Ultra-compact plasmonic modulator for optical inteconnects

TL;DR

This paper presents a CMOS-compatible, ultra-compact plasmonic modulator that leverages the Franz-Keldysh effect in Germanium, achieving low power consumption and efficient coupling for optical interconnects.

Contribution

It introduces a novel plasmonic modulator design with optimized coupling and demonstrates the lowest reported electrical power consumption for silicon photonic modulators.

Findings

Extinction ratio of 3.3 dB achieved

Electrical power consumption as low as 20 fJ/bit

Coupling losses reduced to 1 dB per coupler

Abstract

This work aims to design a CMOS compatible, low-electrical power consumption modulator assisted by plasmons. For compactness and reduction of the electrical power consumption, electro-absorption based on the Franz-Keldysh effect in Germanium was chosen for modulation. It consists in the change of the absorption coefficient of the material near the band edge under the application of a static electric field, hence producing a direct modulation of the light intensity. The use of plasmons allows enhancing the electro-optical effect due to the high field confinement. An integrated electro-optical simulation tool was developed to design and optimize the modulator. The designed plasmonic modulator has an extinction ratio of 3.3 dB with insertion losses of 13.2 dB and electrical power consumption as low as 20 fJ/bit, i.e. the lowest electrical power consumption reported for silicon photonic modulators. In- and out-coupling to a standard silicon waveguide was also engineered by the means of an optimized Si-Ge taper, reducing the coupling losses to only 1 dB per coupler. Besides, an experimental work was carried out to try to shift the Franz-Keldysh effect, which is maximum at 1650 nm, to lower wavelength close to 1.55 {\mu}m for telecommunication applications.