Ultra Compact and Broadband Fiber Facet Graphene Oxide Microlens Array Fabricated on a Beam‐Expanding Fiber Facet Using Femtosecond Laser Direct Writing Technique

We demonstrate an ultra‐compact fiber facet graphene oxide (GO) microlenses array fabricated through femtosecond laser direct writing (FLDW). Taking advantage of the broadband transparency, mechanical, and laser‐tunable optical properties of GO, the device realizes phase modulation in a 400 nm film, enabling multi‐focus beam splitting and focusing. A coreless fiber segment is fusion‐spliced to a standard single‐mode fiber to expand the mode field, and a high‐density array of 19 microlenses is integrated on the beam‐expanding fiber facet; the device achieved focal lengths ranging from 8.0 to 9.6 and numerical apertures (NA) from 0.60 to 0.74. Experimental results at 850, 1310, and 1550 nm demonstrate broadband compatibility. This single‐step fabricated, ultrathin device offers a compact scalable solution for fiber‐probe imaging, multi‐point sensing, micro‐optical manipulation and integrated nanophotonic systems.