LIGHT MODULATION BY TUNABLE INTERFERENCE FILTER.

Device modeling was performed using an optical transmission matrix approach; changes in refractive index were estimated using a quantum-confined Stark effect model based on tunneling resonances. The calculations predict that a 40-period structure should allow modulation of reflectivity between 10 and 86% for sub-bandgap light, more if the substrate is removed. A device wafer was fabricated by computer-controlled MBE. Each of the 40 optical periods consisted of 836 angstrom GaAs quantum wells separated by 70-angstrom Ga//5Al//. //5As barriers. The active layers and GaAs buffer layers were all doped lightly n-type. A semitransparent aluminum Schottky contact layer was deposited in the MBE chamber. Transmission spectroscopy measurements showed qualitative agreement with the predictions. An electric field of 200 kV/cm resulted in a 40-angstrom (5-meV) shift in the high-reflectivity edge, and gave a 7:1 modulation ratio, with an insertion loss of 6 dB, on 1- mu m light.