Epsilon-near-zero Mode Research Articles

Low dissipation spectral filtering using a field-effect tunable III–V hybrid metasurface

Considering the power constrained scaling of silicon complementary metal-oxide-semiconductor technology, the use of high mobility III–V compound semiconductors such as In0.53Ga0.47As in conjunction with high-κ dielectrics is becoming a promising option for future n-type metal-oxide-semiconductor field-effect-transistors. Development of low dissipation field-effect tunable III–V based photonic devices integrated with high-κ dielectrics is therefore very appealing from a technological perspective. In this work, we present an experimental realization of a monolithically integrable, field-effect-tunable, III–V hybrid metasurface operating at long-wave-infrared spectral bands. Our device relies on strong light-matter coupling between epsilon-near-zero (ENZ) modes of an ultra-thin In0.53Ga0.47As layer and the dipole resonances of a complementary plasmonic metasurface. The tuning mechanism of our device is based on field-effect modulation, where we modulate the coupling between the ENZ mode and the metasurface by modifying the carrier density in the ENZ layer using an external bias voltage. Modulating the bias voltage between ±2 V, we deplete and accumulate carriers in the ENZ layer, which result in spectrally tuning the eigenfrequency of the upper polariton branch at 13 μm by 480 nm and modulating the reflectance by 15%, all with leakage current densities less than 1 μA/cm2. Our wavelength scalable approach demonstrates the possibility of designing on-chip voltage-tunable filters compatible with III–V based focal plane arrays at mid- and long-wave-infrared wavelengths.

Excitation of epsilon-near-zero resonance in ultra-thin indium tin oxide shell embedded nanostructured optical fiber

We report a novel optical waveguide design of a hollow step index fiber modified with a thin layer of indium tin oxide (ITO). We show an excitation of highly confined waveguide mode in the proposed fiber near the wavelength where permittivity of ITO approaches zero. Due to the high field confinement within thin ITO shell inside the fiber, the epsilon-near-zero (ENZ) mode can be characterized by a peak in modal loss of the hybrid waveguide. Our results show that such in-fiber excitation of ENZ mode is due to the coupling of the guided core mode to the thin-film ENZ mode. We also show that the phase matching wavelength, where the coupling takes place, varies depending on the refractive index of the constituents inside the central bore of the fiber. These ENZ nanostructured optical fibers have many potential applications, for example, in ENZ nonlinear and magneto-optics, as in-fiber wavelength-dependent filters, and as subwavelength fluid channel for optical and bio-photonic sensing.

Coupling of Epsilon-Near-Zero Mode to Gap Plasmon Mode for Flat-Top Wideband Perfect Light Absorption

Epsilon-near-zero (ENZ) materials, when probed at or near wavelengths corresponding to their zero permittivity crossing points, have unique and interesting properties that can be exploited for enhancing nanoscale light–matter interactions. Here, we experimentally show that over an order of magnitude increase in the absorption band of a periodically patterned metal–dielectric–metal structure can be obtained by integrating an indium tin oxide (ITO) subwavelength nanolayer into the insulating dielectric gap region. Through incorporation of a 12 nm thick ITO layer between the patterned gold nanodisks and the SiO2 dielectric layer, a 240 nm wide, flat-top perfect (>98%) absorption centered at 1550 nm wavelength is enabled. The demonstrated wideband, perfect absorption resonance is shown to be due to coupling between the gap plasmon mode of the metasurface and the ENZ mode in the nanoscale ITO film.

Broadband absorption caused by coupling of epsilon-near-zero mode with plasmon mode

Epsilon-near-zero mode provides a new path for tailoring light-matter interactions on a nanoscale because of its unique characteristics and ability to be used in many scientific fields. Among these applications, broadband absorption has aroused the considerable interest in photonic research. In this paper, we first show that the surface plasmon resonance is excited by the metal disk array structure without dysprosium-doped cadmium oxide nanolayer, and the structure achieves the local effect of light at a certain wavelength. In addition, in order to be able to use this new technique to achieve a broadband absorption, we take advantage of the surface plasmon resonance to excite the epsilonnear-zero mode which cannot be excited under normal incidence but has a very large density of states. Then, we show that over one order of magnitude increase in the absorption band of a periodically patterned metal-dielectric-metal structure can be obtained by integrating a dysprosium-doped cadmium oxide material into the insulating dielectric gap region. We analyze the absorption band at mid-infrared wavelength comprising plasmonic metamaterial resonators and epsilon-near-zero modes supported by dysprosium-doped cadmium oxide material. The two resonance modes lie in the weak coupling regime and achieve a 470 nm wideband light absorption. Finally, we perform numerical simulations by using the finite-difference-time-domain method to investigate the relationship between the epsilon-near-zero mode and the surface plasmon resonance mode. It is sure that the whole broadband mightily has the local effect of light. The epsilon-near-zero mode mainly is excited at the short wavelength of the broadband, and the surface plasmon resonance mode mainly focuses on long wavelength of the broadband. The simulation demonstrates that the two resonance modes are coupled to achieve a broadband absorption. Additionally, the dielectric constants are tunable by doping density, resulting in plasma frequency change, where the real part of the dielectric constant becomes zero at plasma frequency. Broadband absorption theoretically can be realized in any band of mid-infrared wavelength due to plasma frequency changing. Broadband absorption relaxes the single wavelength condition in previous absorption studies, and compared with the narrowband absorption, broadband absorption at present has many applications, such as in absorbers, sensors, filters, coherent thermal emitters, microbolometers, photodectors, solar cells, fingerprint recognition, energy harvesting devices, etc.

Spectral filtering using active metasurfaces compatible with narrow bandgap III-V infrared detectors

Narrow-bandgap semiconductors such as alloys of InAsAlSb and their heterostructures are considered promising candidates for next generation infrared photodetectors and devices. The prospect of actively tuning the spectral responsivity of these detectors at the pixel level is very appealing. In principle, this could be achieved with a tunable metasurface fabricated monolithically on the detector pixel. Here, we present first steps towards that goal using a complementary metasurface strongly coupled to an epsilon-near-zero (ENZ) mode operating in the long-wave region of the infrared spectrum. We fabricate such a coupled system using the same epitaxial layers used for infrared pixels in a focal plane array and demonstrate the existence of ENZ modes in high mobility layers of InAsSb. We confirm that the coupling strength between the ENZ mode and the metasurface depends on the ENZ layer thickness and demonstrate a transmission modulation on the order of 25%. We further show numerically the expected tunable spectral behavior of such coupled system under reverse and forward bias, which could be used in future electrically tunable detectors.

Near-Infrared Strong Coupling between Metamaterials and Epsilon-near-Zero Modes in Degenerately Doped Semiconductor Nanolayers

Epsilon-near-zero (ENZ) modes provide a new path for tailoring light–matter interactions at the nanoscale. In this paper, we analyze a strongly coupled system at near-infrared frequencies comprising plasmonic metamaterial resonators and ENZ modes supported by degenerately doped semiconductor nanolayers. In strongly coupled systems that combine optical cavities and intersubband transitions, the polariton splitting (i.e., the ratio of Rabi frequency to bare cavity frequency) scales with the square root of the wavelength, thus favoring the long-wavelength regime. In contrast, we observe that the polariton splitting in ENZ/metamaterial resonator systems increases linearly with the thickness of the nanolayer supporting the ENZ modes. In this work, we employ an indium-tin-oxide nanolayer and observe a large experimental polariton splitting of approximately 30% in the near-infrared. This approach opens up many promising applications, including nonlinear optical components and tunable optical filters based on con...

Theory of epsilon-near-zero modes in ultrathin films

The physics of the epsilon-near-zero (ENZ) mode, which is supported by a nanolayer at the frequency where the dielectric permittivity vanishes, has recently been a subject of debate. In this Rapid Communication, we thoroughly investigate and clarify the physics of this mode, providing its main characteristics and its domain of existence. This understanding will benefit all the applications that rely on ENZ modes in semiconductor nanolayers, including directional perfect absorption, voltage-tunable devices, and ultrafast thermal emission.