Design of the Bimodal Grating Sensor with a Built-In Mode Demultiplexer

Area of Science:

• Photonics and Optical Sensing
• Integrated Optics
• Nanophotonics

Background:

• Waveguide-based sensors are crucial for detecting environmental changes.
• Existing designs often face limitations in sensitivity and signal discrimination.
• Mode transformation in silicon waveguides offers potential for enhanced sensing capabilities.

Purpose of the Study:

• To develop a highly sensitive optical sensor using silicon wire waveguides.
• To demonstrate efficient mode transformation for improved signal interrogation.
• To achieve accurate refractive index sensing with a compact and manufacturable design.

Main Methods:

• Utilized an asymmetric grating for collinear diffraction and mode transformation (TE0 to TE1).
• Incorporated a mode filter/demultiplexer with a compact directional coupler.
• Employed wavelength interrogation based on spectral peak position of transmitted TE0 mode power.

Main Results:

• Achieved high volume sensitivity of approximately 1600 nm/RIU.
• Demonstrated efficient mode selection with low excess loss (~ -0.5 dB) and minimal crosstalk (< -42 dB).
• Obtained a high sensitivity limit of detection (iLOD) of ~ 2.1 × 10^-4 RIU in water at 1550 nm.

Conclusions:

• The proposed sensor design offers a promising platform for sensitive and accurate environmental index measurements.
• The integration of mode transformation and filtering enhances signal quality for wavelength interrogation.
• The sensor is manufacturable using modern single-step etching processes, paving the way for practical applications.