Glenn D. Boreman

Optical antennas for nano-photonic applications

Antenna-coupled optical detectors, also named optical antennas, are being developed and proposed as alternative detection devices for the millimetre, infrared, and visible spectra. Optical and infrared antennas represent a class of optical components that couple electromagnetic radiation in the visible and infrared wavelengths in the same way as radioelectric antennas do at the corresponding wavelengths. The size of optical antennas is in the range of the detected wavelength and they involve fabrication techniques with nanoscale spatial resolution. Optical antennas have already proved and potential advantages in the detection of light showing polarization dependence, tuneability, and rapid time response. They also can be considered as point detectors and directionally sensitive elements. So far, these detectors have been thoroughly tested in the mid-infrared with some positive results in the visible. The measurement and characterization of optical antennas requires the use of an experimental set-up with nanometric resolution. On the other hand, a computation simulation of the interaction between the material structures and the incoming electromagnetic radiation is needed to explore alternative designs of practical devices.

Near-field imaging of optical antenna modes in the mid-infrared

Optical antennas can enhance the coupling between free-space propagating light and the localized excitation of nanoscopic light emitters or receivers, thus forming the basis of many nanophotonic applications. Their functionality relies on an understanding of the relationship between the geometric parameters and the resulting near-field antenna modes. Using scattering-type scanning near-field optical microscopy (s-SNOM) with interferometric homodyne detection, we investigate the resonances of linear Au wire antennas designed for the mid-IR by probing specific vector near-field components. A simple effective wavelength scaling is observed for single wires with lambda(eff) = lambda /(2.0+/- 0.2), specific to the geometric and material parameters used. The disruption of the coherent current oscillation by introducing a gap gives rise to an effective multipolar mode for the two near-field coupled segments. Using antenna theory and numerical electrodynamics simulations two distinct coupling regimes are considered that scale with gap width or reactive near-field decay length, respectively. The results emphasize the distinct antenna behavior at optical frequencies compared to impedance matched radio frequency (RF) antennas and provide experimental confirmation of theoretically predicted scaling laws at optical frequencies.

Classification of imaging spectrometers for remote sensing applications

The continuing development of new and fundamentally different classes of imaging spectrometers has increased the complexity of the field of imaging spectrometry. The rapid pace at which new terminology is introduced to describe the new types of imaging spectrometers sometimes leads to confusion, particularly in discussions of the relative merits of the different types. In some cases, multiple different terms are commonly used to describe the same fundamental approach, and it is not always clear when these terms are synonymous. Other terminology in common use is overly broad. When a single term may encompass instruments that operate in fundamentally different ways, important distinctions may be obscured. In the interest of clarifying the terminology used in imaging spectrometry, we present a comprehensive system for classification of imaging spectrometers based on two fundamental properties: the method by which they scan the object spatially, and the method by which they obtain spectral information.

Measurement of the resonant lengths of infrared dipole antennas

The resonant lengths of infrared dipole antennas at 10.6 and 3.39 lm are experimentally investigated. For this purpose, submicron-sized microbolometers coupled to dipole antennas with lengths between 0.7 and 20 lm were fabricated on a SiO2-on-Si substrate. The response of the detector to 10.6 lm radiation shows a first resonance for an antenna length between 1.0 and 2.5 lm. A subsequent zero and a second attenuated resonance are observed as the antenna length increases. Similar behavior is observed for illumination at 3.39 lm, with a first resonance occurring at a length shorter than 1 lm. The results permit evaluation of an eAective dielectric permittivity and shows the eAect of the surface impedance of the metal on the propagation of current-wave on the antenna. The resonance behavior is further studied by changing the irradiation conditions of the detectors. Air-side and substrate-side illumination exhibit identical resonant antenna lengths, but diAerent eAciencies of power collection. The antenna patterns as a function of incident angle have also been measured at 10.6 lm, showing a transition from a primary broadside lobe to the development of side lobes for longer antennas. Finally, an antenna response is measured at visible frequencies. Our measurements point out similarities, as well as diAerences, between infrared antennas and their counterparts at microwave frequencies, and provide insights useful for the design optimization of planar infrared antennas. ” 2000 Elsevier Science B.V. All rights reserved.

Infrared frequency selective surface based on circuit-analog square loop design

A frequency selective surface (FSS) was designed to have a resonant spectral signature in the infrared. The lithographically composed, layered structure of this infrared FSS yields a resonant response in absorption to infrared radiation at a wavelength determined by its FSS element structure and the structure of its substrate layers. The infrared spectral characteristics of this surface are studied via Fourier transform infrared spectroscopy and spectral radiometry in the 3 to 15 /spl mu/m region of the spectrum. The design is based on circuit-analog resonant behavior of square loop conducting elements.

Antenna-coupled infrared detectors for imaging applications

Infrared focal plane arrays (IRFPAs) are a critical component in advanced infrared imaging systems. IRFPAs are made up of two parts, a detector array and a readout integrated circuit (ROIC) multiplexer. Current ROIC technology has typical pitch sizes of 20/spl times/20 to 50/spl times/50 /spl mu/m/sup 2/. In order to make antenna-coupled detectors suited for infrared imaging systems, two-dimensional (2-D) arrays have been fabricated that cover a whole pixel area with the penalty of increasing the noise figure of the detector and, therefore, reducing its performance. By coupling a Fresnel zone plate lens to a single element antenna-coupled detector, infrared radiation can be collected over a typical pixel area and still keep low-noise levels. A Fresnel zone plate lens coupled to a single-element square-spiral-coupled infrared detector has been fabricated and its performance compared to single element antenna-coupled detectors and 2-D arrays of antenna coupled detectors. Measurements made at 10.6 /spl mu/m showed a two-order-of-magnitude increase in SNR and a /spl sim/3/spl times/ increase in D/sup */ as compared to 2-D arrays of antenna-coupled detectors.

Performance Optimization of Antenna-Coupled

Signal-to-noise ratio (SNR) is a valuable figure of merit in determining the operating scope of infrared detectors. Antenna-couple metal-oxide-metal diodes have been shown to detect infrared radiation without cooling or applied bias, but so far have been hampered by their SNR. This paper details a comprehensive study of the fabrication parameters that control the formation of the tunneling oxide barrier to optimize the performance of these detectors. Since the tunneling barrier affects both current-voltage and infrared detection characteristics, fabrication parameters can be optimized to improve device performance. The current-voltage characteristics of the devices are detailed in this paper; resistance, nonlinearity, and curvature coefficient are parameterized on fabrication procedures. Infrared detection characteristics are detailed and SNR is studied as a function of device nonlinearity and biasing conditions.

{\rm Al}/{\rm AlO}_{x}/{\rm Pt}

wavelengths, respectively. The permittivity spectra were used to calculate SPP mode heights above the silicon surface and SPP propagation lengths. Reasonable merit criteria applied to these quantities suggest that only the heaviest doped material has sensor potential, and then mainly within the wavelength range 6 to 10 lm. Photon-to-plasmon coupling resonances, a necessary condition for sensing, were demonstrated near 10 lm wavelength for this material. The shape and position of these resonances agree well with simple analytic calculations based on the theory of Hessel and Oliner (1965). V C 2011 American Institute of Physics. [doi:10.1063/1.3672738]

Tunnel Diode Infrared Detectors

Measurements of modulation transfer function (MTF), particularly for staring imager systems, are affected by the position of the test target with respect to the rows and columns of the detector array. We demonstrate that random transparency targets of known spatial-frequency content allow shift-invariant MTF measurement in the visible, 3- to 5-μm, and 8- to 12-μm bands. Design criteria and verification procedures for the targets are presented.

Infrared surface plasmons on heavily doped silicon

The response of antenna-coupled thin-film Ni-NiO-Ni diodes to 633-nm helium-neon laser radiation is investigated. Although these detectors and their integrated dipole antennas are optimized for the detection of mid-infrared radiation, a polarization dependence of the measured response to visible radiation is observed. The strongest signals are measured for the polarization parallel to the dipole antenna axis, which demonstrates antenna operation of the device in the visible in addition to the expected thermal and photoelectric effects. The connection structure of the diode also resonates and contributes to the polarization-dependent signal. The receiving area of the dipole antenna is approximately 2 microm(2) .