A plasmonic sensor based on a dual-side polished photonic crystal fiber operating in a telecommunication wavelength range is proposed and investigated numerically by the finite element method (FEM). We study the effects of structural parameters on the sensor’s performance and analyze their tuning effects on loss spectra. As a result, two configurations are found when the analyte refractive index (RI) changes from 1.395 to 1.415. For configuration 1, an RI resolution of 9.39 × 10⁻⁶, an average wavelength sensitivity of 10,650 nm/RIU (the maximum wavelength sensitivity is 12,400 nm/RIU), an amplitude sensitivity of 252 RIU⁻¹ and a linearity of 0.99692 are achieved. For configuration 2, the RI resolution, average wavelength sensitivity, amplitude sensitivity and linearity are 1.19 × 10⁻⁵, 8400 nm/RIU, 85 RIU⁻¹ and 0.98246, respectively. The combination of both configurations can broaden the wavelength range for the sensing detection. Additionally, the sensor has a superior figure of merit (FOM) to a single-side polished design. The proposed sensor has a maximum wavelength sensitivity, amplitude sensitivity and RI resolution of the same order magnitude as that of existing sensors as well as higher linearity, which allows it to fulfill the requirements for modern sensing of being densely compact, amenable to integration, affordable and capable of remote sensing.

A hexagonal photonic crystal fiber (PCF) sensor with a dual optofluidic channel based on surface plasmon resonance (SPR) effect is proposed. The sensor characteristic is numerically explored by software integrated with the finite element method (FEM). The numerical results show that, when the analyte refractive index (RI) varies from 1.32 to 1.38, high linearity between resonance wavelength and analyte RI is obtained and the value of adjusted R² is up to 0.9993. Simultaneously, the proposed sensor has maximum wavelength sensitivity (WS) of 5500 nm/RIU and maximum amplitude sensitivity (AS) of 150 RIU⁻¹, with an RI resolution of 1.82 $\times$ 10⁻⁵ RIU. Besides, owing to a simple structure and good tolerance of the proposed sensor, it can be easily fabricated by means of existing technology. The proposed sensor suggests promising applications in oil detection, temperature measurement, water quality monitoring, bio-sensing, and food safety.

An exciting prospect for the sensing community is the potential of midinfrared fiber sensors. Taking advantage of the design flexibility of photonic crystal fiber and the high excitation loss of gold layers, a high-performance midinfrared D-shaped sensor based on the surface-plasmon-resonance effect was designed and numerically investigated by a mature finite-element tool. Numerical results showed that the designed fiber is especially suitable for sensing. In an operating wavelength ranging from 2.9 to 3.6 μm, maximal wavelength sensitivity of 11,500 nm/refractive index unit (RIU) and a maximal refractive index (RI) resolution of 8.7 × 10⁻⁶ RIU were obtained by the wavelength-interrogation method when analyte RI varied from 1.36 to 1.37. Maximal amplitude sensitivity of 230 RIU⁻¹ was obtained by the amplitude-interrogation method with a high linearity of 0.99519 and an adequate figure of merit of 142. Additionally, the sensor had good fabrication tolerance. Our sensor is a promising candidate for environmental monitoring.

Refractive index (RI) and temperature (T) are both critical environmental parameters for environmental monitoring, food production, and medical testing. The paper develops a D-shaped photonic crystal fiber (PCF) sensor to measure RI and T simultaneously. Its cross-sectional structure encompasses a hexagonal-hole lattice, with one hole selectively filled with toluene for temperature sensing. By coating the D-shaped surface of the PCF with a metal film and a MoS₂ film, the refractive index-detection channel is formed. Numerical results demonstrate that RI and T can be reflected in the same spectrum, without any interference caused by the two parameters with each other. At an environmental RI of 1.26–1.38, its maximum RI sensitivity is up to 5400 nm/RIU. At a temperature of 20–80 °C, its temperature sensitivity reaches −1.2 nm/°C. This design allows for a broad operational spectrum and an extensive measurement range, which makes it particularly suitable for applications requiring low-RI detection. Moreover, the resonance strength of the sensor is significantly enhanced by introducing a two-dimensional material MoS₂ on the D-surface. Specifically, it reaches 195,149 dB/m when RI = 1.34 at 30 °C. This is much higher than that of most previous studies, and the requirements for inspection equipment can be lowered in this case. These results are essential for progress in simultaneously detecting RI and T.

Chlorpyrifos (CPF) and 2,4-dichlorophenoxyacetic acid (2,4-D) are insecticides and herbicides which has been widely used on farms. However, CPF and 2,4-D residues on corps can bring high risks to human health. Accurate detection of pesticide residues is important for controlling health risks caused by CPF and 2,4-D. Therefore, we developed a fast, sensitive, economical, and lossless surface-enhanced Raman spectroscopy (SERS)-based method for pesticide detection. It can rapidly and simultaneously determine the CPF and 2,4-D mixed pesticide residues on an apple surface at a minimum of 0.001 mg L−1 concentration, which is far below the pesticide residue standard in China and the EU. The limits of detection reach down to 1.28 × 10−9 mol L−1 for CPF and 2.47 × 10−10 mol L−1 for 2,4-D. The limits of quantification are 4.27 × 10−9 mol L−1 and 8.23 × 10−10 mol L−1 for CPF and 2,4-D. This method has a great potential for the accurate detection of pesticide residues, and may be applied to other fields of agricultural products and food industry.