The emitter photocurrent transient of a doubleheterojunction InP/Ga0.47In0.53As/InP bipolar tran... more The emitter photocurrent transient of a doubleheterojunction InP/Ga0.47In0.53As/InP bipolar transistor has been found to be much faster than its ~15-GHz microwave bandwidth would suggest, since optical injection bypasses the base resistance. Slower components, due to holes residing in the base, can be eliminated with appropriate base biasing; this feature may be useful in optical receiver circuits. At a base bias of +0.5 V, the photocurrent transient has a 12-ps duration in response to both 620- and 1530-nm ultrafast optical pulses. At higher biases a slower transient component appears, as does a transient of opposite sign but with the same ~100-ps time constant at lower base biases. One slow component, a charge-neutrality-preserving collector current, has a base-bias-controlled gain; the other components can therefore be made to cancel. The device does not possess gain when operated in this manner, but the data suggest a design for an ultrafast photodetector with gain. The device studied is as fast a photodetector at visible wavelengths as at infrared, and the additional absorption provided by the InP emitter layer increases its short-wavelength sensitivity.
Continuum radiation from 650 to at least 1800 nm has been generated in silica optical fibers pump... more Continuum radiation from 650 to at least 1800 nm has been generated in silica optical fibers pumped by 100-ps pulses at 1064 nm from a mode-locked Q-switched Nd:YAG laser. The peak spectral power density of the ~100-ps pulses exiting the fiber, as high as 8 W/nm near 1250 nm, is easily sufficient to serve as a broadband source for characterizing fast photodetectors. The 5-m length of continuum generating singlemode silica fiber has a numerical aperture of 0.13. It contains 1.8% P2O5 in the cladding and 1.2% in its core; the 6.2-µm core also contains 10% GeO2. We have tested a number of fibers drawn from the same preform but with differing draw tensions and diameters. Efficient near infrared continuum generation and efficient second harmonic generation seem to be mutually exclusive characteristics of these fibers.
To a degree unmatched among other intrinsic conductors, the electronic properties of organic char... more To a degree unmatched among other intrinsic conductors, the electronic properties of organic charge-transfer salts1 are subject to chemical control. Among the derivatives and analogs of TTF-TCNQ,2-7 for example, even minor differences in molecular structure often manifest thanselves as sharp contrasts in electrical behavior. Indeed, despite their general chemical and crystallographic similarities, such compounds span the full range from insulators to the best organic conductors known.
We report a simple means of measuring device response times which is similar to cross-correlation... more We report a simple means of measuring device response times which is similar to cross-correlation techniques on linked pairs of photodetectors but which avoids the bandwidth limitations imposed by interconnecting transmission lines and largely eliminates the need for elaborate device mounting procedures [1,2]. Measurements are therefore possible on devices, such as those which must be mounted singly or those which are embedded in an integrated circuit without direct electrical access, whose intrinsic response speeds were previously not observable.
Modern optimization techniques are used to design high-performance photodetectors. All the design... more Modern optimization techniques are used to design high-performance photodetectors. All the designs created during these optimization studies are then used to train a physics-inspired, two-stage neural network to obtain even better-performing devices.
Most crystalline organic compounds are insulators or semi-conductors with roan temperature conduc... more Most crystalline organic compounds are insulators or semi-conductors with roan temperature conductivities in the range of 10-9 to 10-14Ω-1 cm-1 and exhibit exponentially decreasing conductivity profiles as the temperature is decreased.10 However in the 1960’s Melby and the duPont group made the startling discovery that a few of the many TCNQ (fig. 2) radical ion salts they prepared and studied11–17 had conductivities as high as 102Ω-1 cm-1. While this is low compared with metals like copper (σRT=5xl06 Ω-1 cm-1), it is remarkably high for an organic compound. Why do some of the TCNQ salts exhibit this high conductivity and can the conductivity of organic compounds be increased above 102Ω-1cm-1?
In a theoretical study of dissipative heating in Kerr microresonators we show that thermal effect... more In a theoretical study of dissipative heating in Kerr microresonators we show that thermal effects shift the coexistence wedge and modulational instability curve of continuous waves, so as to block access to frequency combs, and exhibit a path circumventing the obstruction. Thermal oscillations occur beyond a Hopf bifurcation curve.
We have fabricated GaAs motheye structures using contact photolithography printing. We have achie... more We have fabricated GaAs motheye structures using contact photolithography printing. We have achieved an average transmission improvement of 123% from 2000 cm -1 to 700 cm-1 (5 ¿urn-14 ¿urn) relative to an uncoated wafer.
The emitter photocurrent transient of a doubleheterojunction InP/Ga0.47In0.53As/InP bipolar tran... more The emitter photocurrent transient of a doubleheterojunction InP/Ga0.47In0.53As/InP bipolar transistor has been found to be much faster than its ~15-GHz microwave bandwidth would suggest, since optical injection bypasses the base resistance. Slower components, due to holes residing in the base, can be eliminated with appropriate base biasing; this feature may be useful in optical receiver circuits. At a base bias of +0.5 V, the photocurrent transient has a 12-ps duration in response to both 620- and 1530-nm ultrafast optical pulses. At higher biases a slower transient component appears, as does a transient of opposite sign but with the same ~100-ps time constant at lower base biases. One slow component, a charge-neutrality-preserving collector current, has a base-bias-controlled gain; the other components can therefore be made to cancel. The device does not possess gain when operated in this manner, but the data suggest a design for an ultrafast photodetector with gain. The device studied is as fast a photodetector at visible wavelengths as at infrared, and the additional absorption provided by the InP emitter layer increases its short-wavelength sensitivity.
Continuum radiation from 650 to at least 1800 nm has been generated in silica optical fibers pump... more Continuum radiation from 650 to at least 1800 nm has been generated in silica optical fibers pumped by 100-ps pulses at 1064 nm from a mode-locked Q-switched Nd:YAG laser. The peak spectral power density of the ~100-ps pulses exiting the fiber, as high as 8 W/nm near 1250 nm, is easily sufficient to serve as a broadband source for characterizing fast photodetectors. The 5-m length of continuum generating singlemode silica fiber has a numerical aperture of 0.13. It contains 1.8% P2O5 in the cladding and 1.2% in its core; the 6.2-µm core also contains 10% GeO2. We have tested a number of fibers drawn from the same preform but with differing draw tensions and diameters. Efficient near infrared continuum generation and efficient second harmonic generation seem to be mutually exclusive characteristics of these fibers.
To a degree unmatched among other intrinsic conductors, the electronic properties of organic char... more To a degree unmatched among other intrinsic conductors, the electronic properties of organic charge-transfer salts1 are subject to chemical control. Among the derivatives and analogs of TTF-TCNQ,2-7 for example, even minor differences in molecular structure often manifest thanselves as sharp contrasts in electrical behavior. Indeed, despite their general chemical and crystallographic similarities, such compounds span the full range from insulators to the best organic conductors known.
We report a simple means of measuring device response times which is similar to cross-correlation... more We report a simple means of measuring device response times which is similar to cross-correlation techniques on linked pairs of photodetectors but which avoids the bandwidth limitations imposed by interconnecting transmission lines and largely eliminates the need for elaborate device mounting procedures [1,2]. Measurements are therefore possible on devices, such as those which must be mounted singly or those which are embedded in an integrated circuit without direct electrical access, whose intrinsic response speeds were previously not observable.
Modern optimization techniques are used to design high-performance photodetectors. All the design... more Modern optimization techniques are used to design high-performance photodetectors. All the designs created during these optimization studies are then used to train a physics-inspired, two-stage neural network to obtain even better-performing devices.
Most crystalline organic compounds are insulators or semi-conductors with roan temperature conduc... more Most crystalline organic compounds are insulators or semi-conductors with roan temperature conductivities in the range of 10-9 to 10-14Ω-1 cm-1 and exhibit exponentially decreasing conductivity profiles as the temperature is decreased.10 However in the 1960’s Melby and the duPont group made the startling discovery that a few of the many TCNQ (fig. 2) radical ion salts they prepared and studied11–17 had conductivities as high as 102Ω-1 cm-1. While this is low compared with metals like copper (σRT=5xl06 Ω-1 cm-1), it is remarkably high for an organic compound. Why do some of the TCNQ salts exhibit this high conductivity and can the conductivity of organic compounds be increased above 102Ω-1cm-1?
In a theoretical study of dissipative heating in Kerr microresonators we show that thermal effect... more In a theoretical study of dissipative heating in Kerr microresonators we show that thermal effects shift the coexistence wedge and modulational instability curve of continuous waves, so as to block access to frequency combs, and exhibit a path circumventing the obstruction. Thermal oscillations occur beyond a Hopf bifurcation curve.
We have fabricated GaAs motheye structures using contact photolithography printing. We have achie... more We have fabricated GaAs motheye structures using contact photolithography printing. We have achieved an average transmission improvement of 123% from 2000 cm -1 to 700 cm-1 (5 ¿urn-14 ¿urn) relative to an uncoated wafer.
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