Multifunctional integration on optical fiber tips: challenges and opportunities

The flat endface of an optical fiber tip is an emerging light-coupled microscopic platform that combines fiber optics with planar micro- and nanotechnologies. Since different materials and structures are integrated onto the endfaces, optical fiber tip devices have miniature sizes, diverse integrated functions, and low insertion losses, making them suitable for all-optical networks. In recent decades, the increasing demand for multifunctional optical fibers has created opportunities to develop various structures on fiber tips. Meanwhile, the unconventional shape of optical fibers presents challenges involving the adaptation of standard planar micro- and nanostructure preparation strategies for fiber tips. In this context, researchers are committed to exploring and optimizing fiber tip manufacturing techniques, thereby paving the way for future integrated all-fiber devices with multifunctional applications. First, we present a broad overview of current fabrication technologies, classified as "top-down," "bottom-up," and "material transfer" methods, for patterning optical fiber tips. Next, we review typical structures integrated on fiber tips and their known and potential applications, categorized with respect to functional structure configurations, including "optical functionalization" and "electrical integration." Finally, we discuss the prospects for future opportunities involving multifunctional integrated fiber tips.