@article {Yu:21,
	title = {On-chip optical tweezers based on freeform optics},
	journal = {Optica},
	volume = {8},
	number = {3},
	year = {2021},
	month = {Mar},
	pages = {409{\textendash}414},
	publisher = {OSA},
	abstract = {Since its advent in the 1970s, optical tweezers have been widely deployed as a preferred non-contact technique for manipulating microscale objects. On-chip integrated optical tweezers, which afford significant size, weight, and cost benefits, have been implemented, relying upon near-field evanescent waves. As a result, these tweezers are only capable of manipulation in near-surface regions and often demand high power since the evanescent interactions are relatively weak. We introduce on-chip optical tweezers based on freeform micro-optics, which comprise optical reflectors or refractive lenses integrated on waveguide end facets via two-photon polymerization. The freeform optical design offers unprecedented degrees of freedom to design optical fields with strong three-dimensional intensity gradients, useful for trapping and manipulating suspended particles in an integrated chip-scale platform. We demonstrate the design, fabrication, and measurement of both reflective and refractive micro-optical tweezers. The reflective tweezers feature a remarkably low trapping threshold power, and the refractive tweezers are particularly useful for multiparticle trapping and interparticle interaction analysis. Our integrated micro-optical tweezers uniquely combine a compact footprint, broadband operation, high trapping efficiency, and scalable integration with planar photonic circuits. This class of tweezers is promising for on-chip sensing, cell assembly, particle dynamics analysis, and ion trapping.},
	keywords = {Evanescent waves, Optical design, Optical fields, Optical systems, Optical Tweezers, Two photon polymerization},
	doi = {10.1364/OPTICA.418837},
	url = {http://www.osapublishing.org/optica/abstract.cfm?URI=optica-8-3-409},
	author = {Shaoliang Yu and Lu, Jinsheng and Ginis, Vincent and Kheifets, Simon and Soon Wei Daniel Lim and Qiu, Min and Gu, Tian and Juejun Hu and Federico Capasso}
}
