Laser-inscribed optical tap based on two-mode fiber with flexible branching property design

Abstract

Listen

Translate article

In order to construct 5G and beyond 5G networks effectively, it becomes important to prepare a sufficient number of interfaces with optical fiber at arbitrary locations. An optical wavelength- and power-tapping device is expected to provide a flexible junction point in optical networking, and a fiber-based optical device has great advantages in terms of low-loss and high compatibility with existing single-mode fibers. In this paper, we propose a wavelength- and powertunable in-fiber optical tap inscribed in a two-mode fiber (2MF) using a femtosecond laser. This optical tap is composed of a long-period fiber grating (LPG) and an asymmetric tap waveguide that is inserted transversely across the core to the cladding. In the LPG, transmitted LP01-mode light is converted into LP11 mode, and the converted LP11 mode is coupled to the tap waveguide while the LP01 mode passes through the fiber core. The operation wavelength and branching-power ratio can be controlled by the LPG design. We have revealed the optimum design for the tap waveguide. Here, the relationship among diameters of core and tap, the relative refractive indices of core and tap, and the angle between fiber core and tap was considered. We also experimentally confirmed the coupling efficiency to the core and tap when LP01 and LP11 modes were separately launched by using a tap waveguide inscribed in a 2MF. The factors that degraded the coupling efficiency were discussed by comparison with the calculation results.