Plasmonic structure: fiber grating formed by gold nanorods on a tapered fiber

Coupling efficiency of light intensity from the blackbody cavity into a cone-shaped optical fiber

High-temperature blackbody radiation can provide the light source for broadband fiber sensing systems. To improve coupling efficiency, a coupling model of light intensity from the blackbody cavity into a cone-shaped optical fiber was proposed. Influence of parameters of cone-shaped fiber and the blackbody cavity on coupling efficiency of light intensity were analyzed. Results show that coupling efficiency first decreases and then increases with the increase of the angle of cone-shaped fiber. When the angle of the cone is around 30°, coupling efficiency reaches the maximum. Cone-shaped fibers with angles around 8.8°, 19.4°, and 27.4° were fabricated by chemical etching. Experiments were carried out with cone-shaped fibers and a fiber with a flat end face. Results show that compared with the fiber with a flat end face, coupling efficiency of cone-shaped fiber with an angle around 8.8° is lower, cone-shaped fiber with an angle around 19.4° is almost the same, cone-shaped fiber with angle 27.4° is much stronger, and efficiency is improved by approximately 38%. The experimental results are consistent with the theoretical analysis.

Ultrasensitive optical sensing in aqueous solution based on microfiber modal interferometer

In this paper, an ultrahigh sensitivity sensing in aqueous solution for microfiber modal interferometer (MMI) is realized. The group refractive index (RI) difference between HE₁₁ and HE₁₂ mode will come down to 0 at a certain wavelength, resulting in ultrahigh sensitivity near this wavelength. MMI with different diameters have their individual ultrasensitive wavelength band, which indicates the broad range of optional probing wavelength and more liberal diameter condition on fiber fabrication. In the experimentation, infrared absorption band in water around 1360-1600nm is easy to keep away by adjusting the microfiber diameter. As a result, an ultrahigh sensitivity of 14.95 pm/ppm is realized for sodium nitrate at 1320nm, whose equivalent sensitivity is about 1.26 × 10⁵-nm/RIU for RI, which is much higher than most of the existing naked sensors with magnitude of 10²-10⁴nm/RIU.

Plasmonic Optical Fiber-Grating Immunosensing: A Review

Plasmonic immunosensors are usually made of a noble metal (in the form of a film or nanoparticles) on which bioreceptors are grafted to sense analytes based on the antibody/antigen or other affinity mechanism. Optical fiber configurations are a miniaturized counterpart to the bulky Kretschmann prism and allow easy light injection and remote operation. To excite a surface plasmon (SP), the core-guided light is locally outcoupled. Unclad optical fibers were the first configurations reported to this end. Among the different architectures able to bring light in contact with the surrounding medium, a great quantity of research is today being conducted on metal-coated fiber gratings photo-imprinted in the fiber core, as they provide modal features that enable SP generation at any wavelength, especially in the telecommunication window. They are perfectly suited for use with cost-effective high-resolution interrogators, allowing both a high sensitivity and a low limit of detection to be reached in immunosensing. This paper will review recent progress made in this field with different kinds of gratings: uniform, tilted and eccentric short-period gratings as well as long-period fiber gratings. Practical cases will be reported, showing that such sensors can be used in very small volumes of analytes and even possibly applied to in vivo diagnosis.