Ultra-high on-chip optical gain in erbium-based hybrid slot waveguides

John Rönn,Laurent Vivien,Carlos Alonso-Ramos,Zhipei Sun,Weiwei Zhang,Antti Säynätjoki,Harri Lipsanen,Anton Autere,Xavier Leroux,Lasse Pakarinen,Eric Cassan

doi:10.1038/s41467-019-08369-w

Abstract

Efficient and reliable on-chip optical amplifiers and light sources would enable versatile integration of various active functionalities on the silicon platform. Although lasing on silicon has been demonstrated with semiconductors by using methods such as wafer bonding or molecular beam epitaxy, cost-effective mass production methods for CMOS-compatible active devices are still lacking. Here, we report ultra-high on-chip optical gain in erbium-based hybrid slot waveguides with a monolithic, CMOS-compatible and scalable atomic-layer deposition process. The unique layer-by-layer nature of atomic-layer deposition enables atomic scale engineering of the gain layer properties and straightforward integration with silicon integrated waveguides. We demonstrate up to 20.1 ± 7.31 dB/cm and at least 52.4 ± 13.8 dB/cm net modal and material gain per unit length, respectively, the highest performance achieved from erbium-based planar waveguides integrated on silicon. Our results show significant advances towards efficient on-chip amplification, opening a route to large-scale integration of various active functionalities on silicon.

Highlights

Efficient and reliable on-chip optical amplifiers and light sources would enable versatile integration of various active functionalities on the silicon platform
Silicon nitride (Si3N4) was chosen as the passive waveguide material due to its several advantages compared to silicon, including higher transparency at wavelengths below 1.1 μm, ultra-low two-photon absorption effect at telecom wavelengths and smaller propagation losses
The silicon dioxide was deposited with low-pressure chemical vapor deposition, whereas the silicon nitride was deposited with plasma-enhanced chemical vapor deposition

Summary

Introduction

Efficient and reliable on-chip optical amplifiers and light sources would enable versatile integration of various active functionalities on the silicon platform. Solutions relying on hybrid integration of III/V lasers on silicon, developed in the past years[5], bring additional complexity to the fabrication processes and do not provide the long-awaited monolithic approach necessary for the massive development of optical interconnects and on-chip optical signal processing This has set drawbacks for the development of next-generation hybrid integrated circuits, where electrical and optical functions are anticipated to be combined together for the best possible cost-effective and high-performance technology. Silicon-compatible Er:Al2O3 microring and distributed feedback lasers have been reported[8,9,10] Despite their superior performance, the average gain per unit length of the typical erbium-based integrated devices yet remains relatively small (up to few dB/cm) as the erbium-concentration is limited to less than one atomic percent due to quenching and up-conversion effects of active ions at higher concentration levels[11,12,13,14,15]. We report ultra-high on-chip optical gain by integrating atomic scale engineered erbium-doped aluminum oxide directly on silicon nitride slot waveguides with a monolithic, CMOS-

Methods

Results

Conclusion