An apparatus, system, and method are disclosed for copying data from a volatile memory device to a plurality of persistent storage devices in response to a loss of primary power. The detection circuitry is configured to detect gestures or motions of a welding system operator. The etch-stop layer 9 is thin compared to the thickness of the first waveguide layer 3 andor the second waveguide layer 6 and is of a material which enables it to act as an etch-stop when features are etched in the second waveguide layer 6.