I. Introduction
In microscopy applications, the diffraction limit plays a crucial role since it defines the maximum resolution achieved with conventional methods [1]. Due to this limit, the wavelength intrinsically constrains the ultimate far-field resolution since the evanescent waves scattered from the object’s subwavelength details are not present in the far field. Thus, to recover the image’s sub-diffraction details, it is necessary to recover the evanescent field components by scanning directly in the near field or exploiting negative refraction [2]. Recent advances in microscopy have demonstrated the ability to overcome the diffraction limit in both near [3] and far fields [4] by using time-consuming near field-scanning or introducing invasive markers that require extensive image post-processing of the acquisition of multiple far-field images. Other alternative approaches that have been recently proposed use artificial resonant materials – metamaterials – to convert the evanescent field components into propagating waves [2], [5]. Among them, interesting methods such as far field subwavelength imaging using hyperbolic metamaterials [5], or a locally resonant metamaterial lens (metalens) placed in the near-field, combined with time-reversal techniques [6]. Another alternative approach uses superoscillations [7] to tailor the interference of several coherent sources and focus the probe field directly into a subwavelength spot. Unfortunately, implementing these noninvasive approaches is also challenging, due to absorption losses in locally-resonant metamaterials, or the significant sidebands surrounding superoscillations that tend to constrain the signal-over-noise ratio.