Fig. 1. (a) Schematic and (b) SEM image of the fabricated integrated microtoroid-waveguide system; principal diameter D=88  μm, minor diameter d=8  μm, microtoroid-waveguide gap g=300  nm, size of coupling waveguide W=2  μm, H=2  μm (scale bar is 100 μm). Magnified view of the (c) input and output waveguide coupler (scale bar is 100 μm); (d) microtoroid-waveguide system showing the support pedestals for the coupling waveguide (scale bar is 10 μm), and (e) coupling region between the microtoroid and coupling waveguide (scale bar is 1 μm).

Fig. 2. (a) Transmission spectrum of microtoroid resonator. Major diameter is 80 μm, minor diameter is 8 μm, and gap is 300 nm. (b) Lorentzian fitting of a single resonance at 1545.8 nm; (c) Lorentzian fitting of a single resonance at 1464.1 nm; (d) group index as a function of wavelength.

Fig. 3. (a) Simulated transmission spectrum of microtoroid resonator. The major and minor diameters are 80 μm and 8 μm, respectively, and the gap is 300 nm. (b) Simulated mode profile at 1545.78 nm (on-resonance) and (c) at 1549.3 nm (off-resonance).

Fig. 4. SEM images of coupling region between the microtoroid and coupling waveguide with a gap of (a) 200 nm; (b) 300 nm; and (c) 400 nm; (d) measured transmission spectra of the microtoroid-waveguide with gaps of 200 nm (blue line), 300 nm (red line), and 400 nm (yellow line); (e) simulated transmission spectra of microtoroid-waveguide with gaps of 200 nm (blue line), 300 nm (red line), and 400 nm (yellow line).

Fig. 5. (a) SEM image of nested double-spiral waveguide; scale bar is 100 μm; (b) magnified view of the spiral region; scale bar is 10 μm; (c) input and output waveguide coupler; scale bar is 10 μm; (d) transmission spectrum of the nested double-spiral waveguide.

Fig. 6. High-speed testing setup using 30 Gb/s NRZ data and 28 Gb/s PAM4 data.

Fig. 7. (a) Plot of −log(BER) as a function of received power. Black circles denote the experimentally measured BER for B2B 30 Gb/s NRZ data, whereas the black solid line is the fit to the black circles. Red circles denote the experimentally measured BER for 30 Gb/s NRZ data at the output of the waveguide, and the red line is the fit to the red circles. Blue crosses denote the experimentally measured BER for B2B 28 Gb/s PAM4 data, whereas the blue solid line is the fit to the blue crosses. Green crosses denote the experimentally measured BER for 28 Gb/s PAM4 data at the output of the waveguide, and the green line is the fit to the green crosses. (b) Eye diagram for NRZ; (c) eye diagram for PAM4; (d) experimentally measured BER histogram.