Physicists at the Johannes Gutenberg University Mainz (Germany) say they are the first to produce a single, monolithic microresonator device that combines long storage time, small volume, and tunability to arbitrary optical frequencies. The lack of such a light-storage device has prevented many important light-based applications, they note.
As reported in the journal Physical Review Letters, the researchers accomplished this feat by heating and stretching a standard glass fiber until it reached about half the diameter of a human hair and then using a laser to create a bulge-shaped structure in the fiber. Light within this structure is continually reflected at the surface of the fiber and thus travels in a spiral path around the fiber axis. In doing so, the light cannot escape along the fiber because the diameter of the fiber reduces on either side of the structure.
Similar to the motion of a charged particle stored in a magnetic bottle (that is, a particular spatially varying magnetic field), the light oscillates back and forth along the fiber between two points. For this reason, the researchers are calling their novel microresonator a "bottle resonator." It is possible to tune the resonator to a specific optical frequency by simply pulling both ends of the supporting glass fiber. The resulting mechanical tension changes the refractive index of the glass, so that depending on the tension, the round-trip of the light is lengthened or shortened.
Because of its exceptional characteristics and its simple design based on glass-fiber technology, the bottle resonator opens up numerous areas of application. "At Mainz University, we aim to use this novel multifunctional microresonator for coupling minute light fields, consisting of single photons, with single atoms," explains Prof. Arno Rauschenbeutel from the QUANTUM, Quantum-, Atom-, and Neutron-Physics-Division at the Institute of Physics. "If that were successful, one could realize, for example, a glass fiber-based quantum interface between light and matter," says to Rauschenbeutel, who led the work. This would then be an important contribution towards quantum communication and the future realization of a quantum computer.
For further information see the paper, Ultrahigh-Q Tunable Whispering-Gallery-Mode Microresonator, in Physical Review Letters.