On manual alignment of single-mode fiber collimators for free-space optical links.

Precise alignment of single-mode fiber (SMF) collimators is a fundamental challenge in free-space optical (FSO) experiments due to tight spatial and angular coupling tolerances. This application note presents a practical and reproducible three-phase methodology for manual SMF collimator alignment, integrating visual targeting, intermediate multimode fiber coarse capture, and SMF fine alignment. Demonstrated across a 100 m indoor FSO range at 0 dBm transmit power, the approach achieves -15.72dBm coupled optical power in under 5 min. This methodology enables rapid link establishment for proof-of-concept FSO demonstrations, allowing quick verification of efficient coupling prior to investment of time and resources in developing a dedicated pointing, acquisition, and tracking (PAT) system.