Hybrid electro-optic modulator combining silicon photonic slot waveguides with high-k radio-frequency slotlines

Electro-optic (EO) modulators rely on the interaction of optical and electrical signals with second-order nonlinear media. For the optical signal, this interaction can be strongly enhanced using dielectric slot-waveguide structures that exploit a field discontinuity at the interface between a high-index waveguide core and the low-index EO cladding. In contrast to this, the electrical signal is usually applied through conductive regions in the direct vicinity of the optical waveguide. To avoid excessive optical loss, the conductivity of these regions is maintained at a moderate level, thus leading to inherent RC limitations of the modulation bandwidth. In this paper, we show that these limitations can be overcome by extending the slot-waveguide concept to the modulating radio-frequency (RF) signal. Our device combines an RF slotline that relies on BaTiO3 as a high-k dielectric material with a conventional silicon photonic slot waveguide and a highly efficient organic EO cladding material. In a proof-of-concept experiment, we demonstrate a 1 mm long Mach-Zehnder modulator that offers a 3 dB bandwidth of 76 GHz and a 6 dB bandwidth of 110 GHz along with a small pi voltage of 1.3 V (U pi L = 1.3 V mm). We further demonstrate the viability of the device in a data-transmission experiment using four-state pulse-amplitude modulation (PAM4) at line rates up to 200 Gbit/s. Our first-generation devices leave vast room for further improvement and may open an attractive route towards highly efficient silicon photonic modulators that combine sub-1mmdevice lengths with sub-1Vdrive voltages and modulation bandwidths of more than 100 GHz. (C) 2021 Optical Society of America under the terms of the OSA Open Access Publishing AgreementY

Automated summary

This paper presents a method for efficient electro-optic modulators using slot-waveguide structures, which overcome the limitations of modulation bandwidth by applying this structure in modulating radio-frequency signals. Experimental results demonstrate excellent performance, providing a new approach towards efficient silicon photonic modulators with sub-1mm device lengths, sub-1V drive voltages, and modulation bandwidths exceeding 100 GHz.