This work reports the inscription and investigation of phase-shifted fiber Bragg gratings. A method for the inscription of such structures that makes it possible to vary the full width at half-maximum of the transmission notch in the reflection band within the range of 8–76 pm is proposed. The influence of the amplitude of the induced refractive index modulation and length of the formed structure on the studied parameter is investigated and analyzed. The results are presented as curves for data collected experimentally and theoretically. The investigation conducted in this study makes it possible to manufacture structures with known widths of the transmission notches, opening up a wide spectrum of possibilities to design optical elements based on such specific Bragg grating structures (e.g., fiber-optic sensors, tunable transmission filters, and demultiplexers).

Simulation results and experimental data on the operation of an inductively heated sensor of flow velocity, using fiber Bragg gratings as sensitive elements, are presented. The principle of operation of the sensor is based on the cross-correlation method. In the course of the experiment, it was possible to detect the transit time of the heat pulse between the temperature sensors from 0.2 to 0.5 s, which corresponds to the flow velocity in the range of 0.1–0.5 m/s.

The paper presents simulating and experimental results of flowmeter operation with induction heating, where fiber Bragg gratings were used as sensitive elements of temperature sensors. The operating principle of flowmeter based on cross-correlation method. During the experiment, it was detected time response of heat pulse from 0.2 s to 0.5 s that corresponds to a flow velocity range 0.1-0.5 m/s.

Tilted fiber Bragg gratings with different tilt angles have been inscribed in single-mode isotropic optical fiber with an increased photorefractivity using Talbot interferometer and KrF-excimer laser system. Their spectra are studied. Using a confocal laser scanning luminescent microscope the images of gratings in transmitted light were obtained. The calculated dependence of the slope angle of the grating recorded in the Talbot interferometer on the angle between the strokes of the interference pattern created in the interferometer and the transverse section of the optical fiber is experimentally verified.

The results of investigations of the spectral characteristics of chirped fiber Bragg gratings induced in an optical fiber using a Talbot interferometer and a KrF excimer laser system of the master oscillator-power amplifier type with enhanced coherence are presented. Dependences of the full width of the reflection spectrum at half maximum and the reflectivity of chirped fiber Bragg gratings on their length are obtained and analyzed. Through the inscription of seven superimposed chirped fiber Bragg gratings, a diffraction structure with a spectral width of 32 nm was obtained. In addition, a chirped fiber Bragg grating whose spectral response shape is almost rectangular is presented. (C) 2018 Optical Society of America

Subject of Research.The paper presents the study of effect that occurs when pressure is applied to the phase-shifted fiber Bragg gratings perpendicular to the fiber axis. Method. Fiber Bragg gratings inscription was performed using Talbot interferometer, and the introduction of a phase shift – by means of the electrical discharge of an arc fusion splicer. The excimer laser system was used as a radiation source. The change in the reflection spectra at different pressures on the optical fiber is measured. Main Results. Fiber Bragg gratings with a phase shift are obtained by the procedure that excludes the use of high-precision instruments during the phase-shift introduction step. Experiment results are given showing up the distance dependence between the local minima in the reflection spectrum of fiber Bragg grating with a phase shift on the applied mass arising as a result of the induced birefringence. It is shown that the change in spectral characteristics is related to the birefringence effect owing to stresses inside the fiber. As a result, the second local minimum appears in reflectance band. Practical Relevance. Research results can be used in creation of a sensing element of a fiber optic pressure sensor. This study demonstrates the application possibilities of Bragg gratings with a phase shift as sensing elements in fibe

С использованием интерферометра Тальбота и KrF

In this paper, we showed a technique for the formation of phase-shifted fiber Bragg gratings. The analysis of the efficiency of the obtained structures was carried out with the help of an optical spectrum analyzer with the subsequent calculation of the full width at half maximum of a bandpass in reflection spectrum. Fiber Bragg gratings inscription was performed on the Talbot interferometer, the KrF excimer laser system was used as a UV radiation source, and a phase shift was introduced by the electrical discharge of an arc fusion splicer. The experimental dependence between the length of the obtained structure and the full width at half maximum of a bandpass in reflection spectrum of a phase-shifted grating was presented, the value of the last parameter varies in the range from 24 pm to 96 pm.