Self-Assembled Organic Crystalline Microring Cavities with High Q-Factors

Organic crystalline microstructures are recently a target of intense research from the point of view of photonic devices such as microcavities and optical waveguides. A bottom-up method based upon self-assembly produces organic microstructures including oriented needles. A top-down approach, in turn, enabled the fabrication of microstructures of different morphologies and configurations such as microrings and microdisks. In the present study, by using a bottom-up technique we have developed organic microrings of high crystallinity with minimized crystal imperfections. We have found out that the said microrings function as resonators with high quality (Q) factors. We observe a series of sharply resolved peaks in their photoluminescence spectra and assign those peaks to whispering gallery modes formed in the microrings. Their mode numbers are precisely determined from their mode spacings with the maximum of Q-factor being similar to 2000. The number is extremely high compared with those of other organic microrings of the same size.