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What are Photonic Crystals

A new paradigm, with far reaching consequences for photonics, nanotechnology, and the ICT sector, has emerged in the past decade that links the fundamental concepts of the micro-world of solid-state physics and the macro-world of classical wave physics. A new type of photonic structure, the photonic crystal, has been suggested for controlling electromagnetic waves in three dimensions. What semiconductors are to electron waves and electronics, photonic crystals promise to be for light waves and photonics - a periodic change of the properties of the photonic crystals can create a photon band gap analogous to the forbidden electron energy bands in semiconductors. These artificial periodic crystalline structures provide novel and unique ways of controlling many aspects of electromagnetic radiation.

A new class of optical materials

Information and communication are playing an increasing role in the modern society. The future progress in the information data processing is associated with a new generation of compact nanoscale optical devices operating entirely with light. The unique feature of photonic crystals to reflect waves of certain frequencies allows the exploration of the properties of these artificially created materials using the ideas and concepts of the theory of crystal lattices. Being inspired by such a similarity, it was shown that one of the most intriguing properties of photonic band gap crystals is the emergence of exponentially decaying localised defect modes that may appear within the photonic band gaps when a defect is introduced into an otherwise perfect photonic crystal. Understanding the nature of the localised modes and studying their properties are of particular importance for creating novel types of optical waveguides. Indeed, one of the weaknesses of conventional optical waveguides based on confinement due to a total internal reflection is that creating bends is difficult. Since the physical principles for the operation of photonic crystal are different, the light remains trapped in a bent waveguide and the only possible problem is that of reflection. However, it is still possible to get 100% transmission, as was demonstrated theoretically and also experimentally, even for the optical wavelength 1.55 µm transmitted through a 120° sharply bent photonic-crystal waveguide. This is a very important step forward in the current development of waveguide optics based on the photonic crystal technology.

Next paradigm shift for optical networks

Work in photonics crystals have been growing in research laboratories around the world for the past ten years. The first experiments have been performed for microwaves and taking these ideas to the optical wavelengths was difficult. However, the technological advances during last 2 years changed complete the future of these materials and related fundamental concepts. It has only been recently that people have started to see practical solutions to existing optical networking problems offered by photonics crystal materials. At present, new technology breakthroughs and the development of communications grade optical fibers are expected. Photonics crystal fibers and components may just be the next revolution in optical fibers and components. Photonics crystals are based on the optical properties of mundane materials, which can be radically enhanced by periodic micro-structuring. A major challenge is how to weave these enhancements into practical photonic crystal components.

Photonic crystal technology is made up of two parts, photonic crystal fibers and photonic crystal components. Early proponents of photonic crystal fibers foresee fibers with losses of less than 0.01db/km, zero chromatic and polarization-mode dispersion, and are capable of handling high powers. Photonic crystals components are made from thin films of high dielectric, perforated array of holes (looking rather like salami slices of photonic crystal fiber), which can act as efficient vertical cavity resonators and highly disperse components. There is even the thought of making 3D crystals from these materials.

Photonic crystals and all-optical technologies

Information is playing an increasing role in the modern society. Operation of global networks is dependent on a large number of optical fiber links and electronic elements capable of transmitting vast amounts of data over long distances. As the network capacity continues to grow, so does the need for fast signal re-generation and switching devices. In current networks, operation of such devices is often based on conversion of optical pulses to electronic signals, which are then processed, and finally converted back to optical pulses and transmitted further along the fiber links. However, the network performance would be enhanced enormously provided the repeated conversions are avoided, and there is a strong effort among the researchers to develop all-optical networks and components.

Operation of all-optical information and communication devices should involve a non-trivial transformation of input signals, and this can be achieved in nonlinear materials, since in such media light propagation can be controlled by light itself. Then, optical analogues of diodes and transistors can be integrated together to form an optical circuit. One of the main, not yet solved, issues is how to create nonlinear circuits and what kind of "information bits" should be used to build up a high-capacity all-optical network. One of the fundamental ideas to control the flow of light is based on the concept of photonic crystals, dielectric structures with a periodic modulation of the refractive index, considered as an optical analogue of semiconductor materials. Recent results suggest that, employing the concept of nonlinear photonic crystals, we can develop all-optical technologies which will revolutionize the information and telecommunication industry. Such technologies should be based on photonic crystals and take advantage of the slow group-velocities of light, shape-preserving propagation, and operation and reconfiguration flexibility offered by optical solitons.

 

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Last modified: Friday, 03-May-2002 19:03:15 EST