Objective  Fiber optic tweezers have characteristics of compactness, high integration capability, and excellent portability, rendering them advantageous in applications such as chemical analyses, biosynthesis, and drug delivery systems. Single-hole suspension core fiber naturally integrates fiber waveguide and microfluidic channel, which can not only capture particles but also store, transport, analyze, and detect particles such as cells or drug molecules if applied in fiber optic tweezers. However, fiber-optic tweezers typically necessitate integration with microchannels or microfluidic technologies to perform multidimensional manipulations like transportation and sorting. The manufacture of microfluidic devices is complicated, and microfluidic devices and optical fibers as mutually independent devices with low system optical coupling efficiency and integration. Therefore, a simpler more efficient, and highly integrated method for particle or cell manipulation and transport is needed. For this reason, this thesis carries out research on fiber optic tweezer technology based on single-hole suspension core fibers to address the key issue of particle manipulation by suspension core fibers with hollow hole structures.

Methods  The particle manipulation principle of single-hole-suspended-core fiber optical tweezers is analyzed, the analytical model of single-hole-suspended-core fiber optical tweezers is established from the mechanism of the double-beam focused light field, the analytical calculation method of the light trapping force is determined, and the characteristics of single-hole-suspended-core fibers with symmetric and off-core structures are analyzed at the same time. A parabolic-shaped single-hole-suspended-core fiber optical tweezers probe is designed, and its simulation model is used to calculate the optical field and optical trapping force, analyze the energy distribution and the characteristics of the optical trapping force, and investigate the specific effects of the hollow aperture, particle size, and core power on the optical trapping force manipulation performance. A parabolic-shaped single-hole-suspended-core fiber probe with a diameter of 9 μm at the tip of the probe was prepared by the CO₂ laser melt-drawing cone method with pneumatic pressure control, and an experimental system was constructed to realize the manipulation experiments on polystyrene particles with diameters of 2 μm, 5 μm, and 10 μm.

Results and Discussions  Simulations using Rsoft's Beamprop module were performed to analyze the optical field intensity distribution of single-hole-suspended-core fiber optical tweezers with different hollow apertures and core powers. The results show that increasing the hollow aperture enhances the light convergence effect (Fig.2). A model was established based on this simulation to investigate the effects of hollow aperture diameter, particle size, and fiber core power on the force on the particles. It was found that, the large aperture facilitates the provision of stable transverse and longitudinal capture points (Fig.4); Large-diameter particles facilitate longitudinal capture, while transverse capture requires appropriately sized particles (Fig.5); And the power of the suspension core has a significant effect on the transverse and longitudinal optical trapping forces, while the bias core has a lesser effect on the optical trapping forces (Fig.6). Finally, through the preparation and experimental verification of optical tweezers probes, it was confirmed that this parabolic single-aperture, dual-core, bias-suspended fiber optic tweezers could effectively manipulate particles with diameters of 2 μm, 5 μm, and 10 μm, and in particular showed the best performance for the manipulation of 5 μm particles (Fig.12).

Conclusions  A parabolic single-aperture dual-core biased suspended fiber probe structure is proposed. The structural parameters of the probe are optimized through simulation analysis, which significantly affects the optical tweezer optical field and capture force, and the optical tweezer probe is experimentally prepared, thus verifying that the probe can flexibly manipulate particles with diameters of 2 μm, 5 μm, and 10 μm. In particular, it demonstrates an excellent capture and ejection ability for 5 μm particles. These optical tweezers probe enhances the integration potential of fiber optic tweezers and brings new perspectives on particle manipulation and sorting technology, which is of great scientific value.