Dielectric mirror – Mirror made of dielectric materials.Diffraction grating – Optical component which splits light into several beams.Diffraction – Phenomenon of the motion of waves.Bragg diffraction – Physical law regarding scattering angles of radiation through a medium Pages displaying short descriptions of redirect targets.Bragg's law – Physical law regarding scattering angles of radiation through a medium.For example, colour of this porous multi-layered structures will change when the matter filling up the pores is substituted by another, e.g. When designed from mesoporous metal-oxides or polymers, these devices can be used as low-cost vapor/solvents sensors. Reflection of light from such a nanostructured matter results in structural colouration. It has a complete TE band gap, but only a pseudo TM band gap.Įxample of color change in Bragg reflector with change in humidity and comparison to biological structure.īio-inspired Bragg Reflectors are 1D photonic crystals inspired by nature. This DBR is also a simple example of a 1D photonic crystal. The wavelength in the figures below, corresponds to multiples of the cell period. The thicknesses of the air and dielectric layers are 0.8 and 0.2 of the period, respectively. To a 6 layer stack of dielectric contrast of 11.5, between an air and dielectric layers. This also shows the DBR acting as a polarizer.įor TE and TM incidence we have the reflection spectra of a DBR stack, corresponding The TE mode alone is highly reflected by this stack, while the TM modes are passed Was calculated using the transfer-matrix method (TMM), where This reflectivity of the DBR structure (described below) This section discusses the interaction of transverse electric (TE)Īnd transverse magnetic (TM) polarized light with the DBR structure, over several Left half represents TM reflection with a Brewster's angle showed as a white dashed line, right half represents TE reflection. Parameters of the systems: ε = (11.4, 1.0), period of one layer is d = 0.2 + 0.8 = 1, total number of periods is 6. Total reflection map as function of incident angle and dimensionless frequency. They are also used to form the cavity resonator (or optical cavity) in fiber lasers and free electron lasers. Substituting into the formula above gives a bandwidth of about 200 nm for 630 nm light.ĭistributed Bragg reflectors are critical components in vertical cavity surface emitting lasers and other types of narrow-linewidth laser diodes such as distributed feedback (DFB) lasers and distributed bragg reflector (DBR) lasers. A common choice of materials for the stack is titanium dioxide ( n ≈ 2.5) and silica ( n ≈ 1.5). Increasing the number of pairs in a DBR increases the mirror reflectivity and increasing the refractive index contrast between the materials in the Bragg pairs increases both the reflectivity and the bandwidth. The DBR's reflectivity, R that can be achieved with these two values of the refractive index. Calculated reflectivity of a schematic DBR structure
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