Surface plasmon interferometer in silicon-on-insulator: novel concept for an integrated biosensor: Comment

Area of Science:

• Optoelectronics
• Nanophotonics
• Integrated Optics

Background:

• Surface plasmon interferometers on silicon-on-insulator (SOI) are proposed for integrated biosensing.
• Accurate calculation of waveguide mode propagation and sensor sensitivity is crucial for device design.
• Previous analyses may have overlooked the impact of radiation modes in short waveguide structures.

Purpose of the Study:

• To investigate the inaccuracies in calculating waveguide mode propagation and sensitivity by neglecting radiation modes.
• To re-evaluate the sensitivity of a proposed SOI surface plasmon interferometer biosensor.
• To understand the physical mechanism behind the influence of radiation modes in short waveguides.

Main Methods:

• Numerical calculations were performed to analyze waveguide mode propagation.
• The study incorporated radiation modes into the sensitivity calculations.
• Comparison of sensitivity values with and without considering radiation modes.

Main Results:

• Radiation modes cannot be ignored in short waveguide structures, contrary to potential prior assumptions.
• Including radiation modes drastically reduces the calculated sensitivity from over 10,000 dB/RIU to below 1000 dB/RIU.
• Optical power recapture by the output guide from radiation modes explains the reduced interference contrast and sensitivity.

Conclusions:

• Neglecting radiation modes leads to significant overestimation of biosensor sensitivity in short SOI waveguides.
• Accurate modeling must include radiation modes for reliable performance prediction of integrated photonic biosensors.
• The findings highlight the importance of considering all optical modes for short photonic device design.