Definition: a special type of saturable semiconductor absorbers
More general term: saturable absorbers
A saturable Bragg reflector is a kind of semiconductor saturable absorber mirror (SESAM), which can be used for passive mode locking or Q switching. It consists of a Bragg mirror structure and a saturable absorber layer incorporated into the top layers. Most SESAMs are actually of SBR type, but the more general acronym SESAM is more frequently used. It was introduced before the acronym SBR and appears to be logically more compelling, since the absorption losses of such a device are saturated, rather than the reflector itself.
Bibliography
[1]
S. Tsuda et al., “Low-loss intracavity AlAs/AlGaAs saturable Bragg reflector for femtosecond mode locking in solid-state lasers”, Opt. Lett. 20 (12), 1406 (1995), doi:10.1364/OL.20.001406