The multiplexing scheme behind NG-PON2 (ITU-T G.989). It stacks four or more 10-gigabit wavelength pairs on a single fiber and schedules subscribers across both time slots and wavelengths. Where earlier PON generations divided one wavelength by time alone, TWDM multiplies the fiber’s capacity by running several in parallel.
How It Works
- Stacked channels: Four (optionally eight) wavelength pairs each carry a 10 Gbps symmetric channel, giving 40 Gbps or more in aggregate over the same glass and splitters.
- Time-division within each channel: Each wavelength runs the familiar time-slot scheduling of a conventional PON, as in XGS-PON.
- Tunable optics: Each ONT can be retuned to a different wavelength remotely, allowing load balancing, service segregation, and maintenance without site visits.
What It Enables
- Pay-as-you-grow capacity: Light new wavelengths as demand grows.
- Clean service segregation: A wavelength for residential, another for business or mobile backhaul.
Adoption Reality
While the cost of tunable optics kept NG-PON2 a niche technology, the simpler, cheaper XGS-PON became the mainstream upgrade from GPON. Its concepts, however, live on in the wavelength-flexible designs of the 50G-PON era.