Waveguide-Based Microscopy

Abstract

Advances in compact imaging techniques continue to deliver higher resolution, lower-cost components, and increasingly miniaturized systems. Scanning Near-field Optical Microscopy (SNOM), when implemented with waveguides as scanning probes, offers a promising route toward high-resolution imaging in such platforms. The principle relies on coupling light into on-chip waveguides, which are narrow structures that guide light with high precision. After exiting the waveguide, the light reflects off the sample surface and is subsequently recaptured and guided back into the chip. The returning signal is then coupled into a separate waveguide branch. In a previously designed chip-based setup, this signal was directed into an optical fiber and detected by a photodetector, achieving a spatial resolution of 500 nm. By transitioning from stepwise to continuous scanning, the acquisition time was reduced by half, enabling a scan of a 50 × 50 pixel image in under 22 minutes. An alternative approach directs the returning light through grating couplers to a camera, rather than routing it back into a fiber. This configuration supports the use of multiple waveguide probes, enabling scalable imaging. Using four probes simultaneously, a 534 µm wide scan clearly resolves a 250 µm feature, with a pixel size of 1 µm.