High performance thin-film lithium niobate modulator on a silicon substrate using periodic capacitively loaded traveling-wave electrode

Gengxin Chen,Alan Pak Tao Lau,Daoxin Dai,Chao Lu,Zong Wang,Ziliang Ruan,Pucheng Huang,Liu Liu,Kaixuan Chen,Ranfeng Gan,Changjian Guo

doi:10.1063/5.0077232

Abstract

Thin-film lithium niobate (TFLN) based traveling-wave modulators maintain simultaneously excellent performances, including large modulation bandwidth, high extinction ratio, low optical loss, and high modulation efficiency. Nevertheless, there still exists a balance between the driving voltage and modulation bandwidth. Here, we demonstrate an ultra-large bandwidth electro-optic modulator without compromising the driving voltage based on the TFLN platform on a silicon substrate, using a periodic capacitively loaded traveling-wave electrode. In order to compensate the slow-wave effect, an undercut etching technique for the silicon substrate is introduced to decrease the microwave refractive index. Our demonstrated devices represent both low optical and low microwave losses, which leads to a negligible optical insertion loss of 0.2 dB and a large electro-optic bandwidth with a roll-off of 1.4 dB at 67 GHz for a 10 mm-long device. A low half-wave voltage of 2.2 V is also achieved. Data rates up to 112 Gb s−1 with PAM-4 modulation are demonstrated. The compatibility of the proposed modulator to silicon photonics facilitates its integration with matured silicon photonic components using, e.g., hybrid integration technologies.

Highlights

Optical communication systems are widely used all around the world to cope with the ever-increasing need for data transmission
We demonstrate an ultra-large bandwidth electro-optic modulator without compromising the driving voltage based on the Thin-film lithium niobate (TFLN) platform on a silicon substrate, using a periodic capacitively loaded traveling-wave electrode
We demonstrate TFLN based EO modulators using a capacitively loaded traveling-wave (CLTW) electrode on a silicon substrate

Summary

INTRODUCTION

Optical communication systems are widely used all around the world to cope with the ever-increasing need for data transmission. T-shaped periodic structures are added in between the ground and signal electrodes to maintain a small electrode gap (and a low VπL) without largely increasing the distributed capacitance (keeping the impedance matching). This structure would largely decrease the phase speed of the RF signal (i.e., the slow-wave effect).. Compared with EO modulators on the TFLN platform with regular travelingwave electrodes on a silicon substrate, the proposed EO modulator shows excellent high-frequency performance with only a 1.4 dB rolloff at 67 GHz. In addition, the proposed devices show an ultra-low optical insertion loss of 0.2 dB and a large static extinction ratio of >20 dB. On–off keying (OOK) modulation up to 100 Gbit s−1 and PAM-4 modulation up to 112 Gbit s−1 are successfully achieved with a dynamic extinction ratio of >9.7 dB

DEVICE DESIGN AND FABRICATION

MEASUREMENT AND ANALYSIS

CONCLUSION