Linear and passive silicon-on-insulator refractive index sensor utilizing Bragg grating-assisted Michelson...

Area of Science:

• Photonics and Sensing Technology
• Integrated Optics
• Materials Science

Background:

• Conventional refractive index (RI) sensors often exhibit nonlinear responses, limiting their utility for precise gas concentration monitoring.
• The need for robust, linear sensors is critical in applications requiring consistent performance across a wide range of RI variations.

Purpose of the Study:

• To design a linear, passive refractive index sensor using silicon-on-insulator technology.
• To achieve a constant figure of merit (FOM) for reliable gas sensing across diverse RI changes.
• To enable simplified fabrication for mass production.

Main Methods:

• Utilized a Michelson interferometer integrated with two long Bragg gratings to linearize the sensor response.
• Incorporated slotted Bragg gratings in sensing arms to enhance light-medium interaction.
• Employed finite-difference eigenmode (FDE) and finite-difference time-domain (FDTD) simulations for design validation.
• Fabricated and measured Bragg grating devices and Michelson interferometers to compare with simulation results.

Main Results:

• Achieved a constant figure of merit (FOM) of approximately 113 RIU⁻¹.
• Demonstrated a waveguide sensitivity of ~0.72 with specific design parameters (80 nm slot width, 0.01 index modulation depth).
• Validated the sensor's functionality through experimental measurements and simulations, confirming design principles.

Conclusions:

• The proposed linear RI sensor design offers a constant FOM, crucial for accurate gas concentration monitoring.
• The sensor's design allows for direct air exposure, simplifying fabrication and enabling low-cost production.
• The technology is well-suited for mass production due to its simplified fabrication process and robust performance.