Based on the phase transition of vanadium dioxide(VO₂), an ultra-broadband tunable terahertz metamaterial absorber is proposed. The absorber consists of bilayer VO₂ square ring arrays with different sizes, which are completely wrapped in Topas and placed on gold substrate. The simulation results show that the absorption greater than 90% has frequencies ranging from 1.63 THz to 12.39 THz, which provides an absorption frequency bandwidth of 10.76 THz, and a relative bandwidth of 153.5%. By changing the electrical conductivity of VO₂, the absorption intensity can be dynamically adjusted between 4.4% and 99.9%. The physical mechanism of complete absorption is elucidated by the impedance matching theory and field distribution. The proposed absorber has demonstrated its properties of polarization insensitivity and wide-angle absorption, and therefore has a variety of application prospects in the terahertz range, such as stealth, modulation, and sensing.

Active metasurfaces, in which the optical property of a metasurface device can be controlled by external stimuli, have attracted great research interest recently. For optical switching and modulation applications, high‐performance active metasurfaces need to show high transparency, high power efficiency, as well as ultrafast switching and large‐scale fabrication capability. This paper reports Au/VO ₂ ‐based active metasurfaces meeting the requirements above. Centimeter‐scale Au/VO ₂ metasurfaces are fabricated by polystyrene sphere colloidal crystal self‐assembly. The devices show optical modulation on‐off ratio up to 12.7 dB and insertion loss down to 3.3 dB at 2200 nm wavelength in the static heating experiment, and Δ T / T of 10% in ultrafast pump‐probe experiments. In particular, by judiciously aligning the surface plasmon resonance wavelength to the pump wavelength of the femtosecond laser, the enhanced electric field at 800 nm is capable to switch off the extraordinary optical transmission effect at 2200 nm in 100 fs time scale. Compared to VO ₂ thin‐film samples, the devices also show 50% power reduction for all‐optical modulation. Our work provides a practical way to fabricate large‐scale and power‐efficient active metasurfaces for ultrafast optical modulation.

In this paper, we reported a theoretical study of a novel Surface plasmon resonance (SPR) biosensor composed of BK7 prism, gold (Au)/silver (Ag) bimetallic layer, silicon and two-dimensional (2D) materials. The bimetallic layer combines the advantages of Au and Ag and the high refractive index silicon layer enhances the electric field on the surface of the sensor, so that the sensor has a better overall performance in terms of sensitivity and figure of merit (FOM). Compared with ordinary dielectrics, 2D materials have excellent photoelectric properties, such as larger specific surface area, higher carrier density and stronger adsorption capacity, which improve the detection ability of the sensor. The sensitivity of the optimized sensor achieves 297.2°/RIU, 274°/RIU and 246°/RIU when the silicon layer is covered with graphene, MXene (Ti₃T₂C_x) and MoS₂, respectively. Compared with the traditional SPR sensor, the sensitivity of the structure has been significantly improved, and its excellent performance has broad application prospects in biosensing and other fields.

To effectively control the critical thickness of a polydimethylsiloxane (PDMS) film and enhance the sensitivity characteristics of the fiber pressure sensor, we propose a new method to optimize the thickness of the PDMS film in a fiber tube. It is characterized by analyzing the relationship between the diffusion rate of the PDMS and its viscosity, and using an oven to solidify the PDMS to a certain extent to accurately control the diffusion rate and diffusion length of the PDMS in the fiber tube. We also used multiple transfer methods to control the volume of the PDMS in the fiber tube to minimize the thickness of the formed PDMS film. Fabry-Perot interference occurs when the surface of the PDMS film layer filled into the fiber tube and the adjacent single mode fiber/fiber tube form a joint surface. This method forms a new fiber-optic Fabry-Perot pressure sensor that is very sensitive to external pressure parameters. The experimental results show that the optimized film thickness will be reduced to an order of 20 μm. Correspondingly, the fiber-optic pressure sensor has a sensitivity of up to 100 pm/kPa, which is about 100 times that reported in the literature. The structure also has better resistance to temperature interference. To our knowledge, this is the first in-depth study of the effects of the PDMS viscosity coefficient, diffusion rate, and fiber pressure sensitivity in fiber. The film thickness optimization method has some advantages, including a low cost, good controllability, and good application value in high sensitivity pressure and sound wave detection.

A high-sensitivity fiber-optic gas pressure sensor based on a Fabry-Perot interferometer filled with epoxy resin adhesive is proposed. The factors of affecting the pressure sensitivity are theoretically analyzed and verified experimentally. In our experiment, the pressure sensitivity of the epoxy-filled sensor with the thinnest diaphragm thickness of $6.61~\mu \text{m}$ corresponding to the cavity length of $65.45~\mu \text{m}$ is −530.17 pm/kPa from 200 to 300 kPa. The sensitivity of the proposed pressure sensor with the shortest cavity length of $90.43~\mu \text{m}$ corresponding to the film thickness of $10.65~\mu \text{m}$ is −378.18 pm/kPa from 200 to 300 kPa. To further improve the sensitivity, the proposed pressure sensor is optimized, which consists of two cascaded Fabry-Perot interferometers separated by a long section of single-mode fiber to form Vernier effect. Such a pressure sensor based on the epoxy-filled Fabry-Perot interferometer and the Vernier effect obtains a high sensitivity of 2.526 nm/kPa in the local measurement range of 233 to 259 kPa and a low detection limit of 0.00892 kPa. With the advantages of high sensitivity, compact structure and simple fabrication, the proposed pressure sensor has potential applications in the biomedical field and ocean exploration.

The optical Vernier effect is a powerful tool for improving the sensitivity of an optical sensor, which relies on the use of two sensor units with slightly detuned frequencies. However, an improper amount of detuning can easily cause the Vernier effect to be unusable. In this work, the effective generation range of the Vernier effect and the corresponding interferometer configuration are suggested and experimentally demonstrated through a tunable cascaded Fabry–Perot interferometer structure. We further demonstrate a practical method to increase the magnification factor of the Vernier effect based on the device bandwidth. Only the optical path length of an interferometer probe and the sensitivity of the measurement parameters are needed to design this practical interferometer based on the Vernier effect. Our results provide potential insights for the sensing applications of the Vernier effect.