Sample interview questions: Can you explain the concept of photonic crystals and their applications?
Sample answer:
Photonic crystals are periodic structures that can manipulate the behavior of light at the scale of its wavelength. These structures are typically composed of dielectric materials with alternating regions of high and low refractive index, forming a lattice-like pattern. The periodicity of photonic crystals creates a bandgap, which prevents the propagation of certain wavelengths of light through the crystal structure. This unique property enables photonic crystals to control and manipulate the flow of light in various ways.
One of the fundamental concepts behind photonic crystals is the phenomenon of Bragg scattering, which occurs when the wavelength of incident light matches the spacing between the lattice planes of the crystal. This results in constructive interference and the reflection of light, similar to the way in which X-rays are diffracted by a crystal lattice. By carefully designing the lattice spacing and refractive index contrast, photonic crystals can selectively reflect specific wavelengths, creating a photonic bandgap.
The presence of this bandgap allows photonic crystals to control the propagation of light. For example, by introducing defects or modifying the lattice structure, certain wavelengths can be allowed to propagate through the crystal while others are blocked. This property makes photonic crystals highly suitable for the development of optical filters, where specific wavelengths of light can be selectively transmitted or reflected.
Furthermore, photonic crystals can also manipulate the speed and direction of light. By tailoring the refractive index gradient within the crystal, the velocity of light can be altered, leading to phenomena such as slow light or even stopping light altogether. This has significant implications for the development of optical devices, such as delay lines, optical buffers, and … Read full answer