J. E. Henry

Symmetric self-electrooptic effect device: optical set-reset latch, differential logic gate, and differential modulator/detector

The symmetric self-electrooptic-effect device (S-SEED), a structure consisting of two p-i-n diodes electrically connected in series and acting as an optically bistable set-reset latch, is discussed. Applications and extensions of this device are also discussed. The devices do not require the critical biasing that is common to most optically bistable devices and thus is more useful for system applications. They have been optically cascaded in a photonic ring counter and have been used to perform different NOR, OR, NAND, and AND logic functions. Using the same device, a differential modulator that generates a set of complementary output beams with a single voltage control lead and a differential detector that gives an output voltage dependent on the ratio of the two optical input powers have been demonstrated. >

Symmetric self‐electro‐optic effect device: Optical set‐reset latch

We demonstrate an integrated symmetric self‐electro‐optic effect device consisting of two quantum well p‐i‐n diodes electrically connected in series. The device acts as a bistable optical memory element with individual set (S) and reset (R) inputs and complementary outputs (optical S‐R latch). The switching point is determined by the ratio of the two inputs, making the device insensitive to optical power supply fluctuations when both power beams are derived from the same source. The device also shows time‐sequential gain, in that the state can be set using low‐power beams and read out with subsequent high‐power beams. The device showed bistability for voltages greater than 3 V, incident optical switching energy densities of ∼16 fJ/μm2, and was tested to a switching time of 40 ns.

Integrated quantum well self‐electro‐optic effect device: 2×2 array of optically bistable switches

We demonstrate 2×2 arrays of optically bistable devices with very uniform optical characteristics. They are fabricated from an integrated self‐electro‐optic effect device structure consisting of a quantum well p‐i‐n diode grown in series with a load photodiode. Operating power can be optically controlled with a separate beam between ∼40 pW and >470 μW with associated switching times of ∼10 s and <2 μs.

Femtosecond intervalley scattering in GaAs

We report the measurement of intervalley scattering rates for optically excited carriers in GaAs. The measurements were performed using optical pulses of 6 fs duration and an energy distribution centered at 2.0 eV. The average rates for Γ→X and Γ→L intervalley scattering were separately estimated by varying the sample temperature.

Field-effect transistor self-electrooptic effect device: integrated photodiode, quantum well modulator and transistor

The authors propose and demonstrate the integration of a photodiode, a quantum-confined Stark-effect quantum-well optical modulator, and a metal-semiconductor field-effect transistor (MESFET) to make a field-effect transistor self-electrooptic effect device. This integration allows optical inputs and outputs on the surface of a GaAs-integrated circuit chip, compatible with standard MESFET processing. To provide an illustration of feasibility, the authors demonstrate signal amplification with a single MESFET.<<ETX>>

EXCITON SATURATION IN ELECTRICALLY BIASED QUANTUM WELLS

We have measured the heavy hole excitation saturation intensity in GaAs/AlGaAs quantum wells as a function of applied electric field and AlGaAs barrier design. We find that the saturation intensity increased with increasing applied field, and decreasing barrier thickness or height, because of increased carrier sweep‐out rates. Time‐resolved sweep‐out time and temperature‐dependent saturation intensity measurement point out the roles of both thermionic emission and tunneling in the field and barrier‐dependent carrier escape time. By reducing the barrier Al composition from 30 to 20%, we achieved an increase in the saturation intensity by a factor of ∼6.

Femtosecond excitonic optoelectronics

The authors discuss a novel approach to femtosecond optoelectronics which uses the excitonic response to electric fields as a detector and the excitonic nonlinear response to optical fields as a generator. The sensitivity of the quantum-well exciton to applied electric fields is used to measure electrical transients with femtosecond time resolution. The authors examine several mechanisms for femtosecond electrical pulse generation, including exciton ionization and two-photon absorption, and present measurements of the propagation properties of coplanar striplines on ultrathin semiconductor substrates in the 1-100-THz frequency range. The generation and detection of an electrical pulse with a 180-fs risetime propagating on a coplanar stripline on GaAs/AlGaAs quantum wells are demonstrated. >

Spatial light modulator and optical dynamic memory using a 6×6 array of self-electro-optic-effect devices

Using a 6 X 6 array of integrated quantum-well self-electro-optic-effect devices, we demonstrate an optically addressed spatial light modulator able to convert a visible, incoherent image into coherent infrared (IR) light. Depending on the IR wavelength used, the output is either a positive, binary-thresholded version of the input (bistable mode) or its linear, negative (self-linearized) mode. This device can also function as a dynamic bistable memory that can retain its internal state without power for times as long as 30 sec.

Optical logic using electrically connected quantum well PIN diode modulators and detectors

We present new optoelectronic logic devices or circuits consisting of electrically connected quantum well PIN diodes capable of implementing any boolean logic function. One class of circuits uses single beams to represent the logic levels and compares their intensities to a locally generated reference signal. A second class of circuits routes signals as differential pairs. The connections of diodes in these circuits resemble the transistor connections in NMOS and CMOS logic families. We demonstrate simple optical programmable logic arrays (e.g., E = AB + CD) using both of these classes of circuits.

Multistate self-electrooptic effect devices

Multistate self-electrooptic-effect devices (M-SEEDs) containing several quantum-well diodes in series are discussed. It is shown that a device with N diodes in series with a voltage source and illuminated by N diodes in series with a voltage source and illuminated by N light beams has N stable states corresponding to any one (and only one) of the diodes being highly transmissive. This voltage-biased M-SEED can perform contention resolution in the sense required by analog systems, because the diode illuminated by the weakest beam becomes the highly transmitting one on powering up the system. A current-biased M-SEED with N diodes in series with a current supply can have 2/sup N/ stable states, corresponding to any combination of diodes in their transmitting or absorbing states. This same device can also function as a binary image thresholder. The M-SEEDs are multistable in multiple beams, in contrast to previous multistable optical devices that have multiple states for one beam. Electrically and optically enabled symmetric SEEDs (S-SEEDs) that comprise a pair of quantum-well p-i-n diodes in series with a transistor or a third diode are also discussed. This device is the equivalent of an electrical tristate device that is used in some bus architectures. >