In this paper, we theoretically investigate a tunable ultra-narrow band absorber consisting of lamellar structure in the near-infrared wavelength range. The absorption efficiency is 99.9% under normal incidence and the full width at half maximum (FWHM) is only 4nm. The high absorption is attributed to the surface plasmon resonance (SPR), which increases the interaction volume of the optical field. The ultra-narrow band absorber has a high refractive index sensitivity of 1208nm/RIU in a wide refractive index range of 1.33 to 1.40 and a high figure of merit of 302. Besides, the influence of structure parameters on the sensing performance are also investigated. Due to its easiness to be fabricated, the proposed structure has potential in sensing application.
A novel and simple optical fiber structure with a section of no-core fiber for measuring hydrogen concentration is presented. Palladium is sputtered to form the coating on the no-core fiber by magnetron sputtering coater. Under different hydrogen conditions, the absorption of hydrogen induced refractive index changes on the outside coating of no core fiber will lead to the variations of the optical output spectrum. Different concentrations of hydrogen are tested, from 4%-0.5%, shows the concentration is relevant with the response time and recovery time. The response time of this sensor is from 300s (4% H2) to 1800s (0.5% H2) depending on the hydrogen concentration. The recovery time of this sensor is from 1200s (4% H2) to 4800s (0.5% H2) depending on the hydrogen concentration. Furthermore, the repeatability and response time of the sensor of this study are investigated experimentally.
We report a dual-band perfect absorber based on nanodisk array for sensing application in the visible region. Due to the excitation of the magnetic resonance mode, a narrow band absorption peak appears and the absorption rate is greater than 99.9%. The other is due to the excitation of local surface plasmon resonance mode, exhibiting broadband absorption characteristics, and the absorption value is greater than 80%. This structure has a wide angular range absorption characteristic. Finally, we calculated the sensing performance of the structure with refractive index ranging from 1.33 to 1.37. The refractive index sensitivity is 250 nm/RIU and 170 nm/RIU. Therefore, our research provides an important theoretical guidance for narrow-band absorption in the visible region for sensing measurements. This has important application prospects in imaging, sensing and optoelectronic devices.
In this paper, a method of detecting mercury ion (Hg2+) concentration in water samples by using Thymine-1-aceticAcid (T-COOH) functionalized Au nanoparticles enhanced fiber optic SPR sensor is proposed. Firstly, we coat the surface of the optical fiber with Au film, then assemble a layer of mercaptoethymine on the surface of the Au film, and formed the Au-S bond by chemical reaction between the sulfhydryl group and the Au, and exposed the amine group on the surface of the fiber sensing region. Then we use T-COOH to modify the thymine on the fiber optic by the chemical reaction between amine and carboxyl. Similarly, mercaptoethymine and T-COOH were used to modify thymine on the surface of Au nanoparticles, and the optimal ratio of T-COOH : Au nanoparticles = 3:50 was obtained through modification optimization. Then the sandwich structure of Au-T—Hg2+—T-Au NPs was formed when mercury ion was detected, which effectively improved the accuracy and sensitivity of mercury ion detection. Then the concentration of ions is measured. By analyzing the influence of other metal ions and mercury ions in the same concentration of water samples, it is concluded that the fiber optic SPR sensor designed in this paper has high selectivity for mercury ions, so this method has high feasibility.