Optical Fibers in Terahertz Domain

Abstract

The terahertz (THz) frequency range spans between the microwave and the photonic domains. For more than 20 years, it is experiencing growing expansion justified by the new properties offered in telecommunication, spectroscopy, and imaging technologies, enabling numerous applications for today’s society needs. Similarly as the optical fibers in the optical domain, THz fibers are key components for realizing complex, compact, and robust systems that are required by THz applications. Nevertheless, the developments of THz fibers are hindered by the strong degradations of material properties at THz frequencies. These constraints require to investigate and to develop THz fibers with innovative and disruptive designs, which make the development of THz fibers challenging and very stimulating. Numerous strategies are inspired from the recent innovations in the field of specialty optical fibers. Since dry air is certainly the most favorable medium to propagate THz radiations. Two major approaches have been investigated. The first one is based on the propagation of THz waves into a fiber with a design that favors a large portion of evanescent field in air. The second way of beating these limits is by confining the THz waves in a hollow-core fiber with the help of reflectors in the fiber cladding. The main recent developments of THz fibers are presented in this chapter. The guiding mechanism of each THz fiber is detailed, in addition to a presentation of the recent experimental demonstrations and analyses of their drawbacks and advantageous properties.