Femtosecond-laser-assisted implementation of an inline power tap in a multimode fiber

An inline power tap has been demonstrated and realized by inscribing an optical track in a standard 62.5/125 μm multimode fiber. The fiber-optic tap may resort to a single track or a pair of tracks, which can be created by incorporating a single instance or double instances of femtosecond laser scanning, respectively. For the single-track configuration, the built-in tap is formed to traverse the center of the core, while a pair of parallel taps is designed to vertically flank the core for the double-track configuration. The tap ratio can be practically tuned from 1.0% to 3.4% by tailoring the laser-writing power in accordance with the configuration of the tap. The hybrid double-track structure helped reduce the polarization sensitivity to as low as 0.8 dB. The excess loss was consistently kept below 0.2 dB.