Photonic Crystal
Introduction
Photonic crystals are periodic optical nanostructures that affect the motion of photons in much the same way that ionic lattices affect electrons in solids. The periodicity of the nanostructure allows the crystal to manipulate light and create a range of optical effects. Photonic crystals are a significant area of research in the fields of optics and nanotechnology, with potential applications in a variety of areas including optical computing and telecommunications.
History
The concept of photonic crystals was first introduced by Eli Yablonovitch and Sajeev John in 1987. They proposed that a periodic dielectric structure could contain a photonic bandgap, a range of wavelengths that cannot propagate through the crystal. This was analogous to the electronic bandgap in semiconductors, and it was suggested that photonic crystals could be used to control and manipulate light in the same way that semiconductors are used to control and manipulate electrons.
Structure
Photonic crystals are composed of periodic dielectric structures, which can create a photonic bandgap that prevents certain wavelengths of light from propagating through the crystal. The periodicity of the structure is on the order of the wavelength of the light that it affects. This periodicity can be in one, two, or three dimensions, leading to different types of photonic crystals.
One-Dimensional Photonic Crystals
One-dimensional photonic crystals, also known as Bragg stacks, are composed of alternating layers of materials with different refractive indices. The periodicity of the structure is along one axis. These crystals can reflect certain wavelengths of light while allowing others to pass through, creating a color effect.
Two-Dimensional Photonic Crystals
Two-dimensional photonic crystals have a periodic structure in two dimensions. These crystals can confine light in a plane, and are often used in waveguides and other optical devices.
Three-Dimensional Photonic Crystals
Three-dimensional photonic crystals have a periodic structure in all three dimensions. These crystals can completely confine light, preventing it from propagating in any direction. This property makes them useful for a variety of applications, including optical computing and telecommunications.
Properties
Photonic crystals have a number of unique properties that make them useful for manipulating light. These properties are largely determined by the structure of the crystal and the materials used in its construction.
Photonic Bandgap
The most significant property of photonic crystals is the photonic bandgap. This is a range of wavelengths that are forbidden from propagating through the crystal. By selecting the appropriate materials and structure, a photonic crystal can be designed to have a bandgap at any desired wavelength.
Dispersion Relation
The dispersion relation of a photonic crystal describes how the phase velocity of light changes with wavelength. This property can be used to slow down or even stop light, making photonic crystals useful for applications such as optical storage and signal processing.
Nonlinear Effects
Photonic crystals can exhibit a variety of nonlinear optical effects, including frequency doubling and the creation of solitons. These effects can be used to create all-optical switches and other devices.
Applications
Photonic crystals have a wide range of potential applications, many of which are still in the experimental stage.
Optical Computing
Photonic crystals can be used to create optical transistors and other components for optical computing. These devices use light instead of electricity to carry information, potentially allowing for faster and more efficient computers.
Telecommunications
In telecommunications, photonic crystals can be used to create filters and waveguides that can manipulate light signals. They can also be used to create optical switches, which can route light signals without the need for electronic conversion.
Sensors
Photonic crystals can be used to create highly sensitive optical sensors. These sensors can detect changes in the environment by monitoring changes in the properties of the crystal.