FSO Wavelength Selection
Compare 850, 1064, 1310 and 1550 nm for an FSO link by Class 1 eye-safety limit, atmospheric loss over the range, component maturity and cost, and get a weighted recommendation.
Ranking
| λ | Class 1 limit | Atm. loss | Score |
|---|---|---|---|
| 1310 nm | 0.499 W | 4.76 dB | 83/100 |
| 1550 nm | 9.62 mW | 4.26 dB | 71/100 |
| 850 nm | 0.768 mW | 6.34 dB | 62/100 |
| 1064 nm | 1.92 mW | 5.47 dB | 60/100 |
How the scores are made
Eye safety: the IEC 60825-1:2014 Class 1 limit for a CW point source over 100 s, on a log scale from 0 (0.1 mW) to 100 (1 W). At 1310 nm the correction C₇ ≈ 259 lifts the retinal limit to about 0.5 W, above the 9.6 mW corneal limit at 1550 nm; 850 and 1064 nm reach the retina. A wide FSO beam can carry more power than these figures within the same class.
Atmosphere: 100 − 5 × the link loss in dB, from Rayleigh scattering plus Kim's visibility law (as on the atmospheric-loss calculator).
Components and costare fixed editorial ratings. The weights are 0.3 for eye safety (0.05 when it isn't prioritised), 0.35 atmosphere, 0.2 components and 0.15 cost; the total is divided by their sum.
A qualitative guide: link margin, receiver sensitivity, background light and turbulence also set the choice.
Model and references
Illustrative. A simplified model that shows trends and orders of magnitude. Don't use its numbers for design. About the tiers
Qualitative ranking. Eye safety from the IEC Class 1 point-source limit and atmosphere from Kim's law are computed; component and cost ratings are editorial. Ignores link margin, background light, turbulence.
- IEC 60825-1:2014, Safety of laser products – Part 1: Equipment classification and requirements. Class 1 accessible emission limits, correction factor C7.
- Kim I. I., McArthur B., Korevaar E. (2001). Comparison of laser beam propagation at 785 nm and 1550 nm in fog and haze for optical wireless communications. Proc. SPIE 4214, 26–37. Visibility-based aerosol exponent q. doi:10.1117/12.417512