All-optical metamaterial modulators : fabrication, simulation and characterization

Artificially structured composite metamaterials consist of sub-wavelength sized structures that exhibit unusual electromagnetic properties not found in nature. Since the first experimental verification in 2000, metamaterials have drawn considerable attention because of their broad range of potential applications. One of the most attractive features of metamaterials is to obtain negative refraction, termed left-handed materials or negative-index metamaterials, over a limited frequency band. Negative-index metamaterials at near infrared wavelength are fabricated with circular, elliptical and rectangular holes penetrating through metal/dielectric/metal films. All three negative-index metamaterial structures exhibit similar figure of merit; however, the transmission is higher for the negative-index metamaterial with rectangular holes as a result of an improved impedance match with the substrate-superstrate (air-glass) combination. In general, the processing procedure to fabricate the fishnet structured negative-index metamaterials is to define the hole-size using a polymetric material, usually by lithographically defining polymer posts, followed by deposition of the constitutive materials and dissolution of the polymer (liftoff processing). This processing (fabrication of posts: multi-layer deposition: liftoff) often gives rise to significant sidewall-angle because materials accumulate on the tops of the posts that define the structure, each successive film deposition has a somewhat larger aperture on the bottom metamaterial film, giving rise to a nonzero sidewall-angle and to optical bianisotropy. Finally, we demonstrate a nanometer-scale, sub-picosecond metamaterial device capable of over terabit/second all-optical communication in the near infrared spectrum. We achieve a 600 fs device response by utilizing a regime of sub-picosecond carrier dynamics in amorphous silicon and ~70% modulation in a path length of only 124 nm by exploiting the strong nonlinearities in metamaterials. We identify a characteristic signature associated with the negative index resonance in the pump-probe signal of a fishnet structure. We achieve much higher switching ratios at the fundamental resonance (~70%) relative to the secondary resonance (~20%) corresponding to the stronger negative index at the fundamental resonance. This device opens the door to other compact, tunable, ultrafast photonic devices and applications

Simulation and analysis of grating-integrated quantum dot infrared detectors for spectral response control and performance enhancement

We propose and analyze a novel detector structure for pixel-level multispectral infrared imaging. More specifically, we investigate the device performance of a grating-integrated quantum dots-in-a-well photodetector under backside illumination. Our design uses 1-dimensional grating patterns fabricated directly on a semiconductor contact layer and, thus, adds a minimal amount of additional effort to conventional detector fabrication flows. We show that we can gain wide-range control of spectral response as well as large overall detection enhancement by adjusting grating parameters. For small grating periods, the spectral responsivity gradually changes with parameters. We explain this spectral tuning using the Fabry-Perot resonance and effective medium theory. For larger grating periods, the responsivity spectra get complicated due to increased diffraction into the active region, but we find that we can obtain large enhancement of the overall detector performance. In our design, the spectral tuning range can be larger than 1 mu m, and, compared to the unpatterned detector, the detection enhancement can be greater than 92% and 148% for parallel and perpendicular polarizations. Our work can pave the way for practical, easy-to-fabricate detectors, which are highly useful for many infrared imaging applications. (C) 2014 AIP Publishing LLCopen1

Poly(sulfur-random-(1,3-diisopropenylbenzene)) Based Mid-Wavelength Infrared Polarizer: Optical Property Experimental and Theoretical Analysis

Development of polymer based mid-wavelength infrared (MWIR) optics has been limited mainly due to high optical loss of organic polymers used in general optical components. In this study, a MWIR polarization grating based on a sulfuric polymer poly(sulfur-random-(1,3-diisopropenylbenzene)) with a low loss in the MWIR range was fabricated using a simple two-step process: imprint and metal deposition. Fourier-transform infrared (FTIR) spectroscopy measurement showed that this polymeric MWIR polarizer selectively transmitted the polarized IR in transverse magnetic (TM) mode over the transverse electric (TE) mode at normal incidence. The measured extinction ratios (  = The ratio of transmissions in TM and TE) were 208, 176, and 212 at the wavelength of 3, 4, and 5 μm, respectively. The computational simulation and analytical model confirmed that the enhanced TM transmission efficiency and followed a Fabry-Pérot (FP) resonance mode within the created sulfuric polymer film. This polymeric MWIR polarizer demonstrated a great potential for broader applications in IR photonics to realize low-cost and durable optical components

A Low-loss Metasurface Antireflection Coating on Dispersive Surface Plasmon Structure

Over the years, there has been increasing interest in the integration of metal hole array (MHA) with optoelectronic devices, as a result of enhanced coupling of incident light into the active layer of devices via surface plasmon polariton (SPP) resonances. However, not all incident light contributes to the SPP resonances due to significant reflection loss at the interface between incident medium and MHA. Conventional thin-film antireflection (AR) coating typically does not work well due to non-existing material satisfying the AR condition with strong dispersion of MHA’s effective impedances. We demonstrate a single-layer metasurface AR coating that completely eliminates the refection and significantly increases the transmission at the SPP resonances. Operating at off-resonance wavelengths, the metasurface exhibits extremely low loss and does not show resonant coupling with the MHA layer. The SPP resonance wavelengths of MHA layer are unaffected whereas the surface wave is significantly increased, thereby paving the way for improved performance of optoelectronic devices. With an improved retrieval method, the metasurface is proved to exhibit a high effective permittivity () and extremely low loss (tan δ ~ 0.005). A classical thin-film AR coating mechanism is identified through analytical derivations and numerical simulations

Anderson light localization in biological nanostructures of native silk

Light in biological media is known as freely diffusing because interference is negligible. Here, we show Anderson light localization in quasi-two-dimensional protein nanostructures produced by silkworms (Bombyx mori). For transmission channels in native silk, the light flux is governed by a few localized modes. Relative spatial fluctuations in transmission quantities are proximal to the Anderson regime. The sizes of passive cavities (smaller than a single fibre) and the statistics of modes (decomposed from excitation at the gain-loss equilibrium) differentiate silk from other diffusive structures sharing microscopic morphological similarity. Because the strong reflectivity from Anderson localization is combined with the high emissivity of the biomolecules in infra-red radiation, silk radiates heat more than it absorbs for passive cooling. This collective evidence explains how a silkworm designs a nanoarchitectured optical window of resonant tunnelling in the physically closed structures, while suppressing most of transmission in the visible spectrum and emitting thermal radiation. © 2018 The Author(s)1341sciescopu

A Low-loss Metasurface Antireflection Coating on Dispersive Surface Plasmon Structure

Over the years, there has been increasing interest in the integration of metal hole array (MHA) with optoelectronic devices, as a result of enhanced coupling of incident light into the active layer of devices via surface plasmon polariton (SPP) resonances. However, not all incident light contributes to the SPP resonances due to significant reflection loss at the interface between incident medium and MHA. Conventional thin-film antireflection (AR) coating typically does not work well due to non-existing material satisfying the AR condition with strong dispersion of MHA’s effective impedances. We demonstrate a single-layer metasurface AR coating that completely eliminates the refection and significantly increases the transmission at the SPP resonances. Operating at off-resonance wavelengths, the metasurface exhibits extremely low loss and does not show resonant coupling with the MHA layer. The SPP resonance wavelengths of MHA layer are unaffected whereas the surface wave is significantly increased, thereby paving the way for improved performance of optoelectronic devices. With an improved retrieval method, the metasurface is proved to exhibit a high effective permittivity () and extremely low loss (tan δ ~ 0.005). A classical thin-film AR coating mechanism is identified through analytical derivations and numerical simulations

Simulational investigation of self-aligned bilayer linear grating enabling highly enhanced responsivity of MWIR InAs/GaSb type-II superlattice (T2SL) photodetector

Abstract Linear gratings polarizers provide remarkable potential to customize the polarization properties and tailor device functionality via dimensional tuning of configurations. Here, we extensively investigate the polarization properties of single- and double-layer linear grating, mainly focusing on self-aligned bilayer linear grating (SABLG), serving as a wire grid polarizer in the mid-wavelength infrared (MWIR) region. Computational analyses revealed the polarization properties of SABLG, highlighting enhancement in TM transmission and reduction in TE transmission compared to single-layer linear gratings (SLG) due to optical cavity effects. As a result, the extinction ratio is enhanced by approximately 2724-fold in wavelength 3–6 μm. Furthermore, integrating the specially designed SABLG with an MWIR InAs/GaSb Type-II Superlattice (T2SL) photodetector yields a significantly enhanced spectral responsivity. The TM-spectral responsivity of SABLG is enhanced by around twofold than the bare device. The simulation methodology and analytical analysis presented herein provide a versatile route for designing optimized polarimetric structures integrated into infrared imaging devices, offering superior capabilities to resolve linear polarization signatures

Plasmonic-Layered InAs/InGaAs Quantum-Dots-in-a-Well Pixel Detector for Spectral-Shaping and Photocurrent Enhancement

The algorithmic spectrometry as an alternative to traditional approaches has the potential to become the next generation of infrared (IR) spectral sensing technology, which is free of physical optical filters, and only a very small number of data are required from the IR detector. A key requirement is that the detector spectral responses must be engineered to create an optimal basis that efficiently synthesizes spectral information. Light manipulation through metal perforated with a two-dimensional square array of subwavelength holes provides remarkable opportunities to harness the detector response in a way that is incorporated into the detector. Instead of previous experimental efforts mainly focusing on the change over the resonance wavelength by tuning the geometrical parameters of the plasmonic layer, we experimentally and numerically demonstrate the capability for the control over the shape of bias-tunable response spectra using a fixed plasmonic structure as well as the detector sensitivity improvement, which is enabled by the anisotropic dielectric constants of the quantum dots-in-a-well (DWELL) absorber and the presence of electric field along the growth direction. Our work will pave the way for the development of an intelligent IR detector, which is capable of direct viewing of spectral information without utilizing any intervening the spectral filters