Thin film lithium niobate electro-optic modulator with terahertz operating bandwidth.

Andrew J Mercante,Linli Xie,Shouyuan Shi,Robert M Weikle,Peng Yao,Dennis W Prather

doi:10.1364/oe.26.014810

Abstract

We present a thin film crystal ion sliced (CIS) LiNbO3 phase modulator that demonstrates an unprecedented measured electro-optic (EO) response up to 500 GHz. Shallow rib waveguides are utilized for guiding a single transverse electric (TE) optical mode, and Au coplanar waveguides (CPWs) support the modulating radio frequency (RF) mode. Precise index matching between the co-propagating RF and optical modes is responsible for the device's broadband response, which is estimated to extend even beyond 500 GHz. Matching the velocities of these co-propagating RF and optical modes is realized by cladding the modulator's interaction region in a thin UV15 polymer layer, which increases the RF modal index. The fabricated modulator possesses a tightly confined optical mode, which lends itself to a strong interaction between the modulating RF field and the guided optical carrier; resulting in a measured DC half-wave voltage of 3.8 V·cm-1. The design, fabrication, and characterization of our broadband modulator is presented in this work.

Highlights

Despite its ubiquity in fiber-optic telecommunications and attractive nonlinear properties, the evolution of LiNbO3 integrated optics can be considered sluggish relative to its Si and III-V counterparts
We present a thin film crystal ion sliced (CIS) LiNbO3 phase modulator that demonstrates an unprecedented measured electro-optic (EO) response up to 500 GHz
Shallow rib waveguides are utilized for guiding a single transverse electric (TE) optical mode, and Au coplanar waveguides (CPWs) support the modulating radio frequency (RF) mode

Summary

Introduction

Despite its ubiquity in fiber-optic telecommunications and attractive nonlinear properties, the evolution of LiNbO3 integrated optics can be considered sluggish relative to its Si and III-V counterparts. Discrete devices fabricated in bulk single crystalline LiNbO3 generally rely on low index contrast optical waveguides with large bend radii [1], and specialized micromachining processes for sustaining broadband operation [2], which inhibits dense integration. Reduced half-wave voltage length products coupled with the ability to bend and fold the high index contrast optical waveguides leads to a substantially decreased device footprint ideal for future integrated photonic systems. Up to this point the other major advantage of thin-film LiNbO3, the significantly lower permittivity of the material system, has yet to be convincingly exploited [7,8,11,16]. Given the results presented in this work, we propose that optical routing of THz signals can be enabled by an EO up-converting modulator to provide both a simple and effective frontend alternative

Device design and fabrication

Conclusion