Figure 4: Collective resonant PEC tuning of photonic resonators.
(a) Five optical spectra corresponding to step-by-step spectral alignment of five WGM resonators in liquid water. In the first spectrum, the five resonators (1–5) appear in order of their resonant wavelength (λ1<…<λ5). In addition to the spectral merging of the five resonators, a residual non-selective etching is also present and discussed in full in Supplementary Note 3 and in Supplementary Fig. 5. (b) Spectral tuning of two WGM resonators, performed directly in humid air without liquid. In these three latter spectra relative wavelengths are displayed, with the origin being set by the smallest wavelength of the group of resonances. Initially (step 1), the two WGM doublets are disjoint before they begin to merge (step 2), resulting in three transmission dips whose overlap is coloured green. Finally (step 3), both WGM doublets overlap completely. As the resonant cavity-enhanced PEC tuning in humid air is a slow process, we removed here the contribution of slow temperature variations in the laboratory, which typically red-shift all wavelengths by 200 pm for 1 °C of temperature variation (see Supplementary Fig. 6 for extra raw data). The blue arrows indicate the spectral tuning direction. The red dashed line is a model (see text).
