Milestone Photonic Hypercrystal Demonstrates Control of Light-Matter Interaction

Theory becomes reality as a working photonic hypercrystal is created by CCNY and Purdue researchers, achieving 20x spontaneous emission rate and 100x light coupling.
 
In 2014, it was theorized that a structure could be created with the ability manipulate the interactions of light within matter. The theoretical structure was given the name of the photonic hypercrystal, which, in short, have the ability to manipulate light and unparalleled control the propagation of photons.


Phototonic hypercrystals. Image courtesy of Tal Galfsky via CCNY

Over the past few years, there's been a significant amount of research vested in this theoretical idea—and some designs actually had modest practical applications. In 2016, a method that enabled the enhancement of light emission from 2D materials using photonic hypercrystals was discovered. Since then, myriads of researchers have been developing and redesigning the fundamental photonic hypercrystal structure.
Recently, research published in the Proceedings of the National Academy of Sciences claims that there has been a true photonic hypercrystal created that can control light-matter interactions with very few limitations.

Phonotic Materials, Metamaterials, and a New Structure 

The group of researchers, from the City College of New York and Purdue University, combined the unique properties of photonic materials along with those of metamaterials to create the new hypercrystal structure. These two types of materials are especially important in optoelectronics but, unfortunately, they rely on mechanisms that operate on frequency resonance which have limited bandwidth operation and poor light emission.

Several paradigms of the two materials were targeted and combined. On one end of the spectrum are photonic crystals. The principle behind this structure is similar to how semiconductors facilitate electronics. These crystals exploit the Bragg scattering of light waves. This creates a band gap that forbids certain wavelengths of light from passing through. Photonic crystal structure is capable of various optical phenomena, specifically omnidirectional mirroring and the inhibition of spontaneous emission of light.
On the other end of the spectrum are metamaterials. These are synthetic materials composed of various other conventional reagents used to exhibit properties not commonly found in natural materials.

 These metamaterials are designed on an atomic scale—larger than an atom but smaller than the target wavelength—and essentially operate based on structure rather than individual material properties. The structure of the material is based on exact control of specific periodic pattern arrangements which allows the material to effectively absorb, enhance, bend, and block waves. Appropriately designed metamaterials have the unique ability to manipulate electromagnetic waves (light), both electric and magnetic components. By comparison, natural materials are usually only capable of affecting the electric component.


Rendering of metamaterial bending light. Image courtesy of Chemical & Engineering News

While the photonic hypercrystal does share the same crystal structure as a photonic crystal and metamaterial component, it is quite unlike its predecessors. Previous versions differ from photonic crystals in that the repeating structures are smaller than the light’s wavelength and the period scale. They also don’t have a dependent EM response based on the  polarization of the subwavelength unit cells. These differences are especially important in that they solve the issues of relative characterized poor light emission and bandwidth restrictions.

The photonic hypercrystal was reported to be capable of concurrently increasing light coupling by 100 times and spontaneous emission rate by 20 fold from quantum dots fixed on the hypercrystal.

Future Applications

While this may seem trivial to most, the applications in optics are very broad. One of the spotlighted features of the technology could be the introduction of Li-Fi, similar to Wi-Fi in that it wirelessly transmits signals using light instead of radio waves.

In the paper's abstract, the researchers assert that “This platform for broadband control of light–matter interaction will push the boundaries of applications such as ultrafast light-emitting diodes, photovoltaics, and quantum informatics."

 The team will continue their research in this direction, however the technology requires further research and testing. Commercial applications are far off because photonic hypercrystal-compatible devices will need to be engineered.
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