Single-Crystalline Hexagonal ZnO Microtube Optical Resonators Hongxing Dong,1 Zhanghai Chen,1 Liaoxin Sun,1 Wei Xie,1 H. Hoe Tan,2 Jian Lu, Chennupati Jagadish,2 and Xuechu Shen1 1State Key Laboratory of Surface Physics and Department of Physics, Laboratory of Advanced Materials, Fudan University, Shanghai 200433, China 2Department of Electronic Materials Engineering, Research School of Physics and Engineering, The Australian National University, canberra, Australian Capital Territory 0200, Australia Motivation (1) Whispering gallery (WG) resonators have attracted much attention due to their microscopic size, high quality factor Q, and low lasing threshold power. (2) The synthesis of three-dimensional tubular structure of ZnO remains challenging compared with other materials that have bulk lamellar structures, such as graphite or graphite-like structures. (3) The application of a single ZnO micro/nanotube as an optical cavity has not yet been explored. Here, we report the fabrication of high quality ZnO microtubes with hexagonal cross section and the observation of series of WGM resonance in the tubes. Experiment and Discussion Plane wave model for WGM TM polarization, β=1/n, for TE polarization, β=n. High quality ZnO microtubes with hexagonal cross sections are fabricated and studied as novel optical resonators. Whispering gallery modes, Fabry-Perot modes, and an additional set of modes with different polarizations are directly observed at room temperature by using the spatially resolved spectroscopic technique. Cauchy dispersion formula n⊥=1.763+6.916X104/λ2+1.673X109/λ4 n‖=1.767+7.748X104/λ2+0.513X109/λ4 Plane wave model for FPM d=Nhc/2nE Wave-guided mode EDS elemental mappings of Zn and O. Conclusion High quality ZnO microtubes with hexagonal cross sections, fabricated via an oxidation–sublimation process, are studied as novel optical resonators. Whispering gallery modes, Fabry-Perot modes, and an additional set of modes with different polarizations are directly observed in the visible spectral range at room temperature by using the spatially resolved spectroscopic technique. The diameter and wall thickness of the microtube are crucial for light modulation. The experimental results are explained and fitted with a plane wave interference model and Cauchy dispersion formula for refractive indices. References: 1 A. C. Tamboli, E. D. Haberer, et al, Nat. photonics 1, 61 (2007). 2 T. Nobis, E. M. Kaidashev, et al, Phys. Rev. Lett. 93, 103903 (2004) 3 L. X. Sun, Z. H. Chen, et al, Phy. Rev. Lett. 100, 156403 (2008). 3 H. X. Dong, Z. H. Chen, et al, Appl. Phys. Lett. 94, 173115 (2009).