Helical core fibers (HCFs) suffer from low coupling efficiency and unavoidable excitation of higher order modes below the cutoff wavelength because of a core tilt with respect to the symmetry axis of ...the cladding. We propose an effective way of increasing the coupling efficiency to a HCF by untwisting its beginning section in a hydrogen flame. The proposed solution provides also a control over the excitation of higher order modes in HCFs and can be applied in splicing as well as in a free-space launching configuration. We experimentally demonstrate that by using the proposed method, the coupling efficiency between a SMF-28 and HCF can be increased to the level reachable for straight fibers, which is limited only by a modal fields mismatch. We also present detailed numerical and analytical studies of the coupling efficiency between a HCF and SMF versus the pitch distance in the partially untwisted input section of the HCF, which takes into account fundamental and higher-order modes.
Spectral multiplexing of biosensors in a single optical fiber has been a long-standing challenge, which we address here for the first time by combining photonic crystal fibers (PCF) with fiber Bragg ...grating technology. We exploit the features of the optical transmission spectrum of a straight fiber Bragg grating written in a PCF that allows exciting cladding mode resonances within a spectral span of about 60 nm, which is significantly narrower than the width of the transmission spectra of tilted gratings in standard single-mode step-index fibers. More specifically, we consider the cladding mode resonances that feature effective index values close to the refractive index of phosphate buffered saline, and we demonstrate plasmonic label-free biodetection of HER2 (human epidermal growth factor receptor 2) protein. We report on the simultaneous monitoring of the wavelength shifts of said cladding mode resonances from two spatially separated biofunctionalized Bragg gratings and we find that the PCF sensor is able to detect the protein concentration of 8.62 nM with high reproducibility.
•First demonstration of fiber biosensor spectral multiplexing with parallel readout.•Photonic crystal fiber (PCF) plasmonic biosensor for HER2 protein detection.•The PCF microstructure is dedicated for biosensing specifically.•Grating-assisted resonances occupy only ∼60 nm of the spectrum enabling multiplexing.•Multiplexing can allow multi-target detection or reduction of false-negative results.
•Spectral phase interrogated SPR fiber optic sensors was demonstrated.•The detection accuracy of the spectral phase method is improved up to 3 times compared to the conventional spectral method.•A ...special D shape optical fiber was employed allowed for direct metal deposition without extra preprocessing.
We demonstrate for the first time a fiber-optic surface plasmon resonance sensor employing the interrogation method based on spectral interferometric measurements of the phase shift between fiber polarization modes. The sensor was fabricated on a specially designed birefringent D-shape fiber made of silica glass, which exhibits modal birefringence of the order of 10−5 and allows for direct deposition of a metal layer in the vicinity of the core. The sensor characteristics measured using the spectral interferometry method were compared with the reference results obtained using the conventional spectral transmission method. The two measuring techniques show similar sensitivity of 2700 nm/RIU for the refractive index of external medium equal to 1.386, however, the detection accuracy of the interferometric method is up to 3 times better.
We report on a photonic crystal fiber with a large mode area designed for compact high power fiber lasers and amplifiers. The fiber suppresses higher order modes when bent around a 10-cm radius and ...enables single mode operation in small footprint laser and amplifier architectures. We experimentally confirm the peculiar bending properties of this fiber in its passive version, by reporting on the measurement results of fundamental mode loss in bent and straight fibers, and of the influence of the bending plane orientation on this fiber loss.
We report on a new phenomenon of light guidance in a fiber core created by an arrangement of holes making a partially open ring. In such structure there is no complete refractive index barrier to ...confine the light and therefore it cannot guide light if untwisted. However, if the open ring of holes is shifted off the symmetry axis of the twisted fiber then the mode confinement and low loss propagation is possible due to purely geometrical effect related to the increase in the optical path of light following the helical route. Properties of such structures, including confinement loss, modal field distribution, birefringence of fundamental modes were investigated both numerically and experimentally. We also studied the effect of bending, which leads to periodic modulation of the propagation characteristics of the twisted fiber. Furthermore, we demonstrate a possibility of displacement measurements based on bend-induced loss using some of the fabricated fibers, in which the sensitivity to bend is controlled by a twist rate and core structure.
In this study, 2,4,6-trichlorophenyl methacrylate (TClPhMA) was synthesized by the reaction of methacryloyl chloride with 2,4,6-trichlorophenol in the ice bath condition. The obtained monomer was ...extracted by chloroform and purified on a chromatography column. In order to confirm the chemical structure of the new compound, spectroscopic studies (ATR-FTIR,
1
H NMR,
13
C NMR and GC–MS) were undertaken. The obtained TClPhMA was copolymerized with commercially available monomers such as methyl methacrylate, styrene, 1,4-divinylbenzene and 2-hydroxymethyl methacrylate. The copolymers were obtained by bulk polymerization in which benzoyl peroxide was used as a free radical initiator. The thermal properties of the copolymers were investigated by differential scanning calorimetry and thermogravimetry.
In this article we present an all-fiber vector bend sensor by means of a self-fabricated micro-structured multicore optical fiber. The reported solution is based on differential intensity variations ...of the light transmitted along the cores whose changes are influenced by the bending angle and orientation. The unique asymmetric structure of the air-holes in the optical fiber provides each core with different confinement losses of the fundamental mode depending on the bending radius and orientation, making each of the cores bend-sensitive in a range of at least 80°. It has been experimentally demonstrated that the reported sensor enables the bending angle and orientation to be detected in a full range of 360° without any dead-zones, and the possibility of end point detection with millimeter precision. Additionally, a reconstruction of the bending vector has been carried out theoretically, and a good match can be observed between the experimental and theoretical data.
We present a PMMA birefringent fiber with enhanced polarimetric sensitivity to hydrostatic pressure, obtained by enlarging selected holes in the microstructured cladding. The fiber shows a linear ...response to pressure with small hysteresis in the pressure range up to 8.5 MPa and the sensitivity of 48 {\rm rad}/{\rm MPa}\cdot{\rm m} at 600 nm. The average temperature sensitivity measured in the range 22-40 ^{\circ}{\rm C} is 1 {\rm rad}/{\rm K}\cdot{\rm m} at 600 nm. The fiber, however, shows significant hysteresis increasing with the temperature range. We also present the results of numerical simulations of the birefringence and the sensitivity to pressure. The contribution of stress and deformation effects to the overall pressure sensitivity in the investigated PMMA fiber and the silica fiber of the same geometry is compared. This allows us to explain different signs of pressure sensitivity observed in silica and the PMMA fibers.
A novel type of voltammetric sensor – reusable, durable, long-term use gold microelectrodes array was presented, characterized and used for developing the procedure of Se(IV) determination by anodic ...stripping voltammetry. There was a double activation of working microelectrode carried out during the measurements that was ran at the potential of –1.5 V within 2 s at the start of the measurement and then after deposition step at –1.2 V within 1 s. Thanks to such a procedure an increase of Se(IV) peak current and a slight lowering of the background current was observed. The optimization of analytical procedure was performed. A calibration graph was linear in the range from 3 × 10–9 to 3 × 10–8 mol·L–1 (deposition time 180 s). The obtained detection limit for selenium ions determination following deposition time of 180 s was 8.3 × 10–10 mol·L–1. Repeatability of the method calculated as RSD for Se(IV) concentration of 3 × 10-8 mol·L–1 was 3.5% (n = 7). The proposed procedure was successfully applied for Se(IV) ions determination in water certified reference materials. Good recovery of Se(IV) from river water sample was also obtained.
A series of new functionalised carbonaceous materials were prepared by means of oxidation and ammoxidation of commercially available multi-walled carbon nanotubes. The effect of oxygen and nitrogen ...doping on the textural, surface as well as thermal properties of the prepared adsorbents was tested. The materials were characterized by elemental analysis, low-temperature nitrogen sorption, determination of the surface oxygen groups content as well as by coupled thermogravimetric and spectroscopic methods (TG/DSC/MS). Depending of the variant of raw nanotubes modification, the final products were oxygen- and nitrogen-doped materials of medium-developed surface area and mesoporous structure, showing highly diverse acidic-basic character of the surface, from the weakly acidic to slightly alkaline.
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