Sapphire Fiber Research Articles

Integrating fiber optic sensors into metallic components for sensing in harsh environments

The integration of fiber optic sensors into high-temperature materials is critical for real-time monitoring and autonomous operation of engineering systems. This study demonstrated a spark plasma sintering (SPS)-assisted embedding process for integrating sapphire fiber optic sensors into stainless steel components during part fabrication. Optical fibers were encapsulated in stainless steel 316L powders which were sintered at different fabrication conditions using SPS to investigate the effects of sintering parameters on the embedment. Measurements of optical transmittance, combined with microstructural analysis (X-ray computed tomography and scanning electron microscopy) and mechanical testing (tensile and microhardness), were conducted to examine the fiber functionality, fiber–matrix bonding quality, and properties of the sintered materials. The results show that under suitable fabrication conditions, intact optical fibers can be encapsulated in highly-densified (>98 % relative density) stainless steel components. These conditions also led to a good bond at the fiber–matrix interface with micron-sized material interdiffusion across the interface. The sintering parameters were observed to affect fiber optical attenuation, where high temperature, pressure, and hold time during SPS enhanced fiber–matrix bonding and adversely affected optical transmission. Tensile testing confirmed the superior tensile strength and ductility of the matrix fabricated by SPS. Furthermore, the materials exhibited limited strength reduction (∼70 MPa) upon the integration of fibers. This study demonstrates the effectiveness of SPS for fiber-material integration for high-temperature applications.

Сomposites with a Matrix Based on Niobium and Molybdenum Reinforced with Sapphire Fibers

Сomposites with a Matrix Based on Niobium and Molybdenum Reinforced with Sapphire Fibers

Composite Material with a Ti–Al–Nb Matrix Reinforced with Sapphire Fibers

Composite Material with a Ti–Al–Nb Matrix Reinforced with Sapphire Fibers

Сomposites with a Matrix Based on Niobium and Molybdenum Reinforced with Sapphire Fibers

Сomposites with a Matrix Based on Niobium and Molybdenum Reinforced with Sapphire Fibers

Highly cascaded first-order sapphire optical fiber Bragg gratings fabricated by a femtosecond laser.

This Letter reports an innovative technique for fabricating large-scale, highly cascaded first-order sapphire optical fiber Bragg gratings (FBGs) using a femtosecond laser-assisted point-by-point inscription method. For the first time, to the best of our knowledge, this study successfully demonstrates a distributed array of 10 FBGs within highly multimode sapphire crystal fiber, made possible by employing a high-power laser technique to generate larger reflectors with a Gaussian intensity profile. These first-order FBGs offer advantages such as enhanced reflectivity, shorter fabrication time, and simplified spectral characteristics, making them easier to interpret compared with high-order FBGs. The FBGs' resilience and effectiveness are analyzed by subjecting them to temperature tests, proving their capacity for accurate temperature monitoring up to 1500°C-a testament to their suitability for harsh environments. This novel approach broadens the scope for sensing and communication applications in sapphire fibers, particularly under challenging conditions. The novelty of our work lies in successfully overcoming the limitations of previous designs by integrating a cascade of 10 FBGs in sapphire fibers, thereby enhancing multiplexing capabilities, minimizing overlapping of FBG peaks, and ensuring reliable temperature monitoring in industries and applications with thermal gradients.

High-Order Mode Suppression in Sapphire Fiber Bragg Gratings Based on Mode Field Matching Fusion Splicing for Single-Mode Demodulation Systems

High-Order Mode Suppression in Sapphire Fiber Bragg Gratings Based on Mode Field Matching Fusion Splicing for Single-Mode Demodulation Systems

Oxygen sensing with SrTi1−xFexO3-δ thin films on sapphire optical fiber at extreme temperatures

Optical fiber-based sensors are uniquely suited for in-situ sensing applications that involve high operational temperature and harsh chemical conditions, such as solid oxide fuel cell (SOFC) monitoring, chemical manufacturing, and power generation. Single crystal optical fiber, such as α-alumina (sapphire), provides a substrate that exhibits improved stability over off-the-shelf silica fiber at temperatures above 800 °C. In this work, single crystal sapphire fiber is paired with a high-temperature stable perovskite oxide sensing layer, SrTi0.65Fe0.35FeO3-δ (STF35), to demonstrate all-optical oxygen sensing from 0.01 to 0.19 atm at extreme temperatures (800–1000 °C). The defect chemistry associated with the optical oxygen sensing response is also considered within the context of the current literature and modeled under relevant sensor conditions. Stability is evaluated under dry and humid conditions, and low cross-sensitivity with CO2 is demonstrated, indicating viability for operation on the cathode stream within an operational SOFC or within a post-combustion environment.

Anisotropic growth and characterizations of large length-diameter ratio sapphire fibers via laser-heated pedestal growth technique

Sapphire fiber is a promising candidate for harsh environment sensing due to its high melting point, compact structure, and corrosion resistance, where the fiber with a smaller diameter and a larger length-diameter ratio is being widely demanded. In this work, high quality sapphire crystal fibers with minimum diameter of 25 μm and maximum length of 24.5 m were successfully prepared by laser-heated pedestal growth technique, which is the dimension record for crystal fibers that ever reported. Sapphire fibers exhibit anisotropic growth behaviors and the c-oriented sapphire fibers were demonstrated to have higher tensile strength compared to a-oriented sapphire fibers, illustrating superior mechanical properties. Moreover, various essential properties such as flexibility, surface roughness, and crystallinity have also been systematically investigated.

Ultra-high sensitivity microwave-photonic sapphire fiber Fabry-Perot interferometry based on the Vernier effect.

The wavelength of microwave is longer than that of lightwave, causing the interferometric optical path difference induced by the measurand changes to be relatively smaller than that of microwave, which results in the lower sensitivity of sapphire fiber Fabry-Perot interferometer (FPI) sensor in microwave band. To improve sensitivity, a parallel FPI sensing system is constructed, in which a section of sapphire fiber connected to a single-mode transmission fiber is used as a sensing FPI, and a single-mode fiber (SMF) with a slightly different optical path from a sensing FPI is utilized as a reference FPI. By connecting two FPIs in parallel, Vernier effect is formed to improve sensitivity. The influence of relationship between the optical path difference of the reference FPI and the sensing FPI on the sensitivity amplification factor is analyzed based on the microwave interference spectrum of the parallel FPI. A section of sapphire fiber with the length of 8 cm is used as temperature sensor to construct high-temperature sensing system. The results demonstrate that the temperature sensitivity reaches about 2338.68kHz/°C, which is approximately 130 times higher than that of the sensing FPI alone. Furthermore, when the difference of optical path between the sensing FPI and the reference FPI is kept constant while the sensing FPI is unchanged, the amplification factor of the temperature sensitivity is approximately 2.64 times higher with longer length of the reference FPI compared to the situation with shorter length of the reference FPI.

Dependence of Bending Strength on Length and Diameter of Sapphire Fibers Grown by the Stepanov Technique

Dependence of Bending Strength on Length and Diameter of Sapphire Fibers Grown by the Stepanov Technique

A Liquid Metal Temperature Detection System Based on Multi-Node Sapphire Fiber Sensor.

In order to accurately detect the temperature of molten aluminum and overcome the adverse influence of high temperature and corrosiveness on the sensing results, a temperature detection system based on a multi-node sapphire fiber sensor was proposed and developed. Through the structural parameter design of the fiber sensor, the scheme of utilizing the 0.7 mm diameter fiber and 0.5 mm groove was formulated. Simulation and analysis were carried out to determine the ultrasonic response distribution of the signal passing through the whole fiber sensor. The results indicate that the system is capable of distinguishing test signals from various positions and temperatures. Following the completion of the static calibration, the temperature of the molten aluminum was observed in real-time, and the data of the temperature measurements conducted at the two groove locations were compared. According to the obtained results, the test accuracy was greater than 1 degree Celsius and the temperature test stability was good, laying a solid foundation for the potential development of temperature measurement devices.

Improving the efficiency of an optical-to-terahertz converter using sapphire fibers

Objectives. The study aims to improve the efficiency of a large-area photoconductive terahertz (THz) emitter based on an optical-to-terahertz converter (OTC) having a radiating area of 0.3 × 0.3 mm2 for generating high-power THz radiation by using an array of close-packed profiled sapphire fibers having a diameter in the range of 100–300 μm as focusing optics.Methods. As a photoconductive substrate, we used a semi-infinite LT-GaAs layer (low-temperature grown GaAs; GaAs layer grown by molecular beam epitaxy at a low growth temperature). Additional Si3N4 and Al2O3 layers are intended for reducing leakage currents in the OTC and reducing the reflection of the laser pump pulse from the air/semiconductor interface (Fresnel losses), respectively, at a gap width of 10 μm. For forming the antenna electrodes and feed strips, the Ti/Au metal system was used. The simulation was carried out by the finite element method in the COMSOL Multiphysics environment.Results. The use of a profiled sapphire fiber whose diameter has been optimized with respect to the gap parameters to significantly increase the concentration of charge carriers in the immediate vicinity of the electrodes of an OTC is demonstrated. The integrated efficiency of a large-area photoconductive THz emitter was determined taking into account the microstrip topology of the array with a characteristic size of feed strips proportional to the gap width in the OTC and with the upper (masking) metal layer. The maximum localization of the electromagnetic field in close proximity to the edges of electrodes at the “fiber–semiconductor” interface is achieved with a profiled sapphire fiber diameter of 220 μm.Conclusions. By optimizing the diameter of the sapphire fiber, the possibility of improving the localization of incident electromagnetic waves in close proximity to the edges of the OTC electrodes by ~40 times compared to the case without fiber, as well as increasing the overall efficiency of a large-area emitter by up to ~7–10 times, was demonstrated.

An All-Sapphire Fiber Diaphragm-Free Extrinsic Fabry–Perot Interferometric Sensor for the Measurement of Gas Pressure at Ultrahigh Temperature

An all-sapphire fiber extrinsic Fabry–Perot interferometer (EFPI) sensor for the measurement of gas pressure at ultrahigh temperature is proposed and experimentally demonstrated. The sensor head is composed of two segments of sapphire fiber and a sapphire capillary. By using the femtosecond (fs) laser micromachining, a through hole is inscribed in the sapphire capillary wall to allow the gas flow. This EFPI is used to measure the pressure in the temperature range of 25 °C–1400 °C by monitoring the optical cavity length (OCL) of the interferometer. Experiment results show that the sensor exhibits a good linearity within a pressure range from 0 to 5 MPa at a fixed temperature. The pressure sensitivity of the sensor decreases as the temperature increases, and sensitivities are 1.018 and <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$0.188 \mu \text{m}$ </tex-math></inline-formula> /MPa at 25 °C and 1400 °C, respectively. The proposed all-sapphire fiber pressure sensor has the properties of high-temperature resistance, intrinsic safety, small volume, and large measuring range, which can be used in high-temperature and harsh environments.

Thermally robust and highly stable method for splicing silica glass fiber to crystalline sapphire fiber.

This research reports an advancement in splicing silica glass fiber to sapphire single-crystal optical fiber (SCF) using a specialized glass processing device, including data that demonstrate the thermal stability of the splice to 1000°C. A filament heating process was used to produce a robust splice between the dissimilar fibers. A femtosecond laser is used to inscribe a fiber Bragg gratings sensor into the SCF to measure the high-temperature capabilities and signal attenuation characteristics of the splice joint. The experimental results demonstrate that the proposed splicing method produces a splice joint that is robust, stable, repeatable, and withstands temperatures up to 1000°C with a low attenuation of 0.5dB. The proposed method allows placement of SCF-based sensors in the extreme environments encountered in various engineering fields, such as nuclear, chemical, aviation, and metals manufacturing, to enable improvements in process monitoring, product quality, and production efficiency.

Wafer-scale controlled growth of MoS2 by magnetron sputtering: from in-plane to inter-connected vertically-aligned flakes

Recently, Molybdenum disulfide (MoS2) has attracted great attention due to its unique characteristics and potential applications in various fields. The advancements in the field have substantially improved at the laboratory scale however, a synthesis approach that produces large area growth of MoS2 on a wafer scale is the key requirement for the realization of commercial two-dimensional (2D) technology. Herein, we report tunable MoS2 growth with varied morphologies via radio frequency magnetron sputtering by controlling growth parameters. The controlled growth from in-plane to vertically-aligned (VA) MoS2 flakes has been achieved on a variety of substrates (Si, Si/SiO2, sapphire, quartz, and carbon fiber). Moreover, the growth of VA MoS2 is highly reproducible and is fabricated on a wafer scale. The flakes synthesized on the wafer show high uniformity, which is corroborated by the spatial mapping using Raman over the entire 2-inch Si/SiO2 wafer. The detailed morphological, structural, and spectroscopic analysis reveals the transition from in-plane MoS2 to VA MoS2 flakes. This work presents a facile approach to directly synthesize layered materials by sputtering technique on wafer scale. This paves the way for designing mass production of high-quality 2D materials, which will advance their practical applications by integration into device architectures in various fields.

Композит с матрицей на основе Ti—Al—Nb, армированной волокнами сапфира

The structure of a layered composite material with a Ti—Al—Nb matrix reinforced with sapphire fibers has been studied. The composite was produced by diffusion welding under pressure of a multilayer package of alternating titanium and aluminum foils and unidirectional sapphire fibers, the gaps between which were filled with a suspension of niobium powder in polyethylene glycol. The strength of the prototype composite during the three-point bending test was 460 MPa at 20 °C and 140 MPa at 1100 °C. The deformation curves and developed fracture surfaces indicate the non-brittle nature of the fracture of the composite structure containing brittle components.

Жгуты оптических волокон c высоким показателем преломления для проведения ТГц визуализации с субволновым разрешением (обзор)

Bundles or bundles of optical fibers are finding increasing applications in various areas of fiber optics, despite the relatively low resolution of such devices, which does not exceed the wavelength λ. One way to solve this problem is to use materials with a high refractive index, which will allow for strong localization of radiation modes in the fiber. This review discusses the use of sapphire fibers with a high refractive index of n&gt;3 for these purposes. They are used as the basis for fiber bundles operating in the terahertz (THz) range and provide visualization with spatial resolution exceeding the Abbe diffraction limit for free space. Bundles of sapphire fibers of various configurations have been manufactured, consisting of arrays of parallel and non-parallel fibers, and theoretical and experimental evaluations of their spatial resolution have been obtained using both analysis of the paired correlation function of disordered fiber packing and THz imaging. In particular, for a bundle consisting of parallel fibers with metallic coating, the resolution varies with aperture with a mean value of 0.53.λ and can reach 0.3 λ in individual areas. For a bundle with diverging fibers with dielectric coating, the resolution is 0.35 λ, which significantly exceeds the Abbe limit. The developed principles can be transferred to any spectral range where materials for fiber optics with a high refractive index are available. Finally, methods for reconstructing THz images of test binary objects obtained using the proposed bundles are described.

Improved spectral demodulation algorithm with EEMDAD for sapphire fiber Fabry-Perot high-temperature sensing.

In this paper, an improved spectral demodulation algorithm with the ensemble empirical mode decomposition average denoising is proposed to suppress order jumps in the sapphire fiber Fabry-Perot high-temperature sensing system. It is proven that the signal-to-noise ratio of the sensor is closely related to the severity of the demodulation jumps. The proposed algorithm can reduce the fluctuations of key parameters by reducing the noise in the spectrum, thus overcoming this obstacle. The simulations and experiment demonstrate that the algorithm can effectively eliminate the order jumps in both stable and variable temperature environments. The proposed algorithm solves the order jumping problem that has long plagued the demodulation of this system, improves demodulation accuracy, ensures the reliable operation of the high-temperature sensor, and exhibits excellent demodulation performance.

Point-by-point inscribed sapphire parallel fiber Bragg gratings in a fully multimode system for multiplexed high-temperature sensing.

We study the point-by-point inscription of sapphire parallel fiber Bragg gratings (sapphire pFBGs) in a fully multimode system. A parallel FBG is shown to be critical in enabling detectable and reliable high-order grating signals. The impacts of modal volume, spatial coherence, and grating location on reflectivity are examined. Three cascaded seventh-order pFBGs are fabricated in one sapphire fiber for wavelength multiplexed temperature sensing. Using a low-cost, fully multimode 850-nm interrogator, reliable measurement up to 1500°C is demonstrated.

Femtosecond Laser-Based Micromachining of Rotational-Symmetric Sapphire Workpieces

Sapphire is a robust and wear-resistant material. However, efficient and high-quality micromachining is still a challenge. This contribution demonstrates and discusses two novels, previously unreported approaches for femtosecond laser-based micromachining of rotational-symmetric sapphire workpieces, whereas both methods are in principal hybrids of laser scanning and laser turning or laser lathe. The first process, a combination of a sequential linear hatch pattern in parallel to the workpiece’s main axis with a defined incremental workpiece rotation, enables the fabrication of sapphire fibers with diameters of 50 μm over a length of 4.5 mm. Furthermore, sapphire specimens with a diameter of 25 μm over a length of 2 mm can be fabricated whereas an arithmetical mean height, i.e., Sa parameter, of 281 nm is achieved. The second process combines a constant workpiece feed and orthogonal scanning with incremental workpiece rotation. With this approach, workpiece length limitations of the first process are overcome and sapphire fibers with an average diameter of 90 µm over a length of 20 cm are manufactured. Again, the sapphire specimen exhibits a comparable surface roughness with an average Sa value of 249 nm over 20 cm. Based on the obtained results, the proposed manufacturing method paves an innovative and flexible, all laser-based way towards the fabrication or microstructuring of sapphire optical devices, and thus, a promising alternative to chemical processes.