= Distributed Bragg reflector
= DBR
{c}
{synonym}
A <distributed Bragg reflector> uses a periodic <refractive index> structure to make successive weak reflections add coherently. Near the design <wavelength>, constructive <wave interference> produces strong reflection even when a single interface reflects only a small fraction of incident <radiant power>.
A <quarter-wave Bragg stack> alternates layers with optical thickness $\lambda_0/4$ at normal incidence. Measuring transmission across <wavelength> reveals a rejected band rather than a perfectly reflecting surface at every <frequency>. Such <mirrors> provide <wavelength> selection in an <optical resonator>; their reflection band shifts with incidence angle and material <dispersion>.
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