  A review of hollow core whispering gallery resonators (WGRs)is given. After a
short introduction to the topic of whispering gallery resonators we provide a
description of whispering gallery modes in hollow or liquid core WGRs. Next,
whispering gallery mode (WGM) sensing mechanisms are outlined and some
fabrication methods for microbubbles, microcapillaries and other tubular WGM
devices are discussed. We then focus on the most common applications of hollow
core WGRs, namely refractive index and temperature sensing, gas sensing, force
sensing, biosensing, and lasing. The review highlights some of the key papers
in this field and gives the reader a general overview of the current
state-of-the-art.
