Tunable and switchable lasing in a ZnO microwire cavity at room temperature

We present the concept for a wavelength tunable, single mode laser and its realization. The laser is based on a tapered microwire that is mechanically moved relative to the optical pumping area. The radius dependence of the whispering gallery mode (WGM) properties is thus translated into wavelength tuning of the emission. Since the spectral separation of the WGMs is as large as the spectral width of the gain spectrum (both about 50 meV for the demonstrated ZnO wire with radius of around 0.5 μm), continuous single mode tuning is achieved. We thoroughly model the laser properties such as gain spectrum and mode positions based on a plane wave model, taking into account absorption and gain regions within the wire due to inhomogeneous pumping.