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, where one of the channels in the normally single-mode (SM) array is replaced by a multi-mode fiber (MMF). As a result, the tolerances of alignment are significantly relaxed. The proposed method suggests using the 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 √2 (41%). As this scales with mode size, the beam-expansion mechanisms, e.g., utilizing micro-lenses, can further significantly reduce the requirements for fabrication and packaging of photonic devices, making them more robust and cheaper to manufacture.