The optimal hole diameter for a solid-core photonic crystal fiber (PCF) used in Surface Enhanced Raman Spectroscopy (SERS) is generally in the range of 2–3 μm, as indicated by the Google AI overview. This range ensures that the normalized field intensity (I) at the inner wall near the solid core remains sufficiently high while minimizing its variation with wavelength. In other words, dI/dλ should be minimized to maintain consistent enhancement across different wavelengths. Furthermore (dI/dλ)/ I should be the minimum.

From my derivation, I have determined that the most suitable hole diameter is 2.55 μm, which aligns with the expected range of 2–3 μm. I would appreciate your insights and recommendations to further validate this result. Additionally, if you have access to recent peer-reviewed journals supporting this finding, I would greatly appreciate them to strengthen my confidence in this conclusion. Open for discussion.