Showing papers on "Wavelength published in 1995"

Rayleigh-scattering calculations for the terrestrial atmosphere

Abstract: Rayleigh-scattering cross sections and volume-scattering coefficients are computed for standard air; they incorporate the variation of the depolarization factor with wavelength. Rayleigh optical depths are then calculated for the 1962 U.S. Standard Atmosphere and for five supplementary models. Analytic formulas are derived for each of the parameters listed. The new optical depths can be 1.3% lower to 3% higher at midvisible wavelengths and up to 10% higher in the UV region compared with previous calculations, in which a constant or incorrect depolarization factor was used. The dispersion of the depolarization factor is also shown to affect the Rayleigh phase function slightly, by approximately 1% in the forward, backscattered, and 90° scattering-angle directions.

Comparison of optical millimetre-wave system concepts with regard to chromatic dispersion

Abstract: The author reports the impact of chromatic dispersion in optical millimetre-wave systems operating in the 1.55 µm wavelength window. Experimental and theoretical results confirm the dramatical millimetre-power degradation in conventional amplitude modulated systems using, for example, external optical modulators. In comparison, by use of a similar setup a self-heterodyne-based system concept has been investigated showing negligible dependence on the chromatic dispersion.

The origin of periodicity in the spectrum of evoked otoacoustic emissions.

Abstract: Current models of evoked otoacoustic emissions explain the striking periodicity in their frequency spectra by suggesting that it originates through the reflection of forward‐traveling waves by a corresponding spatial corrugation in the mechanics of the cochlea. Although measurements of primate cochlear anatomy find no such corrugation, they do indicate a considerable irregularity in the arrangement of outer hair cells. It is suggested that evoked emissions originate through a novel reflection mechanism, representing an analogue of Bragg scattering in nonuniform, disordered media. Forward‐traveling waves reflect off random irregularities in the micromechanics of the organ of Corti. The tall, broad peak of the traveling wave defines a localized region of coherent reflection that sweeps along the organ of Corti as the frequency is varied monotonically. Coherent scattering occurs off irregularities within the peak with spatial period equal to half the wavelength of the traveling wave. The phase of the net ref...

Finescale parameterizations of turbulent dissipation

Abstract: Fine- and microstructure data from a free fall profiler are analyzed to test models that relate the turbulent dissipation rate (e) to characteristics of the internal wave field. The data were obtained from several distinct been previously available. Observations from the ocean interior with negligible large-scale flow were examined to address the buoyancy scaling of e. These data exhibited a factor of 140 range in squared buoyancy frequency (N 2 ) with depth and uniform internal wave characteristics, consistent with the Garrett-Munk spectrum. The magnitude of e and its variation with N(∼N 2 ) was best described by the dynamical model of Henyey et al. A second dynamical model, by McComas and Muller, predicted an appropriate buoyancy scaling but overestimated the observed dissipation rates. Two kinematical dissipation parametrizations predicted buoyancy scalings of N 3/2 ; these are shown to be inconscient with the observations. Data from wave fields that depart from the canonical GM description are also examined an interpreted with reference to the dynamical models. The measurements came from a warm core ring dominated by strong near-inertial shears, a region of steep topography exhibiting high-frequency internal wave characteristics, and a midocean regime dominated at large wavelengths by an internal tide. Of the dissipation predictions examined, those of the Henyey et al. model in which eN − 2 scales as E 2 , where E is the nondimensional spectral shear level, were most consistent with observations. Nevertheless, the predictions for these cases exhibited departures from the observations by more than an order of magnitude. For the present data, these discrepancies appeared most sensitive to the distribution of internal wave frequency, inferred here from the ratio of shear spectral level to that for strain. Application of a frequency-based correction to the Henyey et al. model returned dissipation values consistent with observed estimates to within a factor of 2. These results indicate that the kinetic energy dissipation rate (and attendant turbulent mixing) is small for the background Garrett and Munk internal wave conditions (0.25eN −2 ∼ 0.7 × 10 − 5 m 2 s − 1). Dissipation and mixing become large when wave shear spectral levels are elevated, particularly by high-frequency waves. Thus, internal wave reflection/generation at steep topographic features appear promising candidates for achieving enhanced dissipation and strong diapycnal mixing in the deep ocean that appears required by box models and advection-diffusion balances

Gravity wave activity in the lower atmosphere: Seasonal and latitudinal variations

Abstract: A climatology of gravity wave activity in the lower atmosphere based on high-resolution radiosonde measurements provided by the Australian Bureau of Meteorology is presented. These data are ideal for investigating gravity wave activity and its variation with position and time. Observations from 18 meteorological stations within Australia and Antarctica, covering a latitude range of 12°S – 68°S and a longitude range of 78°E–159°E, are discussed. Vertical wavenumber power spectra of normalized temperature fluctuations are calculated within both the troposphere and the lower stratosphere and are compared with the predictions of current gravity wave saturation theories. Estimates of important model parameters such as the total gravity wave energy per unit mass are also presented. The vertical wavenumber power spectra are found to remain approximately invariant with time and geographic location with only one significant exception. Spectral amplitudes observed within the lower stratosphere are found to be consistent with theoretical expectations but the amplitudes observed within the troposphere are consistently larger than expected, often by as much as a factor of about 3. Seasonal variations of stratospheric wave energy per unit mass are identified with maxima occurring during the low-latitude wet season and during the midlatitude winter. These variations do not exceed a factor of about 2. Similar variations are not found in the troposphere where temperature fluctuations are likely to be contaminated by convection and inversions. The largest values of wave energy density are typically found near the tropopause.

Concentration and wavelength dependence of the effective third-order susceptibility and optical limiting of C60 in toluene solution

Abstract: The optical limiting action of C60 in toluene solution is mainly due to reverse saturable absorption (RSA). It is shown that the formalism describing nonlinear optical response due to instantaneous two-photon absorption can be used in the case of sequential two-photon absorption, yielding effective values of the relevant parameters of optical nonlinearity due to RSA. The effective two-photon absorption parameter beta eff and the effective nonlinear refractive index parameter gamma eff', which are related respectively to the imaginary and real parts of the effective third-order susceptibility chi eff(3) were measured by the z-scan technique as a function of fullerene concentration and of incident laser intensity and wavelength over the 420-640 nm region. The concentration dependence of these parameters indicates that the solution is optically thin as far as the ground state of C60 is concerned, whereas the wavelength dependence confirms the applicability of the formalism used in the sequential two-photon absorption model. Comparisons are made with other z-scan results on C60.

Influence of frequency and fluid distribution on elastic wave velocities in partially saturated limestones

Abstract: Elastic waves velocities were measured in the laboratory on homogeneous limestones in three different frequency ranges with varying water saturations (Sw). Measurements at frequencies of approximately 1 kHz were obtained using large (1-m length) resonant bars. The conventional pulse transmission technique was used to measure the samples at 50 kHz and 500 kHz. In order to study the influence of the fluid distribution we used two different saturation methods: drying and depressurization. Using a computerized tomography scan to image fluid distribution, we found that during depressurization, saturation was highly homogeneous at the millimetric scale at all saturations. In contrast, during the drying, heterogeneous saturation was observed at high water saturation levels. Results from elastic wave propagation show that compressional and extensional velocities are sensitive to the saturation technique at high water saturation level. Furthermore, the dependence of velocity upon saturation technique is frequency dependent, and dispersion is greatest at high saturations. We attribute this behavior to a scale effect that varies with the size of heterogeneities of the rock and with the wavelength. In addition to global and local flow mechanisms it seems necessary to include a “path dispersion” effect to explain the amount of velocity dispersion observed. For shear waves the experimental results show little variation of the velocity with frequency and very little with fluid distribution.

Method and apparatus for storage and retrieval with multilayer optical disks

Abstract: A multilayer optical disk system, which includes an optical disk unit having a number of connected optical disks A number of light sources, such as diode lasers, are used to provide a number of light beams of different wavelengths A wavelength multiplexer combines the light beams into a single beam which is then axially dispersed so that light of different wavelengths are simultaneously focuses onto the different optical disks A wavelength demultiplexer splits light reflected from the optical disks according to wavelength to produce separate beams which are then separately detected

Pulse oximeter and sensor optimized for low saturation

Abstract: A pulse oximeter sensor with a light source optimized for low oxygen saturation ranges and for maximizing the immunity to perturbation induced artifact. Preferably, a red and an infrared light source are used, with the red light source having a mean wavelength between 700-790 nm. The infrared light source can have a mean wavelength as in prior art devices used on patients with high saturation. The sensor of the present invention is further optimized by arranging the spacing between the light emitter and light detectors to minimize the sensitivity to perturbation induced artifact. The present invention optimizes the chosen wavelengths to achieve a closer matching of the absorption and scattering coefficient products for the red and IR light sources. This optimization gives robust readings in the presence of perturbation artifacts including force variations, tissue variations and variations in the oxygen saturation itself.

0n the dynamics of warped accretion disks

Abstract: We present some analyses of warping modes in inviscid near Keplerian disks taking the three-dimensional structure fully into account. The results of this investigation verify the validity of a vertical averaging approximation for thin disks when the radial wavelength is significantly longer than the disk thickness. They also indicate that long wavelength disturbances may persist for long times. Shorter wavelength disturbances in non-self gravitating disks are found to propagate with little dispersion at a speed related to the sound speed. When self-gravity becomes important, fast and slow waves are found which also propagate with little dispersion. When a small viscosity is included, the evolution of the disturbances becomes more diffusive in character.

Nonlinear wave loads on a slender vertical cylinder

Abstract: The diffraction of water waves by a vertical circular cylinder is considered in the regime where the wave amplitude A and cylinder radius a are of the same order, and both are small compared to the wavelength. The wave slope is small, and a conventional linear analysis applies in the outer domain far from the cylinder. Significant nonlinear effects exist in the complementary inner domain close to the cylinder, associated with the free-surface boundary condition. Using inner coordinates scaled with respect to a, it is shown that the leading-order nonlinear contribution to the velocity potential includes terms proportional to both A2a and A3. The wave load which acts on the cylinder near the free surface includes second- and third-harmonic components which are proportional respectively to A2a2 and A3a. In a conventional perturbation analysis, where A [Lt ] a, these components would be ordered in magnitude corresponding to the different powers of A, but here they are of the same order. The second- and third-order components of the total force are of comparable magnitude for practical values of the wave slope.

Atom wave interferometry with diffraction gratings of light.

Abstract: We have developed a novel interferometer for atom de Broglie waves, where amplitude division and recombination is achieved by diffraction at standing light waves operating as phase gratings. Our new atom interferometer is the exact mirror image of interferometers for light, with the roles of atoms and photons interchanged, and it directly demonstrates coherence of the diffraction of atomic waves at standing light waves. Easy manipulation of the phase, intensity, and polarization of the standing light wave permits novel studies of atomic coherence properties.

Tropical instability wave kinematics: Observations from the Tropical Instability Wave Experiment

Abstract: The kinematics of planetary waves originating from instability of the nearsurface equatorial currents are reported on using velocity measurements from an array of acoustic Doppler current profilers deployed in the equatorial Pacific during the Tropical Instability Wave Experiment. A distinctive wave season was observed from August to December 1990, with wave energy confined primarily above the core of the Equatorial Undercurrent. Particle motions in the horizontal plane are described by eccentric ellipses oriented toward the north, but tilting into the cyclonic shear of the South Equatorial Current. The tilt is maximum near the surface just north of the equator and decreases to the south and with depth. The distribution of wave variance is narrowband in both frequency and zonal wavenumber, with central period, zonal wavelength, and westward directed phase propagation estimated to be 500 hours, 1060 km, and 59 cm s -1 , respectively. Neither the meridional nor the vertical wavenumber component is statistically different from zero. These results generally agree with previous findings on tropical instability waves from the Atlantic and Pacific Oceans, and, in the undersampled arena of geophysical measurements, they provide an example where statistical inference is supported by an ensemble of independent measurements

Analysis of the propagation of plane acoustic waves in passive periodic materials using the finite element method

Abstract: The finite element approach has been previously used, with the help of the ATILA code, to model the scattering of acoustic waves by single or doubly periodic passive structures [A. C. Hladky‐Hennion et al., J. Acoust. Soc. Am. 90, 3356–3367 (1991)]. This paper presents a new extension of this technique to the analysis of the propagation of plane acoustic waves in passive periodic materials without losses and describes with particular emphasis its application to doubly periodic materials containing different types of inclusions. In the proposed approach, only the unit cell of the periodic material has to be meshed, thanks to Bloch–Floquet relations. The modeling of these materials provides dispersion curves from which results of physical interest can be easily extracted: identification of propagation modes, cutoff frequencies, passbands, stopbands, as well as effective homogeneous properties. In this paper, the general method is first described, and particularly the aspects related to the periodicity. Then a test example is given for which analytical results exist. This example is followed by detailed presentations of finite element results, in the case of periodic materials containing inclusions or cylindrical pores. The homogenized properties of porous materials are determined with the help of an anisotropic model, in the large wavelength limit. A validation has been carried out with periodically perforated plates, the resonance frequencies of which have been measured. The efficiency and the versatility of the method is thus clearly demonstrated.

Quantum cascade laser with plasmon‐enhanced waveguide operating at 8.4 μm wavelength

Abstract: A unipolar cascade laser operating at 8.4 μm wavelength is reported. The structure, grown by molecular beam epitaxy in the AlInAs/GaInAs material system, contains a 25‐stage coupled‐quantum‐well active region. The waveguide design is optimized to enhance optical confinement and reduce losses associated with the interface plasmon mode, by taking advantage of the dispersion of the refractive index of the contact layer near the plasma frequency. The peak optical power is 30 mW and the threshold current density 2.8 kA/cm2, at a heat‐sink temperature of 100 K and the highest operating temperature is 130 K. The slope efficiency at 100 K is ∼0.1 W/A, corresponding to a differential quantum efficiency of 5.4% per stage. This work, combined with previous results on shorter wavelength quantum cascade lasers, demonstrates that the wavelength of these new light sources can be tailored over a wide range by changing the active layers’ thicknesses using the same materials.

Guided-wave optical multi/demultiplexer

Abstract: A guided-wave optical multi/demultiplexer is capable of providing a wide wavelength band freely. Each of two directional couplers is constructed so that the coupling ratio of light intensity in the wavelength λ2 is at least 50% and the coupling ratio of light intensity in the wavelength λ3 having a wavelength band in close proximity to the wavelength λ1 is 0% or 100%, the light in the wave band containing the wavelength λ1 and the wavelength λ3 and the light in the wave band containing the wavelength λ2 being multiplexed and demultiplexed.

Phase modulation of atomic de Broglie waves.

Abstract: Cesium atoms prepared in a state of well-defined total energy have been reflected from a vibrating mirror, causing the matter waves to be phase modulated. The mirror is an evanescent light wave whose intensity is modulated in time at a frequency $\ensuremath{ u}$ in the range 0 to 2 MHz; the atoms are reflected at normal incidence. The resulting beam consists of a ``carrier'' plus various sidebands corresponding to de Broglie waves propagating at different velocities. The precision and flexibility of this technique make it a promising tool in atom optics.

Ulysses observations of Alfvén waves in the southern and northern solar hemispheres

Abstract: Alfven waves with periods from 10 hours are shown to be continuously present in the sun's south and north polar regions. Below ≃30° latitude, as revealed by the rapid traversal of the equatorial region by Ulysses, the wave power averaged over a solar rotation decreases abruptly. The correlations between magnetic field and solar wind velocity fluctuations, upon which the wave identification is based, indicate outward propagation in both hemispheres. The Ulysses observations are consistent with many of the properties of Alfven waves seen in the ecliptic in association with high speed streams. Some implications of the waves in the polar regions are explored. Because of the long wavelengths, which reach ≃0.3 AU, the waves resonate with 10-10 3 MeV/nucleon galactic cosmic rays and oppose their entry into the polar caps. The wave amplitudes imply a contribution to the acceleration of the high latitude wind due to momentum transfer of only a few percent.

Modified Boussinesq equations and associated parabolic models for water wave propagation

Abstract: The modified Boussinesq equations given by Nwogu (1993a) are rederived in terms of a velocity potential on an arbitrary elevation and the free surface displacement. The optimal elevation where the velocity potential should be evaluated is determined by comparing the dispersion and shoaling properties of the linearized modified Boussinesq equations with those given by the linear Stokes theory over a range of depths from zero to one half of the equivalent deep-water wavelength. For regular waves consisting of a finite number of harmonics and propagating over a slowly varying topography, the governing equations for velocity potentials of each harmonic are a set of weakly nonlinear coupled fourth-order elliptic equations with variable coefficients. The parabolic approximation is applied to these coupled fourth-order elliptic equations for the first time. A small-angle parabolic model is developed for waves propagating primarily in a dominant direction. The pseudospectral Fourier method is employed to derive an angular-spectrum parabolic model for multi-directional wave propagation. The small-angle model is examined by comparing numerical results with Whalin's (1971) experimental data. The angular-spectrum model is tested by comparing numerical results with the refraction theory of cnoidal waves (Skovgaard & Petersen 1977) and is used to study the effect of the directed wave angle on the oblique interaction of two identical cnoidal wavetrains in shallow water.

Vertical evolution of gravity wave spectra and the parameterization of associated wave drag

Abstract: Extensions of Weinstock's theory of nonlinear gravity waves and a parameterization of the related momentum deposition are developed. Our approach, which combines aspects of Hines' Doppler spreading theory with Weinstock's theory of nonlinear wave diffusion, treats the low-frequency part of the gravity wave spectrum as an additional background flow for higher-frequency waves. This technique allows one to calculate frequency shifting and wave amplitude damping produced by the interaction with this additional background wind. For a nearly monochromatic spectrum the parameterization formulae for wave drag coincide with those of Lindzen. It is shown that two processes should be distinguished: wave breaking due to instabilities and saturation due to nonlinear diffusionlike processes. The criteria for wave breaking and wave saturation in terms of wave spectra are derived. For a saturated spectrum the power spectral density's (PSD) dependence S(m) = AN2/m3 is obtained, where m is the vertical wavenumber and N is the Brunt-Vaisala frequency. Unlike Weinstock's original formulation, our coefficient of proportionality A is a slowly varying function of m and mean wind. For vertical wavelengths ranging from 10 km to 100 m and for typical wind shears, A varies from one half to one ninth. Calculations of spectral evolution with height as well as related profiles of wave drag are shown. These results reproduce vertical wavenumber spectral tail slopes which vary near the −3 value reported by observations. An explanation of these variations is given.

The Role of Longitudinal Waves in Quartz Crystal Microbalance Applications in Liquids

Abstract: The generation of shear waves in liquids by the quartz crystal microbalance (QCM) is evident from the influence of liquid properties on the QCM frequency and electrical characteristics. With the exception of a few reports, contributions from longitudonal waves that arise from nonuniform velocity profiles along the shear direction or nonideal contributions from crystal longtudinal and flexure modes have been largely ignored. The presence of these longitudinal components is demonstrated by the influence of a glass plate, fixed Gel to the QCM surface at a remote distance, on the QCM resonant frequency and electrical impedance characteristics. In agreement with a previous report, these effects can be observed even when the glass plate is positioned >1 cm away from the QCM, substantially longer than the shear wave decay length. Longitudinal standing waves are evident from the periodicity of the resonant frequency, inductance, capacitance, and resistance as the distance between the QCM and the glass plate. The wavelength of the standing waves agrees with that expected for the resonant frequency of the QCM and the fluid medium. The amplitude of the standing waves depends strongly upon the quartz crystal contour, as evident from extremely large frequency excursions observed for plano-convex crystals in witch energy trapping in the center of the resonator is greater than that for plano-plano crystals. Impedance analysis indicates that the frequency excursions are primarily a consequence of changes in the capacitance of the quartz crystals that result from a decrease in the compliance of the quartz resonator due to pressure exerted by the longitudinal waves. Standing waves resulting from reflection from the fluid-air interface are also observed, although the amplitude of the standing waves is smaller than the amplitude observed with the glass reflector plate owing to the larger reflection coefficient for the latter. However, the frequency excursions that result from small changes in the height of the fluid-air interface are substantial relative to frequency changes measured in typical QCM experiments. These results demonstrate that it is important to design QCM experiments to avoid contributions from longitudinal waves

Efficient bandpass reflection and transmission filters with low sidebands based on guided-mode resonance effects

Abstract: Ideal or near ideal filter for reflecting or transmitting electromagnetic waves having wavelength range of approximately 100 nm to 10 cm are disclosed. These filters combine a dielectric multilayer structure with a resonant waveguide grating and they are valid for both TE and TM polarized waves. High efficiency, arbitrarily narrow band, polarized, filters with low sidebands over extended wavelength ranges can be obtained.

High-Order Frequency Conversion in the Plasma Waveguide

Abstract: It is shown that a plasma fiber waveguide can provide phase matching over extended interaction lengths for the generation of high-order harmonics and difference frequencies through wave mixing or parametric amplification. An important consideration is that the plasma waveguide mode structure is independent of wavelength. Phase matching may be achieved through either frequency tuning or waveguide structure tuning.

Fabrication and performance of selectively oxidized vertical-cavity lasers

Abstract: We report the high yield fabrication and reproducible performance of selectively oxidized vertical-cavity surface emitting lasers. We show that linear oxidation rates of AlGaAs without an induction period allows reproducible fabrication of buried oxide current apertures within monolithic distributed Bragg reflectors. The oxide layers do not induce obvious crystalline defects, and continuous wave operation in excess of 650 h has been obtained. The high yield fabrication enables relatively high laser performance over a wide wavelength span. We observe submilliamp threshold currents over a wavelength range of up to 75 nm, and power conversion efficiencies at 1 mW output power of greater than 20% over a 50-nm wavelength range. >

Backscattering enhancement of electromagnetic waves from two-dimensional perfectly conducting random rough surfaces based on Monte Carlo simulations

Abstract: Backscattering enhancement of electromagnetic wave scattering from a perfectly conducting two-dimensional random rough surface (three-dimensional scattering problem) is studied with Monte Carlo simulations. The magnetic-field integral equation formulation is used with the method of moments. The solution of the matrix equation is calculated exactly with an efficient method known as the sparse-matrix flat-surface iterative approach. Numerical examples are illustrated with 32,768 surface unknowns, surface areas between 256 and 1024 square wavelengths, rms heights of 0.5 and 1 wavelength, and as many as 1000 realizations. The bistatic scattering simulations show backscattering enhancement for both copolarized and cross-polarized components. Comparisons are made with controlled laboratory experimental data for which the random rough surfaces are fabricated with prescribed properties of a rms height of 1 wavelength and a correlation length equal to 2 wavelengths. Comparisons are made between simulations and experimental data for the absolute value of the bistatic scattering coefficient. The copolarized scattering coefficient is in good agreement, and the cross-polarized scattering coefficient is in excellent agreement.

Techniques for measuring difference of an optical property at two wavelengths by modulating two sources to have opposite-phase components at a common frequency

Abstract: A technique for making precise spectrophotometric measurements illuminates a sample with two or more modulated light sources at two or more, typically closely spaced, wavelengths. Light from the sources is combined, homogenized, and directed to the sample, and the light from the sample is collected and detected by a photodetector. The optical output powers of two sources are modulated with the same periodicity and with a reversed amplitude. Variations in the concentrations of species in the sample affect the modulation amplitude representing the sum of the optical powers from two sources in such a way as to produce an output signal. That output signal, based on an electrical component varying with a periodicity at the fundamental frequency, provides a measure of the difference in the transmissions (or other optical properties) of the sample at the two wavelengths. Feedback methods, such as null-point detection, provide stable, sensitive measurements. Wavelength-division multiplexing--required for simultaneous measurements at many wavelengths--is achieved by modulating different pairs of sources at different frequencies.

Multiwavelength simultaneous monitoring circuit employing arrayed-waveguide grating

Abstract: A multiwavelength simultaneous monitoring circuit capable of precise discrimination of wavelengths of a WDM (Wavelength Division Multiplexed) signal including multiplexed wavelength waves, and suitable for optical integrated circuits having large resistance to vibration. It includes a reference optical source, an AWG (Arrayed-waveguide grating) having periodic center transmission wavelength (or crossover wavelengths) corresponding to the wavelength spacing between multiplexed waves of the WDM signal, a first wavelength error detector for generating a wavelength error signal of an RF signal (reference optical signal) with respect to a zero-cross wavelength on the basis of a ratio between the levels of the RF signal outputted from two output waveguides of the AWG, a control circuit for locking the zero-cross wavelength to the wavelength of the RF signal in response to the wavelength error signal, and a second wavelength error detector for generating wavelength error signals of the multiplexed waves of the WDM signal by detecting signal levels of respective wavelength signals of the WDM signal outputted from each pair of output ports of the AWG.

Vertical coupled-cavity microinterferometer on GaAs with deformable-membrane top mirror

Abstract: Fabry-Perot microinterferometer is demonstrated that combines a GaAs-AlAs vertical cavity with a suspended movable membrane. Electrostatic displacement of the gold/silicon nitride membrane allows for broad and continuous wavelength tuning of the cavity resonance formed by the combination of the GaAs cavity and the air gap below the membrane. The device exhibits a 32-nm tuning range around the 920-nm center wavelength for 0-14 V applied bias and FWHM linewidths near 3 nm; this corresponds to membrane deflections of up to 0.27 /spl mu/m. Such structures provide the foundation for wavelength selective photodiodes, light emitters, and lasers in which the active wavelength is under voltage control. >