Millisecond Photon Lifetime in a Slow-Light Microcavity

International audience; Optical microcavities with ultralong photon storage times are of central importance for integrated nanophotonics. To date, record quality (Q) factors up to 10^11 have been measured in millimetric-size single-crystal whispering-gallery-mode (WGM) resonators, and 10^10 in silica or glass microresonators. We show that, by introducing slow-light effects in an active WGM microresonator, it is possible to enhance the photon lifetime by several orders of magnitude, thus circumventing both fabrication imperfections and residual absorption. The slow-light effect is obtained from coherent population oscillations in an erbium-doped fluoride glass microsphere, producing strong dispersion of the WGM (group index ng∼106). As a result, a photon lifetime up to 2.5 ms at room temperature has been measured, corresponding to a Q factor of 3×10^12 at 1530 nm. This system could yield a new type of optical memory microarray with ultralong storage times.