Enhanced urine refractive index sensing using a defect-engineered one-dimensional photonic crystal

Area of Science:

• Photonics
• Biomedical Sensing
• Materials Science

Background:

• Photonic crystal (PhC) sensors offer label-free detection capabilities.
• Accurate refractive index (RI) measurement is crucial for biomedical diagnostics, particularly for urine analysis.
• Existing PhC sensors may face challenges in sensitivity, stability, or fabrication robustness.

Purpose of the Study:

• To propose and analyze a defect-engineered one-dimensional photonic crystal (1D PhC) sensor for high-resolution urine refractive index detection.
• To evaluate the sensor's performance metrics including sensitivity, linearity, Q-factor, and figure of merit (FOM).
• To assess the sensor's robustness against fabrication variations.

Main Methods:

• Numerical simulation using the transfer matrix method (TMM) to model the 1D PhC structure.
• Design incorporates alternating TiO₂/MgF₂ layers with a central defect cavity for urine analyte.
• Analysis of defect mode shift, Full Width at Half Maximum (FWHM), Q-factor, and FOM under varying RI and thickness perturbations.

Main Results:

• The proposed 1D PhC sensor exhibits a sharp localized resonance within the photonic band gap.
• A stable red shift of the defect mode was observed with increasing urine refractive index (1.333 to 1.360).
• Achieved high sensitivity (388.57 nm/RIU), excellent linearity, narrow linewidth (avg. FWHM of 0.0305 nm), high Q-factor, and FOM. Tolerance analysis confirmed good fabrication robustness with ±2.5% thickness variation.

Conclusions:

• The defect-engineered 1D PhC sensor demonstrates a promising, balanced performance for practical urine-based biomedical sensing.
• Sensor performance evaluation requires a holistic approach, considering sensitivity alongside linewidth, Q-factor, FOM, and fabrication tolerance.
• The proposed design offers a competitive alternative to existing photonic-crystal sensing platforms.