Ponomarev, Roman S

Garkushin A.A., Zhukov L.O., Ponomarev R.S., Pankov A.S., Volkhin I.L., Maksimenko V.A., Krishtop V.V.

Agliullin T., Sakhabutdinov A., Valeev B., Qaid M.R., Kuznetsov A., Ponomarev R., Nurmuhametov D., Shmyrova A.

Chesnokova M., Nurmukhametov D., Ponomarev R., Agliullin T., Kuznetsov A., Sakhabutdinov A., Morozov O., Makarov R.

This work proposes a simple and affordable technology for the manufacturing of a miniature end-face fiber-optic temperature sensor based on a Fabry–Perot interferometer formed from a transparent UV-curable resin. For the manufactured working prototype of the sensor, the sensitivity and operating temperature range were determined, and the methods for their enhancement were proposed. Due to its small size, the proposed type of sensor can be used in high-precision and minimally invasive temperature measurements, in biology for microscale sample monitoring, and in medicine during operations using high-power lasers. A microwave photonic method is proposed that enables the interrogation of the sensor without using an optical spectrum analyzer.

Masalkin D., Sosunov A., Ponomarev R., Zhuravlev A., Ivanov K.

Morozov O., Agliullin T., Sakhabutdinov A., Kuznetsov A., Valeev B., Qaid M., Ponomarev R., Nurmuhametov D., Shmyrova A., Konstantinov Y.

The paper describes the design and manufacturing process of a fiber optic microphone based on a macro cavity at the end face of an optical fiber. The study explores the step-by-step fabrication of a droplet-shaped macro cavity on the optical fiber’s end surface, derived from the formation of a quasi-periodic array of micro-cavities due to the fuse effect. Immersing the end face of an optical fiber with a macro cavity in liquid leads to the formation of a closed area of gas where interfacial surfaces act as Fabry–Perot mirrors. The study demonstrates that the macro cavity can act as a standard foundational element for diverse fiber optic sensors, using the droplet-shaped end-face cavity as a primary sensor element. An evaluation of the macro cavity interferometer’s sensitivity to length alterations is presented, highlighting its substantial promise for use in precise fiber optic measurements. However, potential limitations and further research directions include investigating the influence of external factors on microphone sensitivity and long-term stability. This approach not only significantly contributes to optical measurement techniques but also underscores the necessity for the continued exploration of the parameters influencing device performance.

Belokrylov M.E., Claude D., Konstantinov Y.A., Karnaushkin P.V., Ovchinnikov K.A., Krishtop V.V., Gilev D.G., Barkov F.L., Ponomarev R.S.

Simple measures to improve the signal-to-noise ratio of optical frequency domain reflectometer (OFDR) readings are described. After applying a two-stage optical amplification of the backscattered signal, as well as eliminating the source of spurious reflections, it was possible to increase the signal-to-noise ratio of the frequency domain trace from 8 to 19 dB. This technique can be applied in fiber optic sensors and metrology of fiber optic and integrated optical elements.

Sbeah Z.A., Adhikari R., Sorathiya V., Chauhan D., Ponomarev R.S., Dwivedi R.P.

This paper presents a plasmonic metamaterial sensor utilizing an I-shaped gold resonator. The sensor is simulated using the finite-element method (FEM) to detect gas and liquid (ethanol solutions) in the infrared wavelength range of 0.5–2.5 µm. The sensor structure consists of three layers, with a VO2 substrate sandwiched between a bottom SiO2 substrate and a top gold resonator. The design exhibits distinct absorption characteristics across the range of 0.5–2.5 µm, tailored for different gas and liquid sensing applications. A comparison is made between the two states of VO2 to investigate the sensitivity of the device. Geometrical parameters, including height and width, are optimized, and three types of comparisons are conducted. First, a sensitivity comparison is made between this work and previously published research. Second, a Quality factor and Figure of Merit comparison is performed. Finally, a sensitivity comparison is made between different sensing techniques and the technique employed in this work. After optimizing the design parameters, the device demonstrates the highest detection sensitivity for gas and ethanol solutions, yielding results of 2800 (nm/RIU) and 2600 (nm/RIU), respectively. The proposed I-shaped gold-based metamaterial exhibits the potential to be utilized as a lab-on-chip biosensor.

Demin V.A., Petukhov M.I., Ponomarev R.S., Kuneva M.

This paper provides a numerical analysis of the behavior of the ion boundary layer formed during proton exchange. Thermal dissociation of benzoic acid melt molecules leads to the formation of benzoate ions and hydrogen ions. The latter can be absorbed by a lithium niobate wafer, with subsequent diffusion of lithium ions in the acid. The mathematical model proposed in the article implies that it is possible to use continuous media approximation to describe this phenomenon. The statement of the current problem includes both diffusion and electrostatic mechanisms of mass transfer and the recombination mechanism of ion interaction. The numerical scheme, based on a two-field method, has shown a steady-state formation, characterized by exponential-like profiles of concentration in the presence of an induced nonuniform electric field. It is important to note that the net charge of the system remains zero. The results of numerical simulation have demonstrated the formation of a boundary layer of benzoate ions. At the same time, nonuniformities that appear in the layer do not create instability that breaks mechanical equilibrium, and they do not lead to a high-scale concentration convection.

Sokolchik D.P., Pankov A.S., Ponomaryov R.S.

Demin V.A., Petukhov M.I., Ponomarev R.S.

The paper presents a theoretical study of the behavior of an ionic boundary layer that occurs in the process of a steady proton exchange in a benzoic acid melt contacting with the surface of a lithium niobate crystal. The penetration of protons into a crystal promotes the injection of oppositely charged ions (lithium and benzoate) from the surface of lithium niobate in the surrounding acid. The transfer of the reaction products and their interaction in benzoic acid is studied numerically. The proposed mathematical model includes the effect of recombination in the volume so that the ions with different charge signs approach each other and form a neutral lithium benzoate. The results of the numerical simulations demonstrate that there are exponential-like concentration profiles of two types of ions, and a non-uniform electric field and pressure distributions develop in the boundary layer under steady-state conditions. In this process, the total charge of the system remains zero. It is shown how the concentration, recombination, and activity of lithium and benzoate ions and the diffusion coefficients affect the profile shapes and the process intensity.

Sosunov A., Masalkin D., Ponomarev R., Umylin V., Zhuravlev A., Laskavyi N., Kuneva M.

Sosunov A.V., Petukhov I.V., Kichigin V., Ponomarev R.S., Mololkin A.A., Kuneva M.

Demin V., Petukhov M., Ponomarev R.

Abstract This paper is devoted to numerical analysis of the behavior of ion boundary layer, forming in the process of proton exchange during the interaction of the benzoic acid melt and lithium niobate wafer. This interaction leads to the dissociation of acid molecules and absorption of released protons by the crystal with following injection of benzoate-ions and lithium ions back into the acid. Mathematical model, offered in the article, implies that it is possible to use continuous media approximation to describe this phenomenon. Statement of current problem includes diffusion and electrostatic mechanisms of mass transfer. In addition, the ions recombination is taken into account in our description. Numerical scheme, based on the two-field finite differences method, shows formation of the steady state, which is characterized by exponential-like profiles of concentration and appearance of induced nonuniform electric field. It is important to note, that full charge of the system remains be equal to zero. Results of numerical simulation demonstrate the formation of boundary layer for benzoate-ion. At the same time, nonuniformities, appearing in the layer, don’t induce instabilities, breaking mechanical equilibrium, and don’t lead to high scale concentration convection.

Kozhevnikov V.S., Ponomarev R.S., Shmyrova A.I.

Abstract The technology for manufacturing optical microlenses on the end of an optical fiber using optical resin is considered. The method of dosing and positioning an adhesive microdroplet is implemented, which allows placement of a resin volume of ~0.2 pL with an error of at most 1 μm at the end of the optical fiber in the core region. The selection of optical resin that maximally meets the requirements of the technological process and physicochemical properties of microlenses has been performed. It is shown that the use of microvibrations makes it possible to control the droplet shape, whose polymerization makes it possible to obtain a lensed fiber with a given shape and focal length. The results of measuring the focal length and the diameter of the mode field of the resulting lens are presented.

Sosunov A.V., Petukhov I.V., Zhuravlev A.A., Ponomarev R.S., Mololkin A.A., Kuneva M.

Tsiberkin K.B., Sosunov A.V., Govorina V.V., Neznakhin D.S., Henner V.K., Sumanasekera G.

Sun P., She X., Zhang L., Han H., Bi R., Shen H., Huang F., Wang L., Shu X.

Choudhury T.T., Masuk N.I., Deb P., Islam M.N., Islam M.A.

Zhou G., Jiang J., Feng Q., Zhou F., Qiu X., Chen Y., Kong X., Ju Z., Cui Y., Zhuang Q.

Tang C., Gao Y., Zhu K., Cao D.

Guo X., Tong X., Sun S., Jiang C.

Sun Z., Xiao X., Zhao W., Ai K., Lv Y., Liu H., Sun Q., Yan Z.

Shi J., Ye Z., liu Z., Yan Z., Jia K., Zhang L., Ge D., Zhu S.

The thin-film lithium niobate (TFLN) modulator is among the most critical devices in photonic integrated circuits (PICs), owing to its large modulation bandwidth, low optical loss, and high extinction ratio. However, it suffers from DC drift issues at low frequencies or long timescales. Here, we have successfully alleviated the DC drift effect of the electro-optical phase shifter (EOPS) at low frequencies by employing a high-energy Ar + ion milling preprocessing. This EOPS can stably output square wave modulation signals at a frequency of 1 Hz, and the output signal exhibits no DC drift under DC voltage modulation within 1 h. Compared with the thermo-optical phase shifter (TOPS), the optimized EOPS not only has higher modulation rate but also exhibits the same stability at low frequency. Furthermore, we applied this ion milling technique to produce a TFLN modulator. At a DC bias voltage of 4.5 V, the bandwidth of the modulator is above 40 GHz and remained a stable output within 30 min.

Sosunov A.V., Petukhov I.V., Kozlov A.A., Masalkin D.N., Kornilicyn A., Sheremet A.G., Kuneva M.

Lithium niobate (LN) is one of the key materials in modern instrument engineering. Currently, photonic devices based on thin films have great potential for use. That is why the role of the surfaces in technological operations strongly increases. Herein, the powerful effect of modifying the surface of LN in oxygen plasma at low pressures on the diffusion coefficient of hydrogen ions is demonstrated. Plasma activation of LN surface leads to changes in chemical composition, found by X‐Ray photoelectron spectroscopy (XPS), Raman, and IR spectroscopy methods that the part of niobium relative to oxygen on the surface of LN decreases. During proton exchange (PE), the deformations of the crystal lattice and the change of refractive index are sharply reduced. No surface damage of LN is observed at direct PE. For the first time, it is possible to form an intermediate phase at low PE temperatures and without annealing. This was previously considered impossible. An explanation is proposed for the adsorption of benzoic acid on the surface of lithium niobate. This effect can be used in ridge waveguides and diffuse optical waveguide technology, nonlinear optical applications, and lab on chip.

Ighalo J.O., Akaeme F.C., Georgin J., de Oliveira J.S., Franco D.S.

Hydrothermal carbonization (HTC) is a novel thermochemical process that turns biomass into hydrochar, a substance rich in carbon that has potential uses in advanced material synthesis, energy production, and environmental remediation. With an emphasis on important chemical pathways, such as dehydration, decarboxylation, and polymerization, that control the conversion of lignocellulosic biomass into useful hydrochar, this review critically investigates the fundamental chemistry of HTC. A detailed analysis is conducted on the effects of process variables on the physicochemical characteristics of hydrochar, including temperature, pressure, biomass composition, water ratio, and residence time. Particular focus is placed on new developments in HTC technology that improve sustainability and efficiency, like recirculating process water and microwave-assisted co-hydrothermal carbonization. Furthermore, the improvement of adsorption capacity for organic contaminants and heavy metals is explored in relation to the functionalization and chemical activation of hydrochar, namely through surface modification and KOH treatment. The performance of hydrochar and biochar in adsorption, catalysis, and energy storage is compared, emphasizing the unique benefits and difficulties of each substance. Although hydrochar has a comparatively high higher heating value (HHV) and can be a good substitute for coal, issues with reactor design, process scalability, and secondary waste management continue to limit its widespread use. In order to maximize HTC as a sustainable and profitable avenue for biomass valorization, this study addresses critical research gaps and future initiatives.

Ankit, Kishor K., Sinha R.K.

Abstract We present a new design and study of metamaterial (MTM) structure for wide bandwidth for biosensor and wireless applications. The geometrical parameters were analyzed and optimized for a triple-band operation in the frequency range of 0.1–16 GHz. The propagation characteristics were obtained using Finite element method. The proposed MTM provides negative permittivity at 1.4 GHz and negative permeability in the 9–16 GHz region. The proposed design exhibits left-handed characteristics in L, C, and Ku microwave region’s frequency band. The electric field (E), magnetic field (H), and surface current distribution of the proposed MTM unit cell have been studied at three different resonance frequencies. The proposed MTM design has a wide bandwidth of 2.2 GHz in C-band and a high effective medium ratio (EMR) of 13.37. The performance of the sensor is evaluated for different biomedical samples in the refractive index range of 1.00 to 1.39. The results indicate that the proposed biosensor has a high sensitivity in triple band of microwave region. The present research work can be highly suitable for Wi-Fi and satellite applications due to its overall performance, including wide bandwidth in the C-band, high EMR, and triple band operation.

Zhang R., Zhao J., Liu W., Sun L., Liang Q., Chen P., Wang X.

Paniagua-Medina J.J., Vargas-Rodriguez E., Guzman-Chavez A.D., Morales-Castro J.C., Correa-Jurado R.J.

Doshi S.P., West G.N., Gray D., Ram R.J.

Patterning of stable, spatially tailored ferroelectric domains in thin-film lithium niobate enables efficient nonlinear optical interactions through quasi-phase matching. The engineering of domain structure is limited by the uncontrolled distribution of defects, which disrupt domain wall motion. Here, we fabricate quasi-phase matching gratings in thin-film lithium niobate with sub 20 nm of period variation. We demonstrate that annealing processed samples at 350 or 500 °C for 48 h, prior to E-field poling, can dramatically reduce the duty cycle variation. We show that maintaining an elevated temperature of 200 °C during poling enhances defect mobility, which leads to more rectangular inverted domains. Moreover, poling at elevated temperatures also increases inversion depth without sacrificing the periodic domain pattern's accuracy or precision. Elevating the temperature prior to and during poling resulted in near-ideal square wave patterning of ferroelectric domains (50% mean duty cycle, sub 10% domain width variation, and 100% depth inversion). This enables effective quasi-phase matching for second harmonic generation in 5.6 mm-long waveguides fabricated from MgO-doped x-cut thin-film lithium niobate.

Salim E.T., Fadhil R.B., Khalef W.K., Fakhri M.A., Gopinath S.C.

Lithium niobate (LiNbO3) is a compound composed of lithium, niobium, and oxygen. It is a crucial material in many optical applications due to its excellent electro-optic, nonlinear optical, and piezoelectric properties. The chemical bath deposition approach has been successfully used to deposit LiNbO3 thin films on quartz substrates. Therefore, due to their unique electrical and optical properties, one-dimensional nanostructures like nanotubes, nanowires, and nanorods are being explored because of their potential uses in new nanoelectronic and optoelectronic devices.

Green M.A., Dunlop E.D., Yoshita M., Kopidakis N., Bothe K., Siefer G., Hinken D., Rauer M., Hohl‐Ebinger J., Hao X.

AbstractConsolidated tables showing an extensive listing of the highest independently confirmed efficiencies for solar cells and modules are presented. Guidelines for inclusion of results into these tables are outlined, and new entries since January 2024 are reviewed.

Garkushin A.A., Krishtop V.V., Storozhev S.A., Volkhin I.L., Nifontova E.V., Urbanovich E.V., Kustov D.A., Kadochikov I.V.

The digital twin was created and a prototype of the power supply system with power transmission via optical fiber was manufactured. This technology belongs to the field of optical, wireless and fiber optic power transmission (OWPT). Verification of correctness of the digital twin operation was carried out. The task of achieving the maximum possible efficiency of the system at varying load was solved. Its value amounted to 14%. The operability of the search algorithm of the double differentiation system developed for this purpose is shown. The principle of its operation consists in the change of optical energy synchronously with the change of load resistance. This allows to reduce losses in the primary and secondary energy converters. In the area of optimal regulation, the algorithm provides the minimum power supply level necessary for the operation of secondary devices, at which the maximum possible efficiency of the whole power supply system is achieved. The presented work is a part of the program of creating an end-to-end intelligent system of the full production cycle of the product, starting from the design of structures of opto- and photovoltaic converters (PC), up to the manufacture of systems adapted to individual customer requirements.

Garkushin A., Urbanovich E., Nifontova E., Storozhev S., Volkhin I., Krishtop V., Maksimenko V.

Makarov R., Qaid M.R., Al Hussein A.N., Valeev B., Agliullin T., Anfinogentov V., Sakhabutdinov A.

In this paper, an application of an artificial neural network algorithm is proposed to enhance the accuracy of temperature measurement using a fiber-optic sensor based on a Fabry–Perot interferometer (FPI). It is assumed that the interrogation of the FPI is carried out using an optical comb generator realizing a microwave photonic approach. Firstly, modelling of the reflection spectrum of a Fabry–Perot interferometer is implemented. Secondly, probing of the obtained spectrum using a comb-generator model is performed. The resulting electrical signal of the photodetector is processed and is used to create a sample for artificial neural network training aimed at temperature detection. It is demonstrated that the artificial neural network implementation can predict temperature variations with an accuracy equal to 0.018 °C in the range from −10 to +10 °C and 0.147 in the range from −15 to +15 °C.

Garkushin A.A., Krishtop V.V., Volkhin I.L., Rasulev R.P., Nifontova E.V., Kadochikov I.V., Maksimenko V.A., Perminov A.V., Shevtsov D.I.

Turov A.T., Barkov F.L., Konstantinov Y.A., Korobko D.A., Lopez-Mercado C.A., Fotiadi A.A.

This work studies the application of low-cost noise reduction algorithms for the data processing of distributed acoustic sensors (DAS). It presents an improvement of the previously described methodology using the activation function of neurons, which enhances the speed of data processing and the quality of event identification, as well as reducing spatial distortions. The possibility of using a cheaper radiation source in DAS setups is demonstrated. Optimal algorithms’ combinations are proposed for different types of the events recorded. The criterion for evaluating the effectiveness of algorithm performance was an increase in the signal-to-noise ratio (SNR). The finest effect achieved with a combination of algorithms provided an increase in SNR of 10.8 dB. The obtained results can significantly expand the application scope of DAS.

Agliullin T., Anfinogentov V., Morozov O., Sakhabutdinov A., Valeev B., Niyazgulyeva A., Garovov Y.

The work is dedicated to a comparative analysis of the following methods for fiber Bragg grating (FBG) spectral response modeling. The Layer Sweep (LS) method, which is similar to the common layer peeling algorithm, is based on the reflectance and transmittance determination for the plane waves propagating through layered structures, which results in the solution of a system of linear equations for the transmittance and reflectance of each layer using the sweep method. Another considered method is based on the determination of transfer matrices (TM) for the FBG as a whole. Firstly, a homogeneous FBG was modeled using both methods, and the resulting reflectance spectra were compared to the one obtained via a specialized commercial software package. Secondly, modeling results of a π-phase-shifted FBG were presented and discussed. For both FBG models, the influence of the partition interval of the LS method on the simulated spectrum was studied. Based on the analysis of the simulation data, additional required modeling conditions for phase-shifted FBGs were established, which enhanced the modeling performance of the LS method.

Agliullin T., Il’In G., Kuznetsov A., Misbakhov R., Misbakhov R., Morozov G., Morozov O., Nureev I., Sakhabutdinov A.

An addressed fiber Bragg structure (AFBS) is a special type of fiber Bragg grating simultaneously performing the functions of a two-frequency radiation shaper and a sensitive element. An AFBS forms a two-frequency optical spectral response at its output, the difference frequency of which is invariant to measured physical fields and is referred to as the address frequency of the AFBS. Each of the AFBSs in the system has its own address frequency; therefore, a number of such structures can be interrogated simultaneously enabling the addressed multiplexing. In this article, we provide an overview of the theory and technology of AFBS, including the structures with three or more spectral components with various combinations of difference frequencies, both symmetrical and asymmetric. The subjects of interrogation of AFBSs, their fabrication and calibration are discussed as well. We also consider a wide range of applications in which AFBS can be used, covering such areas as oil and gas production, power engineering, transport, medicine, etc. In addition, the prospects for the further development of AFBS are proposed that mitigate the shortcomings of the current AFBSs’ state of the art and open up new possibilities of their application.

Cheng Y., Qian Y., Luo H., Chen F., Cheng Z.

In this paper, a narrowband perfect metasurface absorber (MSA) based on micro-ring-shaped structure GaAs array was proposed and investigated theoretically in terahertz (THz) region, which can be applicable for the enhanced refractive index (RI) sensing. Simulation results show that the proposed perfect MSA can achieve an absorbance of 99.9% at 2.213 THz and the Q-factor of about 460.08, which can be confirmed efficiently by the coupling mode theory (CMT). The perfect absorption of the designed structure is mainly contributed to the guided mode of the critical resonance coupling. The absorption properties of the proposed structure can be adjusted by changing the geometrical parameters of GaAs structure. Owing to its higher Q-factor, the proposed MSA can enhance the RI sensing application, and the sensitivity of about 1.45 THz/RIU can be achieved. The research provides a new route for the construction of the highly efficient MSA with potential applications in sensing, detecting, and imaging in THz region. • A narrowband perfect metasurface absorber (MSA) based on micro-ring-shaped GaAs array was proposed. • The MSA can achieve an absorbance of 99.9% at 2.213 THz and the Q-factor of about 481.08. • The absorption properties of the MSA can be adjusted by changing the geometrical parameters of GaAs structure. • The MSA can enhance the RI sensing application, and the sensitivity of about 1.45 THz/RIU be achieved.

Li Z., Cheng Y., Luo H., Chen F., Li X.

A dual-band terahertz (THz) perfect absorber (PA) based on the all-dielectric metamaterial (MM) composed of the vertical-square-split-ring (VSSR) structure InSb array was proposed and investigated numerically. Simulation results show that the absorbance of the proposed PA under room temperature T = 295 K is up to 99.9% and 99.8% at 1.265 THz and 1.436 THz, respectively, which is consistent well with the fitting results of coupling mode theory (CMT). According to the simulated electric field and power loss density distributions, the perfect absorption results from the excitation of the first- and second-order plasmonic resonance mode. Further results show that the designed PA is polarization-insensitive due to the high geometric rotational symmetry, and wide-angle absorption can be achieved for transverse magnetic (TM) waves. The geometric parameters of the VSSR structure InSb and the external environment temperature can be changed to adjust the resonance absorption properties of the designed dual-band PA. The dual-band PA can be functional as a temperature sensor with a sensitivity of about 5.9 GHz/K and 6.4 GHz/K, respectively. Furthermore, the dual-band PA under T = 295 K also can be served as a refractive index sensor with a sensitivity of about 1.3 THz/RIU and 1.0 THz/RIU, respectively. Due to its excellent properties including simple design, easy fabrication, polarization-insensitive and perfect absorption, the proposed dual-band PA may find many potential applications in detecting, imaging, and sensing in the THz region. • Dual-band tunable perfect absorber (PA) based on InSb structure was proposed in THz region. • The absorbance of PA is up to 99.9% and 99.8% at 1.265 THz and 1.436 THz, respectively. • Perfect absorption due to the first- and second-order plasmonic resonance mode in the InSb structure. • The dual-band PA can be served as temperature sensor with sensitivity 5.9 GHz/K and 6.4 GHz/K, and refractive index (RI) sensor with a sensitivity 1.3 THz/RIU and 1.0 THz/RIU, respectively.

Krivosheev A.I., Barkov F.L., Konstantinov Y.A., Belokrylov M.E.

This review describes state-of-the-art software and hardware methods for detecting the frequency shift of a stimulated and spontaneous Brillouin scattering spectrum for the needs of the distributed fiber-optic sensors and fiber-optic metrology industry. Current approaches to optical-fiber probing and signal detection are presented. Digital filtering methods that provide an increase in the signal-to-noise ratio of the spectrum are described. A review of Lorentzian curve fitting (LCF) spectrum approximation methods, correlation methods, artificial intelligence methods, and machine learning methods has been made.

Ponomarev R.S., Konstantinov Y.A., Belokrylov M.E., Shevtsov D.I., Karnaushkin P.V.

A system has been developed for studying the pyroelectric effect in integrated optical modulators (IOMs) based on proton-exchange channel waveguides on a lithium niobate substrate. The system is also able to control the docking of an IOM chip with an optical fiber. A laboratory-certified optical frequency domain reflectometer has been integrated into the system to provide sufficient accuracy in determining the spatial coordinate of the test sample and the high sensitivity in measuring backscattering and reflections. The use of certified metrological instrumentation makes it possible to certify the temperature drift of the refractive index in IOM waveguides and qualitatively observe the variation in the phase state of radiation at each point of the waveguide. The use of an automated signal-processing system, which allows the user to observe all the desired parameters of the test sample with a varying spatial coordinate along the IOM length, has made it possible to reduce the number of routine research procedures in data analysis and to focus on their content. The advantages and drawbacks of replacing the self-made prototype based on a tunable laser with a commercial optical frequency domain reflectometry system are discussed. The created and applied filter based on the algorithm of dynamic nonlinear averaging in space has made it possible to increase the signal-to-noise ratio of data by 6−10 dB.

Wang Q., Zhao K., Badar M., Yi X., Lu P., Buric M., Mao Z., Chen K.P.

This article investigates using optical fibers with enhanced backscattering profiles to improve distributed fiber sensor performance and reduce instrumentation costs. Using a femtosecond (fs) laser direct writing technique, the Rayleigh backscattering profile of a standard telecom fiber was enhanced by more than 40 dB to improve the signal-to-noise ratio (SNR) for optical frequency domain reflectometry (OFDR). The enhanced backscattering signals enable effectively distributed strain measurements using a low-cost tunable laser (TL). Median filtering is applied to denoise cross correlation results to further improve measurement outcomes. Results presented in this article show that a TL with a 1-nm tuning range, which is far less than the tuning range used in commercial OFDR interrogators, can perform effectively distributed strain measurements using sensing fibers with enhanced backscattering profiles. The sensing fiber with over 40-dB backscattering enhancement achieved 4.8-cm spatial resolution in strain measurements with a root mean square accuracy of less than 2.70 $\mu \varepsilon $ when 10–50 $\mu \varepsilon $ were exerted to the sensing fiber. Results presented in this article reveal both the potential and limitations of sensing fibers with enhanced backscattering for OFDR-based distributed fiber sensors.

Sbeah Z.A., Dwivedi R.P., Sorathiya V., Chauhan D., Adhikari R.

We proposed the narrow band graphene metamaterial-based infrared tunable 4-split ring-shaped absorber, it can be fabricated by the chemical vapor deposition method, using Finite Element Method simulations. The proposed design is numerically investigated for the wavelength range 1.2 µm to 1.6 µm and 99.5% of the absorption response was shown. A wide range tunability is achieved by changing the chemical potential of graphene with respect to external applied voltage. The absorption can be seen at three narrowband peaks at 1.205 µm, 1.318 µm and 1.456 µm wavelength in single-layered structure. The device works as metamaterial because it shows the negative refractive index response at resonating frequency. Because of its large tunable range, the device can be used in several applications like optical communication, biosensors, and solar absorbers and can be integrated in photonic integrated circuits.

Zhao J., Cheng Y.

A temperature-tunable terahertz (THz) perfect absorber (PA) composed of a periodic array of deep subwavelength micro-cross-shaped (MCS) structures of the strontium titanate (STO) resonator is proposed and investigated theoretically, which can be applicable for the temperature sensing. Simulation results indicate that the absorbance of 99.8% at 0.221 THz can be achieved when the designed PA is under the room temperature of T = 300 K, which is in good agreement with the calculation done by the coupling mode theory (CMT). The simulated distributions of electric and magnetic fields in the unit-cell structure of the designed PA reveal that the observed perfect absorption is mainly attributed to the Mie resonance of the all-dielectric MCS structure STO. In addition, this designed PA is polarization-insensitive and wide-angle absorption for both transverse magnetic (TM) and transverse electric (TE) waves. The resonance absorption properties of the designed PA can be controlled by changing the geometrical parameters of STO resonator structure. The designed PA can be served as a temperature sensor, which has a sensitivity of about 0.37 GHz K−1 since the electrical property of the STO is dependent on the variation of surrounding temperature. Furthermore, the perfect absorption can also be achieved by the PAs using the square, circular, and ring STO structures. The proposed design concepts of the STO-based tunable PAs can find potential THz applications in sensing, detecting, imaging, and so on.