Abstract

Vertical cavity quantum-well optical modulators utilizing the quantum-confined Stark effect (QCSE) are being increasingly investigated for many uses.¹ Understanding the role of quantum well excitons on phase is crucial for high speed optical switching since such switching will be critically limited by Δn induced pulse broadening. The ratio of phase shift to absorption is typically reported through the chirp parameter where a low chirp parameter is desirable for low-dispersion amplitude modulation. Here we describe how the parasitic Δn can be eliminated in an optimized structure yielding a pure reflection modulator with a zero chirp. At the operating wavelength, such a device would exhibit a high reflectivity change and zero phase change when switched between two bias points. The same theory could be applied to making phase modulators with exactly 180° phase flip or for eliminating parasitic Δn in waveguide modulators that rely upon the QCSE.

© 1993 Optical Society of America