Suspended SOI waveguide with sub-wavelength grating cladding for mid-infrared.

Area of Science:

• Photonics and Optical Engineering
• Materials Science

Background:

• Silicon-on-insulator (SOI) platforms are crucial for integrated photonics.
• Mid-infrared (MIR) applications require specialized waveguide designs for efficient light propagation.

Purpose of the Study:

• To introduce a new SOI waveguide architecture for MIR applications.
• To investigate the impact of sub-wavelength hole lattices on waveguide performance and fabrication.

Main Methods:

• Fabrication of SOI waveguides with sub-wavelength hole lattices.
• Characterization of waveguide propagation loss at 3.8 μm.
• Etching of the buried oxide (BOX) layer using vapor phase and liquid hydrofluoric acid (HF).

Main Results:

• A waveguide with a 300 nm grating period and 150 nm holes achieved 3.4 dB/cm loss after partial BOX removal (560 nm) via vapor phase HF.
• An alternative design with a 550 nm period and 450 nm holes showed 3.6 dB/cm loss after complete BOX removal via liquid phase HF, enabling faster etching.

Conclusions:

• The proposed sub-wavelength lattice structure effectively functions as lateral cladding and facilitates BOX removal.
• Both vapor and liquid HF etching methods are viable for BOX removal, with design choices influencing etching speed and efficiency.
• The developed waveguides demonstrate promising performance for mid-infrared integrated photonic circuits.