First let us start with a simple question. What are the crystals?
Crystals are the ordered patterns of atoms/molecules/ions in three dimensions. Common examples are diamonds, snow flakes and table salt. These crystal are used to control the flow of electrons. So all the electronics such as our phones, tablets, PCs, TVs and the whole world of electronics is centred around controlling the flow of electrons within these crystals (Silicon chips).
Then, what are the Photonic Crystals ?
Photonic crystals are the ordered patterns of the material building blocks. Like the above explained normal crystals, which control the flow of electrons, these Photonic crystals control the flow of photons through them, thus the name Photonic Crystal.
Why we bother about them ?
Because controlling the electrons already gave us so many technologies . However speed of electrons is very slow compared to the speed of photons. Therefore, by using photonic crystals we can make devices that can work 1000 times faster than the electronic devices.
Do we have these photonic crystals in nature?
Why not, you might have seen beautiful butter fly wings, colorful peacock feathers, precious opals, glossy flowers and sparkling beetels. All these have photonic crystals that are carefully designed by nature for hundred of years.
Why do nature created these photonic crystals?
Scientists now finding the answers for these questions. One obvious reason might be to attract their opposite sex partners for mating. Another possibility might be for thermodynamic stability of these creatures.
Since how long we human beings come to know about these photonic crystals?
One dimensional photonic crystals are researched since very long, at least from 1779s.