Photonic CrystalsPresented by Surbhi Verma

(Roll no. – 2k11/EP/072)

About My Internship Institute – Indian Institute of Technology, Delhi Department – Department of Physics (Applied

and Fiber Optics) Topic – Photonic Crystals Aim – To study characteristics of 1D photonic

crystal sensor with two defects using simulation by Crystal Wave

Guide – Prof. Joby Joseph Book used – “Photonic Crystal – Molding the

Flow of Light” by John D. Johnnopolous Software used – Crystal Wave by Photon Design

What are Photonic Crystals? 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 atoms and molecules are replaced by macroscopic media with differing dielectric constants

The periodic potential is replaced by periodic dielectric function (or a periodic index of refraction)

The crystal has a complete photonic band gap if for some frequency range, the photonic crystal prohibits the propagation of EM waves of any polarization travelling in any direction from any source.

Types of PhC A 1-D photonic crystal is periodic in one direction A 2-D photonic crystal is periodic in two directions A 3-D photonic crystal is periodic in three directions Different colors show different dielectrics

Electromagnetism in Dielectric MediaThe Maxwell’s equation are :

Substituting and

Maxwell equations become :

This is the Master Equation

Differentiating eq. (3) and substituting in eq. (2)

Take curl of eq. (4) and substitute

1-D Photonic Crystal Sensor The unique characteristics of an EM wave when

interacting with photonic crystals can be applied to build an optical sensor that interacts with certain material

A sensor will work if there is a strong interaction between sensor and sample material

A sensor based on PhC will have higher sensitivity

We simulate an optical sensor model of 1-D PhC imbedded with two defects.

Model of the Structure The model consists of a Si slab with R.I. = 3.48 Eleven dielectric rods were inserted with rod no. 4 and 8

considered to be defected The slab thickness = 2x103 nm ; length = 17.5x103 nm Regular rods were SiO2 (n=1.44, radius=400nm) First defected rod was Al2O3 (n=1.7). R.I. of second defect was

varied.

Simulation The software used is Crystal Wave by Photon Design Numerical simulation were performed by using finite

difference time domain (FDTD) method.

Characteristics

Change in time average energy density w.r.t. variation in the R.I. of the second defect for a defect radius of 300nm (solid square) and 800nm (solid circle)

Change in time average energy density w.r.t. second defect rod radius with R.I. of 1.40

Results and Conclusion Studied the characteristics of with two defects by

means of FDTD method

Increasing a second defect R.I. with a radius of 800nm will produce linear dependence of the time averaged energy density, which can be potentially applied for an optical based R.I. sensor

A non-linear time averaged energy density for a certain refactive index is obtained if the radius of the rod of the second defect is increased from 300nm to 800nm