Figure 4.

Effect of surface modification on reflectance spectra. The effect of thermal hydrosilylation of undecylenic acid (a) and the UnTHC treatment (b) on the reflectance spectra of PSi-based graded-index microcavities. The solid red line represents spectra for as-anodized samples, and the dashed black line is the spectrum recorded after modification. The inset shows the anodization current profile as a function of anodization time. The constant current region results in a cavity layer that is created between two rugate filters. Full width at half maximum (FWHM) values of the cavity resonance, determined from a Lorentzian fit to experimental data, show values in the order of a few nanometers (c).