Spatial control of photonic nanojets

Area of Science:

• Optics and Photonics
• Nanotechnology
• Materials Science

Background:

• Microspheres have been extensively studied for light focusing, generating high-intensity beams known as photonic nanojets (PNJs).
• Conventional microsphere designs have limitations in precise PNJ characteristic engineering and manufacturing tolerance.

Purpose of the Study:

• To introduce and characterize a novel asymmetrical microstructure for generating and controlling PNJs.
• To demonstrate the precise engineering of PNJ properties through geometrical dimension selection.
• To explore the potential of cascaded asymmetrical elements for ultra-narrow PNJ generation.

Main Methods:

• Fabrication and optical characterization of a new asymmetrical microstructure composed of a supporting stage and a spherical cap.
• Investigation of PNJ generation using single and cascaded asymmetrical elements.
• Analysis of PNJ characteristics, including full width at half maximum (FWHM) and elongation, by varying geometrical dimensions.

Main Results:

• A single asymmetrical microstructure can generate an ultra-elongated PNJ.
• Cascaded asymmetrical elements achieve a PNJ with a FWHM waist down to 0.27λ.
• Ultra-narrow PNJs are achievable even with deviations from optimal dimensions, offering design flexibility.

Conclusions:

• The asymmetrical microstructure offers precise engineering of PNJ characteristics.
• Cascaded asymmetrical structures provide significant design flexibility and manufacturing tolerance compared to conventional microspheres.
• The developed structure holds promise for numerous applications requiring controlled light focusing.