Hybrid Electro-Optic Modulator Combining Silicon Photonic Slot Waveguides with High-k Radio-Frequency Slotlines

TL;DR

This paper presents a hybrid silicon photonic electro-optic modulator with a novel RF slotline design that achieves record-breaking bandwidths over 100 GHz, enabling ultra-fast data transmission at low voltages.

Contribution

It introduces a new RF slotline integrated with a silicon photonic slot waveguide using high-k dielectric BaTiO3, significantly enhancing modulation bandwidth beyond previous limits.

Findings

Achieved a 3 dB bandwidth of 76 GHz and a 6 dB bandwidth of 110 GHz.

Demonstrated data transmission at 200 Gbit/s using PAM4 modulation.

First silicon photonic modulator with bandwidth exceeding 100 GHz.

Abstract

Electro-optic (EO) modulators rely on interaction of optical and electrical signals with second-order nonlinear media. For the optical signal, this interaction can be strongly enhanced by 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). To the best of our knowledge, this represents the largest EO bandwidth so far achieved with a silicon photonic modulator based on dielectric waveguides. 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-1 mm device lengths with sub-1 V drive voltages and modulation bandwidths of more than 100 GHz.