Researchers from University of Tokyo have successfully built fundamental components from the semiconductor germanium for integrated photonic circuits that work at mid-infrared wavelengths and could improve Internet speeds
The researchers built the new components from the material germanium (Ge). Like silicon, which is commonly used in conventional near-infrared photonics, germanium is a group IV semiconductor, which means it is in the same column of the periodic table and has similar electrical properties. Germanium has several properties that make it particularly well-suited to transmit and guide mid-infrared light, said Jian Kang, a Ph.D. candidate in the Takagi-Takenaka group in theDepartment of Electrical Engineering and Information Systems, University of Tokyo, Japan.
Germanium has high optical transparency in the mid-infrared range so mid-infrared light can easily pass through it. Compared to silicon, germanium has a number of other optically interesting properties. These include a higher refractive index, which means light passes more slowly through it. Germanium also has a larger third-order nonlinearity, an optical effect that can be exploited to, for example, amplify or self-focus beams of light. It has a stronger free-carrier effect, which means charge carrying electrons and holes in the material can help modulate light. Germanium also has a stronger thermo-optic effect than silicon, which means the refractive index can be more easily controlled with temperature.
“These properties could make Ge-based devices show higher performance or even realize new functionalities in the mid-infrared,” said Kang. Furthermore, recent progress on lasers made from strained-Ge and GeSn-based materials make germanium a promising material for integrating both the light producing and light steering components on the same photonic chip, Kang said.
“Currently, the Ge device performance may be not as good as state-of-the-art Si-based ones, because the study of Ge-based photonic components for mid-infrared is quite new and there remain many issues in the optimization of the fabrication process,” he said. “Nevertheless, we believe that Ge-based devices have intrinsic advantages.”
Keywords: Germanium(Ge), Silicon, Strained-Ge, GeSn-based materials, Ge-based devices
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