A guide to all-optical switching with epsilon-near-zero materials*

Controlling light through all-optical means is central in fundamental and applied research. An important facet of this is switching one optical pulse by another. A promising avenue for all-optical switching is epsilon-near-zero (ENZ) materials, which have a region of wavelengths where the permittivity approaches zero. In nonmagnetic materials, the refractive index is related to the permitivity by n=√ε and the variation is then δn=δε/√ε. Therefore, ENZ materials will have large index changes even with small permittivity changes. One such class of materials is transparent conducting oxides (TCOs) whose ENZ regime occurs in the telecom range and have relatively small losses there.

Often all-optical switching experiments are performed exactly at the ENZ wavelength. However, we show this is not always optimal for all-optical switching, because of complex coupling of surface interactions. To investigate further, we first discuss the basic concepts of optically pumping ENZ materials composed of TCOs with the Drude model. Then we will describe common experimental configurations such as optically thick and thin ENZ films, ENZ films deposited on metallic and dielectric substrates, and the Kretschmann geometry. Finally, we willdiscuss the important role of losses in ENZ materials.