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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.

In this paper, we studied the basic characteristics of tilted fiber Bragg gratings (TFBGs), inscribed line-by-line. Experimental results showed that if the TFBGs were located within different planes parallel to the fiber axis, the spectra performed differently. For 2°TFBG, if it was located near the central plane, the Bragg resonance was stronger than ghost mode resonance, and the order reversed if it was located near the boundary between core and cladding. As the tilted angle increased, the range of cladding mode resonance increased. When the tilted angle was larger than 12°, the birefringence effect was observed. Based on the birefringence phenomenon, torsion characteristics were experimentally studied; the sensitivity was about 0.025 dB/degree in the linear variation range. The harmonic order of TFBGs also affected the transmission spectrum. Leaky mode resonance was observed in the 8th order TFBG, and torsion (or polarization) influenced the spectrum of the 8th order TFBG. Our research represented the theory of line-by-line inscribed TFBGs and provided an inscription guidance for TFBGs.

Surface plasmon resonance-based fiber-optic sensors are of increasing interest in modern sensory research, especially for chemical and biomedical applications. Special attention deserves to be given to sensors based on tilted fiber Bragg gratings, due to their unique spectral properties and potentially high sensitivity and resolution. However, the principal task is to determine the plasmon resonance wavelength based on the spectral characteristics of the sensor and, most importantly, to measure changes in environmental parameters with high resolution, while the existing indirect methods are only useable in a narrow spectral range. In this paper, we present a new approach to solving this problem, based on the original method of determining the plasmon resonance spectral position in the automatic mode by precisely calculating the constriction location on the transmission spectrum of the sensor. We also present an experimental comparison of various data processing methods in both a narrow and a wide range of the refractive indexes. Application of our method resulted in achieving a resolution of up to 3 × 10−6 in terms of the refractive index.

Optical fibers are of growing interest for biosensing, especially for point-of-care and biomedical assays. Their intrinsic properties bestow them sought-after assets for the detection of low concentrations of analytes. Tilted fiber Bragg gratings (TFBGs) photo-inscribed in the core of telecommunication-grade optical fibers are known to be highly-sensitive refractometers. In this work, we present different strategies to use them for label-free immunoassays. Bare, gold-sputtered, gold-electroless-plated (ELP) and hybrid configurations are biofunctionalized with antibodies, aiming at the detection of cancer biomarkers. We discuss the relative performances of the tested configurations and show that each leads to singular key features, which therefore drives their selection as a function of the target application. The most sensitive configuration presents a limit of detection of 10−12 g/mL in laboratory settings and was successfully used ex vivo in freshly resected lung tissues.

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.