Interferometer Research Articles

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

Modeling and optimization of photonic integrated Silicon-LiNbO3 hybrid interferometer for E-S-C-L wavelength band

Abstract The Silicon on Insulator (SOI) is a potential technology for thin-film optical waveguide, enabling the design of optical interconnects, including modulators and interferometers. The manuscript presents the broadband modulator for phase and intensity modulation. The nanoscale optimized interferometric modulator utilizes Silicon (Si) and Electro-optic material Lithium Niobate (LiNbO3) as the guiding material to work in terahertz regime, without any bends in the structure. Optimization of the structure is validated by the evaluation of the confinement factor at the operational wavelength of 1550 nm using Finite Element Method (FEM) based simulation. To excite the SOI interferometric modulator, an external RF signal with a maximum amplitude of 5 V is used. The hybrid structure of Si and LiNbO3-based modulators shows the electro-optic phenomenon caused by nonlinearities, namely the Pockels effect and Kerr effect, which in turn changes the effective mode index, providing π phase shift along with −0.92 dB/cm absorption loss, 117 μm electrode length at V π Volts and 265 nm 3dB optical bandwidth covering the E-S-C-L optical bands. The device footprint calculated is 667 μm2, whereas the active region footprint is ∼46.8 μm2.

Integrated hybrid optical fiber Mach-Zehnder interferometers for simultaneous measurement of seawater temperature and salinity

An integrated hybrid Mach-Zehnder (MZ) interferometer based on femtosecond laser micromachining for simultaneous measurement of seawater temperature and salinity was proposed. Two microcavities were machined on the multimode fiber (MMF) using a femtosecond laser to form a three-beams MZ interferometer and used to measure seawater temperature and salinity. The simulation results showed that the response of the sensor to temperature and salinity was only affected by the length of the microcavity, and the depth of the microcavity responded to the structural strength of the sensor. The experimental results showed that the temperature sensitivity of the sensor was 4.401 nm/℃ in the temperature range of 5 ∼ 40 ℃, and the salinity sensitivity was 0.784 nm/‰ in the salinity range of 3.52 ‰ ∼ 59.41 ‰. The sensor had the advantages of high sensitivity and integration, which was expected to be applied in the measurement of seawater multi-parameters.

A demonstration of the effect of fringe-rate filtering in the hydrogen epoch of reionization array delay power spectrum pipeline

Abstract Radio interferometers targeting the 21cm brightness temperature fluctuations at high redshift are subject to systematic effects that operate over a range of different timescales. These can be isolated by designing appropriate Fourier filters that operate in fringe-rate (FR) space, the Fourier pair of local sidereal time (LST). Applications of FR filtering include separating effects that are correlated with the rotating sky vs. those relative to the ground, down-weighting emission in the primary beam sidelobes, and suppressing noise. FR filtering causes the noise contributions to the visibility data to become correlated in time however, making interpretation of subsequent averaging and error estimation steps more subtle. In this paper, we describe fringe rate filters that are implemented using discrete prolate spheroidal sequences, and designed for two different purposes – beam sidelobe/horizon suppression (the ‘mainlobe’ filter), and ground-locked systematics removal (the ‘notch’ filter). We apply these to simulated data, and study how their properties affect visibilities and power spectra generated from the simulations. Included is an introduction to fringe-rate filtering and a demonstration of fringe-rate filters applied to simple situations to aid understanding.

Application of the electrical impedance method to steel/steel EHD point contacts

The authors have previously developed the electrical impedance method which simultaneously measure the thickness and breakdown ratio of oil films in EHD (elastohydrodynamic) contacts. Furthermore, using a ball-on-disc-type apparatus, the authors have also confirmed that the accuracy of oil film measurement by the developed method is comparable to that of optical interferometry (i.e., glass-steel contacts). In this study, we discussed the experimental results obtained by applying the electrical impedance method to steel-steel contacts using a steel disc instead of a glass disc. It was found that under the mixed lubrication regime where wear occurs, the oil film thickness obtained by this method is calculated to be significantly thicker than the theoretical value. This can be attributed to the increase in the apparent dielectric constant of the lubricant due to wear particles in the lubricant.

Characterization of optical depth for laser produced plasma extreme ultraviolet source

This study investigates the emission mechanism of laser-produced plasma extreme ultraviolet source (LPP-EUV). In the experiment, the EUV radiation is generated by a 1064 nm laser interacting with slab Sn target. The EUV emission is characterized by EUV energy monitors and an EUV spectrometer. The dependency of CE on laser intensity and plasma relative optical depth is explored by a plasma emission-absorption layer model. The dependency is confirmed by an optical interferometry measurement of plasma electron density for the first time. Our work provides a method for characterizing and optimizing the optical depth of laser driven EUV source.

Preparation and properties of polymer composites filled with modified highly dispersed polyethylene terephthalate

A new method of processing polyethylene terephthalate waste into a highly dispersed polymer filler by chemical treatment in an aqueous ammonia solution has been proposed. The possibility of obtaining highly dispersed polymer filler and polymer composite materials under elevated pressure and temperature by incorporating the filler into an epoxy oligomer has been demonstrated. The size and microphase structure of dispersed modified polyethylene terephthalate were determined using optical microscopy and speckle interferometry. Infrared spectroscopy established the presence of polyamide groups on the surface and preserved polyethylene terephthalate in the center of the particles. The use of 2-(tri-butoxymethyl)oxirane monoepoxide demonstrated that the resulting powder is an active filler and reacts with epoxy groups at elevated temperature, enhancing the strength of the composite after formation. Some operational characteristics of the polymer composites have been determined, and the feasibility of applying the proposed methods to address the disposal of PET containers, including plastic bottles, has been shown. The conditions for producing the fillers, along with the characteristics of the obtained fillers and the polymer composites based on them, have been established.

Optimised use of interferometry, spectroscopy, and stellar atmosphere models for determining the fundamental parameters of stars

Context. Thanks to recent progress in the field of optical interferometry, instrument sensitivities have now reached the level achieved in the domain of new space missions dedicated to exoplanet and stellar studies. Combining interferometry with other observational approaches enables the determination of stellar parameters and helps improve our understanding of stellar physics. Aims. In this paper, we aim to demonstrate a new way of using stellar atmosphere models for a joint interpretation of spectroscopic and interferometric observations. Methods. Starting from a discrete grid of one-dimensional (1D) stellar atmosphere models, we developed a training algorithm, based on an artificial neural network, capable of estimating the spectrum and intensity profile of a star over a range of wavelengths and viewing angles. A minimisation algorithm based on the trained function allowed for the simultaneous fitting of the observational spectrum and interferometric complex visibilities. As a result, coherent and precise stellar parameters can be extracted. Results. We show the ability of the trained function to match the modelled intensity profiles of stars in the effective temperature range of 4500–7000 K and surface gravity range of 3 to 5 dex, with a relative precision to the model that is better than 0.05%. Using simulated interferometric data and actual spectroscopic measurements, we demonstrated the performance of our algorithm on a sample of five benchmark stars. Using this method, we achieved an accuracy within 0.5% for the angular diameter, radius, and surface gravity, and within 20 K for the effective temperature. Conclusions. This paper demonstrates a new method of using interferometric data combined with spectroscopic observations. This approach offers an improved determination of the radius, effective temperature, and surface gravity of stars.

Research on Nanometer Precision Measurement Method of High Order Even Aspheres

Optical aspheres are demanded with extremely high precision to meet functional requirements in space telescopes, extreme ultraviolet lithography, and other modern large optical systems. The nano-precision fabrication of optical aspheres requires high-precision measurements to guide deterministic optical processing. Null test is the preferred method for high-precision measurements. Null optics are required to compensate for the incident wavefront in the null test of optical aspheres. However, wavefront aberrations caused by the transmission flat or transmission sphere of interferometer and null optics can limit measurement accuracy and need to be separated. A nano-precision measurement method is proposed for the even optical aspheres of high order in this paper. A computer-generated hologram is used as a null optic to realize a null test on optical aspheres. Mapping distortion correction is performed on the measurement results to ensure that the transverse coordinates of the measurement results correspond correctly to those of the test surface. Absolute testing is applied to separate the wavefront aberrations caused by the computer-generated hologram and interferometer optics. Finally, the results obtained by this method were used to guide deterministic optical processing, enabling the nano-precision fabrication of optical aspheres.

Quasi-distributed acoustic sensing based on optical path difference demodulation for high-frequency and large-amplitude using an optical fiber interferometer array.

The phase-sensitive optical time domain reflectometry scheme has attracted great research interest in distributed acoustic sensing (DAS) but suffers from a trade-off between the dynamic range and signal frequency. In this paper, an optical path difference (OPD) demodulation method is applied to an interferometer array composed of an ultra-weak fiber Bragg grating (UWFBG) array and an imbalanced Michelson interferometer to solve this problem. As far as we know, this is the first time that OPD demodulation has been applied to DAS. The UWFBG array is interrogated by a frequency-modulated pulse, and the acoustic signal sensed by the fiber between any two adjacent UWFBGs can be retrieved by demodulating the variation of residual OPD of the interferometer formed by them. The proposed method is analyzed theoretically and validated experimentally; compared with the phase demodulation method, a 100-times boost in bandwidth is achieved for a signal with an amplitude of 0.4 µε. Results also show that the proposed method offers increasing signal-to-noise ratios as the frequency increases.

Growth of homoepitaxial single crystal diamond by microwave plasma CVD in H2-CH4-O2 gas mixtures at high microwave power densities

Single crystal diamond growth by microwave plasma assisted CVD in oxygen-containing gas mixtures is attractive in view of possibility to realize a prolonged non-stoped synthesis process and to minimize defects and impurities in the produced material. We studied the homoepitaxial diamond growth on (100) oriented substrates in H2-CH4-O2 environment at high pressures (300 Torr) and high microwave power density (≈400 W/cm3) at variable O2 content (up to 3.5 %) in the plasma. A low-coherence optical interferometry and optical emission (OE) spectroscopy was used to measure in situ the growth rate and probe the plasma chemistry, respectively. Depending on CH4 content the growth rate dependence on the concentration [O2] either shows a maximum at certain [O2], or a monotonic decline, up to complete stop of the growth at some critical O2 percentage (specific for each methane content) in the mixture. We found CH, Hβ, C2 and C3 lines in OE spectra from the plasma to monotonically quenched with O2 adding, particularly, disappearance of the C2 line coincidences with growth rate going to zero. High-quality homoepitaxial diamond layers were produced at moderate growth rate at optimal gas composition and characterized with Raman spectroscopy. Moreover, a significant reduction in the stress on (111) oriented substrates owing to O2 addition was observed.

ATP-induced reconfiguration of the micro-viscoelasticity of cardiac and skeletal myosin solutions.

We study the high-frequency, micro-mechanical response of suspensions composed of cardiac and skeletal muscle myosin by optical trapping interferometry. We observe that in low ionic strength solutions, upon the addition of magnesium adenosine triphosphate (MgATP2-), myosin suspensions radically change their micro-mechanics properties, generating a viscoelastic fluid characterized by a complex modulus similar to a suspension of worm-like micelles. This transduction of energy, from chemical to mechanical, may be related to the relaxed states of myosin, which regulate muscle contractility and can be involved in the etiology of many myopathies. Within an analogous generic mechanical response, cardiac and skeletal myosin suspensions provide different stress relaxation times, elastic modulus values, and characteristic lengths. These discrepancies probably rely on the dissimilar physiological functions of cardiac and skeletal muscle, on the different MgATPase hydrolysis rates of cardiac and skeletal myosins, and on the observed distinct cooperative behavior of their myosin heads in the super-relaxed state. In vitro studies like these allow us to understand the foundations of muscle cell mechanics on the micro-scale, and may contribute to the engineering of biological materials whose micro-mechanics can be activated by energy regulators.

Insights into the growth of GaN thin films through liquid gallium sputtering: A plasma-film combined analysis.

This study presents the detailed characterization of a magnetron-based Ar-N2 plasma discharge used to sputter a liquid Ga target for the deposition of gallium nitride (GaN) thin films. By utilizing in situ diagnostic techniques including optical emission spectroscopy and microwave interferometry, we determine different temperatures (rotational and vibrational of N2 molecules, and electronic excitation of Ar atoms) and electron density, respectively. Beyond providing insights into fundamental plasma physics, our research establishes a significant correlation between gas-phase dynamics, particularly those of gallium atoms (flux and average energy at the substrate) and deposited GaN thin film properties (growth rate and crystalline fraction). These findings underscore the role of plasma conditions in enhancing thin film quality, highlighting the importance of plasma characterization in understanding and optimizing GaN thin film growth processes.

Transport of non-equilibrium quasiparticle excitations in superconducting aluminum

The electron transport of non-equilibrium quasiparticles injected into superconducting aluminum from a normal metal has been experimentally studied at ultralow temperatures. We studied hybrid nanostructures in the form of a T-shaped normal metal electrode (copper) – a dielectric tunnel layer (aluminum oxide) – a superconducting fork (aluminum), which can be considered as a solid-state analogues of a two-beam optical interferometer. At fixed bias voltages larger than the superconducting gap, a non-monotonic dependence of the tunnel current on perpendicular magnetic field is observed. The effect is interpreted as the presence of a coherent component of the quasiparticle current.

TRAPUM pulsar and transient search in the Sextans A and B galaxies and discovery of background FRB 20210924D

ABSTRACT The Small and Large Magellanic Clouds are the only galaxies outside our own in which radio pulsars have been discovered to date. The sensitivity of the MeerKAT radio interferometer offers an opportunity to search for a population of more distant extragalactic pulsars. The TRAPUM (TRansients And PUlsars with MeerKAT) collaboration has performed a radio-domain search for pulsars and transients in the dwarf star-forming galaxies Sextans A and B, situated at the edge of the Local Group 1.4 Mpc away. We conducted three 2-h multibeam observations at L band (856–1712 MHz) with the full array of MeerKAT. No pulsars were found down to a radio pseudo-luminosity upper limit of 7.9$\pm$0.4 Jy kpc$^{2}$ at 1400 MHz, which is 28 times more sensitive than the previous limit from the Murriyang telescope. This luminosity is 30 per cent greater than that of the brightest known radio pulsar and sets a cut-off on the luminosity distributions of the entire Sextans A and B galaxies for unobscured radio pulsars beamed in our direction. A fast radio burst was detected in one of the Sextans A observations at a dispersion measure (DM) of 737 pc cm$^{-3}$. We believe this is a background event not associated with the dwarf galaxy due to its large DM and its signal-to-noise ratio being strongest in the wide-field incoherent beam of MeerKAT.

Two-dimensional vector bending sensor based on single excessively tilted fiber grating.

We introduced a two-dimensional vector-bending sensor using excessively tilted fiber grating (ExTFG) encapsulated in a non-neutral axis position within a flexible cylinder. The asymmetrical structure enabled both TM and TE modes of the ExTFG to achieve the competency of one-dimensional vector bending sensing by cleverly leveraging the orthogonal relationship between these modes to achieve the effect of orthogonal cascading of two one-dimensional sensors. The resonance wavelength changes of the TM and TE modes were monitored under equal excitation states to achieve two-dimensional vector bending sensing, which significantly simplified the manufacturing complexity of the sensor; the longer the off-axis distance, the higher the sensitivity, and the smaller the maximum measurable curvature. Through an optimal parameter designation for the sensor, the results showed that the transmission spectra of TM and TE modes varied significantly depending on the curvature and direction of the sensor bending with a maximum sensitivity of -105 pm/m-1 and 105.5 pm/m-1, -70.25 pm/m-1 and 67.5 pm/m-1, respectively. Subsequently, the direction and curvature of the vector bending could be reconstructed using the established algorithm with the measured wavelength shifts of TM and TE modes. The average relative error was about 2.02% for the reconstructed direction angle and about 3.61% for the reconstructed curvature. The proposed sensor offered higher sensitivity than those based on FBGs and improved stability compared to those based on optical fiber interferometers. Therefore, it holds promising applications in structural health monitoring in complex environments and intelligent machinery.

Double-layer optical fiber interferometer with bio-layer-modified reflector for label-free biosensing of inflammatory proteins

This work discusses label-free biosensing application of a double-layer optical fiber interferometer where the second layer tailors the reflection conditions at the external plain and supports changes in reflected optical spectrum when a bio-layer binds to it. The double-layer nanostructure consists of precisely tailored thin films, i.e., titanium (TiO2) and hafnium oxides (HfO2) deposited on single-mode fiber end-face by magnetron sputtering. It has been shown numerically and experimentally that the approach besides well spectrally defined interference pattern distinguishes refractive index (RI) changes taking place in a volume and on the sensor surface. These are of interest when label-free biosensing applications are considered. The case of myeloperoxidase (MPO) detection—a protein, which concentration rises during inflammation—is reported as an example of application. The response of the sensor to MPO in a concentration range of 1 × 10−11–5 × 10−6 g/mL was tested. An increase in the MPO concentration was followed by a redshift of the interference pattern and a decrease in reflected power. The negative control performed using ferritin proved specificity of the sensor. The results reported in this work indicate capability of the approach for diagnostic label-free biosensing, possibly also at in vivo conditions.

Optical interferometry implementation considerations for sinusoidal low frequency accelerometer measurements and calibrations

Vibration metrology utilizing sine excitation stimulus, based either on fringe counting or minimum point methods, employs Michelson interferometers for the calibration of accelerometers. The former method combines the optical reference and measurements arms from a static mirror and reflected by the accelerometer respectively which are then directed to a suitable photodiode for processing. The stroking motion due to the oscillation of the accelerometer will contribute to the misalignment of the two optical paths and there are three methods to compensate for this. The first requires the mounting of a mirror on the accelerometer itself and the effect of the added mass from the mirror can be accounted for and corrected. The second requires the mounting of three mirrors on the mounting surface of the accelerometer but this requires the alignment of the Michelson interferometer for each mirror. The third is to use two retro reflectors so that the returning measurement beams are always along the same path with the reference; however, this requires the alignment of the interferometer for each retro-reflector. This paper will discuss such considerations on the optical systems, their components and associated instrumentation and discuss the design of an alternative approach that can overcome certain limitations.

Optical interferometry based acoustic field characterization using physics informed neural networks

The acousto-optic effect offers a non-contact way of measuring and visualizing acoustic fields in transparent fluids. Acoustic density fluctuations induce changes in the media's refractive index that can be measured using interferometry. While sensing methods based on acousto-optics have gathered increasing attention, many of such methods are only sensitive to projections of the acoustic field along the optical path, limiting the fields that can be characterized to one or two dimensions, or requiring complex experimental setups. Recently, reconstruction methods that abide by the physics of acoustic wave propagation showed unparalleled performance compared with classical reconstruction methods, reducing the sampling requirements and enabling to characterize three-dimensional acoustic fields. Nonetheless, such reconstruction methods rely on discrete approximations which might be poor at describing spatially complex fields. In this work we use physics-informed neural networks (PINNs) to estimate the acoustic pressure over space from interferometer measurements. The network is flexible enough to represent complex acoustic fields, while its output is constrained to fulfill the wave equation. Once trained on the data available for a given experiment, the PINN can estimate the acoustic pressure at arbitrary positions. The approach is tested in an experimental study, showing an improved performance compared with state-of-the-art reconstruction methods.

Phase shift in optical fiber induced by mechanical stress

This work refers to the vibration optimization of a fiber optic interferometer whose detection performance may be compromised due to external mechanical or acoustic excitations. In such an interferometer, the optical path is split into two arms, with one significantly longer than the other. Optimizing the interferometer involves minimizing the phase difference of light caused by mechanical deformations, particularly in the long arm, resulting from unintended external excitations. Extending previous works from Hocker, who considered isotropic compression and longitudinal stress, we also investigate an additional mechanical load on the fiber: torsional stress. All these different loads will be compared to determine which one induces the most significant phase shift. Ultimately, incorporating protection into the equations will lead to a more realistic model. This approach will allow us to identify the most suitable protective materials to achieve a fiber optic interferometer resilient to external constraints.