Critically coupled Fabry-Perot cavity with high signal contrast for refractive index sensing

Area of Science:

• Photonics and Optical Sensing
• Metamaterials and Nanophotonics
• Spectroscopy and Sensing

Background:

• High signal contrast in refractive index (RI) sensing requires perfect absorption at resonance and minimal absorption off-resonance.
• One-port optical cavities are crucial for sensitive RI detection.

Purpose of the Study:

• To propose and analyze a novel absorption-enhanced Fabry-Perot (MAFP) cavity for enhanced RI sensing.
• To achieve critical coupling in a near-infrared wavelength range for optimized performance.

Main Methods:

• Utilizing a thick gold layer as both a mirror and absorber in a one-port cavity configuration.
• Employing a tailored dielectric metasurface to balance radiation and absorption coupling rates.
• Theoretical analysis using temporal coupled-mode theory.

Main Results:

• The gas MAFP cavity demonstrated a sensitivity of ~1388 nm/RIU with a narrow linewidth (<0.7 nm), resolving RI changes of 5x10^-4 with 100% signal contrast.
• The liquid MAFP cavity achieved a sensitivity of ~996 nm/RIU for RI changes from 1.30 to 1.38.
• Both configurations attained a signal contrast of ~100%.

Conclusions:

• The proposed MAFP cavity design enables highly sensitive and accurate RI sensing with excellent signal contrast.
• The critical coupling condition, achieved through metasurface tailoring, is key to the device's high performance.
• This technology holds promise for advanced gas and liquid sensing applications.