In transformation optics, coordinate transformations are usually mapped onto equivalent (meta-)material parameter distributions. In 2015, we introduced an approach mapping coordinate transformations onto dielectric free-form surfaces. We presented model experiments on cloaking of reflective contact fingers on solar cells. We now report on the fabrication of masters by 3D laser lithography used for soft imprinting. For prototype silicon heterojunction solar cells investigated under 1-sun illumination, we demonstrate the predicted 9% relative efficiency increase. We additionally show that our approach is adaptable to Lambertian sources, thereby cloaking light-emitting diode contacts to achieve spatially homogeneous emission.
In this paper an on-chip device capable of wavelength-selective generation of vortex beams is demonstrated. The device is realized by integrating a spiral phase-plate onto a MEMS tunable Fabry-Perot filter. This vortex-MEMS filter, being capable of functioning simultaneously in wavelength and orbital angular momentum (OAM) domains at around 1550 nm, is considered as a compact, robust and cost-effective solution for simultaneous OAM- and WDM optical communications. Experimental spectra for azimuthal orders 1, 2 and 3 show OAM state purity >92% across 30 nm wavelength range. A demonstration of multi-channel transmission is carried out as a proof of concept.