Plasmonic monolithic lithium niobate directional coupler switches

TL;DR

This paper presents a novel plasmonic monolithic lithium niobate directional coupler switch that achieves ultra-compact, high-efficiency electro-optic modulation suitable for integrated optical communication systems.

Contribution

The work introduces a monolithic LN plasmonic platform with nm-thin gold nanostripes enabling ultra-compact, high-performance electro-optic switches with significant modulation depth and efficiency.

Findings

Achieved 90% modulation depth with 20-μm-long switches.

Demonstrated electro-optic modulation efficiency of 0.3 Vcm.

Enabled ultra-dense integration of active photonic components.

Abstract

From the onset of high-speed optical communications, lithium niobite (LN) has been the material of choice for electro-optic modulators owing to its large electro-optic response, wide transparent window, excellent thermal stability and long-term material reliability. Conventional LN electro-optic modulators while continue to be the workhorse of the optoelectronic industry become progressively too bulky, expensive and power hungry to fully serve the needs of this industry rapidly progressing towards highly integrated, cost-effective and energy efficient components and circuits. Recently developed monolithic LN nanophotonic platform enables the realization of electro-optic modulators that are significantly improved in terms of compactness, bandwidth and energy efficiency, while still demanding relatively long, on the mm-scale, interaction lengths. Here we successfully deal with this challenge and demonstrate plasmonic electro-optic directional coupler switches consisting of two closely spaced nm-thin gold nanostripes monolithically fabricated on LN substrates that guide both coupled electromagnetic modes and electrical signals influencing their coupling and thereby enabling ultra-compact switching and modulatiofunctionalities. The extreme confinement of both slow-plasmon modes and electrostatic fields created by two nanostripes along with their nearly perfect spatial overlap allowed us to achieve a 90% modulation depth with 20-$\mu$m-long switches characterized by a electro-optic modulation efficiency of 0.3 Vcm. Our monolithic LN plasmonic platform enables ultra-dense integration of high-performance active photonic components, enabling a wide range of cost-effective optical communication applications demanding $\mu$m-scale footprints, ultrafast operation, robust design and high environmental stability.