Carrier-induced refractive index changes in forward-biased InGaAs-InAlAs quantum well waveguides are calculated using a Kramers-Kronig transformation of Bar-Joseph’s experimental absorption spectra [Phys. Rev. Lett. 59, 1357 (1987)]. At the l.65-,µm wavelength where the material is nominally transparent, an index change of -0.06 is found for an injection of 6 × 1017 electrons/cm3 . A quantum well waveguide 2 × 2 reversed-Δβ directional coupler switch with an active length of 480 µm is proposed.
Richard A. Soref and Brian R. Bennett, "Carrier refraction in quantum well waveguides," Appl. Opt. 28, 3577-3580 (1989)