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.
Highlights
Today, silicon photonics is a mature technology for integrated photonics, which benefits from a reliable and highvolume fabrication to offer high performance, low cost and compact photonic circuits
Both Si and Ge exhibit strong third-order non-linear optics (NLO) coefficients while two-photon absorption (TPA), which is known to limit the efficiency of nonlinearities, vanishes in the mid-IR [125, 126]
While the use of SOI wafers allows for strong field confinement and tight bends, the combination with Ge permits to obtain high performance active devices required for telecom and datacom applications, at near-IR wavelength
Summary
Silicon photonics is a mature technology for integrated photonics, which benefits from a reliable and highvolume fabrication to offer high performance, low cost and compact photonic circuits. Besides the demonstration of efficient devices, an in-depth understanding of the properties of Ge, SiGe and GeSn is required to properly and finely tune several parameters such as the concentration of Ge or Sn in the alloys, doping or lattice strain It appeared that Ge presents distinctive advantages for mid-infrared (mid-IR) photonics owing to its wide transparency window up to 15 μm and a strong non-linear refractive index. Previous works at telecom wavelength paved the way towards a new playground for photonic researchers as manifold engineering possibilities are opened using Ge, SiGe and GeSn for both passive and active functions In this context, we will review the development of Gebased photonic integrated circuits. To deal with the lattice mismatch between Si and Ge, a two-step growth process has been proposed and largely adopted, in which a thin
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
