Normal mode analysis and characterization of an InGaAs/GaAs MQW field-induced optical waveguide including electrode effects

An InGaAs/GaAs MQW field-induced optical waveguide of our design is described in this paper, and a theoretical electromagnetic analysis of the structure is presented. The device is an optical slab waveguide which can be switched to a buried optical guide having strong lateral and vertical optical confinement by means of a negative bias voltage applied to the overlaying Schottky contact electrode. The spatial distribution of the refractive index within the MQW region is determined for different bias voltages using a combination of experimental measurements that describe field-induced refractive index changes in the waveguide MQW core and a finite-difference representation of the static electric field generated by the electrode. The method of lines is then applied to characterize the optical modes that propagate in the structure for two bias voltages of interest. The electrode is included in the modal analysis via the free electron gas model which yields an equivalent negative permittivity for our aluminum metallization. We have determined that the effect of the metallization on the optical performance of our device is non-negligible. In particular, it has been found that the metallization itself supports guided modes and that it causes a reduction in the confinement and propagation constant of the optical modes guided by the device. Furthermore, these effects are polarization-dependent such that when losses in the MQW region and metallization are considered, the attenuation of power related to the vertically polarized mode is found to be 17 dB greater than the attenuation related to the horizontally polarized mode, implying that our field induced guide also acts as a polarization filter.