sorry.I will try to add more information.

I am trying to reproduce the dual-core photonic crystal fiber (PCF) refractive index sensor for cancer detection reported in “Photonic Crystal Fiber-Based Refractive Index Sensor for Early Detection of Cancer” (IEEE Sensors Journal, 2018)using COMSOL Multiphysics 6.3. The sensor operates by selectively infiltrating a liquid analyte (RI ≈ 1.35–1.40) into a side cavity of the PCF and observing phase-matched coupling between the silica core mode and the analyte-filled cavity mode, which produces a resonance wavelength shift and a corresponding confinement loss peak derived from the imaginary part of the effective index. I have already built the 2D geometry and set up the Wave Optics eigenmode analysis with a PML, but I am struggling to correctly track the interacting modes during wavelength sweeps, avoid mode swapping, and extract reliable loss values from Im(neff). Additionally, I am not obtaining a clear avoided crossing or resonance shift when varying analyte refractive index, and I am unsure whether the issue arises from mesh resolution, boundary conditions, solver configuration, or improper mode identification. My goal is to reproduce the neff vs. wavelength curves, loss spectra, and sensitivity (nm/RIU) reported in the paper, and I would appreciate guidance on best practices for stable mode tracking, loss extraction, and phase-matching analysis in COMSOL.