EFFECT OF GAAS ALGAAS QUANTUM-WELL STRUCTURE ON REFRACTIVE-INDEX/

We investigate the refractive index difference between the GaAs/AlGaAs quantum wells (QWs) and bulk AlGaAs. We find the refractive index dif ference is smaller when the electric field in the nominally intrinsic MQW region is larger, or when the well (GaAs) thickness of the QWs is larger, or when the Al fraction of the QWs is smaller. The maximum ref ractive index difference between the 100 angstrom GaAs/100 angstrom Al 0.2Ga0.8As QWs at zero electric filed and bulk Al0.1Ga0.9As is about 0 .044. Even with a small refractive index difference of 0.0132, the OFF -state reflectance of a normally-off MQW modulator at the designed pho ton wavelength will increase from the desired value of 0% to 90% when the reflectivity of the bottom mirror is 0.99.