| 摘要 |
A doped substrate (12) is described for use around a ridge waveguide (10), for controlling the refractive index of the waveguide material. Instead of simply diffusing dopant in from a surface of the substrate (12) adjacent the waveguide (10), an area of the substrate is etched and dopant diffused in from a side face of the etched region (28, 30). Thus, the dopant profile is established from a horizontal direction, allowing the profile to be controlled. A simple vertically uniform doping profile (12) can thus be provided, leading to a vertically uniform current density, or an anisotropic wet etch can be applied after the initial etch to provide a profile (36) which concentrates the current density at a selected height in the substrate.
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