Genetic algorithm synthesis of impedance-matched infrared ZIMs with wide FOV using a generalized inversion algorithm

The new field of metamaterials has garnered substantial research interest in recent years due to their necessity in developing technologies such as flat 'perfect lenses' [1] and the electromagnetic cloak [2]. Of special interest are the negative index metamaterials (NIMs) which have been experimentally demonstrated in the RF regime as well as at optical wavelengths [3, 4]. Compared with NIMs, zero index metamaterials (ZIMs) have received less attention, but have found themselves useful in arguably more compelling applications such as transformation optics devices, far-field focusing lenses and artificial magnetic mirrors [2, 5, 6]. Most publications only consider the response of ZIMs to normally incident waves [7]. However, these ZIM structures are inherently anisotropic and require illumination by obliquely incident waves in many applications of practical interest. Therefore, the angular response of ZIMs has to be considered if an improved picture of the electromagnetic properties of ZIMs is desired for practical applications. In this paper, we present an impedance-matched low loss infrared ZIM with a wide field-of-view. The ZIM structure is optimized by a genetic algorithm (GA) [8] combined with a generalized inversion method capable of retrieving the effective anisotropic constitutive parameters of the metamaterial with its angular response considered.