Densely Packed Electrooptic AlyGa1−yAs−AlxGa1−xAs Rib Waveguide Modulators and Switches

Rib waveguides (RWG) formed on single heterostructure Al y Ga1− y As−Al x Ga1− x As slab waveguides1 provide a simple and powerful means to achieve the routing requirements of monolithic integrated circuits. The design, fabrication and use of single mode RWG is discussed here in the context of uniquely high lateral packing density and the use of efficient electrooptically controlled phase modulators for switching applications. The RWG are conveniently formed as an added processing step after epitaxial layer growth, requiring only layer thicknesses and compositions suitable for single slab waveguide modes. Doping levels of either type is only required to be ≲ 1017cm−3 and is compatible with future monolithic integration with cw operated lasers. The RWG are electrooptically modulated by applying voltages between metal electrodes overlaying a buffering oxide layer and the substrate.2 The RWG are modulated by the depletion layer field of the semiconductor which does not require a particular doping type. Close overlapping of the depletion layer field with the optical electric field leads to very efficient modulation. The profile of the high index waveguide layer and the respective effective indices for fundamental TE modes at 1.06 μm are shown in Fig. 1. This simple step waveguide model serves as a design guide for the RWG modes. Fig. 1 represents a coupled pair of RWG that serves as the basis of a switch. The effective refractive indices for a step height of 700 Å differ by 0.004. This provides sufficient lateral guiding and permits up to 3.5 μm wide ribs that can carry only one mode per polarization.