Study of waveguide background at visible wavelengths for on-chip nanoscopy

TL;DR

This study compares background noise in tantalum pentoxide and silicon nitride waveguides at visible wavelengths for on-chip super-resolution microscopy, highlighting implications for localization precision and material choice.

Contribution

It provides a comparative analysis of waveguide background effects on localization precision in on-chip nanoscopy, focusing on two common high-refractive index materials.

Findings

Ta2O5 has weaker background at shorter wavelengths compared to Si3N4.

Background increases for Si3N4 at wavelengths below 640 nm.

Higher background reduces localization precision in dSTORM imaging.

Abstract

On-chip super-resolution optical microscopy is an emerging field relying on waveguide excitation with visible light. Here, we investigate two commonly used high-refractive index waveguide platforms, tantalum pentoxide (Ta$_2$O$_5$) and silicon nitride (Si$_3$N$_4$), with respect to their background with excitation in the range 488-640 nm. The background strength from these waveguides were estimated by imaging fluorescent beads. The spectral dependence of the background from these waveguide platforms was also measured. For 640 nm wavelength excitation both the materials had a weak background, but the background increases progressively for shorter wavelengths for Si3N4. We further explored the effect of the waveguide background on localization precision of single molecule localization for direct stochastic optical reconstruction microscopy (dSTORM). An increase in background for Si$_3$N$_4$ at 488 nm is shown to reduce the localization precision and thus the resolution of the reconstructed images. The localization precision at 640 nm was very similar for both the materials. Thus, for shorter wavelength applications Ta$_2$O$_5$ is preferable. Reducing the background from Si$_3$N$_4$ at shorter wavelengths via improved fabrication will be worth pursuing.