Photonic crystal

A photonic crystal is a modern material consisting alternately of elementary cells with a high and low refractive index and dimensions comparable to the wavelength of light from a given spectral range. Phonic crystals are used in optoelectronics. It is assumed that the use of a photonic crystal will allow, for example. to control the propagation of a light wave and will create opportunities for the creation of photonic integrated circuits and optical systems, as well as telecommunications networks with a huge bandwidth (of the order of Pbps).

The effect of this material on the path of light is similar to the effect of a grating on the movement of electrons in a semiconductor crystal. Hence the name "photonic crystal". The structure of a photonic crystal prevents the propagation of light waves inside it in a certain range of wavelengths. Then the so-called photon gap. The concept of creating photonic crystals was created simultaneously in 1987 in two US research centers.

Eli Jablonovich of Bell Communications Research in New Jersey worked on materials for photonic transistors. It was then that he coined the term "photonic bandgap". At the same time, Sajiv John of Prieston University, while working to improve the efficiency of lasers used in telecommunications, discovered the same gap. In 1991, Eli Yablonovich received the first photonic crystal. In 1997, a mass method for obtaining crystals was developed.

An example of a naturally occurring three-dimensional photonic crystal is opal, an example of the photonic layer of the wing of a butterfly of the genus Morpho. However, photonic crystals are usually made artificially in laboratories from silicon, which is also porous. According to their structure, they are divided into one-, two- and three-dimensional. The simplest structure is the one-dimensional structure. One-dimensional photonic crystals are well-known and long-used dielectric layers, which are characterized by a reflection coefficient that depends on the wavelength of the incident light. In fact, this is a Bragg mirror, consisting of many layers with alternating high and low refractive indices. The Bragg mirror works like a regular low pass filter, some frequencies are reflected while others are passed through. If you roll the Bragg mirror into a tube, you get a two-dimensional structure.

Examples of artificially created two-dimensional photonic crystals are photonic optical fibers and photonic layers, which, after several modifications, can be used to change the direction of a light signal at distances much smaller than in conventional integrated optics systems. There are currently two methods for modeling photonic crystals.

first – PWM (plane wave method) refers to one- and two-dimensional structures and consists in the calculation of theoretical equations, including the Bloch, Faraday, Maxwell equations. Second The method for modeling fiber optic structures is the FDTD (Finite Difference Time Domain) method, which consists in solving Maxwell's equations with a time dependence for the electric field and magnetic field. This allows one to carry out numerical experiments on the propagation of electromagnetic waves in given crystal structures. In the future, this should make it possible to obtain photonic systems with dimensions comparable to those of microelectronic devices used to control light.

Some applications of photonic crystal:

• Selective mirrors of laser resonators,
• distributed feedback lasers,
• Photonic fibers (photonic crystal fiber), filaments and planar,
• Photonic semiconductors, ultra-white pigments,
• LEDs with increased efficiency, Microresonators, Metamaterials - left materials,
• Broadband testing of photonic devices,
• spectroscopy, interferometry or optical coherence tomography (OCT) - using a strong phase effect.