DBR Stands for Distributed Bragg Reflector (DBR)
Distributed Bragg Reflector (DBR) is a reflector which is used in waveguides, such as optical fibres. It is in a structured form which is made up of multiple layers of alternating materials with a different refractive index, or by the periodic variation of some characteristics (like height) of a dielectric waveguide, which results in regular variation in the active refractive index in the guide. Each layer boundary causes a partial reflection which is of an optical wave. For those waves whose vacuum wavelength is close to the four times to the optical thickness of the layers, many of the reflections combine with the constructive interference and that layer act as a high-quality reflector.
The range of the wavelength which is reflected is called photonic stopband. Within that range of wavelengths, the light is not allowed to propagate in the structure.
How to Construct a Bragg Mirror?
Take a thin film Bragg reflector which consists of a multilayer- stack of alternative high- index film and low-index films, all one-quarter wavelength thick. The geometrical thickness of the high-index film and low-index film are: –
tH= λ/(4nH) and tL= λ/(4nL) respectively.
NH and NL are the indices of the reflection of the high and low-index films, and λ indicates the centre wavelength of the Bragg mirror.
On every interface of the stack, a part of the incident beam is reflected. That reflected parts have a phase shift of a 180 degree but only if the incident light goes from low-index medium towards a high-index medium. The relative phase difference of all the reflected beams is zero or a multiple of a 360 degree, and therefore they interfere constructively. The intensity of that incident light beam decreases during his travel through the quarter-wave stack and at the same time that reflected light increases if the absorptance A of the pile is negligible.
Some More Information Related to DBR
A Distributed Bragg Reflector (DBR) is made-up or composed entirely of single material-indium tin oxide (ITO)- is reported. The high-refractive-index layers and the low-refractive-index layers of the Distributed Bragg Reflector (DBR) are deposited by oblique-angle deposition, and it consists of ITO thin films with the low and high porosities, which yield an index contrast of Δn = 0.4. If we talk about a single-material Distributed Bragg Reflector (DBR) with three periods so, it achieves a reflectivity of 72.7% in excellent agreement with theory.
The authors also gratefully acknowledge support from Sandia National Laboratories, Crystal IS Corporation, SAIT, i.e. Samsung Advanced Institute of Technology, NYSTAR, i.e. New York State Office of Science, Technology and Academic Research, Army Research Office (ARO), National Science Foundation (NSF) and The Department Of Energy (DOE).
Hope now you are clear with the term Distributed Bragg Reflector, i.e. DBR and many more information related to DBR.