Traditional optical fibres carry information in the form of pulses of laser light, but now it could possibly be better to send information on pulses of darkness from a "dark laser". This is not quite John Cage's 4' 33", but it is almost as weird. Steven Cundiff of Colorado University and colleagues describe a mode-locked quantum-dot diode laser that is normally "on" but is "off" for well defined times; unlike the normal case where the source is normally off with well defined times when it's on. The dark pulses are 70% less intense than the background light. An advantage is that light pulses can smear as they go through a fibre, but dark pulses do not.