Abstract
Electro-optic (EO) polymer cladding modulators are an option for low-power high-speed optical interconnects on a
silicon platform. EO polymers have inherently high switching speeds and have shown 40 Gb/s operation in EO polymer
clad ring resonator modulators (RRM). In EO polymer clad RRM, the modulator’s area is small enough to be treated as
a lumped capacitor; the capacitance is sufficiently low that the modulation speed is limited by the bandwidth of the
resonator. A high Q resonator is needed for low voltage operation, but this can limit the speed and/or require precise
control of the resonator’s wavelength, necessitating power consuming heaters to maintain optimal performance over a
large temperature range. Mach Zehnder modulators (MZM), on the other hand, are not as sensitive to temperature
fluctuations, but typically are relatively long and must employ power consuming terminated travelling wave electrodes.
In this paper, a novel MZM design is presented using an EO polymer clad device. In this device, the electrodes are
broken into short parallel segments and the waveguide folds around them. The segments of the electrode length are
designed to provide good signal integrity up to 20 GHz without termination. The electrodes are driven by a single drive
voltage and provide push-pull modulation. Modulators were designed and fabricated using silicon nitride waveguides
on bulk silicon wafers and were demonstrated at high speed (20 GHz). A VπL as low as 1.7 Vcm is measured on initial
devices. An optimized device could provide 40 Gb/s performance at 1 V drive voltages, ~100 fF total device
capacitance and less than 2 dB optical insertion loss.
