In generalised holography, an arbitrary wave is interfered with an arbitrary desired signal. While the theory has been known for many decades, it is only now with the plentiful availability of coherent light sources and rapid development of nanofabrication technologies required to make holograms that we can ask a question – how do we craft an arbitrarily complex beam on demand, e.g., an arbitrary signal on an arbitrary carrier realised by optical elements?
Optical elements typically rely on either refraction of diffraction – two out of three major manifestations of light interaction with matter – for control and manipulation of the flow of photons. Fusion of diffraction and refraction in a single element by decorating the topology of curvilinear refractive surfaces with diffraction patterns provides an extra layer of control over light propagation and beam formation by miniaturised components. Recent advances in nanotechnology allow the realisation of such challenging micro-systems directly in traditional optical materials like glass or in such exciting piezo/optoelectric materials as lithium niobate. Herein, we demonstrate hybrid refracto-diffractive micro-optical elements such as lenses, axicons and arbitrarily shaped elements with multiplexing and enhanced beam-shaping properties.