4.5 Article

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

Journal

IEEE PHOTONICS JOURNAL
Volume 14, Issue 3, Pages -

Publisher

IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC
DOI: 10.1109/JPHOT.2022.3167695

Keywords

Optical waveguides; Electromagnetic waveguides; Optical sensors; Optical device fabrication; Sensors; Germanium; Slabs; Slot waveguides; mid-infrared; Ge-on-Si; confinement factor; propagation loss

Funding

  1. National Research Foundation of Korea [2020R1F1A1052718, 20012263]
  2. KIST Institutional Program [2E31372]
  3. BK21 FOUR
  4. Korea Evaluation Institute of Industrial Technology (KEIT) [20012263] Funding Source: Korea Institute of Science & Technology Information (KISTI), National Science & Technology Information Service (NTIS)
  5. National Research Foundation of Korea [2020R1F1A1052718] Funding Source: Korea Institute of Science & Technology Information (KISTI), National Science & Technology Information Service (NTIS)

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This article presents a slot waveguide based on the Ge-on-Si platform and characterizes its performance through numerical design and experimental measurements. The results indicate that the slot waveguide has similar propagation loss to channel waveguides, but higher field confinement, making it suitable for sensing applications.
We first demonstrated a slot waveguide based on a Ge-on-Si (GOS) platform with a 3 mu m thickness of the Ge in the mid-infrared wavelength range at 4.2 mu m. 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 CO2. 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.

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