Physics / mechanism
Free-space optics (FSO) transmits data as modulated optical beams through air or vacuum—no fiber, no RF spectrum license. A laser (typically 1550 nm, eye-safe, exploits low atmospheric absorption) is collimated, pointed at a receiver aperture, and detected by an APD or PIN photodiode. Key parameters: link distance (100 m–10 km terrestrial, multi-thousand km LEO-to-ground), atmospheric attenuation (fog: 50–300 dB/km; clear air: <1 dB/km), pointing-acquisition-tracking (PAT) precision (sub-µrad for space links), and modulation scheme (OOK, DPSK, coherent QAM). Commercial terrestrial systems hit 10–100 Gbps today; NASA’s LLCD/LCRD demonstrated 622 Mbps lunar-orbit, and TBIRD achieved 200 Gbps LEO downlink in 2022—current state-of-the-art for space FSO.
Competitive landscape
Fiber wins on reliability and distance where infrastructure exists; RF (microwave, mmWave) wins in fog/low-visibility and non-line-of-sight. FSO’s niche is last-mile backhaul, inter-satellite links (ISL), and secure point-to-point where spectrum licensing or trenching is prohibitive.
Companies using
Connected ideas
Sources
Frontier (open questions)
- To be added.