The characteristics of the dual-core photonic crystal fiber (PCF) sensor are studied using the finite element method (FEM), and the structure is improved according to the numerical simulation results. The results show that whether or not the four large air holes far away from the geometry center of the PCF are filled with analyte has no influence on the wavelength sensitivity of the sensor which means those holes can be replaced by small air holes. The wavelength sensitivity can be tuned by adjusting the sizes of the other large air holes which are as for liquid holes. The dynamic detection range of the refractive index (RI) is from 1.33 to 1.51. In particular, high linearity is obtained in the range of 1.44 to 1.51. The sensitivity is as high as 6021 nm/RIU when the liquid holes are the smallest. When liquid holes are tangential with the envelope of first layer air holes, the wavelength sensitivity is 4028 nm/RIU, and the coefficient of determination (R2) is 0.99822 when the RI of the analyte varies from 1.44 to 1.51 which shows that high sensitivity and good linearity are both obtained.

The absorption characteristics of a photoexcited metamaterial absorber at terahertz frequencies were analyzed in this study. Filling photosensitive semiconductor silicon into the gap between the resonator arms leads to modulation of its electromagnetic response through a pump beam which changes conductivity of silicon. Comparisons of terahertz absorbing properties which were caused by different thicknesses and dielectric constants of polyimide, cell sizes and widths of SRRs, and lengths and conductivities of the photosensitive silicon, were studied by using Finite Difference Time Domain (FDTD) from 0.4 THz to 1.6 THz. The results of this study will facilitate the design and preparation of terahertz modulator, filters and absorbers.

A sensor based on D-shaped photonic crystal fiber (PCF) with elliptical holes is designed and numerical studied by finite element method (FEM). The refractive index (RI) of analyte can be detected by using surface plasma resonance effect and optical fiber with elliptical holes can solve the phase matching problem. The size of central hole, the major axis of the two elliptical holes near polishing plane in first layer and polishing depth are adjusted to explore the influence of these parameters on wavelength sensitivity and amplitude sensitivity of the sensor. Polishing depth has a great influence on wavelength sensitivity of the sensor. As a result, higher sensitivity is obtained with larger polishing depth in the range of 1.33–1.39 and smaller polishing depth is more suitable with RI changing from 1.39–1.42. The wavelength sensitivity of the designed sensor is 10,200 nm/RIU, which means the designed sensor has a promising application prospect.