Mode thermo-optic coefficient engineering of sub-wavelength gratings and its application for a mode-insensitive...

Area of Science:

• Photonics and Optical Engineering
• Materials Science
• Integrated Optics

Background:

• Thermo-optic (TO) coefficients are crucial for phase control in integrated photonic devices.
• Sub-wavelength gratings (SWGs) offer unique optical properties but their TO effects are less explored.
• Existing waveguide designs have limited tunability for individual mode or polarization control.

Purpose of the Study:

• To investigate the dependence of TO coefficients on waveguide parameters in SWG-assisted strip waveguides.
• To demonstrate engineering of TO coefficients for individual spatial modes or polarization states.
• To design and experimentally validate a mode-insensitive thermo-optic switch using engineered SWGs.

Main Methods:

• Simulated and analyzed the thermo-optic coefficients of various waveguide modes in SWG-assisted strip waveguides.
• Varied waveguide parameters such as SWG width, strip width, duty cycle, and pitch.
• Designed a silicon-on-insulator (SOI) thermo-optic phase shifter utilizing an engineered SWG.
• Experimentally demonstrated the performance of the mode-insensitive switch at 1550 nm wavelength.

Main Results:

• TO coefficients were found to be highly dependent on waveguide parameters, offering design flexibility.
• A mode-insensitive thermo-optic switch demonstrated low switching powers (∼29 mW) for TE0-TE2 modes.
• High extinction ratios were achieved: up to 38.2 dB (cross) and 31 dB (bar) for TE0 mode.

Conclusions:

• Sub-wavelength grating structures provide novel degrees of freedom for engineering thermo-optic coefficients in integrated waveguides.
• This approach enables the design of individual mode or polarization-controlled thermo-optic devices.
• The demonstrated mode-insensitive switch highlights the practical application of engineered SWGs in advanced integrated photonic circuits.