Implantable optical fibers have been widely used for optical neuromodulation in deep brain regions. Polymer fiber-based neural devices have natural advantages over silica fibers since their high flexibility would lead to a less inflammatory response in chronic in vivo experiments. Using three kinds of polymer materials: polycarbonate (PC), polysulfone (PSU), and fluorinated ethylene propylene (FEP), we present multifunctional soft polymer fiber (POF)-based brain implants with an Ultra-High Numerical Aperture (UHNA) and integrated Microfluidic Channels (MCs) for wide illumination and drug delivery, respectively. The flexibility of the proposed fiber devices has been found to be 100-fold reduced compared to their commercially available counterparts. Biofluids delivery can be controllably achieved over a wide range of injection rates spanning from 10 nL/min to 1000 nL/min by the structured MCs in the fiber cladding. The illumination area of the UHNA POFs in brain phantom has been increased significantly compared with the commercially available silica fibers. A fluorescent light recording experiment has been conducted to demonstrate the proposed UHNA POFs can be used as optical waveguides in fiber photometry. The limited illumination angle of the optical fiber imposed by current technology has been enlarged by the proposed UHNA POFs and we anticipate our work to pave the way toward more efficient multifunctional neural probes for neuroscience.