GLOphotonics R&D pole has been working on hollow core fiber terminations. Here is an example where endoscopy-driven double-clad hollow core fiber is fused to a bal-lens (The photo is at the far field of the guided light in this special fiber). This pattented device allows dual guidance for next-generation endoscopes where biological tissues can be both processed and imaged.

Picture credit: Delahaye Frédéric