Fully suspended slot waveguides for high refractive index sensitivity

Area of Science:

• Photonics and Optical Engineering
• Materials Science
• Nanotechnology

Background:

• Silicon-on-insulator (SOI) platforms are widely used for photonic integrated circuits.
• Slot waveguides confine light in a low-refractive-index slot, enhancing light-matter interaction.
• Existing SOI slot waveguides are limited by the buried oxide layer's spectral and sensitivity characteristics.

Purpose of the Study:

• To propose and demonstrate a fully suspended mid-infrared (FSMIR) slot waveguide on an SOI platform.
• To investigate the propagation loss and spectral characteristics of the FSMIR slot waveguide.
• To evaluate the sensing performance and compare its sensitivity with conventional SOI slot waveguides.

Main Methods:

• Fabrication of FSMIR slot waveguides using electron-beam lithography and etching on an SOI wafer.
• Mechanical suspension of the waveguide core by lateral subwavelength grating claddings.
• Experimental measurement of propagation loss at 2.25 μm wavelength.
• Numerical simulations to determine effective index and sensitivity.

Main Results:

• First experimental demonstration of an FSMIR slot waveguide on an SOI platform.
• Measured propagation loss of 7.9 dB/cm at 2.25 μm.
• Broad spectral transparency, limited only by silicon absorption, due to the removal of the buried oxide layer.
• Numerical simulations indicate a sensitivity of 1.123, a 9.7% improvement over conventional SOI slot waveguides.

Conclusions:

• The FSMIR slot waveguide offers a promising platform for mid-infrared applications.
• Removal of the buried oxide layer significantly enhances spectral range and sensitivity.
• This design represents a significant advancement for integrated photonics in the mid-infrared spectrum.