Optical trapping is the science of holding and immobilizing particles and cells, for further manipulation and spectroscopic studies. Enhancing the application of optical trapping is limited by size and flexibility of this tool, mostly limited to high numerical aperture objectives. In this work, we show the potential of using structured light to further enhance the capabilities of optical fibres as optical tweezers, to be used for applications in which space and throughput are of importance. Using femtosecond two photon direct laser writing, we produce accurately designed micro-optic probes at the tip of optical fibres to enhance the light field for trapping single particles as well as single live cells. Enhanced trapping efficiency, ease of transporting trapped particle, and potential of performing wide spectrum spectroscopy on the trapped entity are the advantages of the present approach.
An original approach of highly efficient fiber-based optical tweezers using 3D printed diffractive optical elements at an optical fiber facets is presented. As an example Fresnel lens structures, with focal lengths in the range of 50 to 200 µm, are fabricated by femtosecond two photo lithography. Compared to conventional fiber tip tweezers based on chemically wet etched fiber tips, significant trapping efficiency enhancement by a factor of up to 50 is observed in both axial and transverse direction. An outlook on further concepts of enhanced optical fiber tweezers based on 3D diffractive structures will complete the presentation.
A new approach of a highly efficient counter propagating optical fiber based tweezers using 3D printed Fresnel lenses at the fiber facets will be presented. In contrast to conventional fiber tip tweezers the emitted beams of the Fresnel lens fibers are converging resulting in a significantly enhanced trapping efficiency in both axial and transverse direction. The used polymer diffractive Fresnel lens structures are fabricated by femtosecond two photo lithography using a commercial system. The measured trapping efficiencies are found to be up to 90 times higher than for similar results using chemically wet-etched fiber tips. A short outlook on further concepts of enhanced optical fiber tweezers based on 3D diffractive structures will also be given.
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