A simple configuration of a D-shaped five-hole photonic crystal fiber (DFPCF)-based surface plasmon resonance (SPR) refractive index (RI) sensor is proposed. A full vector finite element method is applied to simulate the resonant coupling characteristics of the core modes and the surface plasmon polariton (SPP) modes. In addition to its simple structure, a very small polishing depth can introduce a sufficiently strong evanescent field to excite surface plasmon waves, thus ensuring the mechanical strength of the polished fiber. These two key factors lay the foundation for mass production of the sensors. Further, two air holes above the core induce a tunable evanescent field from the core leakage to the polished surface that adjusts the resonance between core modes and SPP modes. A thin layer of gold film is applied to the polished surface to provide a detection platform for liquid analytes without filling pores, forming the SPR effect. Numerical simulation results show that the proposed DFPCF-based SPR RI sensor exhibits sensing performance that is tunable with the film thickness. A maximum wavelength sensitivity of 20 786 nm RIU ⁻¹ and widest detection range of 1.30–1.50 are achieved. Due to its improved sensing performance, the liquid RI sensor could be a potential candidate for use in biochemical analyte detection, industrial production, and food and environmental quality monitoring.

We propose a tunable ultra-broadband polarization filter based on three-core resonance of the fluid-infiltrated and gold-coated high birefringent photonic crystal fiber (HB-PCF). Gold film was applied to the inner walls of two cladding air holes and surface plasmon polaritons were generated on its surface. The two gold-coated cladding air holes acted as two defective cores. As the phase matching condition was satisfied, light transmitted in the fiber core and coupled to the two defective cores. The three-core PCF supported three super modes in two orthogonal polarization directions. The coupling characteristics among these modes were investigated using the finite-element method. We found that the coupling wavelengths and strength between these guided modes can be tuned by altering the structural parameters of the designed HB-PCF, such as the size of the voids, thickness of the gold-films and liquid infilling pattern. Under the optimized structural parameters, a tunable broadband polarization filter was realized. For one liquid infilling pattern, we obtained a broadband polarization filter which filtered out the light in y -polarization direction at the wavelength of 1550 nm. For another liquid infilling pattern, we filtered out light in the x -polarization direction at the wavelength of 1310 nm. Our studies on the designed HB-PCF made contributions to the further devising of tunable broadband polarization filters, which are extensively used in telecommunication and sensor systems.

A high-sensitivity refractive index (RI) sensor with wide tunable detection range based on the dual-core resonance of photonic crystal fibers are presented and studied by the finite element method. A cladding air hole coated with gold film is designed as the microfluidic channel for surface plasmon resonance sensing. The channel filled with liquid analyte acts as a defective core. The directional energy coupling between the fiber core and the defective core which determines the sensing performance is greatly influenced by both the RI of the filled liquid and the structural parameters. Numerical results show that the sensitivity of the sensor increases with the increase of the diameter of the analyte channel, and the RI detection range decreases with the increase of this diameter. So we tune the detection range by adjusting the diameter of the analyte channel to meet specific measurement requirements. As the diameter increases from 1.5 m to 2.4 m, the detection range shrinks from 1.45–1.62 to 1.45–1.48, both with the high spectral sensitivity 10 392 nm/RIU and 25 040 nm/RIU, respectively. The sensor with wide adjustable detection range shows great advantages in the field of biochemical, chemistry and environmental detection.

The traditional algorithms for generating 3D human point clouds often face challenges in dealing with issues such as phantom targets and target classification caused by electromagnetic multipath effects, resulting in a lack of accuracy in the generated point clouds and requiring manual labeling of the position of the human body. To address these problems, this paper proposes an adaptive method for generating 3D human point clouds based on 4D millimeter-wave radar (Self-Adaptive mPoint, SA-mPoint). This method estimates the rough human point cloud by considering micro-motion and respiration characteristics while combining the echo dynamic with static information. Furthermore, it enhances the density of point cloud generation. It reduces interference from multipath noise through multi-frame dynamic fusion and an adaptive density-based clustering algorithm based on the center points of humans. The effectiveness of the SA-mPoint algorithm is verified through experiments conducted using the TI Millimeter Wave Cascade Imaging Radar Radio Frequency Evaluation Module 77G 4D cascade radar to collect challenging raw data consisting of single-target and multi-target human poses in an open classroom setting. Experimental results demonstrate that the proposed algorithm achieves an average accuracy rate of 97.94% for generating point clouds. Compared to the popular TI-mPoint algorithm, it generates a higher number of point clouds on average (increased by 87.94%), improves the average accuracy rate for generating point clouds (increased by 78.3%), and reduces the running time on average (reduced by 11.41%). This approach exhibits high practicality and promising application prospects.

In this paper, a sensitivity sensor of dual-core photonic crystal fiber (DC-PCF) filled with magnetic liquid is introduced and investigated by the finite element method (FEM). To regulate the energy coupling involving the two cores, the magnetic fluid is filled into the pore between the two cores. To adjust the coupling between the supermodes in the DC-PCF, the refractive index of the magnetic fluid-filled air hole may change due to the external magnetic field. This specifically created a magnetic fluid-filled DC-PCF, the magnetic fluid-filled hole is not used as the core for energy transmission, thus avoiding transmission loss. The dip wavelength and the magnetic field displayed an excellent linear connection between 80 and 260 Oe, depending on the numerical data. The detection sensitivity of the magnetic field reached 515.75 pm/Oe at a short fiber length of 482 m. The designed magnetic fluid-filled DC-PCF has high sensitivity and small volume and has great application prospects in medical and industrial field magnetic field detection.