In order to achieve competitive system costs in mass-production, it is essential that CPV concentrators incorporate sufficient manufacturing tolerances. This paper presents an advanced concentrator optic comprising a Fresnel lens and a refractive secondary element, both with broken rotational symmetry, an optic producing both the desired light concentration with high tolerance (high acceptance angle) as well as an excellent light homogenization by Köhler integration. This concentrator compares well with conventional Fresnel-based CPV concentrators.

Leonhardt demonstrated (2009) that the 2D Maxwell Fish Eye lens (MFE) can perfectly focus 2D Helmholtz waves of arbitrary frequency, i.e., it can perfectly transport an outward (monopole) 2D Helmholtz wave field, generated by a point source, towards a "perfect point drain" located at the corresponding image point. Moreover, a prototype with λ/5 super-resolution property for one microwave frequency has been manufactured and tested . However, software simulations or experimental measurements for a broad band of frequencies have not yet been reported. Here we present simulations with a non-perfect drain for a device equivalent to the MFE, called the Spherical Geodesic Waveguide (SGW), that predicts up to λ /500 super-resolution close to discrete frequencies. These frequencies are directly connected with the wellknown Schumann resonance frequencies of spherical symmetric systems. Out of these frequencies, the SGW does not show super-resolution in the analysis performed.

Abstract:The Simultaneous Multiple Surface (SMS) method in planar geometry (2D) is applied to imaging designs, generating lenses that compare well with aplanatic designs. When the merit function utilizes image quality over the entire field (not just paraxial), the SMS strategy is superior. In fact, the traditional aplanatic approach is actually a particular case of the SMS strategy.

We reply to the comments on our paper "Perfect Drain for the Maxwell fish eye lens" (NJP. 13 (2011) 023038) made by Fei Sun. We believe that Sun's comments have several mistakes in theoretical concepts and simulation results.The "Comments on "Perfect Drain for the Maxwel fish eye lens" " made by Fei Sun can be classified in two sections: theoretical and simulation results. Theoretical results.In relation to the Perfect Drain introduced by Leonhardt in [1] Sun writes: "perfect drain is not only a perfect absorber which can totally absorb all incident radiation without any scattering, but also it can achieve a very sharp electric field around it which is actually a delta function". This is not correct: The electric field calculated by Leonhardt in [1] is not an electric field described by delta function. This field is asymptotic in the source and image point, but unlike a delta function, the field is not zero around the points of divergence. An example of the solution described by Leonhardt in [1] is shown in Fig. 1 where the asymptotic behaviour of the function in the neighbourhood of the object and image point can be clearly seen. What is a delta function is the current density at the drain, as it is at the source, and both appear as excitations in the differential equation of the electric field, as was explicitly shown, for instance, in [2] The system with the drain that we designed in [3] has an electric field distribution identical to that of Leonhardt in Eq. 12 of [1] for all the points outside the drain. When the radius of this drain (which can be arbitrarily selected) tends toward zero, then we get the Leonhardt perfect drain.

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