Geometric optics is the most developed and the most intuitive part of optics. At least this is the impression you are likely to have before you read this manuscript. The authors of this work go beyond conventional optical elements, and consider the so-called generalized lenses, or glenses. These lenses are thin micro-structured sheets, which behave as an asymmetric lens – their focal length is different depending on the direction the light is incident from. This seems like a small modification that will not lead to any qualitative changes in the lens behaviour, but this modification actually makes it possible to design a novel type of an invisibility cloak. Invisibility cloaks have been a hot topic over the past decade, with a few examples demonstrated in various frequency ranges. The idea of the invisibility cloak is to hide an object, at the same time allowing one to see any other object behind the cloak without distortions. Previously predicted and demonstrated invisibility cloaks usually had quite severe limitations, e.g. on the size of the objects they can hide, or on the angle of view, or on the wavelength. The cloak presented in this work, made of a combination of glenses, is predicted to work in a wide frequency range, e.g. covering whole visible spectrum, and be able to hide large objects. The authors developed a ray-tracing software that can treat the unconventional optical elements and using this software they demonstrated how the cloak would work with macroscopic objects. The software is freely available online.

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