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.

A novel surface plasmon resonance (SPR) refractive index (RI) sensor based on the D-type dual-mode photonic crystal fiber (PCF) is proposed. The sensor employs a side-polished few-mode PCF that facilitates the transmission of the fundamental and second-order modes, with an integrated microfluidic channel positioned directly above the fiber core. This design minimizes the distance to the analyte and maximizes the interaction between the optical field and the analyte, thereby enhancing the SPR effect and resonance loss for improved sensing performance. Au-TiO₂ dual-layer material was coated on the surface of a microfluidic channel to enhance the penetration depth of the core evanescent field and tune the resonance wavelength to the near-infrared band, meeting the special needs of chemical and biomedical detection fields. The finite element method was utilized to systematically investigate the coupling characteristics between various modes and surface plasmon polariton (SPP) modes, as well as the impact of structural parameters on the sensor performance. The results indicate that the LP_{11b_y} mode exhibits greater wavelength sensitivity than the HE_{11_y} mode, with a maximum sensitivity of 33,000 nm/RIU and an average sensitivity of 8272.7 nm/RIU in the RI sensing range of 1.25–1.36, which is higher than the maximum sensitivity of 16,000 nm/RIU and average sensitivity of 5666.7 nm/RIU for the HE_{11b_y} mode. It is believed that the proposed PCF-SPR sensor features both high sensitivity and high resolution, which will become a critical device for wide RI detection in mid-infrared fields.

A novel high birefringence gold-coated photonic crystal fiber (PCF) polarization filter based on surface plasmon resonance is proposed. The six elliptical holes arranged in a specific mode surrounding the core are utilized to gain high birefringence, and gold is coated inside the air holes to generate surface plasmons. By improving structural parameters, we achieve one state of polarization to propagate through the filter whereas the other state is severely attenuated. Specially, in the 1550nm communication band, the confinement loss of y-polarized mode can reach 442dB/cm while the corresponding loss of x-polarized mode is only 0.0316dB/cm. The distinction between two losses is over 10000 times. In addition, when the length of the designed PCF filter is 1mm, an extinction ratio of 326dB/cm is obtained. The applicable bandwidth is up to 300nm while the fiber length is merely 50um, which is better than other reported literatures. Owing to above characteristics, the proposed polarization filter can be widely applied in compact and broadband filters in the communication band.