  A series of thin layers of alternating refractive index is known to make a
good optical mirror over certain bands of frequency. Such a device - often
termed the Bragg reflector - is usually introduced to students within the first
years of an undergraduate degree, often in isolation from other parts of the
course. Here we show that the basic physics of wave propagation through a
stratified medium can be used to illustrate some more modern developments in
optics as well as quantum physics; from transfer matrix techniques, to the
optical properties of cold trapped atoms, optomechanical cooling, and a simple
example of a system exhibiting an appreciable level of optical non-reciprocity.
