Figure 2: Resonant PEC tuning of a single GaAs WGM disk resonator.
(a) Optical spectrum before resonant PEC etching, with a doublet associated to two normal modes of the disk, consisting of a mixture of clockwise and counterclockwise WGMs15. (b) Optical spectrum after 4 nm of resonant PEC tuning. The low-contrast oscillations are residual interferences produced by reflections at the waveguide input and output facets. They can be mitigated by proper guide design. (c) Wavelength tuning of the WGM of a GaAs disk resonator immersed in water by subsequent cycles of resonant PEC etching at low optical power, reaching picometre precision. This translates into an etch speed of 0.5–1 nm s−1 for a continuous injected power of 1 μW in the cavity WGM. (d) Wavelength tuning per cycle (see text) as a function of the laser optical output power, which is proportional to the optical power guided in the coupling waveguide. Each point has been obtained by averaging over 100 cycles, the shown error bar is the related s.d.
