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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 55 records · Page 3
All sourcesNASA NTRSDOE OSTI
NASA NTRS1979

Optical communication with two-photon coherent states. II - Photoemissive detection and structured receiver performance

In a previous paper (1978), the authors developed a method of analyzing the performance of two-photon coherent state (TCS) systems for free-space optical communications. General theorems permitting application of classical point process results to detection and estimation of signals in arbitrary quantum states were derived. The present paper examines the general problem of photoemissive detection statistics. On the basis of the photocounting theory of Kelley and Kleiner (1964) it is shown that for arbitrary pure state illumination, the resulting photocurrent is in general a self-exciting point process. The photocount statistics for first-order coherent fields reduce to those of a special class of Markov birth processes, which the authors term single-mode birth processes. These general results are applied to the structure of TCS radiation, and it is shown that the use of TCS radiation with direct or heterodyne detection results in minimal performance increments over comparable coherent-state systems. However, significant performance advantages are offered by use of TCS radiation with homodyne detection. The abstract quantum descriptions of homodyne and heterodyne detection are derived and a synthesis procedure for obtaining quantum measurements described by arbitrary TCS is given.

Shapiro, J. H.↗
NASA NTRS1979

Effects of truncation in modal representations of thermal convection

The Galerkin (including single-mode and Lorenz) equations were examined for convection in a sphere to determine which physical processes are neglected when the equations of motion are truncated too severely. The conclusions were tested by calculating solutions to the equations of motion for different values of the Rayleigh number and for different values of the limit of the horizontal spatial resolution. It was shown that the transitions from steady state to periodic, then to aperiodic convection depend not only on the Rayleigh number but also very strongly on the horizontal resolution. One of the effects of truncation is to enhance the high wavenumber end of the kinetic energy and thermal variance spectra. The numerical examples indicate that as long as the kinetic energy spectrum decreases with wavenumber, a truncation gives a qualitatively correct solution.

Marcus, P. S.↗
NASA NTRS1980

Advances in tunable diode laser technology

The improvement of long-term reliability, the purification of mode properties, and the achievement of higher-temperature operation were examined. In reliability studies a slow increase in contact resistance during room temperature storage for lasers fabricated with In-Au or In-Pt contacts was observed. This increase is actually caused by the diffusion of In into the surface layer of laser crystals. By using a three layered structure of In-Au-Pt or In-Pt-Au, this mode of degradation was reduced. In characterizing the mode properties, it was found that the lasers emit in a highly localized, filamentary manner. For widestripe lasers the emission occurs near the corners of the junction. In order to achieve single-mode operation, stripe widths on the order of 8-10 micrometers are needed. Also, it was found that room temperature electroluminescence is possible near 4.6 micrometers.

Lo, W.↗
NASA NTRS1979

Optical feedback effects on the performance of Pb/1-x/Sn/x/Se semiconductor lasers

The effects of optical feedback on the performance of Pb(1-x)Sn(x)Se semiconductor lasers are reported. Experimental results are presented to demonstrate that uncontrolled optical feedback can occur from optics external to the laser cavity and that these external optical elements can result in the formation of a composite cavity. This composite cavity can sustain a number of narrow closely spaced emission modes with the spectral characteristics of these modes dependent upon the parameters of the cavity. With weak feedback, the spectral width of the amplitude envelope of the new lasing modes resembles that of the original laser mode with no optical feedback. With strongly coupled feedback the envelope of the external cavity modes substantially broadens the apparent linewidth of the laser. It is shown that these effects can be eliminated, and, moreover, they offer the potential for obtaining spectrally narrow single-mode emission from Pb-salt lasers through the use of carefully designed external cavities.

Harward, C. N.↗
NASA NTRS1980

Fiber-optic rotation sensor technology

A concept for an all-waveguide fiber-optic rotation sensor is discussed, and the results of preliminary tests of key elements are described. A single channel waveguide coupler design provides the functions of an optical switch, a 3-dB beam splitter, a phase retarder, and a signal modulator, all of which may be formed on the same chip and interconnected by channel single-mode waveguides. Preliminary test results for the waveguide coupler and for a rotation sensor without the coupler are presented. Signal processing, polarization control, and interconnection of the waveguide components are discussed.

Goss, W. C.↗
NASA NTRS1980

Hypersonic-helium-flow-field measurements with the resonant Doppler velocimeter

A low density of sodium atoms seeded into a hypersonic helium flow is used to quantitatively determine flow-field properties. By observing fluorescence from a point as a single-mode dye laser is tuned through the sodium D2 line, the absorption profile may be found. This profile is fitted to a properly weighted sum of Voigt functions to yield the velocity, temperature, and pressure at the observation point. The fluorescence is strong enough to use this technique for qualitative flow-field visualization.

Zimmermann, M.↗
NASA NTRS1979

Single mode glass fiber welding

The electric-arc welding of commercially available single-mode optical fiber has been demonstrated. A mean transmission of 92% and a maximum transmission of 98% are reported for welds of fiber waveguide of 4.5 microns core diameter.

Nelson, M. D.↗
NASA NTRS1982

The two-photon absorptivity of rotational transitions in the A2 Sigma hyperon + (v prime = O) - X-2 pion (v prime prime = O) gamma band of nitric oxide

A predominantly single-mode pulsed dye laser system giving a well characterized spatial and temporal output suitable for absolute two-photon absorptivity measurements was used to study the NO gamma(0,0) S11 + R21 (J double prime = 7-1/2) transition. Using a calibrated induced-fluorescence technique, an absorptivity parameter of 2.8 + or - 1.4 x 10 to the minus 51st power cm to the 6th power was obtained. Relative strengths of other rotational transitions in the gamma(0,0) band were also measured and shown to compare well with predicted values in all cases except the O12 (J double prime = 10-1/2) transition.

Gross, K. P.↗
NASA NTRS1982

The photospheric velocity field of Procyon

Balloon-borne Ultraviolet Stellar Spectrometer observations of the profiles of two well observed spectral lines in the ultraviolet spectrum of Alpha CMI (Procyon; F5IV-V) are analyzed with a Fourier transform method in order to determine values of various parameters of the velocity field of the upper photosphere. A microturbulent line-of-sight velocity component of 0.9 + or - 0.4 km/s, a macroturbulent velocity component of 5.3 + or - 0.2 km/s, and a rotational velocity component of 10.0 + or - 1.2 km/s were determined. In these calculations a single-moded sinusoidal isotropic macroturbulent velocity function was assumed. The result appears to be sensitive to the assumed shape of the macroturbulence function.

De Jager, C.↗
NASA NTRS1983

Fabricating Grating Couplers on Optical Fibers

Microscopic corrugations form on fiber surfaces. Grating couplers couple signals into and out of single-mode optical waveguides without requiring precise alignment of components, although in-service efficiency has yet to be verified.

Chubb, C. R.↗
NASA NTRS1983

Application of optical fibers to wide-band differential interferometry

A broadband differential optical interferometer that uses an optical-fiber waveguide to transmit coherent light to a surface under inspection is discussed. Input laser light is coupled into two single-mode optical fibers in a stationary input optics enclosure. The fibers transmit the light to a small, remote detection head where it is used in a wide-band differential interferometer to detect continuous and pulsed surface-particle displacements. The effective separation between the input optics and the detection head allows simple surface scanning and probe alignment. Detection of simulated acoustic emission pulses by a prototype test unit is reported.

Garg, A. O.↗
NASA NTRS1983

Rectangular Luneburg-type lenses for integrated optics

Compact Luneburg-type lenses of rectangular outline as viewed from above have been made by thermal evaporation of As2S3 glass onto single-mode LiNbO3:Ti waveguides through suitably shaped masks and subsequent exposure of the glass to ultraviolet light. The best lenses had speeds of f/5.5 at an aperture of 10 mm and focal spots at reduced aperture about 1.2 times the diffraction-limited size. These lenses have a field of view of at least 25 degrees inside the waveguide.

Wood, V. E.↗
NASA NTRS1983

An all fiber-optic sensor for surface acoustic wave measurements

A surface acoustic wave (SAW) sensor constructed from single-mode fiber-optic components is described. An analysis of reciprocal and nonreciprocal modes of operation of the sensor is presented. Results from measurements on a variety of SAW devices illustrate the use of the sensor. The amplitude sensitivity is 0.0003 A for an integration time of 0.1 s.

Bowers, J. E.↗
NASA NTRS1983

Semiconductor optoelectronic devices for free-space optical communications

The properties of individual injection lasers are reviewed, and devices of greater complexity are described. These either include or are relevant to monolithic integration configurations of the lasers with their electronic driving circuitry, power combining methods of semiconductor lasers, and electronic methods of steering the radiation patterns of semiconductor lasers and laser arrays. The potential of AlGaAs laser technology for free-space optical communications systems is demonstrated. These solid-state components, which can generate and modulate light, combine the power of a number of sources and perform at least part of the beam pointing functions. Methods are proposed for overcoming the main drawback of semiconductor lasers, that is, their inability to emit the needed amount of optical power in a single-mode operation.

Katz, J.↗
NASA NTRS1985

Splicing Efficiently Couples Optical Fibers

Method of splicing single-mode optical fibers results in very low transmission losses through joined fiber ends. Coupling losses between joined optical-fiber ends only 0.1 dB. Method needs no special operator training.

Lutes, G. F.↗
NASA NTRS1984

Hybrid integrated optic modules for real-time signal processing

The most recent progress on four relatively new hybrid integrated optic device modules in LiNbO3 waveguides and one in YIG/GGG waveguide that are currently being studied are discussed. The five hybrid modules include a time-integrating acoustooptic correlator, a channel waveguide acoustooptic frequency shifter/modulator, an electrooptic channel waveguide total internal reflection moculator/switch, an electrooptic analog-to-digital converter using a Fabry-Perot modulator array, and a noncollinear magnetooptic modulator using magnetostatic surface waves. All of these devices possess the desirable characteristics of very large bandwidth (GHz or higher), very small substrate size along the optical path (typically 1.5 cm or less), single-mode optical propagation, and low drive power requirement. The devices utilize either acoustooptic, electrooptic or magnetooptic effects in planar or channel waveguides and, therefore, act as efficient interface devices between a light wave and temporal signals. Major areas of application lie in wideband multichannel optical real-time signal processing and communications. Some of the specific applications include spectral analysis and correlation of radio frequency (RF) signals, fiber-optic sensing, optical computing and multiport switching/routing, and analog-to-digital conversion of wide RF signals.

Tsai, C. S.↗
NASA NTRS1984

Optical residue addition and storage units using a Hughes liquid crystal light valve

Optical addition and storage units are described in this paper. These units are implemented using the Hughes Liquid Crystal Light Valve (LCLV) as a spatial light modulator using residue arithmetic for a numerical representation. The main hardware components of the design, besides the light valve, include an array of single-mode optical fibers that provide input information, a polarizing prism in combination with quarter-wave and half-wave retarders for residue arithmetic implementation in the adder, and a holographic array for spatial stability in the storage unit.

Habiby, S. F.↗
NASA NTRS1984

Monolithically integrated array of GaAlAs electroabsorption modulators

The operation of an eight-element monolithic array of GaAlAs electroabsorption modulators has been demonstrated. The single-mode waveguide modulators are implemented in a reverse-biased p-pi-n heterojunction configuration, with center-to-center spacing of 9 microns between adjacent channels. This device may be useful for intensity modulation in high (spatial) resolution applications.

Robinson, D. L.↗