Two German scientists have developed the theory for an all-optical transistor. In their words: “This concept relies on cross-phase modulation between a signal and a control pulse. Other than previous approaches, the interaction length is extended by temporally locking control and the signal pulse in an optical event horizon, enabling continuous modification of the central wavelength, energy, and duration of a signal pulse by an up to sevenfold weaker control pulse.” The article is in Physical Review Letters; access requires a subscription.