Optics, Volume 6, Issue 1 (March 2025) – 5 articles

Repeatable and reliable assessment of corneal biomechanics with spatial resolution remains a challenge. Vibrational Optical Computerized Tomography (V-OCT), based on sound-wave elastography, has made it possible to investigate the natural resonant modes of the cornea and obtain the elastic moduli non-invasively. This pilot study presents a characterization of four corneal vibrational modes from aberrometric, geometrical, and biomechanical approaches in the living human cornea of five healthy volunteers by combining a corneal sound-wave generator, dual Placido–Scheimpflug corneal imaging, and the Ocular Response Analyzer (ORA) devices. Sound-induced corneal wavefront aberration maps were reconstructed as a function of sound frequency and isolated from the natural state. While maps of low-order aberrations (LOA) revealed symmetric geometrical patterns, those corresponding to high-order aberrations (HOA) showed complex non-symmetric patterns. Corneal geometry was evaluated by reconstructing corneal elevation maps through biconical fitting, and the elastic and viscous components were calculated by applying the standard linear solid model to the ORA measurements. The results showed that sound-wave modulation can increase high-order corneal aberrations significantly. Two frequencies rendered the corneal shape more prolate (50 Hz) and oblate (150 Hz) with respect to the baseline, respectively. Finally, both the elastic and viscous properties are sensitive to sound-induced vibrational modes, which can also modulate the corneal stress-strain response. The cornea exhibits natural resonant modes influenced by its optical, structural, and biomechanical properties. Full article

The study of the refractive index of traditional lenses is one of the foundational topics in the field of optics. The refractive index of a lens determines its ability to refract and focus light, making it a key parameter in optical design and applications. For the measurement of the refractive index of blind samples of finished lenses, this paper proposes a measurement method based on the use of a focal length measuring instrument and an aspheric profilometer to measure the surface shape data of the front and back surfaces of the lens. This method combines curve fitting algorithms and curvature radius fitting algorithms, ultimately reconstructing the lens model using Zemax and back-calculating the refractive index of the lens. For the samples employed in this paper, the measurement accuracy of the focal length can achieve 1.06%, the fitting accuracy of the curvature radius can reach 0.138%, and the recovery accuracy of the refractive index can attain 6.303 × 10⁻⁴%. Full article

In this paper, a high-linear-sensitivity fiber curvature sensor based on the sphere-shaped misaligned structure (SSMS) with few-mode fiber (FMF) and single-mode fiber (SMF) was proposed and demonstrated. A spherical structure was prepared at one end of a few-mode fiber, which could effectively excite higher-order modes and generate interference in the misaligned cascade. When external environmental parameters changed, the resonance peaks formed by intermodal interference were displaced, and the shifts generated by different resonant peaks were also different. The experimental results show that the maximum curvature sensitivity was −2.220 nm/m⁻¹, and the linear fitting coefficient reached up to 0.991, which is an extremely high sensitivity among wavelength-modulated curvature sensors. Meanwhile, the strain sensitivity of the sensor was as low as 7.99 pm/μ$\overline{\mathsf{\epsilon }}$, and the temperature sensitivity was 3.958 pm/°C, which is a low temperature sensitivity and low strain sensitivity, and solves the cross-sensitivity problem. With advantages of simple manufacture, low cost, and favorable stability, the sensor is expected to be one of the best candidate instruments for measuring curvature and inclination. Full article

Time synchronization is an important technology in synchronous communication systems to ensure the accuracy of data transmission. Precise time synchronization allows the receiver to correctly interpret the signal at the correct moment. However, as communication rates increase and application scenarios diversify, pulse signal reception quality is often affected by factors such as noise interference and clock stability. In order to address these challenges, we propose a pulse signal recovery method utilizing the least squares algorithm to complete time compensation. By fitting and optimizing the received signal, we can obtain estimated values that closely approximate the actual time, thereby achieving enhanced precision in time synchronization. The results demonstrate that this method effectively reduces estimation errors, improving the system’s time synchronization accuracy to the $ns$ level. This method not only provides an effective solution for enhancing time synchronization precision but also lays the foundation for time synchronization performance in the future. Full article

Pork adulteration detection in beef is important due to health, economic, and religious concerns. This study explored the use of a Shortwave Near Infrared–Hyperspectral Imaging (SWNIR–HSI) system which captured spectral data across 894–2504 nm to detect adulteration of pork in beef. In this study, minced pork in various concentrations ranging from 0–50% (w/w) were added to pure minced beef. Spectra obtained from the SWNIR–HSI were used to develop a partial least square regression (PLSR) model. The study compared the PLSR results between full wavelengths (variables) and selected wavelengths obtained via the variable importance in projection (VIP) method. The best results from the full-wavelength PLSR model yielded a prediction accuracy (R²P) of 0.940 and a standard error of prediction (SEP) of 4.633%, while using VIP-selected wavelengths improved performance, with R²P of 0.955 and SEP of 3.811%. The study demonstrates the potency of SWNIR–HIS, particularly with selected wavelengths, as an effective and nondestructive tool for accurately predicting pork adulteration levels in beef. Full article