Monitoring modulation alignment variation of optical modulators includes receiving an optical signal at an input fiber. The optical signal has been modulated by optical modulators. Photons of the optical signal are received at a photon reactive material operable to produce a reaction in response to the arrival of a predetermined number of photons. Reactions are produced in response to the arrival of the photons of the optical signal. Feedback is generated in response to reactions. The feedback reflects the waveform of the optical signal, and indicates modulation alignment variation among the optical modulators.