An illustration of a binary-phase RIPLE grating and its fabrication process. (a) A grating line pattern is written in a thin layer of photo-resist by electron-beam exposure. (b) The developed photoresist is removed from the exposed spaces, uncovering the underlying chromium layer. (c) The chromium layer is etched-out from the photoresist grating grooves, leaving the substrate surface exposed. (d) The resist layer is washed away. (e) The grating grooves are etched into the substrate, using the chrome lines as a mask. (f) Schematic of a single grating period structured, with the feature parameters marked. The duty cycle is defined by $w/p$.

The first-order DE model of the POC RIPLE grating. (a) Slices of the RCWA computed efficiency cube used in optimizing $w$ and $d$ and (b) the efficiency map over $\lambda$ and $d$ for $w/p=33\%$, locating the optimal depth within the range between 1.3 and $1.5\mu \mathrm{m}$ for maximum overall efficiency. (c) The wavelength slice at $d=1.4\mu \mathrm{m}$, where the efficiency peaks at 96.7% and stays over 70% over the wavelength range of 230 nm from 454 to 685 nm. Makie.jl was used to produce these plots.⁶