The paper demonstrates the research of a fiber Bragg gratings inscription method including translation of a laser beam relative to a phase mask. Passing laser radiation through a phase mask results in diffraction into +1 and −1 orders, which makes it possible to inscribe FBGs inside a fiber core and the laser beam translation allows to obtain long apodized gratings. For each Bragg grating, the dependences of optical characteristics on the parameters of laser radiation are established. The result of inscription FBGs to obtain laser generation is presented in the article as well.

Subject of study. A fiber-optic Fabry-P & eacute;rot interferometer (FPI) with an air cavity between the resonator mirrors is studied. Aim of study. A fiber-optic FPI with an air cavity between the resonator mirrors is designed and fabricated, achieving an increase in the visibility of the interference pattern and the free spectral range. Method. The FPI contains two collimating structures with resonator mirrors coaxially aligned and separated along the optical axis. Each structure includes a coaxially connected optical fiber and a gradient lens formed by a section of a multimode gradedindex optical fiber. The opposite polished end face of the gradient lens with a reflective coating forms the reflective surface of the interferometer resonator. Main results. Interferometer samples with air cavity lengths ranging from 0.5 mm to 5 mm (increased in 0.5 mm steps) were fabricated. The visibility of the interference pattern in the wavelength range of 1300-1310 nm ranged from 0.989 to 0.679, and the free spectral range ranged from 1.707 nm to 0.178 nm. Practical significance. The developed interferometer can be applied as a sensing element in a refractive index sensor for measuring the refractive indices of gases and liquids in the range from 1 to 1.47 with a sensitivity of 190.4 pm/RIU. (c) 2026 Optica Publishing Group. All rights, including for text and data mining (TDM), Artificial Intelligence (AI) training, and similar technologies, are reserved.

We present the results of using a domestically produced component base for the creation of subcarrier wave quantum communication systems. It is shown that such systems demonstrate a quantum bit generation rate of about 10 kbit/s with a channel loss of 1 dB and quantum error coefficient below 3

Subject of study. In this study, a method for dynamic weighting of moving objects by optical power registration using fiber Bragg gratings is investigated. The aim of the study is to develop and validate a method for measuring the parameters of moving objects under laboratory conditions. Method. The developed method is based on registering the change in optical power reflected from a sensing element (SE) composed of two fiber Bragg gratings (FBGs) and a chirped fiber Bragg grating (CFBG). When a load is applied to the SE, the reflection spectrum of the FBG shifts to the sharply increasing region of the spectral response of the CFBG. The optical power reaching the interrogator corresponds to the intensity of the intersection of the two spectral responses of the diffraction structures. A two-channel power meter is used as the radiation receiver. From the received data, the parameters of the moving object can be determined. Main results. . This study proposes a new method for measuring the weight and velocity of moving objects using FBGs and CFBGs. Experimental studies on dynamic and static weighting have been conducted. Based on the experimental data, the dependencies of the signal amplitude on time for different weights, as well as the calculation of the object's velocity, are constructed and shown. Practical significance. . The scientific and technical solution proposed in this study is of interest for the further development and operation of automatic weight control systems. The proposed method can optimize the process of controlling the weight and speed of moving objects, thereby ensuring road safety. (c) 2024 Optica Publishing Group

Subject of study. A fiber-optic temperature sensor based on two superposed regenerated fiber Bragg gratings is studied. Aim of study. A fiber-optic temperature sensor with a range of +25 degrees C to +1000 degrees C based on two superposed regenerated fiber Bragg gratings is developed, and the temperature sensitivity of the resulting sensor is determined. Method. Two superposed standard fiber Bragg gratings (length of 14 mm) with reflectivities of 90% and 70% were heated (heating rate of 500 degrees C/h) from room temperature to the regeneration temperature of 920 degrees C, appropriate for optical fibers meeting the G.657.A2 standard; the gratings were held at this temperature pending complete formation of the regenerated structure. Main results. The development effort and thermal studies (which were performed over a temperature range from +25 degrees C to +1000 degrees C with steps of 100 degrees C) led to the development of a fiber-optic temperature sensor based on superposed regenerated fiber Bragg gratings with reflectance and temperature sensitivities of approximately 40% and 12.7 pm/degrees C and approximately 30% and 12.72 pm/degrees C, respectively. Practical significance. This paper marks the first, to our knowledge, successful superposition of two regenerated fiber Bragg gratings with reflection coefficients greater than 40% and 30%. The sensor developed based on this structure has a wider temperature measurement range with a narrow range of probe wavelengths. This paper also marks the first determination of the temperature sensitivity of a regenerated fiber Bragg grating as a function of its central reflection wavelength. (c) 2025 Optica Publishing Group. All rights, including for text and data mining (TDM), Artificial Intelligence (AI) training, and similar technologies, are reserved.

Subject of study. Cascaded high-signal-attenuation narrowband fiber Bragg gratings connected via a fiber-optic isolator. Aim of study. This study aims to develop a narrowband (82-pm bandpass) spectral filter based on cascaded fiber Bragg gratings. Method. Long, narrow-bandwidth fiber Bragg gratings were written using a phase mask and a scanning beam from a Coherent COMPexPRo 102F krypton fluoride (KrF) excimer laser. Two gratings with identical central Bragg resonance wavelengths were cascaded via a fiber-optic isolator in order to avoid interference effects. Main results. Transmission spectra from the resulting fiber-Bragg-grating cascade had a measured 3-dB filter transmission bandwidth of 82 pm and a maximum attenuation of 46 dB. The filter had a central minimum-transmission wavelength of 1549.9 nm. For comparison, single gratings of the same length with similar attenuation value have a 3-dB bandwidth of 123 pm-much larger than that of the cascaded fiber Bragg grating filter. Practical significance. The narrowband filter based on cascaded fiber Bragg gratings obtained in this paper is suitable for separating carrier wavelengths from subcarrier wavelengths in subcarrier-wave quantum key distribution systems and for use in other communications-link applications requiring selection of a narrow spectral band. (c) 2025 Optica Publishing Group

Weight sensors are widely used in the freight transportation industry. In the systems for weighing vehicles while moving, ceramic, polymer, quartz piezoelectric sensors, load or hydraulic cells, strain gauges are used as sensitive elements. However, most electric sensors are susceptible to electromagnetic interference. Currently, fiber-optic sensors are most actively developed and put into operation due to their relatively low cost, small weight and size parameters, high measurement accuracy and complete passivity to electromagnetic disturbances. Fiber-optic sensors are most often implemented using fiber Bragg gratings, taking into account the convenience of their multiplexing. Mechanical deformations lead to a shift in the wavelength of the Bragg resonance of the grating. At the same time, the problem of using fiber gratings is associated with their sensitivity to temperature. To achieve high accuracy in measuring the deformation value, and accordingly, the weight characteristics of the object, it is necessary to eliminate or compensate for the effect of the sensor temperature on its readings. Most modern studies describe sensors that either operate in laboratory conditions or involve the use of an additional sensor that complicates the circuit for measuring temperature. The paper proposes a method for solving the problem of cross-sensitivity of a fiber diffraction structure to temperature and deformation. The method is based on the use of a pair of closely spaced gratings in the sensitive element of the sensor. One of the gratings has a constant period along the length, and the other has a variable one. The design of the sensitive element ensures the transfer of mechanical load only to the fiber grating with a constant period, and the temperature change equally affects both diffraction structures. A design solution for the sensitive element is proposed that allows for temperature effects compensation without using additional elements. A mathematical model of temperature effects is presented, allowing estimating the dependence of the temperature gradient on time for different thicknesses of the sensitive element. Modeling has showed that for a sample 0.95 cm thick, the temperature gradient inside the substrate is insignificant. With a sharp change in temperature, the equalization of the temperature field within the substrate at a level of 90 % occurs in no more than 2.5 s. The mechanical load on the sensitive element can pass relative to the fiber grating at different angles in connection with which the value of the shift of the central wavelength of the Bragg resonance was studied in detail depending on the point of application and direction of the load. The proposed technology may be of interest in the development and operation of automatic weight and size control systems with temperature compensation without the use of additional sensors. The proposed system is easy to operate and it has a low cost.

Subject of study. A fiber-optic temperature sensor based on measurement of the reflected optical power is studied. Aim of study. A fabrication technique for fiber-optic temperature sensors based on chirped fiber Bragg gratings and measuring the reflected optical power is developed. Method. The fiber-optic temperature sensor consists of a brass probe with two chirped Bragg gratings, one of which is also enclosed in a steel capillary tube and has higher temperature sensitivity than the other grating. Changes in temperature modulate the overlap between the spectra from the first and second Bragg gratings, enabling detection of changes in the optical power reflected by the structures. Main results. An approach is being developed for creating a fiber-optic temperature sensor based on measurement of optical radiation intensity. The sensor has a design operating range of -20 degrees C to +80 degrees C. The sensor was tested by varying the temperature from -20 degrees C to +80 degrees C in 10 degrees C intervals, revealing a sensor sensitivity of -0.015 dB/degrees C. The sensor was also found to have a temperature measurement error of 1.0% (relative to a thermocouple). The deviation in the sensor readings at a steady temperature value is estimated to be 0.06 degrees C. Practical significance. The temperature sensor developed herein is part of the worldwide trend towards cost-effective design solutions. This measurement technique based on modulation of the optical intensity enables the use of a readily available interrogation scheme that does not require expensive equipment such as an optical spectrum analyzer or interrogator. This interrogation scheme also has the advantages of high data recording speed, relatively simple design, and the absence of strict requirements with respect to operating conditions. (c) 2025 Optica Publishing Group

Fiber Mach-Zehnder interferometer (FMZI) micro-cavity length adjustment in tens of nanometers by chemical etching for refractive index sensing system miniaturization was firstly reported. This etching process is capable of adjusting the length of micro-structure at the order of tens of nanometers, and achieving such high precision without involving complicated and expensive nano-fabrication facilities. The chemical etching opens up the fiber micro-cavity and redshifts its resonant wavelength at the rate of 3.6 nm/min, upon an estimated etching speed of 41.5 nm/min. The shift of the micro-cavity’s resonant wave-length close to the LD’s emitting wavelength is achieved by such precise length adjustment for sensing system miniaturization. The miniaturized FMZI is experimentally applied to the refractive index sensing for ethanol solutions. The measured transmission is in good linearity with regards to the solution index and the sensitivity is -12.8 dB for 0.0043 RIU (refractive index unit) difference in this study. The miniaturized FMZI index-sensing system can be portable and operating at a fast speed, which is well suited for practical field applications.

The detailed fabrication processes of fiber Mach-Zehnder interferometers (FMZIs) by nanosecond laser-induced micro-plasma and its simple micro-cavity size adjustment are proposed and demonstrated. The fabrication can be divided into 4 processes: (1) heat transfer, (2) micro-plasma formation, (3) micro-plasma expansion and ablation, (4) cooling down and micro-structure formation. The simple micro-cavity size adjustment is proposed based on the above understanding, instead of the "point processing" of femtosecond laser, here only the focus position is required to be moved. The fabricated FMZI exhibits a high sensitivity of -15,811 nm/RIU (refractive index unit) for the index sensing application.

Subject of study. Theoretical and experimental investigation of a technique for creating a package for the passive temperature compensation of a fiber Bragg grating is presented. Aim of study. The aim is the development of and research on the fiber Bragg grating packaging technique for passive temperature compensation. Method. Passive temperature compensation was based on grating deformation using a passive support made up of several materials with different coefficients of thermal expansion. The optical fiber in which the Bragg grating was inscribed was attached under a certain tension to an element with a high coefficient of thermal expansion. This system was attached to an element with a low coefficient of thermal expansion. With an increase in the temperature, the compensating elements and the fiber grating expanded according to their coefficients of thermal expansion. Thus, the distance between the attachment points of the fiber to the element with a high coefficient of thermal expansion decreased, resulting in a decrease in fiber tension by the exact amount necessary to compensate for the shift in the Bragg resonance of the grating, which is caused by temperature changes. Main results. Anew method of packaging a fiber Bragg grating for temperature compensation using a symmetrical passive support consisting of two materials with different coefficients of thermal expansion was proposed. Using mathematical modeling, the main parameters of the proposed method were calculated for the most effective temperature compensation. The experimental study revealed the temperature dependence of the Bragg resonance wavelength for an ordinary and an athermal grating. The Bragg wavelength shift for the grating in the package was 70 pm over a range of 15 degrees C to 105 degrees C. Practical significance. The scientific and technical solution proposed in the study is of interest in various fields involving the use of fiber Bragg gratings, wherein the stability of the Bragg resonance wavelength plays a key role in the operation of systems. (c) 2024 Optica Publishing Group

Subject of study. This study is devoted to the research and development of a fiber-optic method for identifying a substance by its thermal characteristics and determining the phase of a substance in a gas-liquid mixture flow. Aim of study. The purpose of this study is to develop a fiber-optic sensing element with a single compact design and the possibility of remote measurements for identifying a substance by its thermal characteristics using standard telecommunication fibers. This study also includes examining dynamic systems with changing phases of matter using fully fiber-optic technologies. Method. The hot wire method with fiber optic elements is employed in this study. The creation of the heating area was realized by forming the structure of the taper in the optical fiber, and for measurements, a fiber Bragg grating, which acts as a temperature sensor, was formed. Main results. In this study, what we believe to be a novel scientific and technical solution was developed to create a fiber-optic-sensitive element for identifying a substance by its thermal characteristics. The experiments were conducted using six samples with a specific heat capacity ranging from 1.0 to 4.2 kJ/(kg K). Based on the results, the dependences of the spectral shift of the resonance of the fiber Bragg grating on the values of the specific heat capacities of substances were plotted, and the maximum standard deviation was 0.0088 nm. The results of identifying the phase of a gas-liquid mixture in a flow are also presented. Practical significance. The results of the study are of scientific interest to researchers in areas requiring the analysis of samples with different thermal characteristics, determining the phase change in a flow, detecting the presence of impurities in the flows of known substances, measuring the level of liquids, etc.(c) 2023 Optica Publishing Group

This work is devoted to the development and research of a new optical method for measuring the velocity of a fluid flow and determining the orthogonal directions of such a flow. Comparing with gas flow, measuring the fluid flow rate requires higher heating power and insulation, which is taken into account in this work. The standard hot-wire anemometry method is taken as a basis, but instead of a metal thread, optical fiber is used for measurements. The article presents the design of a sensitive element consisting of two optical fibers. The first fiber contains an array of fiber Bragg gratings and is used as a measurement element. The second fiber has a region with a tapered structure and is used to create a heated area. Velocity measurements are given for the range of 0.02???0.05 m/s, but are limited only by the capabilities of the measuring stand. A unique method for identi-fying the orthogonal flow direction, which has not been described in the literature before, is presented. Differ-ences in the shapes of the curves for the dependences of flow rates moving in the direction and orthogonally to the axis of the sensitive element are presented. The stability of the device is also confirmed by continuous ex-periments for 70 min.

Subject of study. The study analyzes the change in the spectral characteristics of superimposed chirped fiber Bragg gratings during inscription. Aim of study. The dynamics of changes in the spectral characteristics of chirped fiber Bragg gratings during inscription are evaluated. Method. The diffractive structures consisting of four chirped Bragg gratings with a period variable in length are inscribed in a standard telecommunication single-mode optical fiber (G.657.A2) using a KrF excimer laser system and a Talbot interferometer. During the inscription of the fiber structures, the change in the spectral characteristics is estimated depending on the total irradiation dose. Main results. The dependences of the change in the reflection coefficient, the full width at half maximum of the spectral response, and the Bragg resonance wavelength of each chirped Bragg grating of the superimposed structure on the total dose of irradiation are demonstrated. The numerical values of the modulation of the spectral characteristics are presented. Practical significance. The results are important in the field of fiber optics, especially in the development of fiber-optic devices based on Bragg reflectors. The analysis demonstrates the dependences of the change in the spectral characteristics of fiber structures during inscription. The study can be used to optimize the development of fiber-optic devices based on superimposed chirped Bragg gratings, which helps in achieving the required diffractive structure characteristics with high accuracy. (c) 2023 Optica Publishing Group

Subject of study. Afiber-optic temperature sensor, based on a Fabry-Perot interferometer obtained bywelding optical fibers, is developed and characterized. Aim of study. The aim is to develop and characterize a temperature sensor based on a fiber-optic Fabry-Perot interferometer obtained by arc welding and evaluate its temperature-sensing performance. Method. The design of the temperature sensor is implemented based on a Fabry-Perot interferometer obtained by welding optical fibers. The reflecting mirrors of the sensor comprise layers of thin films of titanium dioxide. The interferometer interrogation method is based on the use of a vertically emitting laser operating in the pulsed generation mode. The principle of registering the phase shift between radiation reflected from the interferometer mirrors with changes in temperature is based on auxiliary modulation of the laser radiation wavelength due to a periodic change in the pulse duration. Main results. During the temperature evaluation of the developed sensor, the phase characteristics of the Fabry-Perot interferometer were obtained in the temperature range of C20 degrees C to C380 degrees C. A shift in the operating point was registered with changes in the ambient temperature. The results of the experiment indicated that an increase in the ambient temperature leads to an increase in phase difference between the radiation reflected from the first and second mirrors of the interferometer. Results suggest that the phase sensitivity to temperature change is 0.96, 1.68, and 2.35 rad/degrees C at distances between mirrors corresponding to 5, 8, and 11mm, respectively. Practical significance. The proposed fabrication method for the Fabry-Perot interferometer provides sufficient opportunities for the formation of a resonator with different lengths and also makes it possible to exclude the use of additional materials in its design. Hence, the interferometer exhibits small weight and size parameters, and thus, it can be used in a wide range of applications, including as a sensitive element of a temperature sensor. The sensor interrogation method employed in the study eliminates the need for costly spectral measuring instruments such as optical spectrumanalyzers and interrogators. (c) 2024 Optica Publishing Group

We carried out the development and study of methods for changing the sensitivity of Fiber Bragg Gratings (FBG) to temperature and strain by applying various low-melting metals. Investigation of sensitive elements based on SMF-28 single-mode optical fibers with formed FBG and various metal coatings applied over the fiber have been made. The influence of FBG coating with low-melting metals on its sensitivity to temperature and deformation has been studied. Various fiber-optic sensitive elements have been developed, which are fibers with fiber Bragg gratings formed in them, while coatings of various thicknesses of tin or solder in the form of an alloy of tin and lead (Sn63Pb37) were deposited on the area with such diffraction structures. The presented experimental data are in good agreement with the calculated ones. The temperature sensitivity of the Bragg grating resonance with a solder or tin coatings is 4 times higher than the sensitivity of an uncoated grating. In turn, the analysis of the sensitivity to stretching allows us to conclude that, in comparison with the standard FBG, the sensitivity of the grating in the coating decreases and is about 0.017 pm/(μm/m) compared to 1.2 pm/(μm/m) (for the wavelength of the Bragg resonance 1530 nm) for a standard FBG without coating. The results obtained can be used to control and change the FBG sensitivity to temperature and/or defor

In this paper we study an original technique for creating an amplitude temperature sensor based on n-pairs of chirped fiber Bragg gratings (CFBGs). The scalable design of the sensor allows to increase the range of the measured signal. The use of the amplitude interrogation technique ensures high speed, elementary nature of the scheme and simple operating conditions. The application of superimposed CFBGs as a sensitive element of an amplitude temperature sensor is investigated. As a result of the work, a method for measuring temperature with a fiber-optic sensitive element based on n-pairs of CFBGs is tested. Two superimposed CFBGs are inscribed in a standard telecommunication single-mode optical fiber using a KrF excimer laser system and Talbot interferometer. One of the superimposed structures is used as a reference element of the sensor and the second - as a sensitive element and is placed in a brass tube, where it is fixed on one side with an adhesive joint. The sensor has an accuracy of 0.48 degrees C and a sensitivity of 0.20 mu W/degrees C for temperature measurement in the range of 30-70 degrees C. The results obtained are of great importance in the development of fiber-optic temperature control systems. Implementation of the sensor based on n-pairs of CFBGs allows scaling the power of signal, increasing the ability to detect a slight change in ambient temperature. The created sensor works according to the amplitude polling technique, which is characterized by high accuracy and speed of measurement, minimized scheme, simplified use and easy processing of the detected signal. In addition, the implemented interrogation method corresponds to the trend of developing low-cost fiber-optic systems without losing their main advantages.

A variant of the implementation of a fiber-optic sensor for the direction and magnitude of the bend is proposed. Unlike existing spectral measuring systems, the solution under consideration involves the use of an amplitude polling technique which makes it possible to increase the speed of the sensor when using simpler and more affordable components. A sensitive element based on special diffraction structures consisting of pairs of chirped fiber Bragg gratings has been studied. The sensing elements are mounted on a tooling — a steel rod subjected to bending. The ability of the sensor to determine the magnitude and direction of bending in the deviation range from 0 to 30 mm was demonstrated with a standard deviation of the measured values from the real values of 0.536 mm. This measurement result is achieved by processing data obtained from three measuring devices and by the neural network with a hidden layer of 10 neurons and the sigmoid as the activation function. The research results are essential for modern monitoring systems. The implementation of the direction and magnitude of the bend sensor in the format of a fiber-optic device allows you to overcome the limitations of piezoelectric sensors, due to high noise immunity and resistance to environmental influences. The proposed technological solution makes it possible to avoid the spectral measurement technique that has become widely used in fiber-optic sensor systems. The use of an amplitude sensor for the magnitude and direction of bending will allow its use in devices where there is a need for precise positioning of control elements or structural components subjected to bending. Also, due to the measurement of the desired bending effect by estimating the optical power of the signal, the design of the sensor does not require the presence of a complex measuring device, and the sensor’s performance can be ensured using a cascade of inexpensive, but at the same time high-speed and durable photodetectors.

A highly sensitive vector magnetic field sensor based on a fiber Mach-Zehnder interferometer (FMZI) is proposed and demonstrated. The FMZI is composed of a micro-cavity that is fabricated in a single-step laser -induced micro-plasma process with a modest-powered nanosecond fiber laser. Combined with a magnetic fluid, the micro-cavity-based FMZI is constructed to a magnetic field sensor for vectorial sensing. The presented magnetic sensor exhibits a maximal strength sensitivity of 64 nm/mT that is the highest among reported vector magnetic field fiber sensors to date, to the best of our knowledge.

Subject of study. A high-speed fiber-optic transmitter for the spectral range of 1.55 mu m, based on a vertical-cavity surface-emitting laser (VCSEL) fabricated using wafer fusion technology was investigated. Aim of study. A compre-hensive study of the parameters of the 1.55-mu m range optical transmitter based on a VCSEL at room temperature is presented. Method. The heterostructure of the VCSEL was fabricated using molecular beam epitaxy and wafer fusion technology. The transmitter parameters were investigated with current modulation by a large signal in the non-return-to-zero (NRZ) format. Main results. At 20 degrees C, the transmitter demonstrated maximum output optical power, exceeding 1 mW at the fiber output in single-mode operation. The maximum data rate over a short commu-nication line based on an SMF-28 fiber with current amplitude modulation in the NRZ format reached 30 Gbits/s, limited by the modulation bandwidth reaching a value of approximately 12 GHz (at -3 dB level). With an increase in the length of the fiber-optic communication line, the chromatic dispersion of the fiber and the chirp effect of the laser increase inter-symbol interference, which ultimately limits the speed and range of optical data transmis-sion. Practical significance. The investigated fiber-optic transmitters are promising for both digital and analog transmission of high-frequency optical signals over fiber-optic communication lines.(c) 2023 Optica Publishing Group