Free space super focusing using all dielectric hyperbolic metamaterial.

Despite that Hyperbolic Metamaterial (HMM) has demonstrated sub-wavelength focusing inside of it, sub-wavelength imaging in free space of HMM is rarely introduced. The decay of hyperbolic momentum space outside the hyperbolic medium has hindered the realization of sub-wavelengh focusing in the near field of HMM. Furthermore, manipulating the negatively refracted waves exiting the HMM have addressed another major obstacle to realize free space sub-wavelength focusing. In this work, we report extended sub-wavelength focusing in free space based on negative refraction of light exiting the HMM. The proposed structure is composed of multilayers of doped InAs/intrinsic InAs integrated with metallic slit. We theoretically simulate the doped InAs/intrinsic InAs HMM and investigate the negative refraction behavior outside the HMM. We optimized the structure for achieving high resolution down to 0.2λ, extended to a distance of 3.2 µm in free space. Also, sub-wavelength focusing in free space has been studied at different doping concentrations showing that the small doping concentrations exhibit enhancement in resolution at short distances up to 600 nm away from the HMM. Extending the focusing distance is achieved up to distance 3.5 µm from the hyperbolic structure by manipulating the doping concentration. This proposed lens configuration is expected to find potential usage in mid IR thermal imaging and photolithography application.