Vertical optical modulators utilizing the large absorption changes in quantum wells are promising for optical computing and optical interconnect technologies. While normally-on devices can be applied to interconnect technologies, normally-off reflection or transmission modulators presenting negative differential conductivity are required for producing bistability, in various Self Electo-optic Effect Device SEED1-2 configurations. Reflection Electro-Absorption Modulators REAMs that use a Fabry-Perot F-P cavity have demonstrated high contrast and low insertion loss3 for normally-on devices. The highest performance devices so far have used the Quantum Confined Stark Effect QCSE to increase the optical absorption and consequently change the reflectivity of the device with voltage. The F-P mode of the cavity is usually designed to be below the exciton energy, and the front mirror reflectivity is kept low. These devices use the large absorption change of QCSE and have very low residual absorption since they work below the absorption edge, but are of normally-on type, the higher reflectivity occurring at zero bias. Normally-off transmission or reflection modulators, so far, have always exploited a decrease in absorption at the operating wavelength. They can operate at the exciton wavelength at zero voltage and shift the exciton with bias, utilizing the QCSE1,2,4. This method, however, leads to lower absorption ratios due to transitions into the quantum well continuum. These tend to lower performance, generally increasing the insertion loss in the on-state.
This article is from 'Organization of the Optical Society of America Photonic Science Topical Meeting Series. Volume 7. Quantum Optoelectronics Held in Salt Lake City, Utah on 11-13 March 1991,' AD-A253 823, p30-33.