During the first phase of the project—which is part of the Defense Advanced Research Projects Agency's (DARPA) Defense Sciences Office slow-light program—Zhu says he learned that pulses could be stored and read out at a later time. The second phase was the actual experiment in which data pulses were stored (as acoustic waves in an optical fiber) and retrieved after a certain period of time.
"We really want to demonstrate that methods for storing optical information are much broader than people thought," Gauthier says. "In the current telecommunication systems, you turn the optical signal into an electronic signal and store it in RAM. The optical data pulses are then regenerated by using the electrical signals to turn on and off an auxiliary laser source. But this process generates heat. The faster this is done, the more heat is generated."
For this to work in the real world, the scientists say the communication fibers must be made of a material that provides an acoustic time frame long enough to allow the information to move from optical to sound, then return to optical. One option, Gauthier says, is to work with a new type of glass made from a chalcogenide, which has good semiconductor properties and contains one or more elements from the periodic table's chalcogenide group, also known as the "oxygen family," which includes oxygen, sulfur, selenium and tellurium.
Another option that researchers are exploring is to run the laser beams through a hollow optical fiber filled with gas (such as xenon), which would allow them to use a less powerful laser to induce longer lasting sound waves in the gas. This could potentially create a sound wave 50 times longer and allow the lasers used to be 100 times less powerful—and less energy intensive—thereby delivering more data more quickly at a lower cost.