Phys. Rev. Lett. 116, 133902 (2016)

The development of optical microcavities with high Q-factors and thus long photon storage times would be useful for realizing high-performance optical filters, delay lines and sensors. A French team of researchers have now demonstrated a microcavity with a photon lifetime of 2.5 ms, corresponding to a Q factor of 3 × 1012, at a wavelength of 1,530 nm by harnessing slow-light effects. Vincent Huet and co-workers introduced a slow-light effect by exploiting coherent population oscillations in an erbium-doped fluoride glass whispering-gallery-mode microresonator. The result is a very strong refractive index dispersion and group delay that thus slows down the signal light, increasing the photon storage time of the cavity from 210 ps to 2.5 ms. The team says that the principle could be extended to suit devices intended for on-chip integration to create miniature ultrapure optical or microwave generators.