Low voltage high contrast n-i-p-i based waveguide modulator

Abstract

We have investigated an electroabsorptive n-i-p-i waveguide modulator based on the Franz-Keldysh effect (FKE) especially designed to operate with very low voltages. This is particularly interesting for high speed modulation and applications requiring integration with CMOS technology. The modulator operates at photon energies below the bandgap, and therefore the on-state absorption losses are very low. By applying a voltage between selective contacts to the n-t-p-i structure, the internal field can be changed within a wide range Due to the FKE an increase of the electric field leads to an increase of the absorption coefficient below the bandgap As the interaction length in a waveguide modulator is in the order of several hundred microns, absorption changes of a few 100cm−1 are sufficient to achieve contrast ratios of several orders of magnitude. In addition, the absorption changes due to the FKE extend over a broad wavelength range, which gives a good stability against thermal wavelength detuning and is also important for multiwavelength operation.