Holography has provided some of the first artificially-created optical nanostructures outside of naturally-occurring minerals and biological tissue. A hologram, unlike a conventional photograph, contains a large amount of information about an object such as a phase distribution. This information is stored in the micro- and nano-structure of a recording medium. One example is the refractive index variations recorded in the volume of a photosensitive polymer material. Typically, a hologram is generated by interfering coherent light waves, one of which is scattered off of the object under investigation.
Alternatively, the phase distribution of the hologram can be calculated numerically, and then can be encoded onto a surface using conventional material nano-patterning techniques such as lithography. The desired output image can then be generated by illuminating the surface with the appropriate light source.
Metamaterials are, by their own nature, designed to offer engineered properties such as custom permittivity and permeability values. Metasurfaces, in particular, can be engineered so that a particular phase distribution can be achieved by patterning its two-dimensional area. In addition, due to the availability of sub-wavelength patterning tools, a very accurate phase profile can sometimes be encoded – much more detailed than what can be achieved with coherent light sources.
New photopolymers, developed in the last ten years, now allow us to record essentially ‘grainless’ structures with sinusoidal variation in refractive index extending not only across the surface of a coated film–in x and y coordinates–but throughout its depth, or z-axis, as well. By considering holography as a metamaterial, with the new technology and theoretical models developed for the discipline, MTI is forging unique hybrid forms of recorded and written nanostructures.
At MTI, we use metamaterial holography in a variety of applications such as our flagship laser filtering product metaAIR, which allows unprecedented performance and controls light at the nanoscale.