Fabrication of planar nanomechanical photonic metamaterials

Metamaterials have been around for almost two decades, providing great advances in optics and photonics. Despite many fundamental studies and several predicted applications, only recently have metamaterials found niche applications and started to be implemented in products available to the consumer. Applications are still limited by the static nature of conventional metamaterials, meaning that the function of a specifically designed metamaterial cannot be changed after fabrication. For example, a metamaterial which is designed to absorb at a certain wavelength would become far more useful if it could shift its absorption peak in response to an external control signal. A promising way of overcoming this design limitation is through the exploitation of planar nanomechanical photonic metamaterials. Structurally reconfigurable photonic metamaterials, based on dielectric membranes of nanoscale thickness, can provide a simple platform for achieving high levels of modulation contrast and modulation frequency. These metamaterial systems have tuneable optical properties arising from nanomechanical displacements driven externally through different mechanisms. Using different actuation forces and designs, tuneable devices that are able to change their transmission, absorption or reflection characteristics can be attained. In this tutorial, we will focus on planar nanomechanical photonic metamaterials, while also acknowledging the considerable work developed using other tuneable metamaterial platforms, such as bulk, 3D or multilayer reconfigurable metamaterials. Planar reconfigurable photonic metamaterials are reviewed, nanoactuation mechanisms are explained, nanofabrication processes discussed and some conclusions on future challenges are drawn. Planar nanomechanical photonic metamaterials and their tuneable optical properties can become powerful components for optical devices and optical circuitry, and also be introduced to novel applications. (tutorial)