Germanium-based integrated photonics from near- to mid-infrared applications

TLDR

Germanium has enabled high‑performance silicon photonics, providing mature photodetectors, modulators, and lasers, and its extended transparency window beyond 8 µm has spurred the development of compact mid‑infrared photonic platforms up to 15 µm. This review surveys the most relevant Ge‑based platforms that have demonstrated passive and active building blocks for mid‑IR photonics and examines seminal works on integrated mid‑IR optical sensing. The authors compile and analyze reported Ge‑based platform designs, passive and active device implementations, and sensing demonstrations to illustrate the state of mid‑IR photonics.

Abstract

Abstract Germanium (Ge) has played a key role in silicon photonics as an enabling material for datacom applications. Indeed, the unique properties of Ge have been leveraged to develop high performance integrated photodectors, which are now mature devices. Ge is also very useful for the achievement of compact modulators and monolithically integrated laser sources on silicon. Interestingly, research efforts in these domains also put forward the current revolution of mid-IR photonics. Ge and Ge-based alloys also present strong advantages for mid-infrared photonic platform such as the extension of the transparency window for these materials, which can operate at wavelengths beyond 8 μm. Different platforms have been proposed to take benefit from the broad transparency of Ge up to 15 μm, and the main passive building blocks are now being developed. In this review, we will present the most relevant Ge-based platforms reported so far that have led to the demonstration of several passive and active building blocks for mid-IR photonics. Seminal works on mid-IR optical sensing using integrated platforms will also be reviewed.