Adaptive Parallel Inscription in Multi-Core Fiber

The holographic multi-foci technique has gained extensive applications in femtosecond laser processing as it can remarkably enhance fabrication efficiency. However, in the field of optical fiber processing, due to the position-dependent aberration induced by optical fiber's cylindrical geometry and protective coating, achieving precise control over the intensity uniformity and positioning accuracy of multi-foci presents significant challenges, which complicates the realization of high-quality parallel inscription. Here, an adaptive and high-throughput parallel inscription strategy for multi-core fiber (MCF) is presented. The depth-dependent aberration phase for each focus is derived, facilitating the generation of astigmatism-corrected holograms using the Gerchberg-Saxton-weighted algorithm. Meanwhile, an online image processing algorithm is employed to measure the internal core distribution of MCF, enabling the adaptive update of holograms. As a demonstration, parallel fiber Bragg grating (FBG) array inscription in seven-core fiber is achieved. Experimental results show that the average intra-node reflectivity difference can be controlled within 2 dB. Moreover, 7 FBGs can be inscribed simultaneously within 6 s, improving the inscription efficiency by an order of magnitude. The proposed method is fast, versatile, and robust, thus providing a promising solution for the efficient fabrication of advanced photonic devices inside optical fiber.