Lukens' team created its Talbot carpet in time by passing laser light through a 'phase modulator', a waveguide that also had an oscillating electrical voltage applied to it. As the voltage varied, the speed at which the light teaveled through the waveguide was altered, splitting the light into its constituent frequencies and knocking these out of step. As predicted, at regular time intervals, the separate frequencies recombined destructively to generate time holes. Lukens’ team then used a second round of phase modulation to compress the energy further, expanding the duration of the time windows to 36 picoseconds (or 36 trillionths of a second).
The researchers tested the cloak to see if it was operating correctly by inserting a separate encoded data stream into the fiber during the time windows. They then applied two more rounds of phase modulation — to “undo the damage of the first two rounds”, says Lukens — decompressing the energy again and then combining the separated frequencies back into one. They confirmed that a user downstream would pick up the original laser signal alone, as though it had never been disturbed. The cloak successfully hid data added at a rate of 12.7 gigabits per second.
Unfortunately, the current set-up may be a little too good at hiding things. “We erased the data-adding event entirely from history, so there’s no way that data could be sent as a useful message to anyone, even a genuine recipient,” says Lukens. However, McCall is impressed with the team’s effort and believes that future modifications will allow them, or others, to send secret messages successfully. He credits Lukens' team for significantly boosting the cloak’s efficiency. “This brings temporal cloaks within reach of practical applications,” says McCall.
Ironically, the first application of temporal cloaks may not be to hide data, but to help them to be read more accurately. The team has shown that splitting and recombining light waves in time creates increased periods in which the main data stream can be made immune to corruption by inserted data. “This could be useful to cut down crosstalk when multiple data streams share the same fiber,” says Lukens.
Gaeta agrees that the primary use for cloaking will probably be for innocent, mundane purposes. “People always imagine doing something illicit when they hear ‘cloaking’,” he says. “But these ways for manipulating light will probably be used to make current non-secret communication techniques more sophisticated.”