In this paper, a dual-parameter sensor based on surface plasmon resonance (SPR)-photonic crystal fiber (PCF) is proposed, which can be applied in detecting the magnetic field and temperature. In this sensor, two elliptical channels are designed on both sides of the fiber core. The left channel (Ch 1) is coated with gold film and filled with magnetic fluid (MF) to achieve a response to the magnetic field and temperature using SPR. The right channel (Ch 2) is coated with gold film as well as Ta₂O₅ film to improve the SPR sensing performance. Finally, Ch 2 is filled with polydimethylsiloxane (PDMS) to achieve a response to the temperature. The mode characteristics, structural parameters and sensing performance are investigated by the finite element method. The results show that when the magnetic field is in the range of 50–130 Oe, the magnetic field sensitivities of Ch 1 and Ch 2 are 65 pm Oe⁻¹ and 0 pm Oe⁻¹, respectively. When the temperature is in the range of 17.5–27.5 °C, the temperature sensitivities of Ch 1 and Ch 2 are 520 pm °C⁻¹ and 2360 pm °C⁻¹, respectively. By establishing and demodulating a sensing matrix, the sensor can not only measure the temperature and magnetic field simultaneously but also solve the temperature cross-sensitivity problem. In addition, when the temperature exceeds a certain value, the proposed sensor is expected to achieve dual-parameter sensing without a matrix. The proposed dual-parameter SPR-PCF sensor has a unique structure and excellent sensing performance, which are important for the simultaneous sensing of multiple basic physical parameters.

An all optical fiber CTD sensor used in seawater based on an OMC is demonstrated. And the OMC is fabricated by fusing and tapering two twisted conventional communication fibers based on the improved flame-brushing method. By monitoring the sensing dips, in situ measurement of salinity, temperature and depth (pressure) in seawater can be realized respectively. Especially, the water depth (pressure) sensing function of the OMC is demonstrated for the first time, and the pressure sensitivity is 50 times higher than a bare fiber Bragg grating (with a wide pressure measurement range from 0 MPa to 25 MPa). The highest sensitivities of salinity, temperature and depth are 1596 pm/%, 2326 pm/°C, and 169 pm/Mpa, respectively.These are high enough for the requirements of marine dynamic environmental monitoring and underwater target detection of fiber-optic hydrophone system. The all optical fiber CTD sensor demonstrated here show advantages of easy fabrication, compact structure, high sensitivity, low cost, and compatibility with the optical fiber system, which may find applications in multifunction optical sensors in ocean detections and other applications.

Metamaterial perfect absorbers in the terahertz band are attracting more and more attention. Pure narrowband absorbers as well as broadband absorbers have been proposed one after another in recent years. However, absorbers that can achieve both narrow-band absorption and broadband absorption have hardly been reported. To meet more practical needs, we propose a terahertz metamaterial perfect absorber that combines ultra-broadband and narrowband based on the phase transition properties of vanadium dioxide (VO₂). Its main structure consists of a metal ring and four VO₂ discs, and the absorber can be flexibly switched between ultra-broadband and narrowband absorption by adjusting the ambient temperature. The resonator consisting of metal rings and VO₂ discs are mainly responsible for the formation of absorption peaks. A detailed explanation is given by means of magnetic resonance theory and the impedance matching principle. Compared to recent reports, our design offers a significant improvement in absorption rate and bandwidth and is also flexible in terms of tuning. Moreover, as the phase transition temperature of VO₂ is only slightly higher than room temperature, there are almost no limitations for experimental and practical applications. Therefore, our design will have significant applications in modulation, sensing, energy harvesting, switching devices, etc.

A surface plasmon resonance (SPR) sensor comprising photonic crystal fiber (PCF) is designed for magnetic field and temperature dual-parameter sensing. In order to make the SPR detection of magnetic field and temperature effectively, the two open ring channels of the proposed sensor are coated with gold and silver layers and filled with magnetic fluid (MF) and Polydimethylsiloxane (PDMS), respectively. The sensor is analyzed by the finite element method and its mode characteristics, structure parameters and sensing performance are investigated. The analysis reveals when the magnetic field is a range of 40-310 Oe and the temperature is a range of 0-60 °C, the maximum magnetic field sensitivity is 308.3 pm/Oe and temperature sensitivity is 6520 pm/°C. Furthermore, temperature and magnetic field do not crosstalk with each other's SPR peak. Its refractive index sensing performance is also investigated, the maximum sensitivity and FOM of the left channel sensing are 16820 nm/RIU and 1605 RIU^-1, that of the right channel sensing are 13320 nm/RIU and 2277 RIU^-1. Because of its high sensitivity and special sensing performance, the proposed sensor will have potential application in solving the problems of cross-sensitivity and demodulation due to nonlinear changes in sensitivity of dual-parameter sensing.

Gesture recognition, as a core technology of human–computer interaction, has broad application prospects and brings new technical possibilities for smart homes, medical care, sports training, and other fields. Compared with the traditional human–computer interaction models based on PC use with keyboards and mice, gesture recognition-based human–computer interaction modes can transmit information more naturally, flexibly, and intuitively, which has become a research hotspot in the field of human–computer interaction in recent years. This paper described the current status of gesture recognition technology, summarized the principles and development history of electromagnetic wave sensor recognition, stress sensor recognition, electromyographic sensor recognition, and visual sensor recognition, and summarized the improvement of this technology by researchers in recent years through the direction of sensor structure, selection of characteristic signals, the algorithm of signal processing, etc. By sorting out and comparing the typical cases of the four implementations, the advantages and disadvantages of each implementation and the application scenarios were discussed from the two aspects of dataset size and accuracy. Based on the abovementioned discussion, the problems and challenges of current gesture recognition technology were discussed in terms of the biocompatibility of sensor structures, wearability and adaptability, stability, robustness, and crossover of signal acquisition and analysis algorithms, and the future development directions in this field were proposed.

A novel magnetic field sensor comprising a photonic crystal fiber (PCF) is designed and investigated based on surface plasmon resonance (SPR). We use finite element analysis in order to analyze the sensing characteristics of the magnetic field sensor. The simulation results show that the sensor is very sensitive to the change of refractive index and has good linearity in the refractive index range from 1.43–1.45. The thickness of the metal film and the metal material has great influence on the resonance wavelength and the peak of the loss spectrum, the diameter of the central air hole will affect SPP excitation. When the thickness of gold layer is 50 nm, the refractive index sensitivity is 4125 nm/RIU in the refractive index range from 1.43–1.45. Using the designed sensor for magnetic field sensing, the loss spectrum is red-shifted with the increase of the magnetic field, the highest magnetic field sensitivity can reach 61.25 pm/Oe in the range from 50 Oe to 130 Oe. The sensor not only has high sensitivity of refractive index, but it can also realize accurate measurement of magnetic field. It has huge application potential in complex environment, remote sensing, real-time monitoring, and other fields.