A Process-Tolerant Ring Modulator Based on Multi-Mode Waveguides

We present a novel 3.3-μm radius ring modulator design with dramatically reduced resonance wavelength variations. By implementing a multi-mode waveguide design for the ring waveguides, phase errors from processing non-idealities in waveguide width and etching depth are significantly reduced. Measured resonance wavelengths from four 200-mm wafers fabricated in a commercial 130-nm CMOS foundry showed a total of ~5-nm peak-to-peak variation, which is only about 1/6 of the free spectral range of the ring design. With this tighter control over the absolute resonance positions, the tuning range and tuning power requirements of the ring modulators can be significantly reduced, which in turn enhances their functionality for applications in high density, energy-efficient high-performance computing systems.