Search Results (322)

Low-finesse Fabry–Perot (F–P) cavities, widely applied in the field of micro-displacement measurement, offer significant advantages in reducing the influence of higher-order reflections and improving the accuracy of measurement systems. Generally, an F–P cavity finesse of 0.5 is required to achieve high-precision micro-displacement measurements. However, in optical design, low-finesse cavities impose strict requirements on reflectivity, and maintaining fine stability during cavity movement is challenging. Achieving ideal orthogonal interference with a finesse of 0.5 thus presents considerable difficulties. This study proposes a novel low-finesse F–P cavity design that employs a high-reflectivity spherical reflector and the end face of a fiber collimator as the reflective surfaces of the cavity. By utilizing beam divergence characteristics and geometric parameters, a structure with a finesse of approximately 0.5 is quantitatively designed, enabling a simplified implementation without the need for angular alignment. Compared with conventional approaches, this method eliminates the need for precise angular alignment of the reflective surfaces, significantly simplifying implementation. The experimental results show that, under fixed receiving field angles and beam radii of the fiber collimators, ideal orthogonal interference can be achieved by selecting the radius of the reflective sphere. Under varying working distances, the average finesse values of the interference spectra measured by Collimators 1 and 2 are 0.496 and 0.502, respectively, both close to the theoretical design value of 0.5, thereby meeting the design requirements. Full article

In this study, a terahertz microfluidic multi-band sensor was designed. Unlike previous microfluidic absorption sensors that rely on dipole resonance, the proposed sensor uses a physical mechanism for absorption by exciting higher-order lattice resonances in microfluidic structures. With a Fabry–Perot cavity, the sensor can form an absorption peak with a high quality factor (Q) and narrow full width at half maximum (FWHM). A high Q value and a narrow FWHM are valuable in the field of sensing and provide strong support for high-precision sensing. On this basis, the sensing performance of the device was investigated. The simulation results clearly show that the absorption sensor has ultra-high sensitivity, which reaches 400 GHz/Refractive Index Unit (RIU). In addition, the sensor generates three absorption peaks, overcoming the limitations of a single frequency band in a composite resonance mode and multidimensional frequency response, which has potential application value in the field of volatile organic compound (VOC) sensing. Full article

Optically pumped gas terahertz (THz) lasers (OPGTLs) as reliable sources of THz radiation have been extensively utilized within THz application areas. In this paper, a substrate-free metal mesh coupler based on the metasurfaces principle was designed for continuous wave OPGTL, which is suitable for the Fabry–Perot (FP) THz resonator. The parameters of substrate-free metal mesh are calculated by the Ulrich equivalent circuit model, and the influence of metal mesh period and linewidth on its transmittance is analyzed quantitatively. Taking the THz laser with the 118.8 µm of CH₃OH optically pumped by the 9.6 µm CO₂ laser line for instance, two kinds of metal mesh were devised as input and output couplers of the resonator, and the transmittance and reflectance of the metal meshes are verified by the finite-difference time-domain (FDTD) method. Furthermore, the transmitted and reflected light fields of the FP resonant cavity metal mesh mirrors were simulated by using the FDTD method under the vertical incidence of both pump light and THz waves. Validation of the optical field characteristics of the substrate-free metal meshes confirmed their suitability as ideal input and output coupling cavity mirrors for FP resonant cavities in optically pumped gas THz lasers. Full article

In the aerospace, energy and nuclear energy sectors, dynamic pressure measurement of power equipment and pressure vessels in high-temperature environments is critical for validating design, manufacturing processes and operational condition monitoring. The existing electric sensors are resistant to temperature. It is difficult to meet the pressure measurement requirements of high temperature and high-frequency responses. In this paper, combining the material properties of high-temperature co-fired ceramics (HTCC) with the structural characteristics of Fabry–Perot, an all-ceramic fiber-optic Fabry–Perot high-temperature pulsating pressure sensor based on a HTCC pressure- sensing diaphragm and ceramic high-temperature sintering process, is proposed. Experimental results show that in the pressure range of 6 MPa, the static pressure sensitivity of the sensor is 1.30 nm/MPa, and the linear goodness of fit reaches 0.99913. The dynamic response frequency of the sensor reaches 598.5 kHz. The survival time at high temperature of 800 °C is more than 80 h. The sensitivity to temperature is 0.00475 nm/°C. Full article

In this paper, a MgO-based high-temperature Fabry-Perot (F-P) vibration sensor with a fiber-optic collimator is proposed and experimentally demonstrated at 1000 °C. The sensor is composed of a sensing unit and a fiber-optic collimator. The F-P cavity is formed by the upper surface of the inertial mass block and the countersunk hole of the cover layer. The length of the F-P cavity changes with external vibrations. The sensing unit is prepared by wet etching technology and three-layer direct bonding technology, which ensure its stability and reliability in high-temperature environments. The experimental results indicate that the sensor can operate stably within a range from room temperature up to 1000 °C. The sensitivity and non-linearity of the sensor at 1000 °C are 1.3224 nm/g and 3.8%, respectively. Furthermore, the sensor operates at frequencies of up to 4 kHz while remaining unaffected by lateral vibration signals. The high-temperature F-P vibration sensor can effectively deal with the fiber damage in extreme environments and exhibits considerable potential for widespread applications. Full article

Quasibound states in the continuum (qBICs) have aroused much attention as a feasible stage to investigate optical strong coupling due to their extremely high-quality factors (Q-factors) and extraordinary electromagnetic field enhancement. However, current demonstrations of strong coupling based on qBICs have primarily focused on the visible spectral range, while research in the near-infrared (NIR) regime remains scarce. In this work, we design a nanograting metasurface supporting Friedrich–Wintgen bound states in the continuum (FW BICs). We demonstrate that FW BIC formation stems from destructive interference between Fabry–Pérot cavity modes and metal–dielectric hybrid guided-mode resonances. To investigate the qBIC–exciton coupling system, we simulated the interaction between MoTe₂ excitons and nanograting metasurfaces. A Rabi splitting of 55.4 meV was observed, which satisfies the strong coupling criterion. Furthermore, a chiral medium layer is modeled inside the nanograting metasurface by rewriting the weak expression and boundary conditions. A mode splitting of the qBIC–chiral medium system in the circular dichroism (CD) spectrum demonstrates that the chiral response successfully transferred from the chiral medium layer to the exciton–polaritons systems through strong coupling. In comparison to the existing studies, our work demonstrates a significantly larger CD signal under the same Pascal parameters and with a thinner chiral dielectric layer. Our work provides a new ideal platform for investigating the strong coupling based on quasibound states in the continuum, which exhibits promising applications in near-infrared chiral biomedical detection. Full article

A double-cavity Fabry-Perot (F-P) interferometer sensor based on a polymer-filled hollow core fiber (HCF) has been proposed and experimentally verified. The double cavity of the sensor is formed by filling the hollow core fiber with two kinds of polymer materials and curing these materials, with the other end of the hollow core fiber connected to a single-mode fiber (SMF). The three reflective surfaces of the sensor reflect three beams of light, which interfere to form a spectrum with an envelope. By using Fast Fourier Transform (FFT) and a Fourier filter, the spectrum of each cavity can be separated and, based on this, the demodulation matrix of the sensor can be constructed. By controlling the length of the polymer cavity, a single sensor cavity can achieve high temperature and gas pressure sensitivity, with values of 2.05 nm/°C and 17.63 nm/MPa, respectively. More importantly, the sensor can be used under an environment of 40–110 °C and 0–3.0 MPa, with simple fabrication, good robustness, and better stability and repeatability compared to similar sensors. Based on its high sensitivity and large measurement range, this sensor has broad application prospects in industrial manufacturing and harsh environmental monitoring fields. Full article

In this paper, the vibration sensitivity and zero-expansion temperature of a 100 mm cubic Fabry-Pérot (FP) cavity with reinforced-support are analyzed. Initially, the reinforced-support FP cavity was simulated and analyzed. Simulation results indicate that vibration sensitivity of the FP cavity is less than 1.5 × 10⁻¹⁰/g, and zero-expansion temperature of the FP cavity is influenced by the support structure by approximately 1 °C. Subsequently, experiments were carried out. The experimental results demonstrate that vibration sensitivities of the reinforced-support FP cavity in the Z, X, and Y directions are 1.73 × 10⁻¹⁰/g, 2.09 × 10⁻¹¹/g, and 2.13 × 10⁻¹¹/g, respectively. The zero-expansion temperature is about 29.5 °C. The vibration sensitivity of the reinforced-support FP cavity is comparable to that of the four-point support FP cavity, and zero-expansion temperature of the FP cavity is affected limitedly by the support structure. The same vibration sensitivity as the four-point support cavity and robust vibration resistance may expand the application of the transportable or spaceborne ultra-stable laser with cubic FP cavity. Full article

Pole-zero maps and Bode plots are commonly utilized in control systems and the study of natural phenomena to visualize their origins and behavior. In this paper, these graphical methods are applied to investigate the behavior of cavity variations, ΔL, in a low-finesse Fabry–Pérot interferometer subjected to external perturbations. Both graphical representations are analyzed in the s-plane. The study is theoretically performed, and the theory is corroborated by developing three numerical experiments where small displacements were applied. Based on the theoretical and numerical results, the cavity length variations, $\Delta L$, can be studied on the s-plane applying the pole-zero maps and Bode plots. The two methods, including the theory and the experiments, are in agreement. Considering the theoretical and graphical results, pole-zero maps and Bode plots can be applied on the signal demodulation of optical interferometers and quasi-distributed sensors where local sensors are interferometers. Full article

Fiber-optic Fabry–Pérot (F–P) sensors offer significant potential for non-invasive hemodynamic monitoring, but existing sensing systems face limitations in multi-channel measurement capabilities and dynamic demodulation accuracy. This study introduces a sparse-frequency-scanning white-light interferometry (SFS-WLI) system with an adaptive mode-locked cross-correlation (MLCC) algorithm to address these challenges. The system leverages telecom-grade semiconductor lasers (191.2–196.15 THz sweep range, 50 GHz step) and a Fibonacci-optimized MLCC algorithm to achieve real-time cavity length demodulation at 5 kHz. Compared to normal MLCC algorithm, the Fibonacci-optimized algorithm reduces the number of computational iterations by 57 times while maintaining sub-nanometer resolution under dynamic perturbations. Experimental validation demonstrated a carotid–radial pulse wave velocity of 5.12 m/s in a healthy male volunteer. This work provides a scalable and cost-effective solution for cardiovascular monitoring with potential applications in point-of-care testing (POCT) and telemedicine. Full article

We propose a micro-electromechanical system (MEMS)-integrated Fabry–Pérot (F–P) microcavity designed for a tunable single-photon source based on a single semiconductor quantum dot (QD). Through theoretical simulations, our design achieved a Purcell factor of 23, a photon extraction efficiency exceeding 88%, and an optical cavity mode tuning range of more than 30 nm. Experimentally, we fabricated initial device prototypes using a micro-transfer printing process and demonstrated a tuning range exceeding 15 nm. The device exhibits high mechanical stability, full reversibility, and minimal hysteresis, ensuring reliable operation over multiple tuning cycles. Our findings highlight the potential of MEMS-integrated F–P microcavities for scalable, tunable single-photon sources. Furthermore, reaching a strong coupling regime could enable efficient single-photon routing, opening new possibilities for integrated quantum photonic circuits. Full article

This study investigates the mechanical and optical characteristics of silicon nitride thin films deposited with PECVD at 80 °C for tunable silicon-rich SiN_x-SiO_y-based MEMS optical cavities. Varying the deposition parameters using SiH₄ and N₂ as precursor gases for silicon-rich SiN_x thin films allows us to tune the refractive index to a value as high as 2.40 ± 0.013 at an extinction coefficient of only 0.008, an extremely low surface roughness of only 0.26 nm, and a compressive stress of about 150 MPa. We deposited 6.5-layer pairs of silicon-rich SiN_x/SiO_y-distributed Bragg reflector (DBR) micro-electro-mechanical system (MEMS) mirror that covers the whole 1300 and 1550 nm range. Cavity architectures of 6.5 top and 6 bottom layer-pairs were fabricated in the clean room providing a variety of cavity lengths between 0.615 µm and 2.85 µm. These lengths were then simulated in order to estimate the Young’s Modulus of silicon-rich SiN_x, obtaining values from 56 to 92 GPa. One of the designs was characterised electro-thermally providing a tuning range of at least 86.7 nm centred at 1585 nm. The tunable filters are well suitable for implementation as tuning element in lasers for optical coherence tomography. Full article

To meet the pressure measurement requirements of deep earth exploration, we propose an OFPS (optical fiber pressure sensor) with self-temperature compensation based on MEMS technology. A spectral extraction and filtering algorithm, based on FFT (fast Fourier transform), was designed to independently demodulate the composite spectra of multiple FP (Fabry–Pérot) cavities, enabling the simultaneous measurement of pressure and temperature parameters. The sensor was fabricated by etching on an SOI (silicon on insulator) and bonding with glass to form pressure-sensitive FP cavities, with the glass itself serving as the temperature-sensitive component as well as providing temperature compensation for pressure sensing. Experimental results showed that within the pressure range of 0–100 MPa, the sensor exhibited a sensitivity of 0.566 nm/MPa, with a full-scale error of 0.34%, and a linear fitting coefficient (R²) greater than 0.9999. Within the temperature range of 0–160 °C, the temperature sensitivity of the glass cavity is 0.0139 nm/°C and R² greater than 0.999. Full article

A parallel Fabry–Perot interferometer (FPI) optical fiber sensor, enhanced with UV glue, was proposed for environmental temperature detection. The UV glue is applied to the fiber’s sensing region using a coating method, forming an FP cavity through misalignment welding, allowing the FP to function as a temperature sensor. In parallel, a reference FPI with a similar free spectral range (FSR) is connected, generating a Vernier effect that amplifies small changes in the refractive index (RI) of the sensing region. The study demonstrates that UV glue enhances the temperature-sensing capabilities of the FP, and when combined with the Vernier effect, it significantly improves the sensitivity of a single interferometric sensor. The temperature sensitivity of the parallel-connected FPI is −2.80219 nm/°C, which is 7.768 times greater than that of a single FPI (−0.36075 nm/°C). The sensor shows high sensitivity, stability, and reversibility, making it promising for temperature-monitoring applications in various fields, including everyday use, industrial production, and the advancement of optical fiber temperature-sensing technologies. Full article

This research introduces a novel physical-layer encryption technique for metropolitan-optimized optical transport networks (M-OTNs) that integrates real-time optical signal time-domain scrambling/descrambling with decoy-state quantum key distribution (DS-QKD). The method processes real-time optical data from the optical service unit (OSU) using a series of tunable Fabry–Perot cavities (FPCs), synchronized and updated with a running key. Experimental validation demonstrates secure communication within the optical network’s physical layer during standard OTU2 data transmission (10.709 Gbps), achieving an online transmission distance exceeding 100 km over typical single-mode fiber with a power loss of approximately 1.77 dB. The results indicate that this integrated approach significantly enhances the security of the optical physical layer in M-OTNs. Full article