Wrinkling
instabilities in polymeric bilayers have been exploited
as optical phase gratings with tunable performance. Here, we report
strain modulated 1D and 2D phase gratings fabricated by the ubiquitous
process of plasma-oxidation of polydimethylsiloxane (PDMS). While
surface oxidation provides a remarkably facile glassy skin formation
approach, minimizing delamination and debonding, it inherently results
in a gradient conversion profile emanating from the top film interface.
We examine and quantitatively model the consequences of this gradient
layer on the optical properties of the resulting strain-tunable phase
gratings. Diffraction efficiencies up to 48% are demonstrated. We
then develop and validate a surface reconstruction methodology based
on the diffraction pattern of our sinusoidal gratings and our model,
which we extend to the high deformation regimes and to 2D gratings,
obtained by superposition of two wrinkling generations, where both
amplitudes and wavelengths can be independently tuned. Overall, this
approach provides a rapid, robust and predictive framework for the
design and fabrication of tunable, single, and multiaxial surface
gratings.