Optical micro- and nanofibers for sensing applications

Abstract

This chapter reviews the applications of optical micro/nanofibers (MNFs) and MNF-based photonic devices for sensing of the ambient medium. An optical MNF is usually fabricated by drawing a glass or a polymer optical fiber and has a diameter between ∼100 nm and several μm. The MNF sensors can be either based or not based on the interaction of the ambient medium with the evanescent part of the mode propagating along the MNF. The simplest MNF evanescent sensor is an MNF, which detects changes caused by proximity of chemical/biological species and microparticles at the MNF surface. The advantage of the MNF evanescent sensor compared with other evanescent sensors is that the MNF is more open to the environment and therefore more sensitive to ambient changes. This chapter starts with a brief review of the theory of uniform MNFs, MNF tapers, and MNF-based or MNF-supported photonic resonators (MNF loop resonator, MNF/microsphere resonator, MNF/microdisk resonator, MNF coil resonator, and MNF/microcylinder resonator), which are used as optical sensors. The description of the theory is followed by the review of applications of these devices for sensing. First, the simplest MNF sensors based on straight MNF are considered. They include microfluidic sensor, hydrogen sensor, molecular absorption sensor, humidity and gas sensor, optical fiber surface sensor, and atomic fluorescence sensor. Then the applications of looped and coiled MNFs as a direct-contact gas temperature sensor, an infrared radiation sensor, and a microfluidic sensor are reviewed. Finally, more complex sensors, which consist of MNFs coupled to microspheres, microdisks, microcylinders, and microcapillaries, are considered as refractive index sensors, nanolayer sensors, surface sensors, and also as individual atom and molecule sensors.