Long-Period Grating Based Coupler for Multi-Core Fiber Systems

Abstract

In this work, we propose and demonstrate numerically a long-period grating (LPG) based technique to couple light from a single-mode fiber (SMF) to all cores of a multicore fiber (MCF), i.e., an SMF to MCF coupler. The light launched into the SMF core is coupled to the SMF cladding due to the LPG inscribed in the core. Then, the optical power is transferred between fibers claddings, enhanced by the reduction of the SMF cladding radius. Finally, the MCF cladding optical power is distributed by all cores of the MCF due to identical LPGs inscribed in them. We use the coupled-mode theory to study and design the proposed device. We achieve a coupling efficiency of approximately 90% of the input power in a total length of 15.1 cm. We also study the coupler's sensitivity to the SMF radius and LPGs period. Results show that the proposed device can improve the pumping efficiency of MCF amplifiers.

Analysis of power transfer between two multi-core fibers with long-period gratings

“…The selective nature of the coupler was also demonstrated by only promoting the power transfer at a wavelength around 1480 nm. Although the coupling efficiency is similar to the one proposed in [7], it has the advantage of not requiring any further changes to the fibers. More pairs of cladding modes were suitable for the development of the coupler, so we were able to choose one with lower coupling distance, and therefore a smaller coupler was achieved.…”

“…The proposed technique is based on the one proposed in [7], but, on this work, instead of coupling between a thinned SMF and an MCF, the proposed device distributes the pump light launched into one core of the input 4-core fiber to all the cores of the output 4-core fiber, both commercial fibers. The coupler has three sections: section I, where an LPG is inscribed in just one core of the input MCF; section II, where the MCFs are parallel and next to each other; and section III, where identical LPGs are inscribed in all cores of the output MCF.…”

“…There was already experimentally demonstrated a single-mode fiber (SMF) to SMF coupler, where the coupling was promoted by inscribing similar LPGs in each core [6]. We have numerically demonstrated an SMF to MCF coupler based on LPGs, which showed an efficiency of 90% in 15 cm of length [7]. In the proposed device, the SMF cladding is reduced to increase the power transfer between the fibers, which hinders its experimental implementation and makes the coupler more sensitive to changes.…”

“…Here, we numerically propose and analyse the power transfer between two 4-core fibers, with an LPG inscribed in just the input core of the input MCF and identical LPGs inscribed in the four cores of the output MCF. As in [7], an offset distance between LPGs was used. In this case, the offset is between the input and output MCF LPGs.…”