Investigation of fast light in three-layer waveguides composed of negative-refraction claddings and an air core

An optical medium with abnormal dispersion supports fast light, which possesses a group velocity faster than the speed of light in a vacuum or even takes on a negative value (a backward wave), and shows exceptional promise for optoelectronic applications. In this article, three-layer dielectric waveguides composed of negative refraction cladding, which is made tip of silicon crystal, and an air core are constructed, where the so-called fast light can propagate a backward wave by modifying the thickness of the air core. The dispersion properties of the fast light are investigated analytically. Finally, numerical results are derived by using the finite-element method to verify the analytical results. The proposed structure might find applications in the field of photonic integrated circuits.