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At least 91 records · Page 5
All sourcesNASA NTRSDOE OSTI
NASA NTRS2006

Wavelength-Agile External-Cavity Diode Laser for DWDM

A prototype external-cavity diode laser (ECDL) has been developed for communication systems utilizing dense wavelength- division multiplexing (DWDM). This ECDL is an updated version of the ECDL reported in Wavelength-Agile External- Cavity Diode Laser (LEW-17090), NASA Tech Briefs, Vol. 25, No. 11 (November 2001), page 14a. To recapitulate: The wavelength-agile ECDL combines the stability of an external-cavity laser with the wavelength agility of a diode laser. Wavelength is modulated by modulating the injection current of the diode-laser gain element. The external cavity is a Littman-Metcalf resonator, in which the zeroth-order output from a diffraction grating is used as the laser output and the first-order-diffracted light is retro-reflected by a cavity feedback mirror, which establishes one end of the resonator. The other end of the resonator is the output surface of a Fabry-Perot resonator that constitutes the diode-laser gain element. Wavelength is selected by choosing the angle of the diffracted return beam, as determined by position of the feedback mirror. The present wavelength-agile ECDL is distinguished by design details that enable coverage of all 60 channels, separated by 100-GHz frequency intervals, that are specified in DWDM standards.

Pilgrim, Jeffrey S.↗
NASA NTRS2005

Measurements of Breakdown Field and Forward Current Stability in 3C-SiC P-N Junction Diodes Grown on Step-Free 4H-SiC

This paper reports on initial fabrication and electrical characterization of 3C-SiC p-n junction diodes grown on step-free 4H-SiC mesas. Diodes with n-blocking-layer doping ranging from approx. 2 x 10(exp 16)/cu cm to approx.. 5 x 10(exp 17)/cu cm were fabricated and tested. No optimization of junction edge termination or ohmic contacts was employed. Room temperature reverse characteristics of the best devices show excellent low-leakage behavior, below previous 3C-SiC devices produced by other growth techniques, until the onset of a sharp breakdown knee. The resulting estimated breakdown field of 3C-SiC is at least twice the breakdown field of silicon, but is only around half the breakdown field of <0001> 4H-SiC for the doping range studied. Initial high current stressing of 3C diodes at 100 A/sq cm for more than 20 hours resulted in less than 50 mV change in approx. 3 V forward voltage. 3C-SiC, pn junction, p+n diode, rectifier, reverse breakdown, breakdown field,heteroepitaxy, epitaxial growth, electroluminescence, mesa, bipolar diode

Neudeck, Philip G.↗
NASA NTRS1998

A 640 GHz Planar-Diode Fundamental Mixer/Receiver

The design and performance of a 640 GHz solid-state receiver using a fundamental planar-Schottky-diode mixer, InP Gunn diode oscillator, whisker-contacted Schottky-varactor-diode sextupler and folded-Fabry-Perot diplexer are reported.

oscillator↗
NASA NTRS1972

Circuit model for characterizing the nearly linear behavior of avalanche diodes in amplifier circuits

A nonlinear circuit model for avalanche diodes is proposed. The model was derived by assuming that the bias dependence of the elements in a known small-signal equivalent-circuit model for existing diodes arises in a manner consistent with the theory of an idealized Read-type device. The model contains a nonlinear R-L branch, a controlled source, and a linear depletion capacitance. The model is used in the nearly linear sense to predict intermodulation distortion and gain compression in avalanche diode amplifiers. Computed results for amplifiers with existing diodes are shown to be in good agreement with experiment.

Penfield, P., Jr.↗
NASA NTRS1972

Development of a thermal diode heat pipe for the advanced thermal control flight experiment /ATFE/.

Description of the analysis, design, fabrication, and test of the engineering model of the ATFE diode. Included is a review of several diode concepts that led to selection of the liquid blockage technique for shut-off. The diode is made of stainless steel, 26 in. long, 0.375-in. nominal OD, with self-filling spiral artery wick and ammonia working fluid. In the normal heat pipe mode, at ambient temperatures, the diode capacity is 85 W. For flight, the pipe will deliver 20 W with a 9 F temperature difference between the external evaporator and condenser surfaces. Reverse mode conduction is less than 1.5 W with a 260 F temperature difference.

Swerdling, B.↗
NASA NTRS1974

High-efficiency, low-temperature cesium diodes with lanthanum-hexaboride electrodes

Lanthanum hexaboride electrodes in 1700 K cesium diodes may triple power outputs compared with those demonstrated for nuclear thermionic space applications. Still greater relative gains seem possible for emitters below 1700 K. Further improvements in cesium diode performance should result from the lower collector temperatures allowed for earth and low power space duties. Decreased temperatures will lessen thermal transport losses that attend thermionic conversion mechanisms. Such advantages will add to those from collector Carnot and electrode effects. If plasma ignition difficulties impede diode temperature reductions, recycling small fractions of the output power could provide ionization. So high efficiency, low temperature cesium diodes with lanthanum hexaboride electrodes appear feasible.

Morris, J. F.↗
NASA NTRS1974

High-efficiency, low-temperature cesium diodes with lanthanum-hexaboride electrodes

Lanthanum-hexaboride electrodes in 1700 K cesium diodes may triple power outputs compared with those demonstrated for nuclear thermionic space applications. Still greater relative gains seem possible for emitters below 1700 K. Further improvements in cesium-diode performance should result from the lower collector temperatures allowed for earth and low-power-space duties. Decreased temperatures will lessen thermal-transport losses that attend thermionic-conversion mechanisms. Such advantages will add to those from collector-Carnot and electrode effects. If plasma ignition difficulties impede diode temperature reductions, recycling small fractions of the output power could provide ionization. So high-efficiency, low-temperature cesium diodes with lanthanum-hexaboride electrodes appear feasible.

Morris, J. F.↗
NASA NTRS1976

Diode pumped Nd:YAG laser development

A low power Nd:YAG laser was constructed which employs GaAs injection lasers as a pump source. Power outputs of 125 mW TEM CW with the rod at 250 K and the pump at 180 K were achieved for 45 W input power to the pump source. Operation of the laser, with array and laser at a common heat sink temperature of 250 K, was inhibited by difficulties in constructing long-life GaAs LOC laser arrays. Tests verified pumping with output power of 20 to 30 mW with rod and pump at 250 K. Although life tests with single LOC GaAs diodes were somewhat encouraging (with single diodes operating as long as 9000 hours without degradation), failures of single diodes in arrays continue to occur, and 50 percent power is lost in a few hundred hours at 1 percent duty factor. Because of the large recent advances in the state of the art of CW room temperature AlGaAs diodes, their demonstrated lifetimes of greater than 5,000 hours, and their inherent advantages for this task, it is recommended that these sources be used for further CW YAG injection laser pumping work.

Reno, C. W.↗
NASA NTRS1977

Parametric Performance of a Spiral-Artery, Liquid-Trap-Diode Heat Pipe

A series of parametric investigations are described which determine the effect of various fluid charges on the performance of a 0.635-cm-diam spiral-artery, liquid-trap diode in both the forward and reverse modes. Specific parameters such as forward- and reverse-mode conductances, shutdown times and energies, and recovery to forward-model operation, are evaluated for ethane as a working fluid in the temperature range 170 K to 220 K. Results indicate that the heat pipe will not reliably start up in the forward mode. However, startup can be initiated when preceded by a diode reversal. Also included are data which show the susceptibility of the diode to fluid charge and tilt. The optimum fluid charge was found to be 2.67 g and transport capability at this charge was in excess of 1200 W-cm at 200 K. The diode in the reverse mode exhibited a rapid shutdown (within 9 min) with a shutdown energy of 1150 J (0.32 Wh).

Williams, R. J.↗
NASA NTRS1978

Investigation of a cryogenic thermal diode

This paper describes a series of parametric investigations to determine the effect of various fluid charges on the performance of a 0.635-cm-diameter spiral-artery, liquid-trap diode in both the forward and reverse modes. Specific parameters such as forward- and reverse-mode conductances, shutdown times and energies, and recovery to forward-mode operation, are evaluated for ethane as a working fluid in the temperature range 170 K to 220 K. Results indicate that the heat pipe will not reliably start up in the forward mode. However, startup can be initiated when preceded by a diode reversal. Also concluded are data which show the susceptibility of the diode to fluid charge and tilt. The optimum fluid charge was found to be 2.67 g, and transport capability at this charge was in excess of 1200 W-cm at 200 K. The diode in the reverse mode exhibited a rapid shutdown (within 9 min) with a shutdown energy of 1150 J (0.32 Wh).

Williams, R. J.↗
NASA NTRS1979

Cryogenic thermal diode heat pipes

The development of spiral artery cryogenic thermal diode heat pipes was continued. Ethane was the working fluid and stainless steel the heat pipe material in all cases. The major tasks included: (1) building a liquid blockage (blocking orifice) thermal diode suitable for the HEPP space flight experiment; (2) building a liquid trap thermal diode engineering model; (3) retesting the original liquid blockage engineering model, and (4) investigating the startup dynamics of artery cryogenic thermal diodes. An experimental investigation was also conducted into the wetting characteristics of ethane/stainless steel systems using a specially constructed chamber that permitted in situ observations.

Alario, J.↗
NASA NTRS1979

Shot-noise in resistive-diode mixers and the attenuator noise model

The representation of a pumped exponential diode, operating as a mixer, by an equivalent lossy network, is reexamined. It is shown that the model is correct provided the network has ports for all sideband frequencies at which (real) power flow can occur between the diode and its embedding. The temperature of the equivalent network is eta/2 times the physical temperature of the diode. The model is valid only if the series resistance and nonlinear capacitance of the diode are negligible. Expressions are derived for the input and output noise temperature and the noise-temperature ratio of ideal mixers. Some common beliefs concerning noise-figure and noise-temperature ratio are shown to be incorrect.

Kerr, A. R.↗
NASA NTRS1979

Application of tunable diode lasers as local oscillators in an Infrared Heterodyne Radiometer (IHR)

The utility of diode lasers as local oscillators (LOs) in a heterodyne receiver application was investigated. The CW power, spectral tunability, spectral stability, and spatial intensity distribution of the TDL outputs were measured. A tunable diode laser LO was incorporated into a laboratory Dicke-switched infrared heterodyne setup and used to measure radiometer sensitivity as well as spectroscopic characteristics of selected absorption lines of ammonia. The test results on one of the two tunable diode lasers are emphasized in an attempt to provide a comprehensive data package which may be useful for future planning purposes. The second tunable diode laser exhibits characteristics similar to the fully tested TDL with the exception that some changes in its performance characteristics as it was temperature cycled between room temperature and the operating temperature of approximately 50K occurred.

Savage, M. G.↗
NASA NTRS1981

Simple cryogenic temperature regulator - The Zener diode

For obtaining optimum performance from cooled infrared detectors used in astronomy, it is often necessary to operate the preamplifier transistor (usually a JFET) at a higher temperature than that provided by the cryogen. Various means of elevating the temperature of the FET above the temperature of its environment are considered. A description is presented of a method which uses a 10 V Zener diode (actually an avalanche diode) as a self-stabilizing heater element. The diode is mounted in good thermal contact with the FET, and both are isolated from the work surface by a link of poor conductivity. The diode is driven by a stable, constant voltage power supply.

Storey, J. W. V.↗
NASA NTRS1981

Trimming epitaxial GaAs Schottky-diode parameters via anodic oxidation

Present day receivers operating at millimeter and sub-millimeter wavelengths most often rely, for their first mixers, on Schottky-barrier diodes formed on epitaxial GaAs. Crucial parameters for these diodes are breakdown voltage, series resistance, junction capacitance and forward conduction mechanism. Some of these are improved, others impaired, by change of epitaxy thickness. This paper describes experience with optimizing GaAs Schottky-diode parameters by anodic oxidation thinning of GaAs epitaxial layers. Monitoring of breakdown voltage of epitaxial GaAs in anodic oxidation solution provides indication of when thinning should be stopped in subjection to the breakdown voltage specification of diodes to be made from the material. Mixer and frequency-multiplier performance superior to any previously reported have been achieved by this technique.

Siegel, C. M.↗
NASA NTRS1981

Excess noise in tunable diode lasers

The method and the apparatus for identifying excess-noise regions in tunable diode lasers are described. These diode lasers exhibit regions of excess noise as their wavelength is tuned. If a tunable diode laser is to be used as a local oscillator in a superheterodyne optical receiver, these excess-noise regions severely degrade the performance of the receiver. Measurement results for several tunable diode lasers are given. These results indicate that excess noise is not necessarily associated with a particular wavelength, and that it is possible to select temperature and injection current such that the most ideal performance is achieved.

Rowland, C. W.↗
NASA NTRS1984

Deep diode arrays for X-ray detection

Temperature gradient zone melting process was used to form p-n junctions in bulk of high purity silicon wafers. These diodes were patterned to form arrays for X-ray spectrometers. The whole fabrication processes for these X-ray detectors are reviewed in detail. The p-n junctions were evaluated by (1) the dark diode I-V measurements, (2) the diode C sub I - V measurements, and (3) the MOS C-V measurements. The results showed that these junctions were linearly graded in charge distribution with low reverse bias leakage current flowing through them (few nA at -10 volts). The X-ray detection experiments showed that an FWHM of 500 eV was obtained from these diodes with a small bias of just -5 volts (for X-ray source Fe55). A theoretical model was proposed to explain the extra peaks found in the energy spectra and a very interesting point - cross talk effect was pointed out. This might be a solution to the problem of making really high resolution X-ray spectrometers.

Zemel, J. N.↗
NASA NTRS1984

The 20 GHz solid state transmitter design, impatt diode development and reliability assessment

A single drift gallium arsenide (GaAs) Schottky barrier IMPATT diode and related components were developed. The IMPATT diode reliability was assessed. A proof of concept solid state transmitter design and a technology assessment study were performed. The transmitter design utilizes technology which, upon implementation, will demonstrate readiness for development of a POC model within the 1982 time frame and will provide an information base for flight hardware capable of deployment in a 1985 to 1990 demonstrational 30/20 GHz satellite communication system. Life test data for Schottky barrier GaAs diodes and grown junction GaAs diodes are described. The results demonstrate the viability of GaAs IMPATTs as high performance, reliable RF power sources which, based on the recommendation made herein, will surpass device reliability requirements consistent with a ten year spaceborne solid state power amplifier mission.

Picone, S.↗