Fiber Interferometry Research Articles

On elastic deformations of cylindrical bodies under the influence of the gravitational field

Background Elastic deformations of gravitating cylindrical bodies are relevant for state-of-the-art photonic experiments, as they affect the physical properties of materials under consideration, impacting wave propagation. This is of key importance for a recently planned experiment to explore the influence of the gravitational field on entangled photons propagating in waveguides. The purpose of this work is to determine these elastic deformations as functions of temperature, pressure, and of the gravitational field. We thus determine the deformations of the body due to changes of the gravitational field, and obtain stringent bounds on the control of temperature and pressure so that the effects of the associated elastic deformations on the photons propagating in a waveguide are smaller than the phase shifts associated with the change of the gravitational field. Methods We use the methods of linear elasticity, including thermoelasticity, to determine the stresses and strains of the medium. For this, the symmetry of the cylinder allows us to solve the problem by using Mitchell’s solutions of the equations satisfied by the Airy functions. The boundary conditions are implemented by an approximation of the Hertz contact method. Results We calculate the displacements, the stresses and strains for several classes of boundary conditions, and give explicit solutions for a number of physically motivated configurations. The influence of the resulting deformations on the planned GRAVITES experiment is determined. Conclusions The results are relevant for fiber interferometry experiments sensitive to the effects of the gravitational field on photon propagation. Our calculations give stringent bounds on the environmental variables, which need to be controlled in such experiments.

A comprehensive review of using optical fibre interferometry for intrusion detection with artificial intelligence techniques

A comprehensive review of using optical fibre interferometry for intrusion detection with artificial intelligence techniques

Ultra-wide range non-contact surface profilometry based on reconfigurable fiber interferometry.

Surface characterization is essential for a technical evaluation of device performance and to assess surface dynamics in fabrication units. In this regard, a number of surface profiling techniques have been developed that accurately map sample topography but have significantly limited detection range. Here, we demonstrate a cascaded non-contact fiber interferometer-based approach for real-time high-precision surface profiling with ultrawide detection range (nm to mm). This compact interferometers' system operates by wavelength interrogation that provides a scope to study several types of surfaces and has a tunable cavity configuration for varying the sensitivity and range of the detectable features' size. The proposed system enables nanoscale profiling over 10-1000 nm with resolution of 10 nm and microscale mapping over 1-1000 µm with resolution of 0.2 µm. The technique is utilized to map the features of nanostructured surfaces and estimate the surface roughness of standardized industrial samples.

Highly Sensitive Magnetic Field Sensor Based on Few-Mode Fiber Interferometry

Highly Sensitive Magnetic Field Sensor Based on Few-Mode Fiber Interferometry

On elastic deformations of cylindrical bodies under the influence of the gravitational field.

Large elastic deformations of gravitating cylindrical bodies play a significant role in everyday life. On the other hand, tiny such deformations are relevant for state-of-the art experiments, as they affect the physical properties of materials under consideration, impacting wave propagation. This is of key importance for a recently planned experiment to explore the influence of the gravitational field on entangled photons propagating in waveguides. The purpose of this work is to determine this influence. We use the methods of linear elasticity, including thermoelasticity, to determine the stresses and strains of the medium. For this, the symmetry of the cylinder allows us to solve the problem by using Mitchell's solutions of the equations satisfied by the Airy functions. The boundary conditions are implemented by an approximation of the Hertz contact method. We calculate the displacements, the stresses and strains for several classes of boundary conditions, and give explicit solutions for a number of physically motivated configurations. The influence of the resulting deformations on the planned GRAVITES experiment is determined. The results are relevant for fiber interferometry experiments sensitive to the effects of the gravitational field on photon propagation. Our calculations give stringent bounds on the environmental variables, which need to be controlled in such experiments.

FIBER OPTIC SENSORS

In addition to the benefits, recent developments and cost reductions have sparked interest in fiber optical sensing. In order fiber optic sensors must be made, researchers integrated optoelectronic devices with fiber optic telecommunications' byproducts. In the past few decades, numerous studies using various research methods and fiber optic sensors have been carried out. The most popular sensor types for fiber optics are those based on intensity, phase, and wavelength. An overview of optic sensors and their uses is provided in this paper. Keywords: Fiber optics, smart systems, interferometry, microbending, and fiber Bragg gratings (FBGs)

In-fiber interferometry sensors for refractive index

Compact interferometers based on waveguiding structures have found countless applications in refractive index measurements, chemical sensing, as well as temperature and pressure measurements. The most common fiber devices are based on Mach–Zehnder interferometry and Michelson interferometry—two design concepts that can readily be implemented using simple fiber optic components, such as mode splitters and combiners, fiber optic gratings, and fiber tapers, among others. Fiber interferometry can also be conducted based on the Sagnac effect and the Young (double-slit) interferometer. In this review, we examine and compare over 400 fiber optic interferometers as well as more than 60 fiber optic refractive sensors based on fiber optic cavities. Even though many of the devices show temperature-, strain-, and pressure-sensitivity, we focus our review on refractive index measurements, as these are the most common applications. Many devices were characterized by their inventors using their sensitivity to refractive index changes. While the sensitivity is an important characteristic of the device, it does not easily relate to the smallest resolvable refractive index change or the limit of detection when applied to chemical measurements. Instead, we propose here that one should use the figure of merit, which is defined through the refractive index sensitivity and the width of an interferometer fringe. Using simple assumptions, we were able to mathematically relate the sensitivity and the figure of merit to common design parameters, such as the length of the interferometer arms, the operating wavelength, refractive indices of the fiber and the sample, as well as an overlap parameter, which describes the fraction of the guided wave in the sensing arm that interacts with the sample. We determined this overlap parameter for each reviewed device from the reported interferograms. Our meta-analysis provides for the first time simple and easily applicable guidance to increase the figure of merit of fiber optic interferometers and fiber optic cavities with regard to their ability to detect small refractive index changes. A high figure of merit allows measuring very small refractive index changes such as those of gases at different pressures or of very dilute solutions.

Limits and prospects for long-baseline optical fiber interferometry

Today’s most precise optical instruments—gravitational-wave interferometers and optical atomic clocks—rely on long storage times for photons to realize their exquisite sensitivity. Optical fiber technology is the most widely deployed platform for realizing long-distance optical propagation. Yet, its application to precision optical measurements is sparse. We review the state of the art in the noise performance of conventional (solid-core) optical fibers from the perspective of precision optical measurements and quantum technology that rely on precise transfer of information over long distances. In doing so, we highlight the limitations of this platform and point to the opportunities that structured fiber technology offers to overcome some of these limitations.

Sensitive seismic sensors based on microwave frequency fiber interferometry in commercially deployed cables

The use of fiber infrastructures for environmental sensing is attracting global interest, as optical fibers emerge as low cost and easily accessible platforms exhibiting a large terrestrial deployment. Moreover, optical fiber networks offer the unique advantage of providing observations of submarine areas, where the sparse existence of permanent seismic instrumentation due to cost and difficulties in deployment limits the availability of high-resolution subsea information on natural hazards in both time and space. The use of optical techniques that leverage pre-existing fiber infrastructure can efficiently provide higher resolution coverage and pave the way for the identification of the detailed structure of the Earth especially on seismogenic submarine faults. The prevailing optical technique for use in earthquake detection and structural analysis is distributed acoustic sensing (DAS) which offers high spatial resolution and sensitivity, however is limited in range (< 100 km). In this work, we present a novel technique which relies on the dissemination of a stable microwave frequency along optical fibers in a closed loop configuration, thereby forming an interferometer that is sensitive to deformation. We call the proposed technique Microwave Frequency Fiber Interferometer (MFFI) and demonstrate its sensitivity to deformation induced by moderate-to-large earthquakes from either local or regional epicenters. MFFI signals are compared to signals recorded by accelerometers of the National Observatory of Athens, Institute of Geodynamics National Seismic Network and by a commercially available DAS interrogator operating in parallel at the same location. Remarkable agreement in dynamical behavior and strain rate estimation is achieved and demonstrated. Thus, MFFI emerges as a novel technique in the field of fiber seismometers offering critical advantages with respect to implementation cost, maximum range and simplicity.

Artificial Receptor‐Based Optical Sensors (AROS): Ultra‐Sensitive Detection of Urea

The combined approach of optical fiber interferometry with molecular imprinting technology has shown a tremendous potential for developing a specific and sophisticated bio‐detection system with high degree of resolution and sensitivity. However, the specificity limitation of the fiber optic sensors renders them unsuitable for several key applications. Molecular imprinted polymer (MIP), an indispensable artificial molecular receptor with a complementary structure and functionality for the target analyte, possesses the ability to overcome the limitations of specificity. Therefore, a new class of artificial receptor‐based optical sensors (AROS) constructed from an optical fiber interferometer integrated with artificial MIP for selective and ultrasensitive sensing of urea is demonstrated. The sensor device shows an unprecedented sensitivity of 0.584 × 1011 nm m −1 and a lower detection limit of 17.1 fM with a wide dynamic range of 10−11–10−4 m. This demonstration of an ultrasensitive, selective, and accurate AROS system is bound to find potential applications that requires remote sensing in harsh environmental conditions with large fluctuations in the temperature, pressure, and humidity.

Sensitivity-enhanced microwave-photonic optical fiber interferometry based on the Vernier effect.

This paper proposes optical carrier microwave interferometry (OCMI)-based optical fiber interferometers for sensing applications with improved measurement sensitivity with the assistance of the Vernier effect. Fabry-Perot interferometers (FPIs) are employed in the proof of concept. A single-FPI-OCMI system is first demonstrated for measurements of variations of temperatures by tracking the spectral shift of the interferogram in microwave domain. By cascading two FPIs with slightly different optical lengths, the Vernier effect is generated in the magnitude spectrum of the system with a typical amplitude-modulated signal. By tracking the shift of the envelope signal, temperature measurements are experimentally demonstrated with greatly enhanced sensitivity. The amplification factor for the measurement sensitivity can be easily adjusted by varying the length ratio of the two cascaded FPIs. In addition to the experimental demonstration, a complete mathematical model of the FPI-OCMI system and the mechanism for the amplified sensitivity due to Vernier effect is presented. Numerical calculations are also performed to verify the analytical derivations.

Microwave-photonic optical fiber interferometers for refractive index sensing with high sensitivity and a tunable dynamic range.

We propose and demonstrate an extremely simple yet novel sensing strategy for measurements of a refractive index (RI) based on microwave-photonic optical fiber interferometry. A hybrid interferometric system based on an incoherent optical interferometer (i.e., a Michelson interferometer [MI]) and a coherent optical interferometer (i.e., a Fabry-Perot interferometer [FPI]) is constructed simply by using a low-cost off-the-shelf fiber coupler. The sensing arm of the MI is highly sensitive to a surrounding RI based on Fresnel reflection, where variations of the ambient RI cause changes in both the reflection magnitudes of the resonance frequencies and fringe visibility of the reflection spectra in the microwave domain. The coherent FPI is employed to tune the dynamic range of the MI by adjusting the effective reflectance of the reference arm of the MI. Essentially, other approaches that can vary the reflectance of the reference arm of the MI can also be used to tune the dynamic range of the system based on the proposed strategy. The experimental results are in good agreement with theoretical predictions. The prominent advantages of the sensor, including low cost, ease of fabrication, robustness, compactness, high sensitivity, and tunable dynamic range, make it a strong candidate in various chemical, biological, and environmental applications.

Application Research of Frequency-Modulated Continuous-Wave Displacement Sensor Based on Zero-Crossing Phase Detecting Algorithm

Frequency-modulated continuous-wave (FMCW) interference, as a new technology of laser interferometry, has the advantages of length traceability, large range, high accuracy, simple structure, and optical fiber transmission. Based on the formula of FMCW laser interference displacement, a zero-crossing phase detection algorithm is proposed, which can accurately calculate the initial phase of a cosine signal in a modulation period, and it is successfully applied to the contact laser interference displacement sensor. The experimental results show that the FMCW technology based on the zero-crossing phase detection algorithm can achieve the technical specifications of the contact displacement sensor with a measurement range greater than 15 mm and the standard deviation is less than 0.01 μm. The conversion of noncontact measurement to contact measurement can realize the direct measurement of workpieces with complex surface conditions on the production line, breaking through the limitation of optical measurement and expanding the application of optical fiber interferometry.

Ultra-Sensitive Microwave-Photonic Optical Fiber Interferometry Based on Phase-Shift Amplification

This paper proposes phase-shift-amplified optical fiber interferometry based on microwave photonics (MWP) for sensing applications with substantially-improved sensitivity. The principal idea of the system combines a destructive interference-based phase-shift amplification technique with optical carrier-based microwave interferometry (OCMI). The phase sensitivity of the OCMI system is significantly improved due to the phase amplifier, and more importantly, can be adjusted by simply varying the amplitude ratio of the two beams used in the interferometer. The amplification of the phase sensitivity is numerically investigated and experimentally demonstrated using a Mach-Zehnder interferometer for temperature and strain measurements. The measurement results accurately match theoretical predictions. Moreover, we demonstrate that light-scattering dots in the optical fiber core, created by tightly-focused femtosecond laser pulses, can be used to precisely tune the amplitude ratio of the two-beam interferometer. We postulate that amplification of several orders of magnitude in phase sensitivity can be achieved in the OCMI system by employing micromachining methods.

No-core fiber interferometry pH sensor based on a polyvinyl alcohol/polyacrylic acid and silica/polyvinyl alcohol/polyacrylic acid hydrogel coating.

In this paper, we present an investigation on the sensing performance of a pH sensor based on a modal interferometer formed by a simple NO-core fiber interferometer (NCFI) that operates in transmission mode. The fundamental configuration of this sensor encompasses a single-mode-no-core-single-mode fiber (SMF-NCF-SMF "SNCS") segment chain. The chemical etching method has been used with hydrofluoric (HF) acid to prepare diverse NCF diameters. This was proposed to expand the evanescent fields and enhance sensor sensitivity. Then, the two diverse segments of etched NCF were cladded with polymeric composite fabricated by polyvinyl alcohol/polyacrylic acid (PVA/PAA) hydrogel and pure silica nanoparticles embedded in polyvinyl alcohol/polyacrylic acid (SiO2@PVA/PAA) hydrogel, respectively, for more sensing enhancement. Our results reveal that the PAA/PVA coating is a candidate coating material for acidic sensing, while SiO2@PVA/PAA is more appropriate for the base sensing, in which these coating materials show enhancement in the sensitivity above the NCF structure before an uncoated sensor due to greater enhancement of the evanescent field affected by the coating layer. The experimental results demonstrate a high average sensitivity of 3.42 nm/pH unit for the 11 w.t.% PVA/PAA coated sensor in the pH range from 1 to 7 and 3.2 nm/pH unit in the pH range from 8 to 14. The sensor also displays high repeatability and stability and low cross-sensitivity to temperature. The simple fabrication and high sensitivity of this sensor may prompt many potential applications in the fields of biology and chemistry.

Application of contact laser interferometry in precise displacement measurement

The technology of frequency modulated continuous wave (FMCW) laser interferometer comes from optical interferometry technology, which has the characteristics of less than traditional interferometer devices, high precision, large range and anti-electromagnetic interference. Through in-depth research on the principle of FMCW measurement, taking full advantage of laser interference technology, and combining the features of anti-interference and easy installation of contact sensors, an innovative contact type long-range displacement sensor based on FMCW is proposed. The conversion of non-contact measurement to contact measurement can realize the direct measurement of workpieces with complex surface conditions on the production line, breaking through the limitation of optical measurement and expanding the application of optical fiber interferometry.

Bidirectional Interferometric Flowmeter With Linear Sensitivity and Large Dynamic Range

We propose a bidirectional flowmeter based on specialty fiber interferometry by controlled mode excitation for measuring the frequency of the vortices induced by a bluff body. The proposed arrangement of the cylindrical bluff body with a slit and the interferometric system based on modal excitation allows the bidirectional flowmeter to determine the flow velocities in either direction precisely and effectively. We have encapsulated the specialty fiber interferometer in a protective metal casing, which not only allows the interferometer to respond to the vortex frequency but also provides mechanical stability to the whole flowmeter so at to operate in a harsh environment. Experiments are conducted by introducing the modal interferometer in the slit of the cylindrical bluff body at various flow rates ranging from Reynolds number (Re) = 7200 to 56 600. A linear response is observed between the flow velocity and the vortex frequency from both directions. Thus, this work provides a reconfigurable bidirectional flowmeter, which is sensitive even at low flow rates and demonstrates a large operating range.

High-Speed FBG Interrogation With Electro-Optically Tunable Sagnac Loops

We report high-speed Fiber Bragg Grating (FBG) interrogation based on fiber interferometry. An electro-optical modulator, used as a tunable retarder, is implemented in a fiber Sagnac loop, enabling fast tuning of the interference fringes. Applying an active modulation scheme, the wavelength of the FBG can be retrieved without any requirement of the spectral position of the FBG with respect to the fringes, with no need of tunable sources or spectral analysis. We report experimental results of wavelength measurements with a bandwidth of 100 kHz (only limited by our data acquisition rate) and a dynamic wavelength resolution of σ = 3.7 fm/√Hz (corresponding to a strain resolution of 3.1 nϵ/√Hz). We also show that the system can track a continuous tunable laser sweep of 40 nm along the C-band. The technique is polarization-independent and allows wavelength division multiplexing schemes using only one interferometer for all the sensing points. The system is fully based on low-cost off-the-shelf fiber-optical components, and the free-spectral-range of the interferometer can be easily modified by just changing the length of the polarization-maintaining fiber segment.

Stability investigation of a cryo soft x-ray microscope by fiber interferometry.

We present a stability investigation of the Stockholm laboratory cryo soft x-ray microscope. The microscope operates at a wavelength of 2.48 nm and can image biological samples at liquid-nitrogen temperatures in order to mitigate radiation damage. We measured the stability of the two most critical components, sample holder and optics holder, in vacuo and at cryo temperatures at both short and long time scales with a fiber interferometer. Results revealed vibrations in the kHz range, originating mainly from a turbo pump, as well as long term drifts in connection with temperature fluctuations. With improvements in the microscope, earlier stability issues vanished and close-to diffraction-limited imaging could be achieved. Moreover, our investigation shows that fiber interferometers are a powerful tool in order to investigate position-sensitive setups at the nanometer level.

Compensation method for signal drift induced by time delay difference in phase retrieval algorithm for distributed fiber interferometry using asymmetric 3 × 3 coupler

AbstractPhase retrieval algorithm is an important part of optic‐fiber interferometry system. In this article, drift of the retrieved signal caused by the time delay difference between two interference signals from asymmetric 3 × 3 coupler is theoretically analyzed, and a compensation algorithm to solve this problem is proposed. Through simulation and experiment in real sensing system, the compensation algorithm can effectively eliminate the signal drift induced by the time delay difference, and enhance the accuracy of the signal in real sensing system.