Focusing characteristics of curvilinear half-open Fresnel zone plate lenses: plane wave illumination

Ultra-compact planoconcave zoned metallic lens based on the fishnet metamaterial

“…As it has been explained before, the difference is due to the fact that the refractive index of the lens is dependent on the number of layers; hence, the FL of the non-zoned stepped lens is closer to the value obtained with an ideal isotropic homogeneous zoned lens with n ¼ À0. 25. Moreover, it can be observed that the FWHM values obtained with all the structures are similar.…”

“…1,24 This technique has been used occasionally for classical metallic lenses. 1 However, it has significant importance for microwave and optical dielectric lenses, which are widely known as Fresnel lenses, 25 and for X-rays dielectric lenses. 26 Note that this technique not only reduces volume and weight but also minimizes lens absorption, i.e., losses.…”

“…The lens is designed to operate at f ¼ 56.7 GHz (k 0 ¼ 5.29 mm), where it behaves as an effective NRI medium n ¼ À0. 25, with a focal length (FL) of 9k 0 . Note that the fishnet metamaterial lens is already inherently narrowband, and thus its bandwidth is not affected by the zoning technique.…”

“…[8][9][10] To wrap up all the results presented here and facilitate the comparison among zoned and non-zoned lenses using the fishnet metamaterial and the isotropic homogeneous material with n ¼ À0. 25, simulation results for the FL, FWHM, DF, and the total volume for these three structures are presented in Table I along with the experimental results. It is shown that the resulting FL for the zoned lens 9.35(k 0 ) is close to the values obtained with the non-zoned lens using fishnet metamaterial and the homogeneous medium, 8.96k 0 and 9.01k 0 , respectively.…”

Exploiting the dispersion of the double-negative-index fishnet metamaterial to create a broadband low-profile metallic lens

“…These drawbacks can be overcome by applying the time-honored zoning technique, whereby redundant wavelength phase shift material is removed [1,16,17]. Alike zoned metallic [1] and optical dielectric lenses, also known as Fresnel lenses [17,18], this modification results in a fishnet metamaterial lens with low profile and, therefore, reduced weight and absorption losses [19,20]. The outcome is then a diffractive optical element akin to Fresnel zoned metallic plate lenses [17,18], but with an enhanced impedance matching.…”