Compact and robust MLA-assisted FI/FO device with low loss for MCF systems fabricated by 3D nanoprinting

A fiber FI/FO device based on a micro-lens array (MLA) is proposed in which the compact fiber bundle method is combined with 3D printing, enabling low-loss and high-robustness fiber interconnection. Single-mode fibers (SMFs) are etched by a chemical process and assembled into a fiber array matched to a multi-core fiber (MCF), while a polymer MLA is directly printed on the MCF end facet using a Nanoscribe 3D printing system. The MLA reduces the alignment sensitivity of the fiber array and improves the tolerance of the conventional fiber bundle method, thereby effectively reducing the coupling loss. A seven-core MLA FI/FO device is fabricated as a proof of concept. Benefiting from the MLA's effective beam control capability, the experimental results show that the insertion loss is significantly reduced under different alignment conditions. Under poor alignment conditions, the insertion loss of the device without lenses is about 1.62 dB and is reduced to 0.97 dB after introducing the MLA, corresponding to an improvement of 0.65 dB and demonstrating strong robustness against misalignment. Under good alignment conditions, the insertion loss is further reduced from about 0.77 dB to 0.48 dB, indicating both high tolerance and low-loss potential of the MLA-based FI/FO device. Further measurements show that the average inter-channel crosstalk remains below -60 dB over the entire C + L band, confirming the low-crosstalk performance of the proposed MLA FI/FO device.