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NASA NTRS2004

Modeling of a Variable Focal Length Flat Lens Using Left Handed Metamaterials

Left Handed Metamaterials (LHM) were originally purposed by Victor Veselago in1968. These substances would allow a flat structure to focus electromagnetic (EM) waves because they have a negative index of refraction. A similar structure made from conventional materials, those with a positive index of refraction, would disperse the waves. But until recently, these structures have been purely theoretical because substances with both a negative permittivity and negative permeability, material properties necessary for a negative index of refraction, do not naturally exist, Recent developments have produced a structure composed of an array of thin wires and split ring resonators that shows a negative index of refraction. area smaller than a square wavelength. How small the area is can be determined by how perfectly the lens is polished and how pure the substance is that composes the lens. These lenses must also be curved for focusing to occur. The focal length is determined by the curvature of the lens and the material. On the other hand, a flat structure made from LHM would focus light because of the effect of a negative index of refraction in Snell s law. The focal length could also be varied by simply adjusting the distance of the lens from the source of radiation. This could create many devices that are adjustable to different situations in fields such as biomedical imaging and communication. the software package XFDTD which solves Maxwell s equations in the frequency domain as well as the time domain. The program used Drude models of materials to simulate the effect of negative permittivity and negative permeability. Because of this, a LHM can be simulated as a solid block of material instead of an array of wires and split ring resonators. After a flat lens is formed, I am to examine the focusing effect of the lens and determine if a higher resolution flat lens can be developed. Traditional lenses made from conventional materials cannot focus an EM wave onto an My goal was to model LHMs and create a flat lens from them. This was to be done using

Reinert, Jason↗

NASA NTRS1976

The waveguide laser - A review

The present article reviews the fundamental physical principles essential to an understanding of waveguide gas and liquid lasers, and the current technological state of these devices. At the present time, waveguide laser transitions span the visible through submillimeter regions of the wavelength spectrum. The introduction discusses the many applications of waveguide lasers and the wide variety of laser configurations that are possible. Section 1 summarizes the properties of modes in hollow dielectric waveguides of circular, rectangular, and planar cross section. Section 2 considers various approaches to optical feedback including internal and external mirror Fabry-Perot type resonators, hollow waveguide distributed feedback structures, and ring-resonant configurations. Section 3 discusses those aspects of molecular kinetic and laser theory pertinent to the design and optimization of waveguide gas lasers.

Degnan, J. J.↗

NASA NTRS2004

Coherence Phenomena in Coupled Optical Resonators

We predict a variety of photonic coherence phenomena in passive and active coupled ring resonators. Specifically, the effective dispersive and absorptive steady-state response of coupled resonators is derived, and used to determine the conditions for coupled-resonator-induced transparency and absorption, lasing without gain, and cooperative cavity emission. These effects rely on coherent photon trapping, in direct analogy with coherent population trapping phenomena in atomic systems. We also demonstrate that the coupled-mode equations are formally identical to the two-level atom Schrodinger equation in the rotating-wave approximation, and use this result for the analysis of coupled-resonator photon dynamics. Notably, because these effects are predicted directly from coupled-mode theory, they are not unique to atoms, but rather are fundamental to systems of coherently coupled resonators.

Smith, D. D.↗

NASA NTRS1987

Measurement and analysis of cryogenic sapphire dielectric resonators and DROs

Presented are the experimental and computational results of a study on a new kind of dielectric resonator oscillator (DRO). It consists of a cooled, cylindrically symmetric sapphire resonator surrounded by a metallic shield and is capable of higher Q's than any other dielectric resonator. Isolation of fields to the sapphire by the special nature of the electromagnetic mode allows the very low loss of the sapphire itself to be expressed. Calculations show that the plethora of modes in such resonators can be effectively reduced through the use of a ring resonator with appropriate dimensions. Experimental results show Q's ranging from 3 x 10 to the 8th at 77 K to 10 to the 9th at 4.2 K. Performance is estimated for several types of DROs incorporating these resonators. Phase noise reductions in X-band sources are indicated at values substantially lower than those previously available.

Dick, G. J.↗

NASA NTRS1993

Microwave characterization of slotline on high resistivity silicon for antenna feed network

Conventional silicon wafers have low resistivity and consequently unacceptably high value of dielectric attenuation constant. Microwave circuits for phased array antenna systems fabricated on these wafers therefore have low efficiency. By choosing a silicon substrate with sufficiently high resistivity it is possible to make the dielectric attenuation constant of the interconnecting microwave transmission lines approach those of GaAs or InP. In order for this to be possible, the transmission lines must be characterized. In this presentation, the effective dielectric constant (epsilon sub eff) and attenuation constant (alpha) of a slotline on high resistivity (5000 to 10 000 ohm-cm) silicon wafer will be discussed. The epsilon sub eff and alpha are determined from the measured resonant frequencies and the corresponding insertion loss of a slotline ring resonator. The results for slotline will be compared with microstrip line and coplanar waveguide.

Simons, Rainee N.↗

NASA NTRS2002

Slow Light in Coupled Resonator Optical Waveguides

Recently, we discovered that a splitting of the whispering gallery modes (WGMs) occurs in coupled resonator optical waveguides (CROWs), and that these split modes are of a higher Q than the single-resonator modes, leading to enormous circulating intensity magnification factors that dramatically reduce thresholds for nonlinear optical (NLO) processes. As a result of the enhancements in Q, pulses propagating at a split resonance can propagate much slower (faster) for over (under)-coupled structures, due to the modified dispersion near the split resonance. Moreover, when loss is considered, the mode-splitting may be thought of as analogous to the Autler-Townes splitting that occurs in atomic three-level lambda systems, i.e., it gives rise to induced transparency as a result of destructive interference. In under- or over-coupled CROWs, this coupled resonator induced transparency (CRIT) allows slow light to be achieved at the single-ring resonance with no absorption, while maintaining intensities such that NLO effects are maximized. The intensity magnification of the circulating fields and phase transfer characteristics are examined in detail.

Chang, Hongrok↗

NASA NTRS1987

The role of resonances in planetary rings

The new observations of planetary rings, including those acquired during the encounters of Voyager with Jupiter, Saturn, and Uranus, and the discovery of incomplete rings around Neptune, reveal the great importance of resonances in determining the dynamics and the shape of planetary rings. Several types of resonances play a part in planetary rings. Current questions of interest are related to the nonlinear theory of density waves, the confinement of the Uranian rings, and the arcs of rings around Neptune.

Borderies, N.↗

NASA NTRS2002

Enhancement of Optical Nonlinearities Via Whispering Gallery Mode Splitting

An iterative method is applied to the analysis of N coupled ring-resonators, and the results are compared with multilayered spheres. Splitting of the whispering gallery modes into N higher-Q modes occurs when the round-trip phase shifts in each ring (or layer) are equal, in agreement with results for planar resonators. This mode-splitting is, therefore, a universal phenomenon for resonant structures, and can lead to reduced thresholds for nonlinear optical effects.

Chang, Hongrok↗

NASA NTRS1988

The Titan-1:0 nodal bending wave in Saturn's Ring C

The most prominent oscillatory feature observed in the Voyager 1 radio occultation of Saturn's rings is identified as a one-armed spiral bending wave excited by Titan's-1:0 nodal inner vertical resonance. Ring particles in a bending wave move in coherently inclined orbits, warping the local mean plane of the rings. The Titan-1:0 wave is the only known bending wave that propagates outward, away from Saturn, and the only spiral wave yet observed in which the wave pattern rotates opposite to the orbital direction of the ring particles. It is also the first bending wave identified in ring C. Modeling the observed feature with existing bending wave theory gives a surface mass density of about 0.4 g/sq cm outside the wave region and a local ring thickness of less than about 5 meters, and suggests that surface mass density is not constant in the wave region.

Rosen, Paul A.↗

NASA NTRS2002

Photonic Bandgaps in Photonic Molecules

This talk will focus on photonic bandgaps that arise due to nearly free photon and tight-binding effects in coupled microparticle and ring-resonator systems. The Mie formulation for homogeneous spheres is generalized to handle core/shell systems and multiple concentric layers in a manner that exploits an analogy with stratified planar systems, thereby allowing concentric multi-layered structures to be treated as photonic bandgap (PBG) materials. Representative results from a Mie code employing this analogy demonstrate that photonic bands arising from nearly free photon effects are easily observed in the backscattering, asymmetry parameter, and albedo for periodic quarter-wave concentric layers, though are not readily apparent in extinction spectra. Rather, the periodicity simply alters the scattering profile, enhancing the ratio of backscattering to forward scattering inside the bandgap, in direct analogy with planar quarter-wave multilayers. PBGs arising from tight-binding may also be observed when the layers (or rings) are designed such that the coupling between them is weak. We demonstrate that for a structure consisting of N coupled micro-resonators, the morphology dependent resonances split into N higher-Q modes, in direct analogy with other types of oscillators, and that this splitting ultimately results in PBGs which can lead to enhanced nonlinear optical effects.

Smith, David D.↗

NASA NTRS1988

Diode end pumped laser and harmonic generator using same

A second harmonic, optical generator is disclosed in which a laser diode produces an output pumping beam which is focused by means of a graded, refractive index rod lens into a rod of lasant material, such as Nd:YAG, disposed within an optical resonator to pump the lasant material and to excite the optical resonator at a fundamental wavelength. A non-linear electro-optic material such as MgO:LiNbO.sub.3 is coupled to the excited, fundamental mode of the optical resonator to produce a non-linear interaction with the fundamental wavelength producing a harmonic. In one embodiment, the gain medium and the non-linear material are disposed within an optical resonator defined by a pair of reflectors, one of which is formed on a face of the gain medium and the second of which is formed on a face of the non-linear medium. In another embodiment, the non-linear, electro-optic material is doped with the lasant ion such that the gain medium and the non-linear doubling material are co-extensive in volume. In another embodiment, a non-linear, doubling material is disposed in an optical resonator external of the laser gai medium for improved stability of the second harmonic generation process. In another embodiment, the laser gain medium andthe non-linear material are bonded together by means of an optically transparent cement to form a mechanically stable, monolithic structure. In another embodiment, the non-linear material has reflective faces formed thereon to define a ring resonator to decouple reflections from the non-linear medium back to the gain medium for improved stability.

Byer, Robert L.↗

NASA NTRS1979

The low-noise 115-GHz receiver on the Columbia-GISS 4-ft radio telescope

The superheterodyne millimeter-wave radiometer on the Columbia-GISS 4-ft telescope is described. This receiver uses a room-temperature Schottky diode mixer, with a resonant-ring filter as LO diplexer. The diplexer has low signal loss, efficient LO power coupling, and suppresses most of the LO noise at both sidebands. The receiver IF section has a parametric amplifier as its first stage with sufficient gain to overcome the second-stage amplifier noise. A broad-banded quarter-wave impedance transformer minimizes the mismatch between mixer and paramp. At 115 GHz, the SSB receiver noise temperature is 860 K, which is believed to be the lowest figure so far reported for a room-temperature receiver at this frequency.

Cong, H.-I.↗

NASA NTRS1983

Coherent infrared lidar mission and technology needs for measurements of transport and concentration of tropospheric trace species

The science justification and the feasibility of aircraft-based CO2 Doppler lidar measurements of transport between the free troposphere and the stratosphere (or planetary boundary layer) are discussed for a wide range of seasonal and geographic conditions. Ground-based coherent CO2 lidar aerosol scattering experiments using a stable ring resonator (about 50 mJ/pulse) CO2 laser with external injection locking are reported. Comparative studies of injection-locked CO2 laser unstable resonators and master oscillator power amplifiers are reported for future CO2 lidar missions with respect to requirements of pulse energy, duration/shape, frequency chirp, efficiency for heterodyne detection, and combined Doppler lidar and Differential Absorption Lidar missions.

Hess, R. V.↗

NASA NTRS1986

Swept frequency technique for dispersion measurement of microstrip lines

Microstrip lines used in microwave integrated circuits are dispersive. Because a microstrip line is an open structure, the dispersion can not be derived with pure TEM, TE, or TM mode analysis. Dispersion analysis has commonly been done using a spectral domain approach, and dispersion measurement has been made with high Q microstrip ring resonators. Since the dispersion of a microstrip line is fully characterized by the frequency dependent phase velocity of the line, dispersion measurement of microstrip lines requires the measurement of the line wavelength as a function of frequency. In this paper, a swept frequency technique for dispersion measurement is described. The measurement was made using an automatic network analyzer with the microstrip line terminated in a short circuit. Experimental data for two microstrip lines on 10 and 30 mil Cuflon substrates were recorded over a frequency range of 2 to 20 GHz. Agreement with theoretical results computed by the spectral domain approach is good. Possible sources of error for the discrepancy are discussed.

Lee, R. Q.↗

NASA NTRS1987

Swept frequency technique for dispersion measurement of microstrip lines

Lee, Richard Q.↗

NASA NTRS1989

Sequentially evaporated thin Y-Ba-Co-O superconducting films on microwave substrates

The development of high T sub c superconducting thin films on various microwave substrates is of major interest in space electronic systems. Thin films of YBa2Cu3O(7-Delta) were formed on SrTiO3, MgO, ZrO2 coated Al2O3, and LaAlO3 substrates by multi-layer sequential evaporation and subsequent annealing in oxygen. The technique allows controlled deposition of Cu, BaF2 and Y layers, as well as the ZrO buffer layers, to achieve reproducibility for microwave circuit fabrication. The three layer structure of Cu/BaF2/Y is repeated a minimum of four times. The films were annealed in an ambient of oxygen bubbled through water at temperatures between 850 C and 900 C followed by slow cooling (-2 C/minute) to 450 C, a low temperature anneal, and slow cooling to room temperature. Annealing times ranged from 15 minutes to 5 hrs. at high temperature and 0 to 6 hr. at 450 C. Silver contacts for four probe electrical measurements were formed by evaporation followed with an anneal at 500 C. The films were characterized by resistance-temperature measurements, energy dispersive X-ray spectroscopy, X-ray diffraction, and scanning electron microscopy. Critical transition temperatures ranged from 30 K to 87 K as a function of the substrate, composition of the film, thicknesses of the layers, and annealing conditions. Microwave ring resonator circuits were also patterned on these MgO and LaAlO3 substrates.

Valco, G. J.↗

NASA NTRS1990

Analysis of Microstrip Lines with Alternative Implementation of Conductors and Superconductors

An analysis of microstrip line structures in which either the strip or the ground plane or both are made of a high Tc superconductor is presented. The effect of implementation of a superconductor to the strip and the ground plane is explained with the calculation of a conductor loss of the structure by the Phenomenological Loss Equivalence Method (PEM). The theoretical values are compared with the experimental results from a ring resonator which is made of a gold ground plane and a high Tc superconductor, YBa2Cu3O(7-x), strip.

Kong, K.-S.↗

NASA NTRS1990

High temperature superconducting thin film microwave circuits: Fabrication, characterization, and applications

Epitaxial YBa2Cu3O7 films were grown on several microwave substrates. Surface resistance and penetration depth measurements were performed to determine the quality of these films. Here the properties of these films on key microwave substrates are described. The fabrication and characterization of a microwave ring resonator circuit to determine transmission line losses are presented. Lower losses than those observed in gold resonator circuits were observed at temperatures lower than critical transition temperature. Based on these results, potential applications of microwave superconducting circuits such as filters, resonators, oscillators, phase shifters, and antenna elements in space communication systems are identified.

Bhasin, K. B.↗