Experimental Demonstration of Germanium-on-Silicon Slot Waveguides at Mid-Infrared Wavelength

Abstract

We first demonstrated a slot waveguide based on a Ge-on-Si (GOS) platform with a 3 µm thickness of the Ge in the mid-infrared wavelength range at 4.2 µm. We numerically designed the slot waveguide to have a large field confinement in the slot for sensing application. Based on the design, we fabricated the GOS slot waveguide with a slot gap of 200 nm, which is coupled with in-out grating couplers. We characterized the propagation loss of the waveguides by the cut-back method and carefully compared it with channel waveguides. In fundamental TE mode, the propagation loss in the channel waveguide and the slot waveguide were quite similar (5.20 and 4.86 dB/cm, respectively), whereas the field confinement was much higher in the slot waveguides. Additionally, we simulated and analyzed the loss of the devices in terms of radiation, sidewall roughness scattering, material absorption by free-carrier absorption (FCA), and CO 2 . These results strongly suggest that the fabricated slot waveguide based on the GOS platform would be one of the promising building blocks for the optical gas sensor platform.

Room-temperature waveguide-integrated photodetector using bolometric effect for mid-infrared spectroscopy applications

“…The ion implantation process is a well-established technique in current semiconductor technologies, enabling fabrication ease, cost-effectiveness, and scalability. Additionally, this approach can be readily adopted into various Si-or Ge-based MIR photonic platforms, including SOI 39 , suspended-Si 36 , Ge-on-Si (GOS) 40 , suspended-Ge 41 , Ge-on-SOI 42 , and Ge-OI 34,35 . Furthermore, as bolometry with FCA in Ge is not wavelength-speci c, the operational range is extendable across the entire MIR spectrum without encountering cutoff regions.…”

Sustainable Production of Ultrathin Ge Freestanding Membranes

“…Germanium (Ge) is at the forefront of many applications in optoelectronics and photonics including lasers [1,2], wave guides [3,4], photodetectors [5][6][7], THz transmission [8], thermophotovoltaic [9][10][11], and high-efficiency solar cells [12]. Moreover, thanks to the closely matching thermal and crystallographic properties of Ge and gallium arsenide (GaAs), Ge substrates provide a compelling alternative for epitaxial growth of III-V compounds, while offering wafer diameters up to 300 mm.…”

Coupled Strip-Array Waveguides for Integrated Mid-IR Gas Sensing

“…Intensive work has been conducted for the detection of gases at mid-IR wavelengths, such as carbon dioxide (CO 2 ), carbon monoxide, acetylene, and methane, using strip, slot, ridge, and photonic-crystal waveguides on technology platforms spanning from silicon, silicon on insulator (SOI), silicon on sapphire (SOS), chalcogenide glass, germanium on silicon, germanium on SOI, germanium on silicon nitride, and silicon on silicon nitride [5][6][7][8][9][10][11]. While several groups have focused on the theoretical optimization and experimental validation of waveguide structures for CO 2 detection in the 4.26 µm band [12][13][14][15][16], several challenges toward the realization of fully integrated CO 2 sensors remain open. In particular, cost-effective on-chip mid-IR gas sensors rely on the development of thermal sources and detectors; however, their integration with the waveguide is still a challenge.…”