Search Results (70)

Land seismic data are always contaminated by surface waves, which demonstrate strong energy, low velocity, and long vibrations. Such noises often mask deep effective reflections, seriously reducing the data’s signal-to-noise ratio while limiting the imaging accuracy of complex deep structures and the efficiency of hydrocarbon reservoir identification. To address this critical technical bottleneck, this paper proposes a surface wave joint reconstruction method based on stationary phase analysis, combining the cross-correlation seismic interferometry method with the convolutional seismic interferometry method. This approach integrates cross-correlation and convolutional seismic interferometry techniques to achieve coordinated reconstruction of surface waves in both shot and receiver domains while introducing adaptive weight factors to optimize the reconstruction process and reduce interference from erroneous data. As a purely data-driven framework, this method does not rely on underground medium velocity models, achieving efficient noise reduction by adaptively removing reconstructed surface waves through multi-channel matched filtering. Application validation with field seismic data from the piedmont regions of western China demonstrates that this method effectively suppresses high-energy surface waves, significantly restores effective signals, improves the signal-to-noise ratio of seismic data, and greatly enhances the clarity of coherent events in stacked profiles. This study provides a reliable technical approach for noise reduction in seismic data under complex near-surface conditions, particularly suitable for hydrocarbon exploration in regions with developed scattering sources such as mountainous areas in western China. It holds significant practical application value and broad dissemination potential for advancing deep hydrocarbon resource exploration and improving the quality of complex structural imaging. Full article

Optical temperature sensors with intrinsic characteristics of explosion-proof are particularly suitable for the petrochemical industry, etc. However, their applications remain limited by environmental compatibility, etc. Here, we developed an all-optic temperature sensor using an anti-bending single-mode optical fiber in a 3.5 m length and a 0.25 mm outer diameter to match a stainless tube with a 0.4 mm inner diameter. The fiber was threaded into the tube, well bonded with epoxy at both ends of the tube, and configured as one arm of a low-coherent Michelson interferometer. Then, the tube with an embedded sensing fiber was fabricated into a spring, whose final length was about 70 mm with an outside diameter of 13 mm. Changes in temperature alter the lengths of the stainless tube spring in a thermoelastic way, thereby modifying the inner fiber length and producing an optical path difference between the sensing fiber and the packaged reference arm of the interferometer. A temperature calibration was carried out from −25 to 65 °C, and the results demonstrated that the hysteresis of the spring sensor was within ±1.16 °C and the sensitivity was 0.34 °C, which was verified by using a platinum resistance temperature sensor (PT-100). This work provides a reference for further intrinsic optical temperature sensor design. Full article

Non-contact, non-destructive testing of surface microgeometry plays a key role in such industries as microelectronics, additive manufacturing, and precision engineering. This paper presents the development and experimental testing of a digital holographic system based on a low-coherence laser diode operating at two close wavelengths, designed to measure height differences in the micrometer range. The method is based on a Michelson interferometer and reconstruction of the complex amplitude of the object wave, which allows phase measurements with subsequent phase conversion into heights. The tests were carried out on micrometer roughness standards with a trapezoidal profile with a groove depth from 24.5 μm to 100 μm and a profile width from 65 μm to 150 μm, as well as on reference strokes with a width from 25 to 200 μm. The obtained data demonstrate the possibility of three-dimensional and two-dimensional visualization of the objects under study with a relative error in height from 5.3% to 11.6% and in width up to 18.6%. It is shown that the system allows reliable measurement of defects of metal surfaces in the range from 25 to 100 μm both vertically and horizontally. Thus, the developed method can be used for high-precision, non-destructive testing in a wide range of technological tasks. Full article

Optical-carried microwave interferometry (OCMI) has attracted increasing attention in recent years, as it combines the ease of phase extraction and manipulation of microwave techniques with the low-loss transfer of optical fibers. Conventional OCMI implementations typically employ broadband light sources and coherent photodetection, which inevitably suffer from dispersion, polarization fading, and phase drift, severely limiting the achievable sensing distance. In this work, we proposed an optimized OCMI architecture that adopts incoherent photodetection combined with electric-domain microwave interferometry. Comprehensive theoretical analysis and systematic experiments demonstrate that the proposed system enables robust, dynamic, and long-haul fiber transfer delay (FTD) measurements, no less than in 15 km length, with improved resolution and stability. It provides new insight for building long-haul FTD sensor networks. Full article

This study explores the relationship between nutrient concentration (NC) and epidermal thickness (d) of the leaves of hydroponically grown Brassica rapa and its attenuation coefficients (m) using portable Time-Domain Optical Coherence Tomography (TD-OCT), which is a non-invasive imaging technique that uses low-coherence interferometry to generate axial scans of plants’ leaves by measuring the time delay and intensity of backscattered light. The portable TD-OCT system in this study has an axial and lateral resolution of 7 m and 3 m, respectively, a scanning depth of 12 mm, and a 1310 nm Super Luminescent Diode (SLD). Several studies suggest that the differences in d and m are related to nutritional, physiological, and anatomical status. The study used the Kratky method, a simple non-circulating hydroponic system, to cultivate Brassica rapa with varying NC (25%, 50%, 75%, 100% (control), and 125%). Each treatment group used two plants. The TD-OCT sample probe was placed on a fixed holder and was oriented vertically so that light was directed downward onto the leaf’s surface to obtain the depth profile (A-scan). The distance between the probe and the leaf was adjusted to obtain the optimum interference signal. Five averaged A-scans were obtained per leaf on the 7th, 18th, and 21st days post nutrient exposure. The logarithm of the averaged A-scan is linearly fitted to extract m. The results showed a positive correlation between NC and m, which suggests that plants produce more chlorophyll and develop denser cells and increase m. There was no correlation obtained between NC and d. The study demonstrates the potential of TD-OCT as a non-destructive tool for assessing plant health and monitoring growth dynamics in hydroponic systems and m as a sensitive indicator of plant health as compared to d. The continued exploration of TD-OCT applications in agriculture can contribute to improving crop management strategies and promoting sustainable food production practices. Full article

Background/Objectives: Accurate biometric measurements are critical for achieving optimal refractive outcomes in cataract surgery. This study evaluated the agreement of biometric measurements between a swept-source optical coherence tomography (SS–OCT) biometer (Argos^®, Movu Inc.) and an optical low-coherence interferometry (OLCI) biometer (Aladdin^®, Topcon Corp.). Parameters analyzed included axial length (AL), anterior chamber depth (ACD), lens thickness (LT), keratometry (K1, K2), and white-to-white corneal diameter (WTW). Methods: A total of 170 eyes were examined, and agreement was assessed using Bland–Altman analysis, intraclass correlation coefficients (ICCs), and Pearson correlation coefficients. Results: Excellent agreement was observed for AL (ICC = 0.975), ACD (ICC = 0.960), LT (ICC = 0.951), K1 (ICC = 0.921), and K2 (ICC = 0.927). Moderate agreement was found for astigmatism axis (ICC = 0.655) and cylinder power (ICC = 0.891). Poor agreement was noted for astigmatism-related Jackson cross-cylinder vectors J0 (ICC = 0.334) and J45 (ICC = −0.311), as well as for WTW (ICC = 0.338). Bland–Altman plots demonstrated narrow limits of agreement for most parameters, with mean differences of 0.009 mm for AL and 0.06 mm for ACD. Conclusions: Both devices demonstrated high degrees of agreement for core biometric parameters, supporting their clinical interchangeability. However, the variability in WTW and astigmatism-related measurements highlights the need for caution when precise corrections are required. Full article

Background/Objectives: Precise intraocular lens (IOL) power calculations are essential for achieving optimal refractive outcomes in cataract surgery. This study compares the predictive accuracy of swept-source optical coherence tomography (SS-OCT) and optical low-coherence interferometry (OLCI) in biometry measurements and refractive outcomes. Methods: This retrospective study included 170 eyes from 102 patients undergoing cataract surgery. Biometry was performed using Argos^® (MOVU Inc., Komaki, Japan) (SS-OCT) and Aladdin^® (Topcon Corp., Tokyo, Japan) (OLCI), measuring axial length (AL), anterior chamber depth (ACD), lens thickness (LT), white to white (WTW), and keratometry. Results: Postoperative outcomes, including uncorrected and corrected distance visual acuity (UDVA, CDVA), spherical equivalent (SE), and refractive error, were assessed at one and six months. Predictive accuracy was evaluated by mean error (ME), mean absolute error (MAE), median absolute error (MedAE), and the percentage of eyes within ±0.25 D to ±1.00 D of predicted SE. Conclusions: Both technologies achieved high refractive accuracy, with 97.7% (SS-OCT) and 97.2% (OLCI) of eyes within ±1.00 D of target SE. SS-OCT demonstrated superior axis alignment, while OLCI provided enhanced postoperative SE. Significant differences were observed in LT (p = 0.030) and ACD (p = 0.009). Postoperative UDVA of 20/20 or better was achieved in 98% of SS-OCT eyes and 100% of OLCI eyes. SS-OCT and OLCI provide comparable refractive outcomes and high reliability in cataract surgery. Full article

The development of optical methods for surface vibration measurements is currently of great interest. We propose a modified tandem low-coherence technique that utilizes the phase information of the low-coherence signal to detect surface vibrations. The resolution of this scheme is less than 1 nm for a 20 kHz bandwidth. The proposed technique is not just limited to measurements of surface vibrations, but it can also be used for interferometric fiber-optic sensors. Full article

Artificial microstructures, especially metamaterials, have garnered increasing attention in numerous applications due to their rich and distinctive properties. Starting from the principle of multi-beam interference, we have theoretically devised a beam configuration consisting of six symmetrically distributed coherent beams to generate two-dimensional microstructures with diverse shapes of unitcells under different polarization combinations. In particular, a split-ring metamaterial template is achieved with two adjacent circularly and four linearly polarized beams with such single-step holographic interferometry. Furthermore, simulation results show that the orientation and shape of the split-ring unitcell can be accurately adjusted by controlling the polarization position, polarization degree, or power ratio of the coherent beams. The optimal parameters to produce a high-quality split-ring metamaterial with a contrast higher than 0.97 are obtained. These results provide useful guidance for the effective and low-cost fabrication of metamaterials with diverse unitcells. Full article

This paper proposes and implements a novel scheme for recording signals from fibre optic sensors based on tandem low-coherence interferometry with an integrated optical reference interferometer. The circuit allows precision control of the phase shift. Additionally, the paper illustrates the potential for detecting vibration and object deformation using fibre optic Fabry–Perot sensors connected to the registration system. Full article

Conventional Fourier domain Optical Coherence Tomography (FD-OCT) systems depend on resampling into a wavenumber (k) domain to extract the depth profile. This either necessitates additional hardware resources or amplifies the existing computational complexity. Moreover, the OCT images also suffer from speckle noise, due to systemic reliance on low-coherence interferometry. We propose a streamlined and computationally efficient approach based on Deep Learning (DL) which enables reconstructing speckle-reduced OCT images directly from the wavelength (λ) domain. For reconstruction, two encoder–decoder styled networks, namely Spatial Domain Convolution Neural Network (SD-CNN) and Fourier Domain CNN (FD-CNN), are used sequentially. The SD-CNN exploits the highly degraded images obtained by Fourier transforming the (λ) domain fringes to reconstruct the deteriorated morphological structures along with suppression of unwanted noise. The FD-CNN leverages this output to enhance the image quality further by optimization in the Fourier domain (FD). We quantitatively and visually demonstrate the efficacy of the method in obtaining high-quality OCT images. Furthermore, we illustrate the computational complexity reduction by harnessing the power of DL models. We believe that this work lays the framework for further innovations in the realm of OCT image reconstruction. Full article

In recent years, phase linking (PL) methods in radar time-series interferometry (TSI) have proven to be powerful tools in geodesy and remote sensing, enabling the precise monitoring of surface displacement and deformation. While these methods are typically designed to operate on a complete network of interferograms, generating such networks is often challenging in practice. For instance, in non-urban or vegetated regions, decorrelation effects lead to significant noise in long-term interferograms, which can degrade the time-series results if included. Additionally, practical issues such as gaps in satellite data, poor acquisitions, or systematic errors during interferogram generation can result in incomplete networks. Furthermore, pre-existing interferogram networks, such as those provided by systems like COMET-LiCSAR, often prioritize short temporal baselines due to the vast volume of data generated by satellites like Sentinel-1. As a result, complete interferogram networks may not always be available. Given these challenges, it is critical to understand the applicability of PL methods on these incomplete networks. This study evaluated the performance of two PL methods, eigenvalue decomposition (EVD) and eigendecomposition-based maximum-likelihood estimator of interferometric phase (EMI), under various network configurations including short temporal baselines, randomly sparsified networks, and networks where low-coherence interferograms have been removed. Using two sets of simulated data, the impact of different network structures on the accuracy and quality of the results was assessed. These patterns were then applied to real data for further comparison and analysis. The findings demonstrate that while both methods can be effectively used on short temporal baselines, their performance is highly sensitive to network sparsity and the noise introduced by low-coherence interferograms, requiring careful parameter tuning to achieve optimal results across different study areas. Full article

Fringe projection profilometry (FPP) is extensively utilized for the 3D measurement of various specimens. However, traditional FPP typically requires at least three phase-shifted fringe patterns to achieve a high-quality phase map. In this study, we introduce a single-shot FPP method based on common path polarization interferometry. In our method, the projected fringe pattern is created through the interference of two orthogonal circularly polarized light beams modulated by a liquid crystal spatial light modulator (LC-SLM). A polarization camera is employed to capture the reflected fringe pattern, enabling the simultaneous acquisition of four-step phase-shifting fringe patterns. The system benefits from advanced anti-vibration capabilities attributable to the common path self-interference optical path design. Furthermore, the utilization of a low-coherence LED light source results in reduced noise levels compared to a laser light source. The experimental results demonstrate that our proposed method can yield 3D measurement outcomes with high accuracy and efficiency. Full article