Adaptive Parallel Inscription in Multi‐Core Fiber

Abstract 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.