On-fiber photonic nanojet enables super-resolution in en face optical coherence tomography and scattering nanoscopy

Photonic nanojet (PNJ) of subwavelength spot-size originating at shadow side of a microsphere is projected as an imperative optical tool for micro-nano optics applications. Lack of a free hold PNJ source limits its vast potential. A state-of-the-art PNJ is introduced on a chemically etched encaved optical fiber nanoprobe holding a microsphere. Nanoprobe generating optical beam of spot-size ~2 μm, is focused on the microsphere resulting in PNJ of varying spot-size, 0.8λ to 0.5λ, over its’ length ~13λ at 660 nm wavelength. A PNJ centered around 840 nm wavelength combined with an effective numerical aperture ~2 results in an en-face optical coherence tomography (OCT) image of lateral resolution ~247 nm and phase map with optical thickness, ~70 nm for a standard DVD. Further, the PNJ based backscattered nanoscopy of silver nano-particles is exhibited with resolution ~40 nm. This commercially viable PNJ head can be an ideal platform for various microscopies and other applications. Sub-diffraction resolution is a long-standing goal for optical imaging; hence, the authors present a photonic nanojet head at an optical fiber tip, generating a subwavelength spot over a long range. The nanoject enhances the lateral resolution of en face Optical Coherence Tomography (~250 nm) and enables detection of silver nanoparticles (~40 nm)