Two different integration schemes for front-end optical receivers have been demonstrated for GaAs- and InP-based material systems. An InP-based p-i-n FET vertically integrated circuit exhibits a bandwidth greater than...
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Two different integration schemes for front-end optical receivers have been demonstrated for GaAs- and InP-based material systems. An InP-based p-i-n FET vertically integrated circuit exhibits a bandwidth greater than 2 GHz. The FET exhibits an extrinsic g/sub m/=450 mS/mm and f/sub T/=9 GHz. The GaAs-based planar structure consists of a modulated-barrier photodiode and a doped channel FET made with the same epitaxial layers. The detector has an optical gain of 200, and the FET performance is characterized by g/sub m/=250 mS/mm, f/sub T/=12 GHz, and f/sub max/=21 GHz.< >
Kerr electrooptic field mapping measurements were made in liquid nitrogen at 70 psi and -177 degrees C. A sensitive measurement technique was used whereby a small-signal AC voltage was superimposed on a DC level. The ...
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Kerr electrooptic field mapping measurements were made in liquid nitrogen at 70 psi and -177 degrees C. A sensitive measurement technique was used whereby a small-signal AC voltage was superimposed on a DC level. The nonlinear optical effect then gave an optical signal with a DC level and AC harmonic at the same frequency as the AC voltage. The amplitude of the AC optical signal was proportional to the local electric field and was measured with a lock-in amplifier. For 6330-nm-wavelength light the Kerr constant was measured to be B approximately=10/sup -16/ m/V/sup 2/. Steady-state electric fields between parallel stainless steel electrodes of gap 7 mm and area 31.6 cm/sup 2/ were shown to be essentially uniform for field strengths up to 90 kV/cm with no significant space charge distortion. The DC voltage-current characteristic was also measured and found to be nonohmic, reaching constant current of approximately=13 nA over the voltage range of approximately=30-60 kV.< >
The stress balance boundary condition at the free surface of a one dimensional electrofluidized or magnetically stabilized bed is reviewed. Conditions for zero interfacial force balance at the top of the bed are inves...
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The stress balance boundary condition at the free surface of a one dimensional electrofluidized or magnetically stabilized bed is reviewed. Conditions for zero interfacial force balance at the top of the bed are investigated. For the case of a uniformly fluidized bed, it is shown that a nonzero particle collision pressure is necessary for a force free bed surface. For the case where the collision pressure is neglected, it is shown that the electrofluidized or magnetically stabilized bed must be nonuniform at equilibrium. Stability criteria for a semi-infinite bed show that a critical field strength is necessary for stabilization. Below this critical condition the bed is convectively unstable. The temporal and spatial responses of a stabilized bed to small signal variations in superficial gas velocity, electrode position, and applied potential are calculated. Specific attention is directed to sinusoidal time variations in superficial gas velocity, where at low frequencies a standing wave character results for the fluidized bed variables.
The DC and microwave performance of a strained In/sub 0/./sub 65/Ga/sub 0/./sub 35/As/In/sub 0/./sub 52/A1/sub 0/./sub 48/As HEMT (high-electron-mobility transistors) is reported. Its design is based on theoretical an...
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The DC and microwave performance of a strained In/sub 0/./sub 65/Ga/sub 0/./sub 35/As/In/sub 0/./sub 52/A1/sub 0/./sub 48/As HEMT (high-electron-mobility transistors) is reported. Its design is based on theoretical and experimental studies including low- and high-field transport characterization of heterostructures with different strains. The intrinsic DC transconductance and cutoff frequence of 1.4- mu m-long gate HEMTs are 574 mS/mm and 38.6 GHz, respectively. The increased indium (In) composition in the channel enhances the drift velocity from 1.35*10/sup 7/ to 1.55*10/sup 7/ cm/s at 300 K.< >
Charge separation near a liquid/solid interface is explored by electrokinetic pumping of Freon TF and transformer oil using high-voltage traveling waves. Fluid-head-displacement measurements show strong dependencies o...
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Charge separation near a liquid/solid interface is explored by electrokinetic pumping of Freon TF and transformer oil using high-voltage traveling waves. Fluid-head-displacement measurements show strong dependencies on peak voltage amplitude (1.0-2.5 kV), frequency (0.1-20 Hz), and liquid conductivity (10/sup -13/-10/sup -9/ S/m). For any conductivity, reverse pumping (opposite to the traveling wave direction) occurs when the ratio of the voltage to the frequency is small, but switches to forward pumping when the ratio is large. The greatest displacement occurs when the dielectric relaxation and charge migration times are comparable. Preliminary measurements of average volume charge density, by sampling a portion of the liquid, relate net positive charge to forward pumping and net negative charge to reverse pumping. A charge transport analysis coupled to viscous dominated flow describes some features of the pumping.< >
Recent Kerr electrooptic field and charge mapping measurements in electron-beam-irradiated and high-voltage-stressed solid dielectrics are analyzed in terms of a drift-dominated conduction model. A one-dimensional mod...
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Recent Kerr electrooptic field and charge mapping measurements in electron-beam-irradiated and high-voltage-stressed solid dielectrics are analyzed in terms of a drift-dominated conduction model. A one-dimensional model with a lossy dielectric medium is treated. Attention is directed to the transient decay after the excitation is removed and the terminals are either short- or open-circuited. The effects of relaxation are investigated.< >
A frequency-selective amplifier was used to make sensitive Kerr electro-optic field mapping measurements with a small signal AC voltage superimposed on a DC level. With several different electrode materials, including...
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A frequency-selective amplifier was used to make sensitive Kerr electro-optic field mapping measurements with a small signal AC voltage superimposed on a DC level. With several different electrode materials, including brass, stainless steel, and aluminium, the authors have observed very significant levels of field distortion due to positive space charge on the order of 400 mu C/m/sup 3/. It was possible to measure field strengths as low as 100 V/cm with typical average field strengths tested over the range of 500 V/cm to 29 kV/cm. The transient evolution of these fields was also measured, showing the transition from a uniform to a highly nonuniform field on a time scale on the order of 60 s.< >
Double Channel HEMT's are used as variable resistor elements in a bridged-T attenuator with broadband characteristics (0.5-12GHz), and wide dynamic range (12-16dB). A small insertion loss (2.8dB minimum) is obtain...
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Double Channel HEMT's are used as variable resistor elements in a bridged-T attenuator with broadband characteristics (0.5-12GHz), and wide dynamic range (12-16dB). A small insertion loss (2.8dB minimum) is obtained with the help of the heterojunction approach which results in smaller ON-channel resistances than MESFET technology.
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