Distributed Bragg reflector

It is a structure formed from multiple layers of alternating materials with different refractive index, or by periodic variation of some characteristic (such as height) of a dielectric waveguide, resulting in periodic variation in the effective refractive index in the guide.

Each layer boundary causes a partial reflection and refraction of an optical wave.

For waves whose vacuum wavelength is close to four times the optical thickness of the layers, the interaction between these beams generates constructive interference, and the layers act as a high-quality reflector.

The range of wavelengths that are reflected is called the photonic stopband.

Within this range of wavelengths, light is "forbidden" to propagate in the structure.

This formula assumes the repeated pairs all have a quarter-wave thickness (that is

A common choice of materials for the stack is titanium dioxide (n ≈ 2.5) and silica (n ≈ 1.5).

This section discusses the interaction of transverse electric (TE) and transverse magnetic (TM) polarized light with the DBR structure, over several wavelengths and incidence angles.

This reflectivity of the DBR structure (described below) was calculated using the transfer-matrix method (TMM), where the TE mode alone is highly reflected by this stack, while the TM modes are passed through.

For TE and TM incidence we have the reflection spectra of a DBR stack, corresponding to a 6 layer stack of dielectric contrast of 11.5, between an air and dielectric layers.

The wavelength in the figures below, corresponds to multiples of the cell period.

Bio-inspired Bragg reflectors are 1D photonic crystals inspired by nature.

Reflection of light from such a nanostructured matter results in structural colouration.

When designed from mesoporous metal-oxides[5][6][7] or polymers,[8] these devices can be used as low-cost vapor/solvents sensors.