Abstract

While single quantum wells are capable of large absorption changes (Δα), their switching speed is limited by large refractive-index changes (An); creating a large chirp coefficient. Here we discuss the experimental creation of asymmetric Fabry-Perot reflection modulators, which incorporate coupled quantum wells in the active region (cavity); yielding pure amplitude reflection modulators with a zero chirp parameter over the entire voltage swing (5 V bias). The asymmetric coupled quantum wells modulate absorption via the spatial separation of carriers [oscillator strength modulation (OSM)] which allows large changes in absorption with zero change in refractive index during switching. Specifically, the coupled-well system used here consists of 50-Å GaAs wells and a 20-Å In_0.2Ga_0.8As quantum wells separated by 10-Å Al_0.33Ga_0.67As barriers.¹ By using in situ growth monitoring, the cavity’s Fabry–Perot resonance can be placed at the quantum well zero-chirp wavelength creating reflection modulation. In addition to describing the creation and results of such devices, we describe the limitations on reflectivity changes induced by the use of the OSM technique as compared with other techniques that cannot provide zero chirp.

© 1996 Optical Society of America