Material limitations on the detection limit in refractometry

Area of Science:

• Optical sensing
• Nanophotonics
• Biomedical engineering

Background:

• Refractometric sensors utilize changes in refractive index to detect analytes.
• High-Q optical cavities offer enhanced sensitivity for such measurements.
• Silicon-based resonators are promising for integrated photonic sensing applications.

Purpose of the Study:

• To determine the fundamental detection limits of refractometric sensors based on high-Q optical cavities.
• To investigate the influence of material properties and cavity parameters on sensor performance.
• To evaluate the sensing capabilities of silicon photonic crystal resonators in bio-liquid environments.

Main Methods:

• Theoretical analysis of the classical detection limit for refractometric sensing.
• Modeling of high-Q optical cavities, considering finite Q factors and filling fractions.
• Simulation of silicon photonic crystal resonators operating in the near-infrared and visible spectrum.

Main Results:

• The ultimate classical detection limit is fundamentally bounded by the imaginary part of the complex refractive index (η).
• Sensor detection limits decrease with finite Q factors and optimized filling fractions.
• For silicon resonators, the detection limit is largely independent of filling fraction in the infrared transparency window (λ ≳ 1100 nm).
• In the visible spectrum, silicon absorption significantly impacts the detection limit, making it strongly dependent on the filling fraction.

Conclusions:

• High-Q optical cavities provide a pathway to ultra-sensitive refractometric detection.
• The choice of material and operating wavelength is critical for optimizing sensor performance.
• Silicon photonic crystal resonators show potential for biosensing, with performance characteristics varying across different spectral regions.