A compact wavelength tunable 10 Gb/s silicon racetrack modulator with integrated thermo-optic heater is demonstrated using a waveguide with asymmetric cross section, combining the compact footprint of microdisk modulators with the design simplicity of regular racetrack or ring modulators. The outer perimeter of the asymmetric racetrack modulator is fully etched to maximize optical confinement, while the inner waveguide edge is shallowly etched to maintain an electrically conductive path to the embedded p-n diode and to control the propagation of the asymmetric optical mode and its coupling to the bus waveguide. Resistive heating elements based on highly doped Si strips are implemented at the outer edge of the modulator for thermo-optic control. The asymmetric modulators can be fabricated along with Si wire waveguides and shallowly etched fiber grating couplers using a simple process flow involving just two Si pattering steps. Devices with a bending radius of 10 µm and a novel “T�-shaped p-n diode layout have been fabricated and exhibit electro-optic modulation and heater efficiencies of 28 pm/V and 42 pm/mW, respectively. At 10 Gb/s, a stable extinction ratio of 10dB is demonstrated from a 2Vpp drive swing, which can be maintained over a wavelength range of ~4.6 nm by thermally tuning the modulator. This is equivalent with a temperature variation of about 62 ºC.
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