ABSTRACT
Microfibers (MFs) and advantages of their applications for humidity sensor design are the main topics discussed in the present chapter. Optical microfibers are optical fibers with diameters, which are comparable with the wavelength of the transmitted light. These MFs can be fabricated using various approaches discussed in this chapter. Experiments have shown that conventional optical fibers allow limited access to the evanescent field and show inefficient light–environment interactions that make it difficult to use such fibers for many micro/nanoscale sensing application. The development of optical MFs provides a more efficient and promising solution to meet the challenge. The small diameter of optical MFs provides several advantages over conventional optical fibers, important for sensor applications: (1) more effective access to the evanescent field, (2) greater versatility of configuration, and (3) low-loss connection. As it is shown in this chapter, all types of humidity sensors can be realized using microfibers, including fiber Bragg grading (FBG) structures, Mach–Zehnder interferometers (MZI), Michelson interferometers (MI), and microring resonator-based humidity sensors. The analysis carried out in this chapter indicates that the MF can really serve as a basic element for optical humidity sensors. Due to their favorable properties of high fractional evanescent fields, low dimension, low loss, and high flexibility for optical sensing, MF-based optical resonators and interferometers may offer advantages of high sensitivity, fast response, small footprints, high spatial resolution, and low detection limits. However, the same analysis shows that the above-mentioned approach has disadvantages, which can limit the application of MF in real sensors designed for the sensor market.
