High-Q Fabry⁻Pérot Micro-Cavities for High-Sensitivity Volume Refractometry

Area of Science:

• Photonics and optical sensing
• Microcavity resonators
• Optofluidics

Background:

• Fabry-Pérot cavities are crucial for optical sensing but often face limitations in quality factor and sensitivity.
• Previous designs for on-chip refractometers have drawbacks that hinder performance and applicability.
• Accurate modeling of microcavity behavior is essential for optimizing device design.

Purpose of the Study:

• To report a novel Fabry-Pérot microcavity structure with enhanced performance.
• To achieve the highest reported quality factor for an on-chip Fabry-Pérot resonator.
• To develop a highly sensitive on-chip volume refractometer using the novel cavity structure.

Main Methods:

• Designed a microcavity using two cylindrical Bragg micromirrors for beam confinement.
• Integrated external fiber rod lenses (FRLs) for input and output coupling.
• Employed Gaussian-optics equations for device modeling and design criteria.
• Utilized mixtures of ethanol and deionized water to test refractometer sensitivity.

Main Results:

• Achieved a quality factor exceeding 9800 for the on-chip Fabry-Pérot resonator.
• Demonstrated a high sensitivity of approximately 1000 nm/refractive index unit (RIU) for the refractometer.
• Validated the device's performance as a micro-opto-fluidic refractometer using varying analyte concentrations.
• Gaussian-optics modeling provided a more realistic performance prediction compared to ray-optics.

Conclusions:

• The novel Fabry-Pérot microcavity structure offers superior performance in terms of quality factor and sensitivity.
• This design overcomes limitations of previous Fabry-Pérot resonators and refractometers.
• The device shows significant potential for advanced micro-opto-fluidic sensing applications.