Large-scale optical trapping using a gradient-thickness protected microbottle resonator.

Area of Science:

• Optics and Photonics
• Biomedical Engineering
• Materials Science

Background:

• Near-field optical trapping has potential in bioparticle research but suffers from low efficiency and shallow penetration depth.
• Existing methods are sensitive to particle perturbations, limiting robustness and practicality.

Purpose of the Study:

• To develop a novel optical trapping method that overcomes the limitations of near-field approaches.
• To demonstrate a scalable and robust optical trapping system for bioparticle manipulation.

Main Methods:

• Fabrication of a thin-walled hollow microbottle resonator with gradient-wall thickness.
• Excitation of axial high-order Whispering Gallery Modes (WGMs) using fiber taper coupling.
• Utilizing mode field strength antinodes for trapping instead of the evanescent field.

Main Results:

• Demonstrated large-scale optical trapping over an axial span exceeding 195 μm.
• Achieved a low threshold power of 0.198 mW for 500-nm polystyrene particles.
• The gradient-thickness protected (GTP) microbottle resonator showed enhanced robustness against particle perturbations.

Conclusions:

• The GTP WGM microbottle resonator offers a scalable and robust framework for optical manipulation.
• This technology enables tunable localized optical trapping for applications in single-particle analysis and bioparticle sensing.