Boron Nitride: The Future Photonic Chip
Imagine squeezing light as though it were toothpaste in a tube and forcing it through a nano material over a vast distance. In other words, it will travel for over a mile through a space just one hundredth of a millionth of a metre wide.
This is the future of information processing for electronic devices ranging from weapons systems to infrared cameras, and it is based on the hyperbolic properties of boron nitride.
A hyperbolic material is one which has optical characteristics that cannot be observed in nature. It behaves as both a metal and semiconductor at the same time and along different axes of its crystal structure. The crystal structure of these materials can confine a beam of light into a space much smaller that the light’s own wavelength.
Boron nitride is the world’s second-hardest substance after diamond. It can have a cubic structure of alternate boron and nitride atoms connected by string covalent binds in a tetrahedral pattern like diamond. This is used commonly for manufacturing abrasives and cutting tools. A hexagonal version consists of sheets of hexagonal rings of atoms such as graphite and is used as a lubricant and in cosmetics.
Scientists have developed powerful lasers over recent decades by confining the ultraviolet and infrared wavelengths of the electromagnetic spectrum. But the problem has been that when this is attempted with visible light, transmission losses are high. Consequently, the range over which the light travels is very limited.
This limitation has caused problems in the development of photonic circuits which can carry information in light much faster than an electronic circuit that carries information using electrons. The problem was solved by coupling the incoming light wave with plasmons – waves emitted by electrons on the surface of a metal when light impacts on it. Crystals of hexagonal boron nitride are used to achieve this effect.
The result is a miniature optical-electronic circuit whose components are a fraction of the wavelength of light in size. This research is still at an early stage. Much work needs to be done on how to control the plasmon flow at a nano-scale level and how to configure circuit architecture. Ultimately, the circuit may be designed to switch between different frequencies depending on its applications.
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