Search Results (104)

In ocean engineering, the demand for fiber-optic vector hydrophones (FOVHs) is increasing. The performance of a FOVH depends on phase consistency between its pressure and acceleration channels, which should match the acoustic field’s properties. Phase polarity, which refers to the alignment of the output signal with the acoustic field direction, is critical. Incorrect phase polarity during sensor assembly can disrupt phase consistency and invalidate directional measurements. This study investigates phase polarity in mandrel FOVHs that use the Phase Generated Carrier (PGC) technique. We develop a theoretical model combining the PGC algorithm with elastic mechanics to analyze the response of acoustic signals. Our model shows that correct demodulated signal polarity requires a specific physical setup: the pressure sensor’s long arm should be on the inner mandrel and the short arm on the outer, while the accelerometer’s positive axis should follow the vector from the long to its short arm. These results are validated through standing wave tube experiments and lake tests. This research provides practical guidelines for the installation and calibration of FOVHs, ensuring phase consistency in underwater acoustic sensing. Full article

A non-intrusive mattress based on an optical-fiber Michelson interferometer is designed for daily sleep monitoring. The optical phase signal of the optical-fiber Michelson interferometer caused by the heartbeat and respiration is demodulated by the phase-generated carrier (PGC) method. The physiological signals and vital indicators including heart rate (HR), respiration rate (RR), and signal energy (SE) are extracted from the optical phase by algorithmic processing. A series of experiments are conducted to confirm the feasibility of the mattress for sleep monitoring. The mattress not only can achieve HR and RR counting, but also can record the waveform of the sleep-induced signal accurately. The body states can also be distinguished by the SE. In an all-night sleep monitoring experiment, the HR measured by the mattress is compared with the HR measured by a commercial smart band, showing a maximum error of 6 bpm (beat per minute). The designed mattress based on an optical-fiber Michelson interferometer shows good performance and great potential in non-intrusive sleep monitoring. Full article

Onboard the MetOp satellite series, Infrared Atmospheric Sounding Interferometer (IASI) is a Fourier Transform spectrometer based on the Michelson interferometer. IASI acquires interferograms, which are processed to provide high-resolution atmospheric emission spectra. These spectra enable the derivation of temperature and humidity profiles, among other parameters, with exceptional spectral resolution. In this study, we evaluate a novel, rapid retrieval approach in the interferogram domain, aiming for near-real-time (NRT) analysis of large spectral datasets anticipated from next-generation tropospheric sounders, such as MTG-IRS. The Partially Sampled Interferogram (PSI) method, applied to trace gas retrievals from IASI, has been sparsely explored. However, previous studies suggest its potential for high-accuracy retrievals of specific gases, including CO, CO₂, CH₄, and N₂O at the resolution of a single IASI footprint. This article presents the results of a study based on retrieval in the interferogram domain. Furthermore, the optical pathway differences sensitive to the parameters of interest are studied. Interferograms are generated using a fast Fourier transform on synthetic IASI spectra. Finally, the relationship to the total column of carbon monoxide is explored using three different algorithms—from the most intuitive to a complex neural network approach. These algorithms serve as a proof of concept for interferogram classification and rapid predictions of surface temperature, as well as the abundances of H₂O and CO. IASI spectra simulations were performed using the LATMOS Atmospheric Retrieval Algorithm (LARA), a robust and validated radiative transfer model based on least squares estimation. The climatological library TIGR was employed to generate IASI interferograms from LARA spectra. TIGR includes 2311 atmospheric scenarios, each characterized by temperature, water vapor, and ozone concentration profiles across a pressure grid from the surface to the top of the atmosphere. Our study focuses on CO, a critical trace gas for understanding air quality and climate forcing, which displays a characteristic absorption pattern in the 2050–2350 ${\mathrm{cm}}^{-1}$ wavenumber range. Additionally, the study explores the potential of correlating interferogram characteristics with surface temperature and H₂O content, aiming to enhance the accuracy of CO column retrievals. Starting with intuitive retrieval algorithms, we progressively increased complexity, culminating in a neural network-based algorithm. The results of the NN study demonstrate the feasibility of fast interferogram-domain retrievals, paving the way for operational applications. Full article

This study explores the integration of reduced graphene oxide (rGO) into an optoelectronic XOR logic gate to enhance BB84 protocol encryption in quantum communication systems. The research leverages the nonlinear optical properties of rGO, specifically its nonlinear refraction characteristics, in combination with a Michelson interferometer to implement an optoelectronic XOR gate. rGO samples were deposited using the Langmuir–Blodgett technique and characterized in morphology and structure. The optical setup utilized a frequency-modulated laser signal for the interferometer and a pulsed laser system that generates the quantum information carrier. This integration of quantum encryption with nonlinear optical materials offers enhanced security against classical attacks while providing adaptability for various applications from secure communications to quantum AI. Full article

The generation of high-quality mid-infrared free-electron laser (MIR-FEL) radiation depends critically on precise control of electron beam parameters, including energy, energy spread, transverse emittance, bunch charge, and bunch length. At the PBP-CMU Electron Linac Laboratory (PCELL), effective beam diagnostics are essential for optimizing FEL performance. However, dedicated systems for direct measurement of transverse emittance and bunch length at the undulator entrance have been lacking. This paper addresses this gap by presenting the design, simulation, and analysis of diagnostic stations for accurate characterization of these parameters. A two-quadrupole emittance measurement system was developed, enabling independent control of beam-focusing in both transverse planes. An analytical model was formulated specifically for this configuration to enhance emittance reconstruction accuracy. Systematic error analysis was conducted using ASTRA beam dynamics simulations, incorporating 3D field maps from CST Studio Suite and fully including space-charge effects. Results show that transverse emittance values as low as 0.15 mm·mrad can be measured with less than 20% error when the initial RMS beam size is under 2 mm. Additionally, quadrupole misalignment effects were quantified, showing that alignment within ±0.95 mm limits systematic errors to below 33.3%. For bunch length measurements, a transition radiation (TR) station coupled with a Michelson interferometer was designed. Spectral and interferometric simulations reveal that transverse beam size and beam splitter properties significantly affect measurement accuracy. A 6% error due to transverse size was identified, while Kapton beam splitters introduced additional systematic distortions. In contrast, a 6 mm-thick silicon beam splitter enabled accurate, correction-free measurements. The finite size of the radiator was also found to suppress low-frequency components, resulting in up to 10.6% underestimation of bunch length. This work provides a practical and comprehensive diagnostic framework that accounts for multiple error sources in both transverse emittance and bunch length measurements. These findings contribute valuable insight for the beam diagnostics community and support improved control of beam quality in MIR FEL systems. Full article

When interferograms in space heterodyne spectrometers exhibit tilted or distorted fringes, significant errors may occur in the demodulated spectral information. To address this issue, we propose a method for interferogram correction based on automatic spectral analysis. Simulations on erroneous interferograms of monochromatic and polychromatic light demonstrate that this method effectively corrects fringe tilts and significantly improves spectral demodulation accuracy. The standard deviations between the corrected spectra and ideal spectra for monochromatic and polychromatic light are 0.016 and 0.019, respectively, compared to 0.104 and 0.127 for uncorrected spectra. Additionally, the method successfully corrects experimental interferograms of potassium and neon lamps, accurately demodulating characteristic peaks of potassium and neon emission lines. It also enables accurate displacement measurement in a Michelson interferometer experiment. This method, through automatic analysis and one-sided spectral correction, efficiently and accurately corrects erroneous interferograms and enhances spectral demodulation accuracy, showing broad application potential. Full article

A spatial light modulator (SLM) is a key element in several applications, but it is subject to surface deformation due to manufacturing imperfections or environmental factors. Therefore, the current study aims to analyze and compensate for such deformations in a phase-only SLM using a Michelson interferometer. The recorded interferogram represents the interference between the wavefront reflected from the SLM surface (object wave) and a reference wave. Noise in the recorded interferogram can degrade the accuracy of phase measurements. Various digital filtering techniques were applied to improve the signal-to-noise ratio (SNR) of the interferogram. The filtered interferogram enabled accurate phase extraction through Fourier transform processing and side peak selection using a spatial carrier frequency method. Additionally, phase errors caused by the tilt of the reference beam were corrected. Thereafter, the conjugate of the corrected phase distribution was used to calculate a phase-only computer-generated hologram (CGH), which was displayed on the SLM to compensate for surface deformations. The effectiveness of the proposed compensation procedure was confirmed by a second phase measurement, which demonstrated improved SLM performance. This study highlights the impact of combining the interferometric techniques with digital processing for precise surface deformation analysis. Full article

The Takagi-Sugeno (T-S) fuzzy control is a nonlinear method that uses a combination of linear controllers as its control law. This method has been applied in various fields of scientific research: buck converters, biomedicine, civil engineering, etc. To the best of the authors’ knowledge, although works on traditional fuzzy control and optical interferometry have already been published, this is the first time that T-S fuzzy (specifically) is applied to demodulate interferometry signals. Through a proof-of-concept experiment, the paper describes the fusion of an open-loop interferometer with an external closed-loop digital observer based on T-S fuzzy (both simple and inexpensive), which actuates like a closed-loop interferometer (but without its drawbacks). The observer design is based on stability conditions using linear matrix inequalities (LMIs) solutions. The system is maintained at the optimal ${90}^{\circ }$ operation point (compensating for environmental drifts) and enables the demodulation of optical phase signals with low modulation index. Simulations and measurements were performed by using a Michelson interferometer, verifying that the method demodulates signals up to $\pi /2$ rad amplitudes and higher than 100 Hz frequencies (with maximum error of 0.45%). When compared to the important arc tangent method, both presented the same frequency response for the test PZT actuator. Full article

This study presents the design, simulation, and experimental validation of six fundamental laser interferometer types: Sagnac, Mach–Zehnder, Michelson, Twyman–Green, Fizeau, and Fabry–Pérot. Using ZEMAX OpticStudio in non-sequential mode with the physical optics propagation (POP) algorithm, the simulations provide detailed insights into the optical performance of these interferometers. A direct comparison is made between the simulated and experimental fringe patterns, coherent irradiance distributions, and phase plots, demonstrating strong agreement and validating the accuracy of computational modeling for interferometric analysis. The Mach–Zehnder and Michelson configurations exhibit high adaptability and measurement precision, while the Fabry–Pérot interferometer achieves superior spectral resolution. Twyman–Green interferometry proves particularly effective in mapping surface irregularities for optical testing. The results confirm the reliability of ZEMAX OpticStudio for high-precision optical system design and analysis. The novelty of this work lies in the comparative study between ZEMAX simulations and experimental interferometric results, particularly fringe patterns and phase distributions. This approach provides a clearer understanding of interferometer performance and enhances the accuracy of optical metrology, offering valuable insights for both theoretical modeling and practical applications. Full article

The Michelson interferometer for global high-resolution thermospheric imaging (MIGHTI) aboard the NASA ionospheric connection (ICON) satellite offers extensive atmospheric wind field data for mid-latitude regions and has recently released its version 5 (v05) data. We conducted a comprehensive comparison and validation of MIGHTI v05 level 2.2 data for the period from December 2019 to October 2022, covering all MIGHTI data in orbit. In a comparison of raw wind speeds, MIGHTI demonstrates good agreement with the ground-based Fabry–Pérot interferometer (FPI), meteor radars, and the space-borne instrument TIMED Doppler interferometer (TIDI). However, some differences still exist. Comparisons with meteor radars revealed differences attributable to observational altitude, day–night variations, and latitude distribution. Below 100 km, MIGHTI and meteor radar exhibit excellent consistency (r = 0.819 for zonal and r = 0.782 for meridional winds). Day–night differences are minimal, with closer amplitude values observed at night. MIGHTI shows stronger correlations with low-latitude meteor radar, with coefficients of 0.859 (zonal) and 0.891 (meridional) at Ledong. The meridional wind correlation is better in low-latitude regions, in contrast to mid-latitudes. Similar observations were made in a comparison with FPI, emphasizing the need for caution when considering the meridional wind component of MIGHTI at observational boundaries (~40 °N). In addition to comparing raw wind speed data, we analyzed the amplitude of fluctuations extracted by MIGHTI and TIDI by employing the least squares method to extract planetary waves. The results indicate that both TIDI and MIGHTI observe the same fluctuation events, but TIDI extracts larger fluctuation amplitudes than MIGHTI. Finally, we present, for the first time, the spatial structure of a five-day wave that occurred in March 2020. Full article

In this paper we demonstrate a new approach to the measurement of dispersion of light reflected in integrated optical devices. The approach utilizes the fact that light reflected from the end facet of an integrated waveguide will interfere with light reflected from points inside the device under test (DUT), effectively creating a Michelson interferometer. The distance between the measured fringes of this interferometric signal will depend directly on the group delay experienced in the device under test, allowing for fast and easy measurement of waveguide dispersion. This approach has been used to determine the dispersion of a fabricated linearly chirped Bragg gratings waveguide and the result agrees well with the designed value. Full article

Space-based gravitational wave (GW) detection employs the Michelson interferometry principle to construct ultra-long baseline laser interferometers in space for detecting GW signals with a frequency band of 10⁻⁴–1 Hz. The spaceborne telescope, as a core component directly integrated into the laser link, comes in various configurations, with the off-axis four-mirror design being the most prevalent. In this paper, we present a high-performance design based on this configuration, which exhibits a stable structure, ultra-low wavefront aberration, and high-level stray light suppression capabilities, effectively eliminating background noise. Also, a scientifically justified positioning of the entrance and exit pupils has been implemented, thereby paving adequate spatial provision for the integration of subsequent optical systems. The final design realizes a wavefront error of less than λ/500 in the science field of view, and after tolerance allocation and Monte Carlo analysis, a wavefront error of less than λ/30 can be achieved with a probability of 92%. The chief ray spot diagram dimensions are significantly small, indicating excellent control of pupil aberrations. Additionally, the tilt-to-length (TTL) noise and stray light meet the stringent requirements for space-based gravitational wave detection. The refined design presented in this paper proves to be a more fitting candidate for GW detection projects, offering more accurate and rational guidance. Full article

The stable and high-precision acquisition of attitude data is crucial for sustaining the long-term robustness of laser links to detect gravitational waves in space. We introduce an effective method that utilizes an adaptive weight optimization approach for the fusion of attitude data obtained from charge-coupled device (CCD) spot-positioning-based attitude measurements, differential power sensing (DPS), and differential wavefront sensing (DWS). This approach aims to obtain more robust and lower-noise-level attitude data. A system is designed based on the Michelson interferometer for link simulations; validation experiments are also conducted. The experimental results demonstrate that the fused data exhibit higher robustness. Even in the case of a single sensor failure, valid attitude data can still be obtained. Additionally, the fused data have lower noise levels, with root mean square errors of 9.5%, 37.4%, and 93.4% for the single CCD, DPS, and DWS noise errors, respectively. Full article

This study presents an all-optical approach based on an XOR logic gate for encryption by interference and the assistance of multiphotonic effects exhibited by carbon nanotubes. We integrate a Michelson interferometer to propose the encryption system. The key innovation lies in the use of multiwalled carbon nanotubes (MWCNT) to control the XOR operation through intensity-dependent nonlinear optical absorption. We introduce control based on nanosecond nonlinear optical absorption in MWCNT. By measuring irradiance propagation through thin-film samples of MWCNT, we demonstrate a threshold-based binary data recording system that is highly resistant to unauthorized access. The combination of interferometric response, MWCNT-based intensity control, and multicriteria decision analysis through nonlinear absorption presents a powerful and versatile approach to optical encryption. This method has the potential to be a base for secure communication systems and optical computing, with possible extensions to biological computing and microbiology. While challenges in power optimization and scaling remain, this research marks a significant step towards advanced, ultrafast encryption systems. Full article