Adiabatic tapered mode converter for selectively-oxidized waveguide devices

In recent times a new class of semiconductor photonic device has gained popularity. These devices use lateral selective oxidation to create highly efficient, low-threshold-current edge-emitting lasers where both the optical waveguide and lateral current confinement are achieved by lateral selective oxidation of AlGaAs. We have also recently explored use of selective-oxidation waveguides for low-drive-voltage high-speed optical phase modulators and electroabsorption modulators suitable for >40 Gb/s optical modulation. We propose a new concept for an adiabatic tapered mode converter for buried-oxide waveguide devices. Within this new converter the optical mode of the laser or modulator is expanded or shrunk, depending on the direction of light travel, to move light efficiently between the very small (1.5 /spl times/ 0.3 /spl mu/m FWHM) mode size of the oxidized device and the large, 10 /spl mu/m, modal field diameter of conventional single-mode optical telecom fiber. The new design achieves this by variation of the width of a selectively-oxidized waveguide mesa and a novel upper mesa, or rib, forming a wedding-cake-type overall structure.