Why Multimode was Superseded by Singlemode
Multimode fibre dominated early fibre transmission systems, but in the 1980’s there was a return to the ideal Single-mode waveguide envisaged by Charles Kao & George Hockham.
1/. The risk and unpredictability of Modal Noise
- Discovered during the Hitchin Stevenage system development
Coherent Lasers +lossy Multimode = Multipath interference
2/. Unpredictability of the bandwidth concatenated fibres
- Multimode fibres from different suppliers had different refractive index profiles.
Joined sections have unpredictable modal dispersion
3/. Mechanical precision of fibre and connectors improved
4/. The move to longer (lower loss) wavelengths made the light spot size larger
5/. Transoceanic systems demanded very low dispersion
- Why Multimode was Superseded by Singlemode
- The reasons