High-frequency gravitational waves can be detected by observing the frequency modulation they impart on photons. In this paper, authors discuss fundamental limitations to this method related to the fact that it is impossible to construct a perfectly rigid detector. Several novel methods are proposed, to search for O(MHz-GHz) gravitational waves based on the frequency modulation induced in the spectrum of an intense laser beam, by applying optical frequency demodulation techniques, or by using optical atomic clock technology. The authors find promising sensitivities across a broad frequency range.