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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]

In this paper we present a novel twist measurement technique based on the influence of changes in the input light polarization state on the tilted Bragg grating. In the proposed sensor with the interrogation method, changes in the amplitudes of high-order cladding modes are measured by wavelength-matched fiber Bragg grating filters working in reflection mode. The key element of the method is the use of parameters of two selected parts of one cladding mode that are in close proximity to each other. Application of appropriate technological parameters to the manufactured photonic structures of the sensor and interrogation filter elements allows to obtain high-resolution measurement with simultaneous immunity to temperature fluctuations. The differential character of the proposed method also provides independence from changes in the optical power of the illuminating light source. [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]

The tilted fiber Bragg grating (TFBG), as a versatile and robust tool for many sensing applications with a particular focus on vapor deposition processes, is reviewed. Recent work employing the TFBG as an optical probe for monitoring the metal-organic (MO)CVD of noble-metal, single-source precursors is discussed extensively. This work also establishes the broad scope that utilizes TFBGs and other optical fiber configurations to interrogate thin film growth and the associated optical properties. While it cannot possibly cover the full scope of applications with respect to the TFBG device, this review highlights the recent advances of TFBG-based sensing for CVD, and progress towards the applicability of TFBGs as evanescent field-based sensors. [ABSTRACT FROM AUTHOR]

The ubiquity and importance of anions in many crucial roles accounts for the current high interest in the design and preparation of effective sensors for these species. Therefore, a tilted fiber Bragg grating sensor was fabricated to investigate individual detection of different anion concentrations in ethyl acetate, namely acetate, fluoride and chloride. The influence of the refractive index on the transmission spectrum of a tilted fiber Bragg grating was determined by developing a new demodulation method. This is based on the calculation of the standard deviation between the cladding modes of the transmission spectrum and its smoothing function. The standard deviation method was used to monitor concentrations of different anions. The sensor resolution obtained for the anion acetate, fluoride and chloride is 79×10−5 mol/dm3, 119×10−5 mol/dm3 and 78×10−5 mol/dm3, respectively, within the concentration range of (39–396)×10−5 mol/dm3. [ABSTRACT FROM AUTHOR]

• Multiplex cross-sensitive have been implemented through the TFBGs manufacturing process. • Available sensors for biochemical and mechanical that can be caused by a controlled tilted angle and exposure dose. • TFBGs sensing spectra with particular emphasis on cladding, ghost, and Bragg mode have been proposed. The controllable cross-sensitivities of tilted fiber Bragg gratings (TFBGs) are strongly related to the control of the parameters during the manufacturing process. The TFBG spectrum characterization, which can demonstrate cross-sensitivities, is controlled by the process parameters. Cross-sensitivities analyses in biochemical surrounding refractive index (SRI) (cladding mode) and mechanical sensing (Bragg and ghost mode) are evaluated through processing parameters, including the rotating tilted angles of phase-mask, laser exposure dose time, and reducing fiber diameters. The results of this study show the cross-sensing ability in both biochemical and mechanical sensing that can be caused by a controlled tilted angle was 10° and exposure dose of five minutes while obtaining the cladding and Bragg modes of TFBGs with broad spectral coverage. [ABSTRACT FROM AUTHOR]

A simple refractive-index fiber sensor based on a tilted Bragg fiber grating (TFBG) interacting with multimode fiber (MMF) is described. The sensor structure is formed by insertion of a small section of MMF between the single-mode fiber and the TFBG. The average reflective power in the cladding modes of the TFBG reflected a different power as the surrounding refractive index changes, while the power of the reflected Bragg mode keeps unchanged. Therefore, the power of the reflected Bragg mode can be used as a reference to compensate any possible fluctuation of the light source power. © 2010 Wiley Periodicals, Inc. Microwave Opt Technol Lett 52: 1375–1377, 2010; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.25178 [ABSTRACT FROM AUTHOR]

Abstract: A new type fiber bending sensor based on a tilted fiber Bragg grating (TFBG) interacting with a multimode fiber (MMF) is presented. The sensing head is formed by insertion of a small section of MMF between a single-mode fiber (SMF) and the TFBG. The average reflective power in the cladding modes decreases with the increase of curvature. The measurement range of the curvature from 0 to 2.5m−1 with a measurement sensitivity of −802.4nW/m−1 is achieved. The proposed sensor is also proved as temperature-independent from the experimental investigation. [Copyright &y& Elsevier]

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]

We report on the study of an intensity-based optical fiber sensor for gasoline quality monitoring. The sensor setup employs two Bragg gratings with different spectral responses to interrogate the optical response of a tilted Bragg grating. The sensor operation is based on the tilted Bragg grating sensitivity to external refractive index changes, which are translated as power variations by the interrogation scheme. Gasoline–ethanol solutions with concentrations ranging from 0% to 60% ethanol were used to demonstrate the sensor performance. The results allowed to estimate that the sensor is able, within its resolution limit, to detect ethanol concentration variations of 1.5% in gasoline–ethanol solutions and discriminate temperature variations of 0.5 °C. The all-optical sensor setup is compact and robust, making it a competitive alternative for the realization of fuel quality analyses in practical applications. [ABSTRACT FROM AUTHOR]

A new design for a hybrid fiber‐planar refractive index sensor based on the surface plasmon resonance effect is presented. The key element of the design is a thin layer of gold covering a tilted fiber Bragg grating. In the study, a specially developed microfluidic chip is used to perform measurements directly in the flow of the investigated liquid. Rigidly mounting the sensor to the base of the fluid chip is proposed. The presented experimental data demonstrate the high stability of the sensor readings and the low noise level during measurements in a liquid flow. The proposed construction is a promising decision for application in compact immunoassay systems based on microfluidic technologies. A new design of a combined fiber‐planar plasmon sensor is presented. The sensor based on tilted fiber Bragg grating is integrated into a microfluidic chip channel, and rigidly mounted to the chip base along the entire length. High stability of the sensor readings and the low noise level during measurements are demonstrated. This design is perspective for different lab‐on‐chip applications. [ABSTRACT FROM AUTHOR]