Mixed-Mode Fiber Array Alignment and Coupling to Photonic Integrated Circuits

This study investigates alignment and coupling between a photonic integrated circuit (PIC) and a mixed-mode fiber array (FA), where one of the channels in the normally single-mode (SM) array is replaced by a multimode fiber (MMF). As a result, the tolerances of alignment are significantly relaxed. The proposed method suggests using the single-mode fiber (SMF) at the input and the MMF at the output of the PIC. In such a transmission configuration, the tolerances are relaxed by a factor of $\surd 2$ (41%). As this scales with mode size, the beam-expansion mechanisms, for example, utilizing microlenses, can further significantly reduce the requirements for fabrication and packaging of photonic devices, making them more robust and cheaper to manufacture.