Numerical Analysis of Mushroom-type Traveling Wave Electroabsorption Modulators Using Full-Vectorial Finite Difference Method

Larger width of P-cladding layer in p-i-n waveguide of traveling wave electroabsorption modulator (TWEAM) results in lower resistance and microwave propagation loss which provides an enhanced high speed electro-optical response. In this paper, a fullvectorial finite-difference-based optical mode solver is presented to analyze mushroom-type TWEAM for the first time. In this analysis, the discontinuities of the normal components of the electric field across abrupt dielectric interfaces which are known as the limitations of scalar and semivectorial approximation methods are considered. The optical field distributions in mushroom-type TWEAM and conventional ridge-type TWEAM of the same active region for 1.55 μm operation are presented. The important parameters in the high-frequency TWEAM design such as optical effective index which defines optical velocity and transverse mode confinement factor are calculated. The modulation response of mushroom-type TWEAM is calculated by considering interaction of microwave and optical fields in waveguide and compared to that of conventional ridge-type TWEAM. The calculated 3dB bandwidths for ridge-type and mushroom-type TWEAM are about 139 GHz and 166 GHz for 200 μm and 114 GHz and 126 GHz for 300 μm waveguide length, respectively.