Photonic crystal based interferometric design for label-free all-optical sensing applications

Area of Science:

• Photonics and Optical Engineering
• Nanotechnology
• Materials Science

Background:

• Optical sensing devices offer high selectivity for detecting chemicals and gases in industrial and biomedical fields.
• Photonic crystal (PC) based sensors provide compact and efficient on-chip sensing platforms.
• Interferometric PC devices enhance sensitivity by detecting minute changes in optical path length.

Purpose of the Study:

• To propose and analyze a new Mach-Zehnder Interferometer (MZI) design utilizing low-symmetric silicon photonic crystals (Si PCs).
• To demonstrate the MZI's compatibility with CMOS technology for practical applications.
• To investigate the Fano resonances and interferometric tunability for enhanced sensing capabilities.

Main Methods:

• A novel MZI configuration was designed using periodically aligned, symmetry-reduced PC unit cells in the MZI arms.
• The all-dielectric MZI system was numerically investigated in both spectral and spatial domains.
• Sensitivity, quality factor (Q), and Figure-of-Merit (FoM) were calculated for gaseous and liquid analytes.

Main Results:

• The proposed MZI exhibits Fano resonances, allowing efficient control of transmission spectra for refractive index change detection.
• Optical sensitivity reached approximately 300 nm/RIU for gaseous analytes and 263.2 nm/RIU for liquid analytes.
• High quality factors (Q > 45000) and FoM values (up to ~8950 RIU⁻¹) were achieved, indicating enhanced sensing performance.

Conclusions:

• The low-symmetric PC-based MZI design is suitable for efficient optical sensing of toxic gases and liquids.
• The device offers controllable output power and enhanced optical sensing performance.
• This interferometric configuration holds potential for advanced photonic sensor applications.