Core-independent inscription of LPGs in twin-core fiber by CO2 laser and coupling between LPGs

Long-period fiber gratings (LPGs) have been demonstrated to be inscribed independently of each other into two separate cores of a twin-core fiber (TCF) by using point-by-point CO 2 laser irradiation. The TCF is hydrogen-loaded to reduce the energy density of the CO 2 laser required in the inscribing process of the grating, so that each core of TCF can be addressed individually. The field distributions and effective refractive indices of the core and cladding modes were calculated theoretically. The measured results coincide well with calculated results. An integrated TCF-LPG-assisting coupler is proposed and a peak coupling efficiency of 48% is achieved experimentally. The point-by-point core-independent inscription of LPGs in the TCF provides a flexible platform to fabricate integrated fiber devices.