Nippon Telegraph and Telephone Corporation and collaborating labs fill demonstrated the world's highest density optical fiber using a deployable optical fiber diameter of less than 250 µm. This optical fiber contains 19 optical paths (cores) that can support six kinds of optical signals (modes), and it provides 114 (= 6 modes × 19 cores) spatially multiplexed communication paths (channels) in one optical fiber.
Source: phys.org