Fiber-based inline optical tap with tunable wavelength and bandwidths

We propose a fiber-based optical tap with tunable wavelength and bandwidths by inscribing a long-period fiber grating (LPG) and an asymmetric tap waveguide in a two-mode fiber (2MF) using a femtosecond laser. We show experimentally that 22% of the input power could be tapped and detected from the fiber-side face, and that the tapping wavelength can be controlled by changing the pitch of the LPG. The fabrication conditions to improve coupling efficiency are revealed from experimental results. Furthermore, we determine that the bandwidths of LPG can be narrower than 20 nm by changing the host fiber. We confirmed that our proposed optical tap also has advantages in terms of fabrication tolerance.