 1.45 μm. The measured losses at this wavelength are approximately 6 dB/m for a MOF with a 2.2 μm diameter core. The effective area of a particular fiber is 3.5 μm 2 and the nonlinear coefficient is calculated to be 437 W −1km −1. By pumping a 20 cm long fiber at 1.56 μm with a sub-nJ femtosecond laser source, we generate a supercontinuum (SC) spanning over 800 nm in the 1–2 μm wavelength range.

Experimental and Theoretical Study of Light Propagation in Suspended-Core Optical Fiber

We analyze coupling and propagation of light through a suspended-core microstructured optical fiber. Itis experimentally demonstrated that light-coupling efficiency and mode distribution strongly depend on relativepositionofthefiber’scoreandalightbeamandlightpolarization. Theexperimentalresultsaresupportedwithnumericalsimulations. Thedevelopednumericalmodelconfirmedalltheobserveddependences.PACSnumbers:42.70.Qs,42.81.Qb,42.81.

Sensing with suspended-core optical fibers

The development of optical fibers with suspended cores has enabled the demonstration of a range of powerful new techniques for chemical and biological sensing. Here the fabrication, design and application of this new class of fibers are reviewed. The performance and potential of sensors based on these fibers is evaluated, including dip sensors for sensing small sample volumes, exposed-core fibers for real-time and distributed measurements, and surface functionalized fibers for the specific detection of chemicals and biomolecules.