Extending plasmonic response to the mid-wave infrared with all-epitaxial composites.

Highly doped semiconductor "designer metals" have been shown to serve as high-quality plasmonic materials across much of the long-wavelength portion of the mid-infrared. These plasmonic materials benefit from a technologically mature semiconductor fabrication infrastructure and the potential for monolithic integration with electronic and photonic devices. However, accessing the short-wavelength side of the mid-infrared is a challenge for these designer metals. In this work we study the perspectives for extending the plasmonic response of doped semiconductors to shorter wavelengths by leveraging charge confinement, in addition to doping. We demonstrate, theoretically and experimentally, negative permittivity across the technologically vital mid-wave infrared (3-5 µm) frequency range. The semiconductor composites presented in our work offer an ideal material platform for monolithic integration with a variety of semiconductor optoelectronic devices operating in the mid-wave infrared.

Ghost-induced exact degeneracies.

We show that ghost waves-a special class of nonuniform waves in biaxial dielectric media-can lead to exact frequency degeneracies in guided modes. These degeneracies offer a new way of controlling mode interactions with a broad range of potential applications, from integrated waveguides to nonlinear optics and optical sensing.

Photonic hypercrystals for control of light-matter interactions.

Photonic crystals (PCs) have emerged as one of the most widely used platforms for controlling light-matter interaction in solid-state systems. They rely on Bragg scattering from wavelength-sized periodic modulation in the dielectric environment for manipulating the electromagnetic field. A complementary approach to manipulate light-matter interaction is offered by artificial media known as metamaterials that rely on the average response of deep-subwavelength unit cells. Here we demonstrate a class of artificial photonic media termed "photonic hypercrystals" (PHCs) that combine the large broadband photonic density of states provided by hyperbolic metamaterials with the light-scattering efficiency of PCs. Enhanced radiative rate (20×) and light outcoupling (100×) from PHCs embedded with quantum dots is observed. Such designer photonic media with complete control over the optical properties provide a platform for broadband control of light-matter interaction.

Incoherent perfect absorption in lossy anisotropic materials.

We show that perfect absorption of incoherent light is possible in a semi-infinite slab of anisotropic dielectric even in the presence of loss. The operating frequency of the proposed system is free of any dependence on physical dimensions.

Broadband Enhancement of Spontaneous Emission in Two-Dimensional Semiconductors Using Photonic Hypercrystals.

The low quantum yield observed in two-dimensional semiconductors of transition metal dichalcogenides (TMDs) has motivated the quest for approaches that can enhance the light emission from these systems. Here, we demonstrate broadband enhancement of spontaneous emission and increase in Raman signature from archetype two-dimensional semiconductors: molybdenum disulfide (MoS2) and tungsten disulfide (WS2) by placing the monolayers in the near field of a photonic hypercrystal having hyperbolic dispersion. Hypercrystals are characterized by a large broadband photonic density of states due to hyperbolic dispersion while having enhanced light in/out coupling by a subwavelength photonic crystal lattice. This dual advantage is exploited here to enhance the light emission from the 2D TMDs and can be utilized for developing light emitters and solar cells using two-dimensional semiconductors.

Optical phase retrieval using conical refraction in structured media.

We propose a method of optical phase retrieval based on the conical refraction imaging in structured media. We show that a multilayered dielectric photonic crystal functioning as a conically refractive flat lens can be used to reconstruct phase information of complex optical signals. Our method enables a single simultaneous measurement of multiple images on the same image plane and allows a rapid stable recovery of the optical phase. The planar geometry of the proposed device is compatible with current nano-fabrication techniques and, therefore, can find broad applications in optical signal processing and imaging.

Polarization oscillations of near-field thermal emission.

We consider the polarization of thermal emission in the near field of various materials, including dielectrics and metallic systems with resonant surface modes. We find that, at thermal equilibrium, the degree of polarization exhibits spatial oscillations with a period of approximately half the optical wavelength, independent of material composition. This result contrasts with that of Setala et al. [Phys. Rev. Lett.88, 123902 (2002)PRLTAO0031-900710.1103/PhysRevLett.88.123902], who find monotonic decay of the degree of polarization for systems in local thermal equilibrium.

Optical absorption of hyperbolic metamaterial with stochastic surfaces.

We investigate the absorption properties of planar hyperbolic metamaterials (HMMs) consisting of metal-dielectric multilayers, which support propagating plane waves with anomalously large wavevectors and high photonic-density-of-states over a broad bandwidth. An interface formed by depositing indium-tin-oxide nanoparticles on an HMM surface scatters light into the high-k propagating modes of the metamaterial and reduces reflection. We compare the reflection and absorption from an HMM with the nanoparticle cover layer versus those of a metal film with the same thickness also covered with the nanoparticles. It is predicted that the super absorption properties of HMM show up when exceedingly large amounts of high-k modes are excited by strong plasmonic resonances. In the case that the coupling interface is formed by non-resonance scatterers, there is almost the same enhancement in the absorption of stochastically perturbed HMM compared to that of metal.

Frequency comb formation and transition to chaos in microresonators with near-zero dispersion.

We investigate the frequency comb formation in microresonators with near-zero dispersion, study the route from integrability to chaos in the corresponding nonlinear system, and demonstrate the key role of nonlinear dynamics of such a system for frequency comb generation and stability.

Planar hyperbolic polaritons in 2D van der Waals materials.

Anisotropic planar polaritons - hybrid electromagnetic modes mediated by phonons, plasmons, or excitons - in biaxial two-dimensional (2D) van der Waals crystals have attracted significant attention due to their fundamental physics and potential nanophotonic applications. In this Perspective, we review the properties of planar hyperbolic polaritons and the variety of methods that can be used to experimentally tune them. We argue that such natural, planar hyperbolic media should be fairly common in biaxial and uniaxial 2D and 1D van der Waals crystals, and identify the untapped opportunities they could enable for functional (i.e. ferromagnetic, ferroelectric, and piezoelectric) polaritons. Lastly, we provide our perspectives on the technological applications of such planar hyperbolic polaritons.

Zeroth-order transmission resonance in hyperbolic metamaterials.

We present a new approach to subwavelength optical confinement, based on hyperbolic media in planar Fabry-Perot geometry. Unlike higher-order resonance modes in indefinite metamaterial cavities, the predicted resonance corresponds to 0th-order mode and can be observed in planar systems. Our approach combines subwavelength light confinement with strong radiative coupling, enabling a practical planar design of nanolasers and subwavelength waveguides.

Roadmap on Label-Free Super-Resolution Imaging.

Label-free super-resolution (LFSR) imaging relies on light-scattering processes in nanoscale objects without a need for fluorescent (FL) staining required in super-resolved FL microscopy. The objectives of this Roadmap are to present a comprehensive vision of the developments, the state-of-the-art in this field, and to discuss the resolution boundaries and hurdles which need to be overcome to break the classical diffraction limit of the LFSR imaging. The scope of this Roadmap spans from the advanced interference detection techniques, where the diffraction-limited lateral resolution is combined with unsurpassed axial and temporal resolution, to techniques with true lateral super-resolution capability which are based on understanding resolution as an information science problem, on using novel structured illumination, near-field scanning, and nonlinear optics approaches, and on designing superlenses based on nanoplasmonics, metamaterials, transformation optics, and microsphere-assisted approaches. To this end, this Roadmap brings under the same umbrella researchers from the physics and biomedical optics communities in which such studies have often been developing separately. The ultimate intent of this paper is to create a vision for the current and future developments of LFSR imaging based on its physical mechanisms and to create a great opening for the series of articles in this field.

Super-resolution imaging via spatiotemporal frequency shifting and coherent detection.

Diffraction limit is manifested in the loss of high spatial frequency information that results from decay of evanescent waves. As a result, conventional far-field optics yields no information about an object's subwavelength features. Here we propose a novel approach to recovering evanescent waves in the far field, thereby enabling subwavelength-resolved imaging and spatial spectroscopy. Our approach relies on shifting the frequency and the wave vector of near-field components via scattering on acoustic phonons. This process effectively removes the spatial frequency cut-off for unambiguous far field detection. This technique can be adapted for digital holography, making it possible to perform phase-sensitive subwavelength imaging. We discuss the implementation of such a system in the mid-IR and THz bands, with possible extension to other spectral regions.

Cylinder light concentrator and absorber: theoretical description.

We present a detailed theoretical description of a broadband omnidirectional light concentrator and absorber with cylinder geometry. The proposed optical "trap" captures nearly all the incident light within its geometric cross-section, leading to a broad range of possible applications--from solar energy harvesting to thermal light emitters and optoelectronic components. We have demonstrated that an approximate lamellar black-hole with a moderate number of homogeneous layers, while giving the desired ray-optical performance, can provide absorption efficiencies comparable to those of ideal devices with a smooth gradient in index.

Metric signature transitions in optical metamaterials.

We demonstrate that the extraordinary waves in indefinite metamaterials experience an (--++) effective metric signature. During a metric signature change transition in such a metamaterial, a Minkowski space-time is created together with a large number of particles populating the space-time. Such metamaterial models provide a tabletop realization of metric signature change events suggested to occur in Bose-Einstein condensates and quantum gravity theories.

Chaos-assisted directional light emission from microcavity lasers.

We study the effect of dynamical tunneling on emission from ray-chaotic microcavities by introducing a suitably designed deformed disk cavity. We focus on its high quality factor modes strongly localized along a stable periodic ray orbit confined by total internal reflection. It is shown that dominant emission originates from the tunneling from the periodic ray orbit to chaotic ones; the latter eventually escape from the cavity refractively, resulting in directional emission that is unexpected from the geometry of the periodic orbit, but fully explained by unstable manifolds of chaotic ray dynamics. Experimentally performing selective excitation of those modes, we succeeded in observing the directional emission in good agreement with theoretical prediction. This provides decisive experimental evidence of dynamical tunneling in a ray-chaotic microcavity.

Semiclassical description of non magnetic cloaking.

We present a semiclassical description of non-magnetic cloaking. The semiclassical result is confirmed by numerical simulations of a gaussian beam scattering from the cloak. Further analysis reveals that certain beams penetrate the non-magnetic cloak thereby degrading the performance.

Experimental Demonstration of Hyperbolic Metamaterial Assisted Illumination Nanoscopy.

An optical metamaterial is capable of manipulating light in nanometer scale that goes beyond what is possible with conventional materials. Taking advantage of this special property, metamaterial-assisted illumination nanoscopy (MAIN) possesses tremendous potential to extend the resolution far beyond conventional structured illumination microscopy. Among the available MAIN designs, hyperstructured illumination that utilizes strong dispersion of a hyperbolic metamaterial (HMM) is one of the most promising and practical approaches, but it is only theoretically studied. In this paper, we experimentally demonstrate the concept of hyperstructured illumination. A ∼80 nm resolution has been achieved in a well-known Ag/SiO2 multilayer HMM system by using a low numerical aperture objective (NA = 0.5), representing a 6-fold resolution enhancement of the diffraction limit. The resolution can be significantly improved by further material optimization.

Analysis of stealth communications over a public fiber-optical network.

We evaluate the security performance of the recently proposed "stealth" approach to covert communications over a public fiber-optical network. We present quantitative security analysis to assess the vulnerability of such systems against different attacks executed by an eavesdropper. We demonstrate the security advantage of the system by examining the BER/SNR performance as a function of the fidelity of the decoder used by an eavesdropper. Effective key length is constructed as a security metric to gauge the level of confidentiality implicit in the secure transmission.