High performance refractive index sensor based on low Q-factor ring resonators and FFT processing of wavelength...

Area of Science:

• Optical biosensing
• Nanophotonics
• Biomedical engineering

Background:

• Micro-ring resonators (MRRs) are widely used for biosensing applications.
• Accurate detection of resonance shifts is crucial for sensitive biosensing.
• Previous simulation studies have explored methods for resonance shift calculation.

Purpose of the Study:

• To experimentally validate a Fast Fourier Transform (FFT) method for calculating resonance shifts in MRR biosensors.
• To investigate the impact of various factors on the performance of the FFT method.
• To achieve a record limit of detection for optical biosensors.

Main Methods:

• Utilized a tunable laser at 850 nm and an MRR with a quality factor of 1.5×10^4.
• Investigated the effect of resonance peak number, laser power wavelength dependence, and MRR transfer function asymmetry.
• Developed and experimentally validated the FFT method on a TriPleX platform using sucrose solutions.
• Implemented noise exclusion techniques from the microfluidic system.

Main Results:

• Performance improved by a factor of 2 with four-peak transfer functions compared to single-peak.
• Wavelength dependence of laser power had minimal impact on performance.
• MRR transfer function asymmetry significantly increased measurement errors.
• Achieved a wavelength resolution of 0.08 pm with a 0.5 pm scanning step.
• Measured MRR sensitivity of 93.7 nm/RIU.

Conclusions:

• The FFT method, optimized with techniques to mitigate asymmetry and noise, significantly enhances biosensor performance.
• The developed system demonstrates a potential limit of detection as low as 8.5×10^-7 RIU.
• This represents a record performance for optical sensors at this scanning step level, paving the way for advanced diagnostics.