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Keep in mind that multiple wavelengths are already used in parallel in optical signaling -- "Modern systems can handle 160 signals and can thus expand a basic 100 Gbit/s system over a single fiber pair to over 16 Tbit/s." - https://en.wikipedia.org/wiki/Wavelength-division_multiplexi...

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Also keep in mind that running multi-mode communication brings a new set of problems and challenges (dispersion, non-linear effects, ...) and thus the "expansion" usually comes with some sort of trade-off for a successful implementation (frequency of repeaters etc).

The systems the parent cites are single-mode. You can run 160 wavelengths through a single-mode fiber. This is done in optical transport systems for "long haul". The wavelengths are close together just far enough apart to accommodate the bandwidth needed for each channel.

Multimode fiber is used for short distances after demultiplexing the wavelengths, typically in data centers.

Although I would not say that 100 Gb/s on a single wavelentgh is "basic" at this point in time.

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