Fig. 1. (a) Schematic of the femtosecond laser direct writing system and (b) concept of the femtosecond laser-inscribed device. BS, beam splitter; DM, dichroic mirror; CCD, charge-coupled device.

Fig. 2. (a) Design of the input end facet and output end facet of the FIFO device; (b) captured output end facet of the FIFO device; (c) captured cross section of applied 19-core fiber; and (d) design of the 2D track of the waveguide.

Fig. 3. (a) Experimental setup of the 19-channel FIFO system based on a pair of FIFO devices; (b) 1-km 19-core fiber; (c) 19-channel FIFO device; (d) SMF array. OC, optical coupler.

Fig. 4. Intensity profiles of the output light fields of (a) 19-channel FIFO device and (b) 1-km 19-core fiber.

Fig. 5. (a) Measured insertion losses of 19 different channels of the FIFO device at 1550 nm and (b) evaluated insertion losses of channels 10, 14, and 19 from 1528 to 1625 nm.

Fig. 6. Measured crosstalk of 19 different channels to other channels.