Omnidirectional light concentrators and absorbers revisited: Almost flat absorbers inside almost circular (spherical) lenses

We extend our previously developed theory of a circular omnidirectional absorber - `an optical black hole'. We introduce a new, elliptically flattened design that could have elliptic cylinder, oblate or prolate spheroidal shapes. As a result, the absorbing core could now be flattened to a strip (elliptic cylinder) or a disk (oblate spheroid) and therefore match well-established planar fabrication techniques. First, we present a general and complete theoretical description that includes 3D oblique incidence, and then test the theory with ray-tracing and full-wave simulations of elliptic absorbers that confirm flawless performance at complete acceptance angles.