Dynamically tunable reflecting Near infrared band-pass filter based on hybrid graphene-nanometallic structure is demonstrated by numerical simulation. The proposed filter is constructed by unit cells with graphene monolayer embedded into the nanometallic grating structure. The gradual transition of graphene monolayer from very thin metal to dielectric play the key role to tune the reflection spectrum of the structure. Its frequency spectrum is also analyzed, which clearly shows a blueshift of passband with increasing graphene Fermi energy. The filter parameters are investigated by varying graphene Fermi energy through external voltage gates. The modulation depth, center frequency, bandwidth and quality factor of the filter could be tuned. We achieved stable modulation depth as high as 0.735, and quality factor as high as 3.4. The center frequency can be tuned in a broad range from 210 to 230 THz and bandwidth tuning from 60 to 95 THz. The effect of nanogap size and environment refractive index is also numerically investigated. These results are very promising for the future use and integration of the proposed filters as a key element of optical communication system and infrared sensing.
New capabilities in mid- to long-wave infrared sensing and telecommunications require ultracompact waveguides that support long propagation lengths. Hybrid waveguides supporting the coupling between a dielectric strip-waveguide mode (long propagation) and a surface polariton mode (tightly confined mode) are promising candidates. Here, an infrared (λ0 = 10.6 μm) hybrid waveguide design is presented that achieves enhanced mode confinement but with minimal impact on propagation distances. Modal area confinement is enhanced by the integration of a thin layer of epsilon-near-zero material, aluminum nitride near the longitudinal optical phonon resonance, which supports supercoupling, a term that describes the effect of field enhancement caused by squeezing energy into arbitrary-sized regions. While SPhPs are inherently transverse magnetic modes, a transverse electric (TE) mode is sought to best exploit the ENZ supercoupling phenomenon. By adding a thin high index layer (GaAs) over the 4H-SiC substrate, a mimic TE mode is achieved. The epsilon-near-zero supercoupling-enhanced mimic TE hybrid SPhP waveguide presented exhibits modal confinement improvement by as much as a factor of 4 while maintaining more than 95% of the original propagation length.
Metamaterials, or synthetic materials that have engineered material parameters, have been utilized to demonstrate extraordinary usefulness in the control of electromagnetic waves. In this paper, a novel metalens design in the near infrared band from 1.5μm to 3μm is presented. It consists of a Fresnel zone plate (FZP)-type metasurface which is called a plasmonic waveguide coupler (PWC), situated on a slab of type I hyperbolic metamaterial (HMM) that lies on a silicon substrate which has a silver nanodipole embedded within it. The PWC is made out of rings of Indium Tin Oxide (ITO) and the type I HMM is constructed using a periodic stack of ITO and silicon layers that, through effective medium theory (EMT), act as a slab of type I HMM. Together the PWC and the HMM slab serve to focus incoming radiation onto a focal point marked by the location of the silver (Ag) nanodipole. The Ag nanodipole allows for high subwavelength confinement of optical modes because the in-focal point component of the electromagnetic field vector couples to the plasmonic resonance of the dipole. The maximum achieved resolution is up to 0.01667 λ at an operating wavelength of 1.53 μm and electric field intensity enhancement of 106 is achieved. The enhancement in field is related to the principal localized surface plasmon resonances (LSPRs) around the resonator’s edges on the interface between the Ag nanodipole and the substrate.
In recent years, the field of nanophotonics has been used to miniaturize optical interconnects with long propagation lengths. In the ultraviolet to near-infrared regime, noble metals support light coupling to free electron oscillations, or plasmons, resulting in propagating surface waves called surface plasmon polaritons (SPPs). From mid to long infrared light applications, SPP-like effects in polar dielectrics with phonons can be achieved. Hexagonal boron nitride (hBN) is a two-dimensional van der Waals material in which a slab of hBN can support hyperbolic phonon polaritons (HPhPs). Hybrid waveguides result from the coupling between polariton modes and a high-index dielectric waveguide. Coupled-mode theory is used to describe the resulting hybrid modes and predicts both upper and lower hybrid modes from mode splitting or repulsion. However, only upper hybrid branches have been studied extensively in hybrid polariton waveguides. The lower mode is shown to exist and characterized in terms of mode area and propagation length. The lower hybrid mode formed by the coupling between HPhPs in hBN to a high-index waveguide is compared with the upper hybrid mode. It will be shown via a figure of merit that the lower hybrid mode is advantageous compared to the upper hybrid mode when the cylinder diameters correspond to the maximum coupling strength.
The field of nanophotonics consists of interesting phenomena such as polaritons; quasi-particles that arise from lightmatter coupling. Some of the well-studied kinds of polaritons include surface plasmon polaritons (SPPs) and surface phonon polaritons (SPhPs). Surface enhanced infrared absorption (SEIRA) technique is a popular application of SPPs where the limitation of low molecular absorption cross section in IR-spectroscopy can be overcome by the introduction of SPPs in this technique. Especially in sensing applications, resonant SEIRA uses resonant metal nanoantennas in order to increase the EM near-fields on the nanometer scale, increasing light-matter interaction and thus amplifying the measured signature of very small particles. Mode coupling between metallic resonant structures and phonon polaritons supported by polar dielectric materials (e.g., h-BN, AlN, and SiC) in the IR regime with resulting field enhancement and transparency windows exhibiting Fano-like line shape will be presented. Finite element analysis is implemented to characterize the individual modes, validated against theory, in order to identify and fully characterize the resulting coupled modes in the integrated structure. Coupled-mode theory analysis reveals the anti-crossing modal coupling behavior via extinction cross-section.
KEYWORDS: Antennas, Signal attenuation, Wave propagation, Near field, Infrared radiation, Long wavelength infrared, Gaussian beams, Gold, Reflection, Near field optics
Low-loss planar transmission lines are required for integrated optical or plasmonic nanocircuits. Full characterization of these lines is necessary for designing nanocircuits. This paper shows a method to calculate the attenuation and propagation constants of a patch-antenna-coupled microstrip transmission line (MTL) at 28.3THz that is suitable for measurement implementation via near-field microscopy techniques. After illumination with a Gaussian beam, a standing wave is formed by the electric near field along the MTL observed at the metal-air interface. By fitting an analytical standing wave expression to the near-field standing wave, the attenuation and propagation constants are determined. With the MTL characterized, a similar technique can be applied to determine the input impedance of an unknown load fed by the MTL. The quantification of antenna impedance and transmission line parameters provide requisite information for improving impedance matching and collection efficiency. Ansys High Frequency Structure Simulator (HFSS) is implemented to predict the computational results.
In the past few years leaky-wave antennas have been a very active area of antenna research due to their beam-scanning abilities. With the surge in graphene and 2D material research applications, there have been efforts to design graphenebased antennas in the terahertz and infrared spectrum due to graphene’s ability to strongly localize electromagnetic waves which leads to the ability to miniaturize and reconfigure antennas through electrical bias, magnetic bias, acoustic bias or chemical doping. It has also been seen that uniaxial metasurfaces such as graphene strips or phosphorene monolayers demonstrate extreme topological transitions from closed elliptical, quasi-isotropic to open hyperbolic canalization regimes. Here we design a planar long-wave infrared leaky-wave antenna based on periodic graphene strips. The leaky-wave antenna consisting of the graphene strips shall radiate at different angles at long-wave infrared wavelengths but more importantly radiate at 28.3THz at different angles for different values of biasing of the monolayer controlled by the chemical potential of the monolayers. We also explore the anisotropy of ultrathin hyperbolic reconfigurable metasurfaces represented by graphene strips in the context of a leaky-wave antenna. The different canalization regimes of the graphene strip metasurface are explored for applications in the field of flatland optics and planar antenna arrays.
In recent years, plasmonic resonant antennas have seen widespread consideration in many detection and chemistry applications due to their potential for enhancing and confining the emission and polarization of electromagnetic fields. Examples include optical couplers to ultra-compact photodetectors, high-resolution optical microscopy, enablers of single molecule Raman signal detection and heating elements that facilitate nanostructure growth. An asymmetric cross-bowtie antenna is investigated for providing a broad circular polarized frequency response in the long wave infrared (LWIR). The asymmetric cross-bowtie antenna is constructed with two perpendicular bowtie antennas with differing arm lengths. The asymmetric cross-bowtie antenna is numerically analyzed using a finite element method (FEM) solver; Ansys High Frequency Structural Simulator (HFSS). The two perpendicular bowtie antennas, under illumination, provide a wide-band localized circularly-polarized field within a shared antenna feed-gap. At the center frequency of 28.3 THz (10.6μm), a circularly-polarized state over 30% bandwidth is achieved. The antenna is then loaded with a metal-oxide-metal diode in order to design a circularly polarized antenna-coupled detector.
Numerical computation using HFSS finite element analysis was conducted in order to determine the dispersion relation (complex index) of the surface plasmon polariton (SPP) mode. SPP result from the interaction or coupling between electromagnetic fields in the form of light and delocalised electrons on a metal interface. SPPs has the effect of confining electromagnetic radiation on the order that is smaller than the wavelength. In this work, the correspondence by H.P Hsu (IEEE Trans. Microw. Theory Techn., 11(4), (1963).) was used in the study of SPP modes comparing both analytical calculations and numerical calculation from ANSYS HFSS to ascertain the veracity of the correspondence for SPP surface waves, and calculating the attenuation coefficient using quality factor, Q, obtained from HFSS eigenmode calculations. Silicon dioxide and silver with the use of measured complex permittivity for silver is used to conduct this study. Numerically-obtained results for propagation length and SPP effective index are compared to analytical calculations from the well-known SPP dispersion relationship.
Surface polaritons have been shown to provide subwavelength confinement. Surface phonon polaritons (SPhPs), electromagnetic waves coupled to lattice vibrations in a polar dielectric, allow for highly confined propagating modes beyond the limit of diffraction within the mid to long infrared (IR). In recent years, it has been shown that hybrid plasmonic and phononic waveguides can support long-range hybrid modes that result from the coupling between SPhPs and a high index dielectric tracer. This work investigates the use of a hybrid phononic waveguide as a building block of a ring resonator that operates in the long wave infrared (LWIR) spectrum. Critical coupling condition and trade-off between ring diameter and output power are characterized. LWIR ring resonators hold promise for numerous applications including modulation, biosensing, photodetectors, and chemical sensing.
Surface phonon polaritons, SPhPs, result from the coupling or interaction of light with a phonon resonance. There has been extensive research into utilizing surface plasmon polaritons, SPPs, for subwavelength confinement of propagating waveguide modes for photonic integrated circuits. This work investigates the use of a multilayer system or insulatormetal-insulator (IMI) heterostructure as a SPhP-enhanced infrared waveguide where the metal response is due to phonons in a polar dielectric’s Reststrahlen band. In addition, an IMI heterostructure supports types of modes: an even mode and odd mode that have their own unique trade-offs. For the odd mode as the metal film thickness decreases the confinement of the SPhPs decreases, and thus resulting in an increase in the SPhPs propagation length. Conversely, the even mode shows the opposite behavior with decreasing metal film where the confinement increases as propagation length decreases. This endeavor investigates the trade-off between the even and odd IMI modes, and the characterization of propagation length and model confinement, as applied to a hybrid phononic waveguide.
Surface phonon polaritons (SPhPs), similar to it cousin phenomenon surface plasmon polaitons (SPPs), are quasi-neutral particles resulting from light-matter coupling that can provide high modal confinement and long propagation in the mid to long infrared (IR). Mach-Zehnder interferometer (MZI) is a combination of two connected optical directional couplers (ODC). With the use of SPhPs, sub-wavelength feature sizes and modal areas can be achieved and to this end a hybrid SPhP waveguide, where propagation length and modal area can be trade-off, will be employed in the design of an ODC and MZI. This endeavor analyzes and characteristics both an ODC and MZI using commercially available numerical simulation software employing finite element method (FEM). The ODC and MZI are design using a novel SPhP hybrid waveguide design where a 4H-SiC substrate provides the polariton mode. The output ports power and relative phase difference between ports are investigated. SPhP enhanced ODC and MZI has applications including, but not limited to, next-generation ultra-compact photonic integrated circuits and waveguide based IR sensing.
KEYWORDS: Antennas, FSS based metamaterials, Wave propagation, Thermography, Infrared radiation, Radio propagation, High dynamic range imaging, Absorption, Reflectometry, Polarization
We design, fabricate, and characterize a frequency-selective surface (FSS) with directional thermal emission and absorption for long-wave infrared wavelengths. The FSS consists of an array of patch antennas connected by microstrips, the ensemble of which supports leaky-wave-type modes with forward and backward propagating branches. The branches are designed to intersect at 9.8 μm and have a broadside beam with 20-deg full width at half maximum at this wavelength. The absorption along these branches is near unity. Measurement of the hemispherical directional reflectometer shows good agreement with simulation. The ability to control the spectral and directional emittance/absorptance profiles of surfaces has significant applications for radiation heat transfer and sensing.
Planar leaky-wave antennas (LWA) that are capable of full-space scanning have long since been the pursuit for applications
including, but not limited to, integration onto vehicles and into cameras for wide-angle of view beam-steering. Such a
leaky-wave surface (LWS) was designed for long-wave infrared frequencies with frequency scanning capability. The LWS
is based on a microstrip patch array design of a leaky-wave impedance surface and is made up of gold microstrip patches
on a grounded zinc sulphide substrate. A 1D composite right/left-handed (CRLH) metamaterial made by periodically
stacking a unit cell of the LWS in the longitudinal direction to form a LWA was designed. This paper deals with loading
the LWA with a nickel bolometer to collect leaky-wave signals. The LWA radiates a backward leaking wave at 30 degrees
at 28.3THz and scans through broadside for frequencies 20THz through 40THz. The paper deals with effectively placing
the bolometer in order for the collected signal to exhibit the designed frequency regime. An effective way to maximize the
power coupling into the load from the antenna is also explored. The benefit of such a metamaterial/holographic antennacoupled
detector is its ability to provide appreciable capture cross-sections while delivering smart signals to subwavelength
sized detectors. Due to their high-gain, low-profile, fast response time of the detector and ease of fabrication,
this IR LWA-coupled bolometer harbors great potential in the areas of high resolution, uncooled, infrared imaging.
Coupled-resonances can be used in applications that include, but are not limited to, surface-enhanced infrared
spectroscopy (SEIRS), surface-enhanced Raman spectroscopy (SERS), biosensing, and index sensing. Fano resonance in
analogue plasmonic systems has been described as the coupling of a bright (superradiant) mode and a dark (subradiant)
mode via the near field.Dark and bright mode interactionsareinvestigated with the use of a Fano resonant metamaterial
(FRMM) where the metamaterial is a dual nano-slot metasurface on a silicon cavity. The FRMM is numerically
simulated using Ansys High Frequency Structure Simulator (HFSS). The FRMM is coupled to the carbon double bond
in polymethyl methacrylate (PMMA) to demonstrate mode splitting and signal enhancement. Then the dual nano-slot is
compared to the complementary dual nano-rod configuration.
Surface plasmon polariton (SPP) waveguides harbor many potential applications at visible and near-infrared (NIR)
wavelengths. However, dispersive properties of the metal in the waveguide yields weakly coupled and lossy plasmonic
modes in the mid and long wave infrared range. This is one of the major reasons for the rise in popularity of surface phonon
polariton (SPhP) waveguides in recent research and micro-fabrication pursuit. Silicon carbide (SiC) is a good candidate in
SPhP waveguides since it has negative dielectric permittivity in the long-wave infrared (LWIR) spectral region, indicative
that coupling to surface phonon polaritons is realizable. Introducing surface phonon polaritons for waveguiding provides
good modal confinement and enhanced propagation length. A hybrid waveguide structure at long-wave infrared (LWIR)
is demonstrated in which an eigenmode solver approach in Ansys HFSS was applied. The effect of a three layer
configuration i.e., silicon wire on a benzocyclobutene (BCB) dielectric slab on SiC, and the effects of varying their
dimensions on the modal field distribution and on the propagation length, is presented.
The goal in the design of an efficient and low-noise antenna coupled receiver is to achieve a maximal capture cross section for the incident electromagnetic radiation compared to the dimensions of the sub-wavelength sized sensor loading the antenna. Collection efficiency captures this concept of power output/input and is made up of several subefficiencies. In the ideal case all of the available, incident power is collected and transferred to the load. However, many of the fundamental limits of antennas are based on theory describing the transmitting mode, whereas certain questions remain open for receiving antennas. Textbook antenna theory predicts that only 50% of available incident power can be absorbed by an antenna, yet under specific conditions this limitation can be surpassed. Two considerations are presented; (1) fundamental limits on antenna absorption, and (2) practical participation of dissipative media in achieving impedance matching between antenna and load, and the associated performance compromise. Specifically we seek to determine whether antenna-coupled detectors can approach unity absorption efficiency under matched conditions. Further, we identify practical conditions that must be met in order to overcome fundamental limitations that inhibit total absorption. Then antenna loss is split into radiative and dissipative terms in order to identify trade-offs between impedance matching and radiation efficiency.
A circular polarized (CP) infrared (IR) leaky wave surface design is presented. The metasurface consists of an array of
rectangular patches connected by microstrip and operating over the long-wave infrared (LWIR) spectrum with
directional wave emission and absorption. The surface is composed of periodically aligned arrays of sub-wavelength
metal patches separated from a ground plane by a dielectric slab. The design combines the features of the conventional
patch and leaky wave antenna leading to a metasurface that preferentially emits CP IR radiation by use of axial
asymmetrical unit cells. This is a deviation from reported structures that mainly employ a phase shifter to combine
linearly polarized waves in order to attain circular polarization. The performance of this leaky wave surface is verified
through full-wave simulation using the ANSYS HFSS finite element analysis tool. The leaky wave phenomenon is
demonstrated by the frequency and angular dependence of the absorption while circular polarization is characterized via
stokes parameters. The main beam of this surface can be steered continuously by varying the frequency while
maintaining circular polarization within the main beam direction. A CP leaky wave at 10.6 μm with a scanning angle of
30° is demonstrated. Metasurfaces exhibiting spectral and polarization selectivity in absorption/emission hold the
potential for impact in IR applications including detection, imaging, thermal management, energy harvesting and
tagging.
A slot metasurface (metascreen) designed to have resonance that couples with the 1733 cm-1 absorption peak of the C=O
molecular bond of PMMA (polymethyl methacrylate) is presented. The metasurface is made of a gold layer perforated
with periodically-placed slots and stood off above a reflective ground plane with silicon substrate. The metasurface is
modeled using ANSYS HFSS and including measured optical properties for gold, silicon and PMMA in the infrared
spectrum. PMMA forms a thin overcoat and exhibits a strong absorption resonance at wavenumber 1733 cm-1.
Coupling between the metasurface and PMMA is observed via normal mode splitting. Mode splitting has been analyzed
from classical coupled mass spring oscillators to exciton-photons coupling in microcavities. The coupled systems can be
described with a Hamiltonian matrix and solved for the eigenfrequencies. Parametric analysis of coupled response as a
function of the design geometry is provided. Coupling energy, reflectance spectrum, and dispersion plots showing the
anticrossing behavior of hybrid modes are presented as characterization of resonance coupling and normal mode
splitting. Slot metasurface results are compared to the complementary structure (nanorod metasurface) in order to
explore the duality of the complentary metasurfaces and their coupled responses. Coupled resonances have application in
biosensors for molecule detection, surface-enhanced infrared absorption (SEIRA), and infrared imaging.
KEYWORDS: Near field scanning optical microscopy, Antennas, Sensors, Near field, Signal detection, Scattering, Atomic force microscopy, Optical microscopy, Data modeling, Numerical modeling
Apertureless scattering-type Scanning Near-field Optical Microscopy (s-SNOM) has been used to study the electromagnetic response of infrared antennas below the diffraction limit. The ability to simultaneously resolve the phase and amplitude of the evanescent field relies on the implementation of several experimentally established background suppression techniques. We model the interaction of the probe with a patch antenna using the Finite Element Method (FEM). Green's theorem is used to predict the far-field, cross-polarized scattering and to construct the homodyne amplified signal. This approach allows study of important experimental phenomena, specifically the effects of the reference strength, demodulation harmonic, and detector location.
KEYWORDS: Antennas, FSS based metamaterials, Wave propagation, Infrared radiation, High dynamic range imaging, Gold, Long wavelength infrared, Radio propagation, Reflectometry, Electromagnetism
We design, fabricate, and characterize a Frequency Selective Surface (FSS) with directional thermal emission and
absorption for long-wave infrared wavelengths (LWIR). The FSS consists of an array of patch antennas connected by
microstrips, the ensemble of which supports leaky-wave type modes with forward and backward propagating branches.
The branches are designed to intersect at 9.8 μm, and have a broadside beam with 20° FWHM at this wavelength. The absorption along these branches is near-unity. Measurement of the hemispherical directional reflectometer (HDR)
shows good agreement with simulation. The ability to control the spectral and directional emittance/absortpance profiles
of surfaces has significant applications for radiation heat transfer and sensing.
Metal-Oxide-Metal diodes offer the possibility of directly rectifying infrared radiation. To be effective for sensing or energy harvesting they must be coupled to an antenna which produces intense fields at the diode. While antennas significantly increase the effective capture area of the MOM diode, it is still limited and maximizing the captured energy is still a challenging goal. In this work we investigate integrating MOM diodes with a slot antenna Frequency Selective Surface (FSS). This maximizes the electromagnetic capture area while minimizing the transmission line length which helps reduce losses because metal losses are much lower at DC than at infrared frequencies. Our design takes advantage of a single self-aligned patterning step using shadow evaporation. The structure is optimized at 10.6 µm to have less than 2% reflection (polarization sensitive) and simulations predict that 70% of the incident energy is dissipated into the oxide layer. Initial experimental results fabricated with e-beam lithography are presented and the diode coupled FSS is shown to produce a polarization sensitive unbiased DC short circuit current. This work is promising for both infrared sensing and imaging as well as direct conversion of thermal energy.
Millimeter-wave (mmW)/sub-mmW/THz region of the electro-magnetic spectrum enables imaging thru clothing and other obscurants such as fog, clouds, smoke, sand, and dust. Therefore considerable interest exists in developing low cost millimeter-wave imaging (MMWI) systems. Previous MMWI systems have evolved from crude mechanically scanned, single element receiver systems into very complex multiple receiver camera systems. Initial systems required many expensive mmW integrated-circuit low-noise amplifiers. In order to reduce the cost and complexity of the existing systems, attempts have been made to develop new mmW imaging sensors employing direct detection arrays. In this paper, we report on Raytheon’s recent development of a unique focal plane array technology, which operates broadly from the mmW through the sub-mmW/THz region. Raytheon’s innovative nano-antenna based detector enables low cost production of 2D staring mmW focal plane arrays (mmW FPA), which not only have equivalent sensitivity and performance to existing MMWI systems, but require no mechanical scanning.
As microbolometer pixel dimensions for infrared imagers continue to decrease, the need for full-wave analysis
in the design process is enhanced. Using reflectance as the validation point, an electromagnetic model of a dual-layer
microbolometer pixel design was created for a 25 μm pixel design, and an in-depth study of the design was performed.
With this model validated, further explorations were completed with a reduced size pixel. While simulating multiple
variations of specific parameters, such as bridge thickness, upper and lower cavity heights, and different absorber
configurations, a new evaluation metric of dissipated power in the structure was studied. This metric, provided by finite
element analysis, provides great insight into absorption properties within the microbolometer structure, properties that
cannot be directly measured but that are critical to the functionality of the pixel design. In this paper parametric analysis
of microbolometer pixel designs are presented via both reflectance and dissipated power full-wave analysis.
Nanometer high performance InP Schottky detectors are scaled to IR wavelengths. The increased cutoff frequency of the Schottky detector was accomplished by both reducing its capacitance to attofarad range and also by reducing the contact resistance. The Schottky detectors were fabricated on InGaAs/InP substrates with the doping level as high as 1 x 1019 cm-2. The typical Schottky detector anode size was 0.1 x 1 μm2. Planar broadband antennas were designed for LWIR wavelengths to couple the radiation into the nanometer size detector. Several different IR antenna designs were evaluated, including complimentary square spirals, bow ties and crossed dipoles. A 6 × 7 array of antenna-coupled Schottky detectors was characterized at DC, yielding a 20 KΩ zero-bias resistance and a responsivity of 6 A/W for the entire array. The arrays were characterized at 2.5 THz, as well as in the IR (3-5μm and 10.6 μm). The current results for polarization sensitivity confirm that an antenna-coupled mechanism is responsible for the measured responsivity with the highest value measured at the THz range.
We demonstrate the first long wave infrared (LWIR) transmission line design and characterization. Two of the widely used transmission-lines: coplanar striplines (CPS) and microstrip (MS) lines are characterized at IR frequency (28.3THz), in terms of transmission line parameters: characteristic impedance (Zo), attenuation constant (α) and effective index of refraction (neff), through modeling, fabrication and measurement. These transmission-line parameters cannot be directly measured, what can be measured is the antenna response. So we compute, measure and compare the response of the dipole antenna connected to these transmission lines as a function of transmission-line length. The response depends on the transformation of antenna impedance along the transmission-line length according to the transmission-line parameters (Zo, α and neff ) of the line. Comparison of measured and computed response validates extracted transmission-line parameters. This paper demonstrates excellent agreement between measured and computed response for both types of transmission-lines under study.
Infrared antennas are a novel type of detectors that couples electromagnetic radiation into metallic structures and feed it to a rectifying element. As their radio and millimeter counterparts, they can be characterized by parameters explaining their response in a variety of situations. The size of infrared antennas scales with the detected wavelength. Then, specifically designed experimental set-ups
need to be prepared for their characterization. The measurement of the spatial responsivity map of infrared antennas is one of the parameters of interest, but other parameters can be defined to
describe, for example, their directional response, or polarization response. One of the inputs to measure the spatial responsivity map is the spatial distribution of the beam irradiance illuminating
the antenna-coupled detector. The measured quantity is actually a map of the response of the detector when it moves under the beam illumination. This measurement is given as the convolution of the actual responsivity map and the beam irradiance distrbution. The uncertainties, errors, and artifacts incorporated along the measurement procedure are analyzed by using the Principal Component Analysis (PCA). By means of this method is possible to classify different sources of uncertainty. PCA is applied as a metrology tool to characterize the accuracy and repeatability of the experimental set-up. Various examples are given to describe the application of the PCA to the characterization of the deconvolution procedure, and to define the responsivity and the signal-to-noise ratio of the measured results.
Missile Defense Agency/Advanced Systems, in partnership with both EUTECUS/University of Notre Dame (UND) and ITN Energy Systems/University of Central Florida (UCF) has embarked on developing a multispectral imaging IR sensor. This technology, when matured, could revolutionize IR sensor technology by reducing the need for cooling, eliminating lattice matching and avoiding epitaxial fabrication processes. This paper describes the approaches employed by both EUTECUS/UND and ITN/UCF teams to integrate nano-antenna technology with the existing cellular neural network (CNN) processor to produce multispectral IR sensors. This effort is a leap into the performance realm where biological systems operate.
We present the first mm-wave characterization of Semimetal Semiconductor Schottky (S3) diodes for direct detector applications from 94 GHz to 30 THz. The S3 devices use molecular-beam epitaxy growth of binary compounds that are closely lattice-matched and crystallographically perfect across the heterointerface to reduce 1/f and burst noise while maintaining ultra-high-frequency performance. The S3 diodes are fabricated from an InAlGaAs/InP based material system with both the Schottky layer and contact layer having n and n+ doping levels. The semimetal Schottky contact is ErAs which is grown in-situ during the MBE growth. By varying the InAlAs percentage content in the epitaxial layer structure, the diode dc I-V characteristics and its zero bias responsivity are optimized. Diode s-parameter data from dc-100 GHz is used to determine the diode responsivity as a function of frequency and diode capacitance and resistance. These measurements then allow the device intrinsic and extrinsic equivalent-circuit elements to be optimized for direct detection from 94 GHz to ~30 THz.
Fresnel Zone Plate Lenses (FZPLs) have been successfully coupled to infrared (IR) antennas producing a responsivity enhancement of about two orders of magnitude. However, their lateral extension may compromise their applicability in focal-plane-arrays (FPA) IR imagers, where the dimensions of the pixel are constrained by the FPA spacing. When designing optimum-gain FZPLs for FPAs, we are lead to the requirement of FZPLs operating at very low F/#s (marginal rays propagating at a large angle in image space). In this case, Finite-Difference Time-Domain techniques (FDTD) are used to refine the physical-optics modelling results, producing a result closer to the actual case encountered in a high-fill-factor FPA. In this contribution, we analyze the FZPL designs by using FDTD techniques. The main result of the FDTD computation is the gain factor defined as the ratio of the response of the IR antennas coupled with the FZPL, compared to the same antennas without the FZPL.
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