Broadband field enhancement in epsilon-near-zero multilayer thin films

Abstract

Coherent perfect absorption (CPA) is an optical phenomenon in an absorbing medium by interaction of two counter-propagating coherent waves and turns it into some form of internal energy. It is the timereversed counterpart of a laser and this is why a coherent perfect absorber is called as an anti-laser. It has many potential applications in the many fields.(1) Many researches are focused on CPA with nanostructured metamaterials (MMs). In this study we employ and design unpatterned indium tin oxide (ITO) thin films for CPA at epsilon-near-zero (ENZ) wavelength in the near infrared (NIR) regime.(2,3) Also, we introduce CPA conditions in terms of reflection/transmission amplitude coefficient and phase that can be obtained from the scattering matrix. Figure 1(a) presents the ENZ ITO CPA thin film structure of [ZnSe/ITO1(22.04 nm)/ITO2 (73.44 nm)/ITO1(22.04 nm)/ZnSe] configuration at 45o incident angle. The CPA bandwidth with greater than 99% absorption is as large as 270 nm as shown in Fig. 1(b), which is about 10 times wider than that of a single layer ENZ CPA film. This design method using the admittance matching can be used for various nanophotonic devices, such as optical modulators, sensors, switches, detectors, transducers and notch filters.