Optimization of photonic nanojets generated by multilayer microcylinders with a genetic algorithm.

Area of Science:

• Photonics
• Optical Engineering
• Materials Science

Background:

• Photonic nanojets (PNJs) are highly focused light beams generated by dielectric microparticles.
• Controlling PNJ characteristics like length and width is crucial for applications in nanoscopy and sensing.
• Multilayer microstructures offer tunable optical properties for PNJ manipulation.

Purpose of the Study:

• To optimize multilayer microcylinder structures for enhanced photonic nanojet (PNJ) properties.
• To achieve ultra-long and ultra-narrow PNJs using a genetic algorithm and Mie theory.
• To explore the application of optimized PNJs in high-sensitivity refractive index sensing.

Main Methods:

• Utilized a genetic algorithm combined with Mie theory for structural optimization.
• Designed and simulated five-layer microcylinder structures for PNJ generation.
• Investigated PNJ elongation, waist narrowing, and refractive index sensing capabilities.

Main Results:

• Achieved an ultra-long PNJ with a beam length of approximately 107.5 times the illumination wavelength.
• Generated a PNJ with a subwavelength full-width at half maximum waist of ~0.22 times the illumination wavelength.
• Demonstrated the potential for ultra-small detectable refractive index variations using PNJ beam length.

Conclusions:

• Optimized five-layer microcylinders can precisely control PNJ characteristics, enabling ultra-long and ultra-narrow beams.
• The developed method offers a pathway for creating novel devices for optical nanoscopy and biophotonics.
• PNJ-based refractive index sensing shows promise for highly sensitive measurements in various applications.