Ice Microsphere Optical Cavities

Whispering gallery mode (WGM) optical microcavities have played an essential role in both fundamental research and practical applications, such as cavity quantum electrodynamics, optomechanics, microlasers, and optical sensors. While microcavities made of various materials (e.g., SiO2, As2S3, polymethylmethacrylate) have been extensively investigated, exploiting new materials for microcavities holds great promise for expanding the functionalities of the microcavities. As one of the most ubiquitous and important solids on earth's surface, ice exhibits intriguing optical properties that render it an excellent material for optical applications. Here, ice microsphere optical cavities are demonstrated for the first time. By rapidly freezing water microdroplets, ice microspheres are batch‐fabricated with relatively smooth surfaces and diameters of 5–50 µm. Excitation of a series of WGMs within ice microsphere cavities is achieved over a broad spectral range from near‐ultraviolet to near‐infrared region (380–1600 nm) with quality factors up to 1.4 × 103. Considering the extremely low absorption coefficient of ice in the ultraviolet, this work provides an exceptional platform for exploring ultraviolet microcavity photonics and its diverse applications. A structurally stable ice microsphere with a relatively smooth surface is demonstrated and its optical resonance properties are explored experimentally for the first time. By evanescent and free‐space coupling, respectively, whispering gallery modes within the ice microsphere cavities are excited in a broad spectral range from near‐ultraviolet to near‐infrared, providing a promising platform for exploring microcavity photonics in the ultraviolet.