Towards miniaturised instrumentation realised via metasurfaces

The miniaturisation of optical instrumentation is a vital step in order to produce sensors in a form that can be integrated into manufacturing lines, providing the feedback required to control and optimise such processes. While incremental progress has been achieved by using conventional optical technologies, a markedly different route is needed to achieve the step-change in size and weight reduction required. Metasurfaces, which are nanostructured surfaces that can simultaneously manipulate the phase, polarisation and amplitude of light, offer a new basis upon which truly miniaturised optical instrumentation can be realised. Here we present our initial work on using metasurfaces to miniaturise a single-shot dispersive profile interferometer (SDPI), which is a line profile measuring instrument designed for the measurement of moving substrates in roll-to-roll applications. A key optical element in the SDPI is a line spectrometer, which provides for the spectral evaluation of light to be measured for each point along the entrance slit. Current line spectrometers are large and bulky, which creates a significant impediment to compactness. However, we have designed a metasurface that allows the necessary optical operations to be carried out in an ultra-compact and lightweight form. The metasurface has been fabricated by etching pillars into a layer of GaN on an Al2O3 substrate. We present our results covering the performance characterisation of this metasurface spectrometer and the subsequent steps towards developing an instrument based around it. The experimental results will demonstrate a significant reduction in size and weight compared to a comparable approach based on conventional optics with improved optical functionality.