Search

Plasmonic tilted fiber Bragg gratings (TFBGs) have emerged as versatile tools for refractometric analyses and biochemical sensing. Their applications have significantly blossomed these last years, from proteins and cellular bioassays to operando monitoring in batteries, to cite just a few. They are widely recognized for their cutting‐edge performance and low limits of detection, arising from their dense multimodal spectral nature featuring tens of narrowband cladding mode resonances. Their comb‐like spectrum is so rich that numerous demodulation techniques have been reported, without benchmark of their relative performance while they possess important distinctions. This review highlights developments in detangling techniques from the pioneering works based on single‐peak analysis up to the most recent approaches involving Fourier analysis, the implementation of machine learning, and cascaded spectral decomposition processes. To fairly compare the different techniques of the literature, we implemented each analysis on original experimental refractometric calibrations, revealing the assets of the most updated methods. This paper therefore reviews these demodulation techniques based on the same datasets, obtained under the same conditions. We show and discuss the results obtained from bioassays and pinpoint the importance of advanced analytical methodologies to maximize the reproducibility, reliability and performance of plasmonic‐based TFBGs biosensors. [ABSTRACT FROM AUTHOR]

This article proposes an unequivocal method of labeling and numbering the cladding modes propagating in single-mode opticalwaveguides with tilted periodic structures. The unambiguous determination of individual propagating modes in this type of optical fiber is crucial for their use in sensory systems. The selection of the appropriate spectral range and mode determines the sensitivity and measuring range of tilted fiber Bragg grating (TFBG) sensors. The measurement methods proposed by individual research teams using TFBGs as transducers are usually based on the selection of specific modes. Unification of the labeling of modes and their numbering enables comparison of the basic metrological parameters of individual measurement methods and reproduction and verification of the proposed sensors and methods in the laboratories of other scientific and research centers.

Featured Application: The research results could find applications in many areas where measurement of bending radius or distance between elements is required in harsh environments with explosion danger or in flammable gases atmospheres. The use of optical fibers and light as a information medium eliminates the danger of sparks and explosions as a results. In this article we deal with the influence of polarization on determining the bending radius in TFBG (tilted fiber Bragg grating) sensors. The spectrum of TFBG structures changes under the influence of many factors at the same time. In the case of bending radius measurements, additional factors may be the temperature and polarization state of the introduced light. So far, only the cladding mode envelope algorithm has been used to determine the bending radius. An interesting issue seems to be establishing the influence of cross-sensitivity of the spectrum on changes in polarization during bending measurements. In addition to the envelope algorithm, algorithms for spectral length and average deviation from the local mean were examined. As a result of the analysis of experimental data, it was found that the level of polarization's influence on the result may be significant in determining the bending radius. Reducing the influence of polarization can be achieved by using algorithms providing wavelength parameters. Additionally, in order to reduce the influence of polarization, we proposed the use of the PLS (partial least squares regression) algorithm for the processed spectrum. [ABSTRACT FROM AUTHOR]

This article proposes an unequivocal method of labeling and numbering the cladding modes propagating in single-mode opticalwaveguides with tilted periodic structures. The unambiguous determination of individual propagating modes in this type of optical fiber is crucial for their use in sensory systems. The selection of the appropriate spectral range and mode determines the sensitivity and measuring range of tilted fiber Bragg grating (TFBG) sensors. The measurement methods proposed by individual research teams using TFBGs as transducers are usually based on the selection of specific modes. Unification of the labeling of modes and their numbering enables comparison of the basic metrological parameters of individual measurement methods and reproduction and verification of the proposed sensors and methods in the laboratories of other scientific and research centers. [ABSTRACT FROM AUTHOR]

In this paper, we proposed a high-sensitive glucose sensor using the tilted fiber Bragg gratings (TFBGs). The TFBGs with different tilt angle has been fabricated by phase mask scanning method with an argon ion double-frequency 244 nm laser. As tilt angle increases, the bandwidth of the cladding mode excited by TFBGs gradually expands and cladding mode region shifts towards shorter wavelengths. The higher-order cladding modes appeared at the shorter wavelength side demonstrate a larger separation in the spectrum. TFBGs with different tilt angles for glucose concentration measurement have been investigated experimentally. When the concentration of glucose solution increases, the surrounding refractive index changing make the cut-off mode resonance shift to a longer wavelength. In addition, the tilt angle of TFBGs does affect the glucose sensitivity, that the larger tilt angle is, the higher sensitivity could achieve. In this work, a maximum glucose sensitivity of 80.91 pm/(mg/ml) could be obtained for TFBGs with tilt angle of 10°. The proposed TFBGs with superiorities of high glucose sensitivity and wider detection range, makes it potential for glucose detection in the field of chemical and biomedical sensing. • A high-sensitive glucose sensor based on tilted fiber Bragg gratings (TFBGs) is proposed, with detailed spectral analysis. • The cut-off mode resonance shows a red-shift with glucose concentration increasing, proving the potential in glucose detection. • The glucose sensitivity of TFBGs varies with tilt angle, which could achieve 80.91 pm/(mg/ml) with 10° TFBGs. [ABSTRACT FROM AUTHOR]

In this article we deal with the influence of polarization on determining the bending radius in TFBG (tilted fiber Bragg grating) sensors. The spectrum of TFBG structures changes under the influence of many factors at the same time. In the case of bending radius measurements, additional factors may be the temperature and polarization state of the introduced light. So far, only the cladding mode envelope algorithm has been used to determine the bending radius. An interesting issue seems to be establishing the influence of cross-sensitivity of the spectrum on changes in polarization during bending measurements. In addition to the envelope algorithm, algorithms for spectral length and average deviation from the local mean were examined. As a result of the analysis of experimental data, it was found that the level of polarization’s influence on the result may be significant in determining the bending radius. Reducing the influence of polarization can be achieved by using algorithms providing wavelength parameters. Additionally, in order to reduce the influence of polarization, we proposed the use of the PLS (partial least squares regression) algorithm for the processed spectrum.

Surface plasmon (SP) excitation in metal-coated tilted fiber Bragg gratings (TFBGs) has been a focal point for highly sensitive surface biosensing. Previous efforts focused on uniform metal layer deposition around the TFBG cross section and temperature self-compensation with the Bragg mode, requiring both careful control of the core-guided light polarization and interrogation over most of the C + L bands. To circumvent these two important practical limitations, we studied and developed an original platform based on partially coated TFBGs. The partial metal layer enables the generation of dual-comb resonances, encompassing highly sensitive (TM/EH mode families) and highly insensitive (TE/HE mode families) components in unpolarized transmission spectra. The interleaved comb of insensitive modes acts as wavelength and power references within the same spectral region as the SP-active modes. Despite reduced fabrication and measurement complexity, refractometric accuracy is not compromised through statistical averaging over seven individual resonances within a narrowband window of 10 nm. Consequently, measuring spectra over 60 nm is no longer needed to compensate for small temperature or power fluctuations. This sensing platform brings the following important practical assets: (1) a simpler fabrication process, (2) no need for polarization control, (3) limited bandwidth interrogation, and (4) maintained refractometric accuracy, which makes it a true game changer in the ever-growing plasmonic sensing domain.

Gold-coated tilted fiber Bragg gratings (TFBGs) have been highly studied over the last years, mainly for biosensing purposes. They present a comb-like spectrum of narrow-band cladding mode resonances that is often demodulated by tracking the change of a selected peak. In this paper, we report a twentyfold more sensitive demodulation method based on the intersection of the upper and lower envelopes of gold-coated TFBG spectra. This method has been successfully applied in biosensing experiments towards the detection of HER2 (Human Epidermal Growth Factor Receptor-2) proteins, a relevant biomarker for breast cancer. Practical improvements have also been implemented. First, a uniform FBG has been superimposed on the TFBG to reduce the read-out wavelength span to 10 nm instead of 70 nm while keeping the temperature-compensated measurements. Second, a micro-fluidic system has been implemented to smoothly deliver the samples to the sensor. These 3 originalities make this sensing platform even more attractive for use in practical applications. [ABSTRACT FROM AUTHOR]

• Machine learning approach for automatic estimation of responses using different TFBGs. • Estimation based on the optical spectral characteristics of TFBGs as a function of RI. • Root mean squared errors as small as 0.008 RIU for the trained samples. • The approach can be used to enhance the reproducibility of large set of TFBG sensors. This paper presents the development of an approach for automatic estimation of the regression coefficients as a function of the refractive index (RI) in Tilted Fiber Bragg Gratings (TFBGs) based on their optical spectral characteristics. The methodology is based on machine learning approach, where different samples are analyzed in various test conditions to obtain a dataset for the training of a kNN regression algorithm. In this case, the spectral characteristics related to the wavelength spacing between adjacent cladding mode resonances, number of valleys and amplitude of the normalized spectra are correlated with the linear regression algorithm for RI estimation using the machine learning approach. The analysis are performed as a function of the wavelength shift and optical power, considering two regions on the transmitted spectrum and the envelope of the curve. Furthermore, the number of valleys and the area of the envelope curve are also analyzed as a function of the refractive index, which result in six analyzed features. The Principal Components Analysis (PCA) is used to reduce the number of features to two principal components. The results of the proposed algorithm are obtained with different trained and untrained samples, which indicates a root mean squared error (RMSE) of around 0.003 RIU for the trained samples and 0.008 RIU for the untrained ones. Therefore, the results indicate the usefulness of the proposed approach, which can be used to enhance the reproducibility of large set of TFBG sensors in practical applications. [ABSTRACT FROM AUTHOR]

• The GSST-TFBG has an extended SRI range, and the resonance amplitudes remain strong and detectable beyond the cut-off point. • The s-mode resonances are practically insensitive whereas the p-mode remains sensitive to the changes of SRI. • Refractive index measurement for transformer oil using GSST-coated TFBG. In this work, a tilted fiber Bragg gratings coated with a 130 nm thick Ge-Sb-Se-Te (GSST) layer, a high refractive index soft glass had been fabricated and demonstrated for the refractometric test of transformer oil. The findings indicated that the introduction of the high refractive index coating had enhanced the polarization property and extended the refractive index detection range of the tilted fiber Bragg gratings beyond the cut-off point of the cladding modes. In the experiment with transformer oils, the Ge-Sb-Se-Te -coated tilted fiber Bragg gratings has shown a good linear sensitivity of 9.952 dB/RIU for the refractive index range of 1.472–1.484 RIU. [ABSTRACT FROM AUTHOR]

The paper reports on the results of the development of tilted fiber Bragg grating-assisted selective biosensors. The main sensing principle is based on the dependence of an optical evanescent field parameters on the composition of the medium under study. Sensors feature functional coatings of antibodies against protein molecules common in blood composition – fibrinogen and D -dimer. The work explores and clearly demonstrates the selective sensitivity of sensors to specific proteins by the example of simultaneous measurements using a pair of sensors functionalized with different antibodies. [Display omitted] • Fiber sensors with functional coatings provide for specific detection of proteins. • Complex processes in biological solutions affect the refractive index unpredictably. • Differential signal of two similar sensors could be used as a mean of detection. • Specific binding of an antigen to a functional coating can change layers' geometry. [ABSTRACT FROM AUTHOR]

• The method for refractive index measurement using cascaded TFBGs is presented. • Proposed method allows to significant reduction of interferences from input light polarization. • Sensitivity of proposed setup is compared to conventional setup. • Influence of the input light polarization is reduced by 90% compared to single TFBG. This paper presents a possibility to improve the reliability of the measurement of the liquid solution refractive index using tilted fiber Bragg gratings (TFBGs) under various inputs of light polarization angle. The application of a specialized setup of cascaded TFBGs provides a great improvement in the stability of cladding resonances under various light polarization. In the present paper, the analysis of the amplitude of the cut-off cladding mode shows that the dependence of this parameter in the case of the proposed structure is reduced by 96.101% compared with a single TFBG with the same internal tilt angle of 7° and a depth of periodic refractive index perturbations. Stabilization of the spectra under various polarizations of inputted light could be observed in the case of all cladding modes, which could be used to improve the surrounding refractive index (SRI) measurement over a wider range. [ABSTRACT FROM AUTHOR]