Dual-spot alignment facilitates seamless integration of fiber-wireless-fiber links into optical access networks

Most existing fine alignment strategies for indoor optical wireless communication (OWC) rely on a single-spot angle measurement originally designed for long-distance OWC systems. However, for indoor short-distance links, this approach causes lateral offset and significant link loss. In this work, we propose a dual-spot fine alignment method that enables simultaneous measurement and compensation of both lateral offset and angle misalignment. Based on this method, fiber-wireless-fiber (FWF) terminals are developed to enable a bidirectional, auto-aligned laser link. Experimental results demonstrate a maximum link loss of 5.7 dB, with fluctuations below 1 dB across a full-angle field of view of 70° × 45° over a 3 m distance. This low-loss performance eliminates the need for optical amplification, facilitating seamless integration into optical access networks.