Optical Device Simulation

In birefringent materials, the phase velocity of a light wave depends on the polarization and the propagation direction. Mathematically this means that the permittivity of such materials is a tensor. Materials for which two of the components are identical are referred to as uniaxial. If all three components are different from each other, the material is called biaxial.

Examples of birefringent materials found in nature are crystals with asymmetric crystal structures, such as Quartz. Hyperbolic materials are a special case where one of the tensor components has a negative sign. The material, therefore, demonstrates dielectric properties for one polarization and metallic for the other polarization. Another way to create birefringence is to stress isotropic materials such that they are deformed and their isotropy is lost.

A special form of optical anisotropy is the magneto-optical effect. If a magneto-optically active material is magnetized, the refractive index of the left-hand and right-hand polarized light will differ orthogonally to the magnetized axis. Magneto-optical effects are widely used for optical isolation because the biasing magnetic field breaks time-reversal symmetry and makes the effect non-reciprocal. Let us assume that we launch light with a polarization angle of let us say 45° into a waveguide. This light leaves our example waveguide 90° polarized. If this light is now reflected back into the waveguide then it is not reverted to the original input state of 45° polarization but rotated further to 135°.

A nonlinear relation between the displacement field and the electric field means the refractive index is dependent on the electric field. The dependence of the refractive index on the optical intensity can be used to build, for example, a bistable element.