We can tune them slightly with differences in temperature if I recall correctly, but there are limited uses for a few nanometers up or down in wavelength. If there's now a versatile multi wavelength generator for numerous specific discrete frequencies, you may be able to just cool it down to access nearby bands.
However, the article is talking about discrete wavelengths. The device gives you a choice between a bunch of different fixed wavelengths.
It isn't actually tunable to specific frequencies.
Disclaimer: skim read article plus I know very little about the topic