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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]

The apparent increase in magnetic field measurement has led to a growing demand for new sensing technologies. However, a long-lasting challenge unaddressed is how to achieve ultrahigh sensitive magnetic field measurement in both amplitude and orientation. Here, we demonstrate a compact-in-size and simple-to-implement fiber-optic magnetometer for highly sensitive vector magnetic field measurement. The sensor is based on magnetic nanoparticles coated tilted fiber Bragg grating inscribed in a commercial single mode fiber. The sensing mechanism stems from the backward coupled cladding mode resonances with narrow bandwidth (Q factor > 104), which is highly sensitive to slight surface refractive index perturbation. The switching of the magnetic field direction on the surface of fiber induces redistribution of coated magnetic nanoparticles with spatial anisotropy density and scattering by formation of magnetic chains hereafter the effective index is changed, which in turn modulates the cladding mode resonance with wavelength shift and amplitude attenuation. Through calculating the peak-to-peak intensity of target cladding modes of TFBG, the external magnetic field was precisely measured with an intensity sensitivity of 0.39 dB/mT and a direction sensitivity of 0.038 dB/rad. The inherent core mode can be used as a reference to get rid of temperature crosstalk and light source disturbance. The proposed sensor is compact in size and easy to be used in hard-to-reach place, showing good potentials for industrial applications. [ABSTRACT FROM AUTHOR]

This study proposes a refractive index sensor based on tilted fiber Bragg gratings (TFBGs) that connect metal-reflective spherical ends. The proposed fabrication method enables it to reflect light to increase the overall energy spectrum. We used the end of the fiber with a spherical shape and the coating reflective metal to compare the reflective energy in TFBGs. The reflective technique was employed to deposit nickel (Ni) and silver (Ag) onto the surface of the spherical end of TFBGs to precisely form the spherical-shaped tilted fiber Bragg gratings (STFBGs). The Ni-covered NiSTFBG sensor had an average sensitivity of 8.028 nm/RIU wavelength, which is a 1.64-fold improveme nt. The result shows the backward reflected wave is reflected by the metal layer has improved performance for the wavelength and transmission loss via the reflected metal spherical-shaped end of tilted fiber Bragg gratings. [ABSTRACT FROM AUTHOR]

This study proposes a refractive index sensor based on tilted fiber Bragg gratings (TFBGs) that connect metal-reflective spherical ends. The proposed fabrication method enables it to reflect light to increase the overall energy spectrum. We used the end of the fiber with a spherical shape and the coating reflective metal to compare the reflective energy in TFBGs. The reflective technique was employed to deposit nickel (Ni) and silver (Ag) onto the surface of the spherical end of TFBGs to precisely form the spherical-shaped tilted fiber Bragg gratings (STFBGs). The Ni-covered NiSTFBG sensor had an average sensitivity of 8.028 nm/RIU wavelength, which is a 1.64-fold improveme nt. The result shows the backward reflected wave is reflected by the metal layer has improved performance for the wavelength and transmission loss via the reflected metal spherical-shaped end of tilted fiber Bragg gratings. [ABSTRACT FROM AUTHOR]

Multicore optical fibers are of great interest in the optical sensing field. Their core diversity and spatial distribution enable the development of sensing mechanisms that are not possible in single-core fibers. In this paper, we study the use of the inter-core crosstalk phenomena for the implementation of a surrounding refractive index (SRI) sensor. The selective inscription of a tilted fiber Bragg grating (TFBG) intentionally increases the inter-core crosstalk between the inscribed cores and makes it sensitive to the SRI. With this technique we simplify the measurement of the SRI and improve the identification and tracking of the excited cladding modes, as compared with the analysis of the transmission spectrum of a TFBG in single-core fibers. The proposed device is also sensitive to temperature. Temperature is obtained from the crosstalk wavelength shift with a measured sensitivity of 9.75 pm/°C. The SRI is obtained from the measurement of the crosstalk optical power. For increasing SRIs the cladding modes gradually fade, reducing the crosstalk optical power. We observed that the higher the tilt, the higher the sensor sensitivity. For a 7° TFBG the SRI sensitivity obtained is −74.2 dB/RIU from 1.31 to 1.39 and −250.8 dB/RIU from 1.39 to 1.44. [ABSTRACT FROM AUTHOR]

A reflective fiber-optic refractometer based on a broadband cladding-to-core recoupling for a wide range of refractive index measurement is proposed and experimentally demonstrated. The sensing probe contains a tilted fiber Bragg grating (TFBG) together with an in-fiber “cladding” mirror upstream. The “cladding” mirror is made by a 0.3-μm-thick gold film with a transparent aperture to permit all the core-guided light go through but reflect the light in the cladding. The downstream TFBG couples the forward propagating core mode to backward propagating cladding modes and such cladding modes are reflected to the TFBG again by the in-fiber “cladding” mirror and recoupled to the fiber core through the same TFBG. With this special design, all the transmitted cladding modes now can be effectively monitored in reflection. Compared with the reported “in-fiber” and “fiber-to-fiber” coupling TFBG refractometer, our sensor demonstrates a much broader surrounding refractive index operating range with a very linear sensitivity of 528 nm/RIU. A tunable laser is used to improve the measured accuracy and a sensitivity of 7973 dB/RIU was obtained, with a limit of detection of 10−6 RIU. The sensor works with very controllable cross-sensitivities because the core mode is temperature dependent but insensitive to surrounding refractive index. [ABSTRACT FROM AUTHOR]

A sensitivity-enhanced strain sensor constructed by a 7-mm-long thin-core fiber (TCF) splicing with a 10-mm-long tilted fiber Bragg grating (TFBG) was proposed. The modal interferometer formed by the TCF will interact with the spectrum of the TFBG to form an overlapped spectrum, which will extremely increase the axial strain sensitivity of the TFBG. Experimental results showed that the wavelength shifts of the resonant dip in the overlapped spectra for the applied axial strain have a high sensitivity of 0.67 pm/ $\mu \varepsilon $. Meanwhile, the proposed sensor has the temperature self-compensation function for the variation of the external temperature simply by measuring the relative wavelength shifts of the Bragg mode of the TFBG. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM PUBLISHER]

In this letter, we propose a novel method of edge filter linear demodulation using tilted fiber Bragg gratings (TFBGs) in a fiber sensor system. Based on the filter characteristics of TFBGs and the same temperature characteristics as the FBG, the strain sensor demodulation system with dynamic temperature compensation can be achieved. An experimental system is built up to achieve one or multichannels of sensor demodulation. The experimental results were analyzed in detail. Using this method based on intensity, linear demodulation with a bandwidth of 6 nm can be achieved. The advantages of this system are an all-fiber design, quasi-static and dynamic operation, and potential high-speed demodulation. [ABSTRACT FROM PUBLISHER]

This work reports on the experimental investigation of the spectral effects induced by uniform high refractive index nano-coatings deposited on weakly tilted fiber Bragg gratings (TFBGs). To this aim, weakly TFBGs with different tilt angles were fabricated and then coated with thin overlays of syndiotactic polystyrene. Automated dip coating technique was used to obtain ring-shaped coatings with thickness ranging in hundreds of nanometers. The transmission spectra of the obtained devices were collected in order to outline the effects of thickness, tilt angle, and surrounding refractive index. Experimental results reveal interesting differences with respect to the uncoated case, both in terms of spectral envelope and wavelength shifts related to cladding modes coupling. [ABSTRACT FROM PUBLISHER]

A wavelength monitor based on a pair of tilted fiber Bragg gratings is reported. The monitor exhibits a subpicometer wavelength selectivity over a broad wavelength range (>30 nm), and a low insertion loss (<1 dB) for laser light with polarization matching the reference polarization of the device. Simulations show that a wavelength coverage up to 100 nm is possible and that the resolution degradation due to changes in the polarization state can be avoided by proper design of the gratings. [ABSTRACT FROM PUBLISHER]

A novel method for measuring modal power distribution (MPD) in multimode fibers is proposed using built-in tilted fiber Bragg gratings (TFBGs). For each degenerated guided mode group, a portion of the guided power can be coupled to the corresponding radiation mode through a TFBG imprinted into the same fiber, and then measured separately with a spatial filter. The power coupling coefficients between the guided and radiation modes are obtained by solving a set of linearly independent equations acquired under a number of launching conditions. With these coefficients obtained, the MPD under any excitation condition can then be obtained by simply measuring the powers of radiation modes. The proposed method is successfully demonstrated with a few-mode fiber. [ABSTRACT FROM PUBLISHER]