Lawrence E. Smith

Diode‐clamped symmetric self‐electro‐optic effect devices with subpicojoule switching energies

We describe symmetric self‐electro‐optic effect devices (S‐SEEDs) with clamping diodes connected to the center node of the devices to ensure both diodes of the S‐SEEDs have an electric field across them at all times. These diode‐clamped S‐SEEDs operate over a greater wavelength range, with greater powers before saturating, and have lower optical switching energies compared to conventional S‐SEEDs. An 8×8 array of diode‐clamped S‐SEEDs has been built and tested. We have demonstrated bistable operation with voltage swings of only 2 V over a wavelength range of 15 nm. Required optical switching energies of 340–580 fJ were measured at input powers from 500 nW to 100 μW for devices with 10×10 μm mesas. This is the lowest reported switching energy for any SEED with acceptable bistable characteristics.

Field-effect-transistor self-electro-optic-effect-device (FET-SEED) electrically addressed differential modulator array

We describe a 6 × 6 array of electrically addressed field-effect-transistor self-electro-optic-effect-device differential modulators in which each element has a single-stage amplifier to permit an input voltage of less than 1 V to control the output modulators, which can operate at as high as 10 V. The variations in the switching voltages across the array are less than ±70 mV, and the individual array elements are operated at as high as 2 Gbits/s. We also measure cross talk between adjacent elements within the array, measure the dependence of the switching time on the input voltage swing, and calculate the dependence of the switching time that is due to the photocurrent of the modulators.

Ambipolar lifetimes in GaAs/AlGaAs self-electro-optic-effect devices

We have used an electrical technique to determine the ambipolar lifetime in p‐i‐n GaAs/AlGaAs self‐electro‐optic‐effect devices in which the i region consists of a multiple quantum well structure (MQW). From an analysis of the voltage drop in the i region obtained from the forward current‐voltage characteristics, values for the ambipolar lifetimes are derived for diodes with different MQW. A value of 80–90 ps is determined for the ambipolar lifetime which is found not to change significantly when the AlxGa1−xAs barrier thickness or composition is reduced from 65 to 35 A or x∼0.3 to 0.2, respectively, in the MQW. Since these changes in the barrier have previously been shown to improve photoresponse efficiency of the p‐i‐n diode, it is inferred that the carrier escape and collection times are smaller than 80–90 ps in devices with thin (35 A) or low (x∼0.2) AlxGa1−xAs barrier.

High-power, high-efficiency, and highly uniform 1.3-um uncooled InGaAsP/InP strained multiquantum-well lasers

In order to meet the increasing market needs for uncooled lasers for such applications as fiber- in-the-loop, high efficiency, high power, and highly reliable 1.3 micrometer uncooled InGaAsP/InP strained multi-quantum well Fabry-Perot lasers were fabricated with 50 mm wafer processing. Slope efficiency as high as 0.39 W/A and peak power as high as 46 mW at 85 degrees Celsius was obtained by optimizing the device structure for high temperature operation. We have also demonstrated excellent uniformity and reproducibility over 6 wafers. Reliability was also shown to be very good. More than 10,000 chips sites are available on a 50 mm wafer, and the cost is expected to be low. Because of the high performance, these lasers are expected to be used for various applications.

Reverse Leakage Current in GaAs/AlGaAs Self Electro-Optic Effect Devices

The self-electro-optic effect device (SEED) and the symmetric SEED (S-SEED) have demonstrated considerable applications for photonic switching and logic functionality. A SEED consists of a p-i-n, mesa diode, with a multiple-quantum-well structure for the i region. The symmetric SEED consists of two p-i-n mesa diodes connected in series. The S-SEED has been fabricated in functional arrays containing as many as 32×64 elements. The SEED and S-SEED are operated under a reverse bias, thus low reverse leakage is desired. As the magnitude of the reverse leakage current increases, more incident laser power is required to switch device states and then hold that state. Therefore, understanding the origins of the reverse leakage current and its dependence on mesa and array size is imperative for optimizing device performance.