Active optoelectronic devices made from semiconductor multiple quantum wells (MQWs) have been attracting much attention recently because of the large optoelectronic properties observed in these materials. For example, an electroabsorption effect in GaAs/AlGaAs MQWs [1] has been observed with a change in optical absorption coefficient as large as Δ α = 15,000 cm −1 . Recently, much progress has been made in applying this technology to long-wavelength materials. For example, a GaSb/AlGaSb [2] waveguide modulator was reported with a Δ α = 5500 cm −1 at a wavelength of λ = 1.55 μm . A waveguide device made from GaInAs/InP MQWs [3] that had Δ α = 400 cm −1 at λ = 1.55 μm , and produced an on/off ratio R = 8:1 has been reported. Also, a waveguide device with an insertion loss as low as 2.9 dB in InGaAs/InP MQWs [4] at λ = 1.67 μm has been reported, but the 47:1 on/off ratio was achieved in a waveguide that was fairly long ( L = 375 μm ), and the Δ α was only 640 cm −1 . For applications in high-performance lightwave systems, shorter devices with larger Δ α are necessary so that higher speeds can be achieved.

A 2 × 2 array of individually driven MQW modulators has been fabricated. Because of the large electroabsorption effect in MQWs, good on/off ratios can be achieved in a single pass through a set of 50 MQWs. Each device has an on/off ratio of approximately 1.45 : 1, and the modulator displays rise and fall times of roughly 400 ps.

For many short-distance communication applications in the telephone loop plant or local area networks where cost is a significant factor, use of a traditional bidirectional optical fiber communications system with 2 lasers, 2 fibers, and 2 detectors is unattractive. Additionally, such traditional systems require the placement of a laser at the user site, where an environment hostile to the laser might be encountered. These considerations have led to interest in nontraditional system architectures which require fewer components.[1] One approach which has been demonstrated is the use of a single fiber connecting the two users, with a laser at one end, and a photodetector and lithium niobate waveguide modulator at the other.[2] In this system, which operated at a wavelength of 1.3 μm, a portion of the light emerging from the optical fiber is passed through the modulator, returned to the fiber, and detected at the laser location. Data rates of 34 Mbit/sec and 565 Mbit/sec were achieved over a 2 km span in the modulator-to-laser and laser-to-detector directions, respectively.