The phenomena of slow and stopped light has attracted significant research interest owing to an array of potential applications, which include optical modulators and switches, optical buffering, memory devices, enhanced optical nonlinearities etc. In the recent years, new mechanisms of attaining slow and stopped light in optical waveguides have been incepted. Precisely, these effects have been identified in photonic crystal waveguides.
It has also been observed theoretically and experimentally that slow light effect can be realized in a number of waveguide configurations that include single negative and double negative materials. In addition, the concept of rainbow trapping in negative index material that allows for slow or even stopping of light over large bandwidths has been proposed.
Implementation of hyperbolic metamaterial in waveguide structure has been observed to allow for field enhancing, plasmon propagation, and slowing and stopping light. Substituting metal layer by graphene can be used to gain new functionality of hyperbolic metamaterial structures. The conductivity of single layer graphene is dependent on chemical potential and frequency. For this reason, it is possible to alter the optical attributes of the graphene structure by controlling its chemical potential.
Anna Tyszka-Zawadzka, Bartosz Janaszek, Paweł Szczepański at the Institute of Microelectronics and Optoelectronics in Poland presented a study of slow light inside graphene hyperbolic metamaterial waveguide operation in SCLU telecom bands. They analyzed a structure that was a symmetric planar waveguide made of type II graphene-based hyperbolic metamaterials and air cladding. Their work is now published in Optics Express.
In the study, the authors assumed that the permittivity tensor components depend on the graphene hyperbolic metamaterial structure parameters such as graphene layer and dielectric thickness, and frequency. In addition, the proposed structure was assumed lossless given that it does not affect the existence of slow light phenomenon.
The graphene hyperbolic metamaterial was composed of ultrathin graphene-dielectric stacks. The researchers assumed that the z-axis was the propagation direction. Considering that the multilayer structure was subwavelength-scaled, the authors used the effective medium theory to describe the optical properties of the metamaterial.
For an appropriate design of the graphene hyperbolic metamaterial structure forming waveguide layer as well as geometry of the waveguide, it was observed that it allowed for shaping the dispersion attributes through the application of an external biasing. For instance, for the selected width of waveguide it was possible to tune the propagation of the fundamental mode, which is, supporting or cutting off, stopping and shifting critical points for a selected wavelength within the bands through the application of an ideal biasing voltage.
Obtaining the tapered waveguide enabled stopping of light in the entire SCLU wavelength region and selecting the number of guided modes that could be stopped. These results indicate that it is possible to apply the proposed waveguides in a number of applications demanding control of light propagation. Moreover, it can be implemented in tunable optical buffers, photonic memory cells, and optical modulators and switches.
Anna Tyszka-Zawadzka, Bartosz Janaszek, Paweł Szczepański. Tunable slow light in graphene-based hyperbolic metamaterial waveguide operating in SCLU telecom bands. Vol. 25, No. 7 | 3 Apr 2017 | OPTICS EXPRESS 7264.Go To Optics Express