Optical Review最新文献

We propose a novel method for measuring circular dichroism (CD) using polarization-modulated dual-comb spectroscopy (PM-DCS). This method utilizes two tightly phase-locked optical frequency combs to realize rapid and precise polarization modulation, eliminating the need for mechanical polarization modulators, and achieves high-speed, high-precision control of the polarization states. The experimental results demonstrated successful polarization switching between left- and right-circularly polarized light, enabling accurate detection of the CD spectra. Moreover, this method supports customizable polarization switching, realizing applications such as simultaneous circular-linear dichroism measurements. Our findings offer a pathway for high-sensitivity, broadband, and dynamic polarization measurements, extending applications in the analysis of chiral materials, particularly in the fields of chemistry, biology, materials science, and device characterization, where the ability to perform real-time high-sensitivity measurements is essential.

Information transmission capacity in optical fiber networks can be rapidly escalated using Dense Wavelength Division Multiplexing (DWDM). However, non-linearities in fiber such as Four Wave Mixing (FWM) cause adverse effects in DWDM and ultra-DWDM networks. In this work, differential quadrature phase shift keying (DQPSK) modulation is employed to minimize the impact of FWM effect. The system performance can be improved by properly adjusting the switching and bias voltage of the dual-port Mach-Zehnder Modulator (MZM). Here, the performance of the proposed method is compared with other advanced modulation techniques such as Quadrature Phase Shift Keying (QPSK), Differential Binary Phase Shift Keying (DBPSK) and 16-Quadrature Amplitude Modulation (QAM). The results reveal optimal performance with maximum FWM minimization for the proposed method at a switching voltage of 3 V.

Concerns about sun exposure have increased, leading to increased interest in the quality of sunscreen products, particularly regarding their content of heavy metals that may pose a health risk. This study aims to evaluate the concentrations of some heavy metals in sunscreens using two analytical techniques: atomic absorption spectroscopy (AAS) and laser induced breakdown spectroscopy (LIBS), and to compare the results of both methods. Two commercial samples representing two different quality products were analyzed: a low-quality sample (R10) and a high-quality sample (R11). Sunscreen samples were dried at 55 °C for 1 h (before LIBS analysis) to remove excess moisture and to provide a stable plasma, as the sunscreen matrices had high contents of water and oil. Two computational methods were used to estimate element concentrations The first is an electron density method to determine the concentrations of elements such as Zn, Ni, Pb, Hg, and Cd. The second is a new method known as the relative density method (LIBS-Qc), a simplified method that does not rely on electron temperature and has proven highly efficient in calculating concentrations. The results showed that the mercury concentration was higher in sample R10 (11.083) than in sample R11 (6.607). The new method (LIBS-Qc) also showed good agreement with the results of the AAS technique, indicating its potential as an effective and rapid alternative for the analysis of heavy elements in commercial products.

A Mach–Zehnder interferometer (MZI) based on the two-end etching of multi-core fiber (MCF) is proposed and experimentally demonstrated. The MZI consists of a seven-core fiber with two-end etching and is sandwiched in two single-mode fibers. To study the influence of different etching time on MZI, BOE solution is used to etch MCF. Due to the fact that BOE solution is a mixture of HF and NH₄F, the etching rate of BOE on the MCF is slower, which is more conducive to observing the etching appearance of the MCF. The effect of etching on MZI spectrum is analyzed theoretically. Experimental results confirm and show that the humidity increases from 25%RH to 95%RH, the MZI energy monitoring point decreases, and its humidity response sensitivity is − 0.045 dB/%RH. Since the temperature also affects the sensor response, the temperature is also measured. The temperature increases from 35℃ to 85 ℃, and the MZI temperature response sensitivity is 0.0465 nm/℃. A quick and reliable time response has also been demonstrated and shows potential for future applications.

This paper presents several ultrathin multi-band terahertz bandpass filters (BPFs) based on metal-dielectric-metal (MDM) metasurfaces, achieving independently tunable multi-band transmission characteristics through parametric adjustment of the geometric parameters (side length w, gap spacing (varDelta s), and loop count N) of the square-loop arrays. The designed tri-band filter is primarily analyzed for its excellent performance at 0.72/1.23/2.23 THz, including a roll-off rate >30 dB/THz, average transmittance of 97% (peak insertion loss (< -0.10) dB), and out-of-band rejection ratio >25 dB. The multi-band spectral response is validated via finite integration technique (FIT) simulations in CST Microwave Studio, combined with surface electric field distribution analysis and effective medium theory (EMT) to elucidate the propagation mechanism of THz waves and the functional roles of each structural layer. A systematic investigation of geometric parameter dependencies on transmission performance is also conducted. The designed BPF exhibits potential applications in electromagnetic interference suppression, ultrasensitive biosensing, and dynamic THz signal multiplexing, owing to its multi-band transmission, polarization insensitivity, and compact footprint.

Thermal imaging cameras operate effectively at night or in low-light conditions, enhancing the accuracy of human pose recognition in such environments. To address the issue of insufficient accuracy in traditional human pose recognition methods under low-light conditions, this study proposes an improved algorithm based on the YOLOv8 model, referred to as YOLOv8-SLG. Considering the peculiarity that thermal images reflect temperature information rather than optical features, traditional convolutional networks may produce unnecessary redundancy in feature extraction. To address this issue, first, we improve the detection accuracy and preserve the network structure by replacing the original convolution with SCConv building blocks in the backbone network of YOLOv8n in order to reduce spatial and channel redundancy between features in the convolutional neural network. Second, we enhance local feature detection by integrating the LSKA attention mechanism into the neck network, reducing computational complexity and memory requirements while maintaining accuracy. Finally, we enhance the multi-scale processing capability and reduce the number of parameters per detection head through shared GroupNorm convolution to improve target localisation and classification performance. Experimental results show that these enhancements significantly improve the model’s performance for human pose recognition tasks in complex contexts. Compared to the original YOLOv8n model, the proposed algorithm improves the precision, recall, mAP50, and mAP50-95 metrics by 1.33%, 1.79%, 1.86%, and 2.01% to 97.7%, 94.6%, 96.7%, and 75.1%, respectively. In addition, YOLOv8-SLG reduced model parameter calculations by 8.14%. It can detect human poses in thermal images in real time accurately, and comparison with other mainstream human pose detection algorithms confirms the effectiveness and superiority of the method.

In this paper, a single-polarized photonic crystal fiber(PCF) filter for the communication band was proposed. The polarization properties of PCF with a single gold-coated liquid-filled hole have been investigated by the full vector finite element method(FEM). Extensive simulations reveal that near the 1310 nm communication wavelength, the y-polarized core mode exhibits a significantly higher peak loss intensity of 453.46 dB/cm compared to the x-polarized core mode's substantially lower value of 2.068 dB/cm. With a length of 500 μm of the designed PCF, the bandwidths of the crosstalk less than -20 dB can reach to 213 nm. Fiber filters can accurately implement the filtering function for a single communication window. It is expected to play a key role in optical communication, optical sensing and other related fields, providing strong support for technological development and application expansion in these fields.

This article proposes an elliptical photonic crystal fiber (PCF) structure for broadband polarization filtering and refractive index (RI) sensing. By employing an elliptical core and elliptical air holes, the design achieves a high resonance intensity for y-polarization of 789 dB/cm, with a corresponding x-polarization loss of 0.29 dB/cm at a communication wavelength of 1.31 μm, resulting in a polarization extinction ratio of 2721. For a fiber length of 200 μm, the structure attains a crosstalk (CT) value of 137.0 dB at 1.31 μm. Furthermore, it exhibits a bandwidth of 1.04 μm with CT levels exceeding 20 dB, spanning the wavelength range from 1.16 to 2.2 μm. The same elliptical PCF structure can also function as a RI sensor, achieving a sensitivity of 8600 nm/RIU within a sensing range of 1.29–1.31. Additionally, replacing the elliptical holes with fully circular holes in the proposed fiber maintains a wide polarization-filtering bandwidth and yields a high RI sensitivity of 21,400 nm/RIU over the range 1.37–1.39. These results indicate that fully circular holes based on the proposed PCF structure represent a viable alternative for applications in both polarization filtering and RI sensing.

This paper explores the propagation characteristics of Airyprime beams in an inhomogeneous medium with periodic potential, from both theoretical and numerical simulation perspectives. By using the method of separation of variables, the Gross–Pitaevskii equation with periodic potential was solved to obtain the breather soliton solution and breathing period. Additionally, considering the medium and beam parameters, numerical simulations were performed to study the propagation characteristics of Airyprime beams and the superposition between two Airyprime beams. First, the influence of initial medium parameters (modulation intensity P and modulation frequency ω) on the propagation characteristics was studied. Then, the effect of initial beam parameters (initial chirp C and position x₀) on the propagation characteristics was analyzed. Finally, the superposition between two Airyprime beams with different phases (varphi = 0) (varphi), amplitudes A, and initial separations x₀ was investigated. By changing the initial medium parameters, the breathing period and central position of the breather soliton can be controlled; by adjusting the initial beam parameters, the deflection direction, size, and maximum intensity of the breather soliton can be manipulated. Changing the phase (varphi = 0) (varphi), amplitude A, and initial separation x₀ of the two Airyprime beams can form different bound-state breather solitons. The results provide a theoretical foundation for the propagation and control of Airyprime beams, as well as for their potential applications in optical communication.

In this paper, a dual hollow-core anti-resonant fiber polarization beam splitter (DHC-ARF PBS) with ultra-wide splitting bandwidth is proposed. The effects of the structure parameters of the DHC-ARF PBS on the splitting performances, including the coupling length, coupling length ratio, confinement loss, and higher-order mode extinction ratio (HOMER), are investigated using the finite element method. The simulation results show that under the optimal structure parameters, the proposed DHC-ARF PBS has larger HOMER (> 100) within the working wavelength range, indicating its good single-mode transmission characteristics. Moreover, the proposed DHC-ARF PBS has a short splitting length of 2.07 cm and an ultra-wide splitting bandwidth of 610 nm (1320 ~ 1930 nm), which covers the whole E, S, C, L, and U bands and a portion of O band. It is believed that the proposed DHC-ARF PBS will have significant applications in the optical communication and sensing systems.