I think the comparison is still reasonable: while we do not have scalable quantum computers, the technologies developed for them have actually seen a lot of use: squeezed light and non-classical light, color centers, Josephson junctions, nonlinear-optics at the single-photon level, to name a few "terms of art" that should be google-able, are crucial for precision sensing and telecom.
The nonlinear optics is what enables optical signal modulators. For modulation of classical optical signals it is not necessary to have a "strong nonlinearity at the single photon level". However, that is being developed for quantum computing applications and as a side effect it makes today's optical modulators much better.
Telecom signal modulators are almost exclusively based on the Kerr effect or acousto-optics. Both effects have been known for at least 100 years and have nothing to do with nonlinear optics. The development of modern modulators was always driven by telecom and then applied to scientific experiments, not the other way round.
