Tilted Fiber Bragg Grating Research Articles

Sensitivity improvement of reflective tilted FBGs

Tilted fiber Bragg gratings are used as energy couplers in which the core mode and cladding modes can be coupled together. Cladding modes have extensive importance in sensing applications due to their sensitive characteristics to the surrounding refractive index. The cladding modes are investigated theoretically by studying a three-layer model of optical fibers, whereas the core mode is investigated by studying a two-layer model of optical fibers. The analysis reveals that to increase the coupling of the energy transferred from the core mode to cladding modes, the cladding radius needs to be decreased. Such behavior is illustrated through studying the change in the electric field distribution and is used to improve the sensitivity of the sensing refractive index of the surrounding medium.

Plasmonic fiber-optic vector magnetometer

A compact fiber-optic vector magnetometer based on directional scattering between polarized plasmon waves and ferro-magnetic nanoparticles is demonstrated. The sensor configuration reported in this work uses a short section of tilted fiber Bragg grating (TFBG) coated with a nanometer scale gold film and packaged with a magnetic fluid (Fe3O4) inside a capillary. The transmission spectrum of the sensor provides a fine comb of narrowband resonances that overlap with a broader absorption of the surface plasmon resonance (SPR). The wavelength of the SPR attenuation in transmission shows high sensitivity to slight perturbations by magnetic fields, due to the strong directional scattering between the SPR attenuated cladding modes and the magnetic fluid near the fiber surface. Both the orientation (2 nm/deg) and the intensity (1.8 nm/mT) of magnetic fields can be determined unambiguously from the TFBG spectrum. Temperature cross sensitivity can be referenced out by monitoring the wavelength of the core mode resonance simultaneously.

Simultaneous Measurement of Liquid Level and Temperature Using Tilted Fiber Bragg Grating

We present a tilted fiber Bragg grating (TFBG)-based fiber optic sensor for the simultaneous measurement of liquid level and temperature. Due to different responses of cladding modes and core mode in TFBG spectrum to liquid level and temperature changes, both values can be measured independently. The examined 3.5° TFBG exhibits linear liquid level, as well as temperature, responses and sensitivities of −0.456 ± 0.009 dB/mm and 11.4 ± 0.2 pm/°C, respectively. In addition, greater sensor applicability is proposed for liquids having lower refractive indexes using TFBG with greater tilt angle. The presented system is capable of being applied in chemical, food, and automotive industries as well as, thanks to its all-fiber structure, in potentially hazardous environments where the immunity to electromagnetic fields or/and electric isolation is required.

Carbon nanotube-deposited tilted fiber Bragg grating for refractive index and temperature sensing

A tilted fiber Bragg grating (TFBG) deposited with carbon nanotube (CNT) is proposed to simultaneously measure the surrounding refractive index (SRI) and temperature. Assisted by the interaction between the CNT deposition layer and the TFBG’s cladding mode, the increase in SRI could significantly attenuate the coupling intensity of cladding modes, while the resonant wavelengths keep almost unchanged. Therefore, the temperature response of the CNT-deposited TFBG could be further obtained by tracking the shifted resonant wavelength. In addition, the CNT deposition greatly enhances the sensing capability in a low refractive index region of $1\sim 1.428$ , presenting great potentials in biochemical sensing.

倾斜光纤光栅研究进展

倾斜光纤光栅研究进展

Wavelength tunable TFBG based microwave sensor using surface plasmon resonance

A noble idea is used to propose a wavelength tunable tilted Fiber Bragg Gratings based microwave sensor using surface plasmon resonance. The Bragg wavelength shifts linearly about 6pm/°C, due to the temperature change. This temperature variation occurs because of the microwave–metal interaction at cladding layer of the optical fiber based proposed sensor. The wavelength tuning can be achieved by using tilted Fiber Bragg Gratings. To use the wavelength sources of 850nm, 1310nm and 1550nm, tiled Fiber Bragg Gratings with grating periods of 293.65nm, 452.56nm and 535.47nm respectively are required in the same fiber with certain distances among them.

Tilted Fiber Bragg Grating Sensors for Reinforcement Corrosion Measurement in Marine Concrete Structure

In this paper, the tilted fiber Bragg grating is proposed as a corrosion sensor and experimentally demonstrated for measuring and evaluating corrosion of steel rebars in wet conditions. To expedite the corrosion process, the impressed current technique was used to achieve a 28.9% mass loss in the rebar for a total time of 24 h. It is observed that the cladding resonant wavelengths red-shift during the corrosion process and the wavelength shifts are greater for higher order resonances. The proposed technique can be used for monitoring steel corrosion.

Compact Optical Fiber 3D Shape Sensor Based on a Pair of Orthogonal Tilted Fiber Bragg Gratings.

In this work, a compact fiber-optic 3D shape sensor consisting of two serially connected 2° tilted fiber Bragg gratings (TFBGs) is proposed, where the orientations of the grating planes of the two TFBGs are orthogonal. The measurement of the reflective transmission spectrum from the pair of TFBGs was implemented by Fresnel reflection of the cleaved fiber end. The two groups of cladding mode resonances in the reflection spectrum respond differentially to bending, which allows for the unique determination of the magnitude and orientation of the bend plane (i.e. with a ± 180 degree uncertainty). Bending responses ranging from −0.33 to + 0.21 dB/m−1 (depending on orientation) are experimentally demonstrated with bending from 0 to 3.03 m−1. In the third (axial) direction, the strain is obtained directly by the shift of the TFBG Bragg wavelengths with a sensitivity of 1.06 pm/με.

Highly sensitive detection of urinary protein variations using tilted fiber grating sensors with plasmonic nanocoatings

Surface plasmon resonance (SPR) optical fiber biosensors can be used as a cost-effective and relatively simple-to-implement alternative to well established bulky prism configurations for high sensitivity biological sample measurements. The miniaturized size and remote operation ability offer them a multitude of opportunities for single-point sensing in hard-to-reach spaces, even possibly in vivo. The biosensor configuration reported in this work uses a tilted fiber Bragg grating (TFBG) in a commercial single mode fiber coated with a nanometer scale silver film. The key point is that by reducing the silver film thickness to around 20–30nm (rather than 50nm for optimal SPR excitation), different modes of the TFBG spectrum present very high but opposite sensitivities to refractive index (RI) changes around the TFBG. Experimental results obtained with the coated TFBG embedded inside a microfluidic channel show an amplitude sensitivity greater than 8000dB/RIU (Refractive Index Unit) and a limit of detection of 10−5RIU. Using this device, the effect of different concentrations of protein in rat urine was clearly differentiated between healthy samples, nephropatic samples and samples from individuals under treatment, with a protein concentration sensitivity of 5.5dB/(mg/ml) and a limit of detection of 1.5×10−3mg/ml. Those results show a clear relationship between protein outflow and variations in the RI of the urine samples between 1.3400 and 1.3408, pointing the way to the evaluation and development of new drugs for nephropathy treatments. The integration of TFBGs with microfluidic channels enables precise measurement control over samples with sub-microliter volumes and does not require accurate temperature control because of the elimination of the temperature cross-sensitivity inherent in TFBG devices. Integration of the TFBG with a hypodermic needle on the other hand would allow similar measurements in vivo. The proposed optical fiber/microfluidic plasmonic biosensor represents an appealing solution for rapid, low consumption and highly sensitive detection of analytes at low concentrations in medicine as well as in chemical and environmental monitoring.

(Invited) Metallic Nanocoatings on Optical Fibers as a Sensor Platform

Deposition of gold metal on a tilted fiber Bragg grating (TFBG) demonstrates the utility of this optical fiber as a sensor for the conditions at the fiber's surface, including the continuity of a deposited metal film. Two precursors for the deposition of metallic gold are contrasted: gold(I) N'N'-dimethyl N,N”-diisopropylguanidinate (1) and gold(I) tert-butyl-imino-2,2-dimethylpyrrolidinate (2). Characterization of the deposition by optical fiber spectroscopy highlights the difference in thermal stability and growth rate of these two compounds. Compound 1 has a tremendous growth rate (220 nm/min) but is very thermally unstable, while 2 is much more thermally stable, and shows a lower growth rate of 1 nm/min.

Refractive index sensor based on combination of tilted fiber Bragg grating and waist-enlarged fusion bitaper

Refractive index measurement by using the combination of a tilted fiber Bragg grating (TFBG) and a waist-enlarged fusion bitaper (WEFBT) is proposed and demonstrated. The both devices can couple light between core and cladding modes with coupling coefficients depending on ambient refractive index. It is found that the proposed refractive index sensor offers two measurement ranges respectively from 1.333 to 1.428 and from 1.383 to 1.453 when different sensing segment is used, in addition to advantages of reflection operation mode and intensity-modulated measurement.

INVITED] Cell sensing with near-infrared plasmonic optical fiber sensors

Surface Plasmon resonance (SPR) optical fiber biosensors are a miniaturized counterpart to the bulky prism configuration that offer remote operation in very small volumes of analyte. They have the potential to yield in situ (or even possibly in vivo) molecular detection. They usually result from a gold-coated fiber segment for which the core-guided light is brought into contact with the surrounding medium. Recently, SPR excitation was achieved with tilted fiber Bragg gratings (TFBGs) photo-imprinted in the fiber core and surrounded by a thin gold layer. These gratings probe the surrounding medium with near-infrared narrowband (~100pm linewidth) resonances, which enhances both the penetration depth of the evanescent field in the external medium and the wavelength resolution of the interrogation. They also constitute the unique configuration able to probe all the fiber cladding modes individually, with high Q-factors. We use these unique spectral features in this work to target and detect extracellular membrane receptors in native membranes of different human epithelial cell lines. A differential diagnosis has been demonstrated between two systems, a cell line with overexpressed membrane receptors (the positive control) and another cell line with a low number of these receptors (a negative control). Such results bring an important step towards the demonstration of in situ diagnosis.

Graphene-coated tilted fiber-Bragg grating for enhanced sensing in low-refractive-index region.

We propose and experimentally demonstrate a method to significantly extend the sensitive window of tilted fiber-Bragg grating (TFBG) into low-refractive-index region with the integration of graphene coating. The coupling between cladding modes of TFBG and graphene coating results in an obvious modification of the cladding-mode envelope, which provides a sensitive regime relying on graphene's complex refractive index. Interacting the graphene-coated TFBG with various aqueous solutions, we observe strongly enhanced sensitivity in the low-refractive-index region of 1-1.428, which is about 10-fold extended from that of the unloaded TFBG. The graphene-coated TFBGs present great potentials in the biochemical sensing window.

Surface plasmon excitation at near-infrared wavelengths in polymer optical fibers.

We report the first excitation of surface plasmon waves at near-infrared telecommunication wavelengths using polymer optical fibers (POFs) made of poly(methyl methacrylate) (PMMA). For this, weakly tilted fiber-Bragg gratings (TFBGs) have been photo-inscribed in the core of step-index POFs and the fiber coated with a thin gold layer. Surface plasmon resonance is excited with radially polarized modes and is spectrally observed as a singular extinction of some cladding-mode resonances in the transmitted amplitude spectrum of gold-coated TFBGs. The refractometric sensitivity can reach ∼550 nm/RIU (refractive index unit) with a figure of merit of more than 2000 and intrinsic temperature self-compensation. This kind of sensor is particularly relevant to in situ operation.

Evanescently coupled optical fiber refractometer based a tilted fiber Bragg grating and a D-shaped fiber.

A novel tip-reflective and power-referenced refractometer based on strong fiber-to-fiber optical coupling for a large range of surrounding refractive index (SRI) (from 1.33 to 1.45) is proposed and experimentally demonstrated. A short D-shaped fiber stub is placed in parallel and close contact to another standard circular fiber containing a weakly tilted Bragg grating (TFBG). The TFBG couples the light from the circular fiber's core into its cladding where it remains guided. Apart from the direct light coupling over the contact interface, the evanescent field from the guided cladding modes penetrates the surroundings and reaches the D-fiber core by tunneling across the medium into which the fiber pair is located. The amount of tunneling depends strongly on the SRI so that the total amount of light collected by the D-fiber provides a measure of the SRI. Sensitivities ranging from ~1000 to 13000 nW/RIU (Refractive Index Unit) have been obtained and the result is independent of temperature (within +/-10 nW of uncertainty). The measurement can be temperature-referenced through measurement of the TFBG spectrum if needed.

Polarization-resolved sensing with tilted fiber Bragg gratings: theory and limits of detection

Polarization based sensing with tilted fiber Bragg grating (TFBG) sensors is analysed theoretically by two alternative approaches. The first method is based on tracking the grating transmission for two orthogonal states of linear polarized light that are extracted from the measured Jones matrix or Stokes vectors of the TFBG transmission spectra. The second method is based on the measurements along the system principle axes and polarization dependent loss (PDL) parameter, also calculated from measured data. It is shown that the frequent crossing of the Jones matrix eigenvalues as a function of wavelength leads to a non-physical interchange of the calculated principal axes; a method to remove this unwanted mathematical artefact and to restore the order of the system eigenvalues and the corresponding principal axes is provided. A comparison of the two approaches reveals that the PDL method provides a smaller standard deviation and therefore lower limit of detection in refractometric sensing. Furthermore, the polarization analysis of the measured spectra allows for the identification of the principal states of polarization of the sensor system and consequentially for the calculation of the transmission spectrum for any incident polarization state. The stability of the orientation of the system principal axes is also investigated as a function of wavelength.

(Invited) Metallic Nanocoatings on Optical Fibers as a Sensor Platform

Optical fibres are excellent platforms on which to build a sensor: they substrate is inexpensive, and produced in tonnes per year. The technology effectively couples light and materials, and employs inexpensive (telecommunication) tools to interrogate the results. We are working on a tilted fibre Bragg grating (TFBG) sensor using atomic layer deposition (ALD) to modify the surface interface (Figure 1). By printing a FBG into the core of an optical fibre, light “modes" that were confined to the core can be directed to the cladding interface. These light modes can then sense changes in this interface, and these changes can be read if the light is directed back into the core. Depositing nanoparticulate films onto the cladding surface alters the effect on these cladding modes. They undergo a wavelength shift and a "peak-to-peak" amplitude change that is significantly different than is seen in uncoated fibres. We have been exploring the deposition of copper, silver, and gold metal films on optical fibre surfaces and investigating the changes in the light modes. The changes in the light modes that interact at the fibre metal interface are sensitive to the surrounding index of refraction. So, by using a high-permittivity dielectric material between the fibre and the metal coating, the sensitivity can be changed. Thus, the sensor platform that will be discussed consists of an optical fibre coated in a high-K dielectric material, and then further decorated with metal nanoparticles. The dielectric material is typically deposited by ALD, and the metal is typically deposited by either chemical vapour deposition or atomic layer deposition. This presentation will cover an overview of the chemistry of the precursor compounds for thin film deposition, the film deposition processes, and an interpretation of the resulting sensing ability of the cladding light modes. The wavelength shift is stronger when the device experiences a higher surrounding refractive index (SRI). This happens at low thicknesses, and can be exploited as an SRI detector. Interestingly, there is a significant difference in the spectra for a monolayer of discrete nanoparticles compared to a connected metallic film, also making these devices useful for detecting conductive film deposition. Figure 1

Fiber-Optic SPR Immunosensors Tailored To Target Epithelial Cells through Membrane Receptors.

We report, for the first time, the use of a surface plasmon resonance (SPR) fiber-optic immunosensor for selective cellular detection through membrane protein targeting. The sensor architecture lies on gold-coated tilted fiber Bragg gratings (Au-coated TFBGs) photoimprinted in the fiber core via a laser technique. TFBGs operate in the near-infrared wavelength range at ∼1550 nm, yielding optical and SPR sensing characteristics that are advantageous for the analyses of cellular bindings and technical compatibility with relatively low-cost telecommunication-grade measurement devices. In this work, we take consider their numerous assets to figure out their ability to selectively detect intact epithelial cells as analytes in cell suspensions in the range of 2-5 × 10(6) cells mL(-1). For this, the probe was first thermally annealed to ensure a strong adhesion of the metallic coating to the fiber surface. Its surface was then functionalized with specific monoclonal antibodies via alkanethiol self-assembled monolayers (SAMs) against extracellular domain of epidermal growth factor receptors (EGFRs) and characterized by peak force tapping atomic force microscopy. A differential diagnosis has been demonstrated between two model systems. The developed immunosensors were able to monitor, in real time, the specific attachment of single intact cells in concentrations from 3 × 10(6) cells mL(-1). Such results confirm that the developed probe fits the lab-on-fiber technology and has the potential to be used as a disposable device for in situ and real-time clinical diagnosis.

High Resolution NIR TFBG-Assisted Biochemical Sensors

Tilted fiber Bragg gratings (TFBGs) have shown to be a suitable tool for exciting surface plasmon waves in a comparable manner as in typical attenuated total reflection Kretschmann configurations. In this paper, we present a comparative analysis of the characteristics of prism and grating configurations for generating surface plasmon resonance (SPR) for 800 and 1550 nm wavelengths. Results indicate that longer wavelength SPR may present advantages in sensing. Recent label-free biochemical sensing results using NIR TFBGs with and without SPR coatings demonstrate limits of detection ranging from the nM to the pM range without the need for thermal stabilization.

<italic>In-Situ</italic> Monitoring Method for Solution Volatilization Using Tilted Fiber Bragg Grating

A method for in-situ monitoring the solution volatilization without successive solution extraction based on tilted fiber Bragg grating (TFBG) is presented and experimentally demonstrated. By measuring and analyzing the uniquely enriched spectral characteristics of TFBG, the alcohol volatilization behavior in the binary solution of alcohol-glycerol has been illustrated. The evolution of alcohol volatilization shows a negative exponential trend. During the volatile time of 0 ~ 50 h, the alcohol concentration is reduced from 50% to 15.93%. Using this method, we can conveniently construct a real-time, remote, and in situ monitoring system for gas- and liquid-phase mass transfer, and it is capable of being employed in harsh environment because of its all-fiber structure.