Storing light in optical fibers using sound waves

Increasing traffic on the Internet demands faster optical transmission networks. Future high-speed communication networks may rely largely on all-optical components that are intrinsically faster than their electronic counterparts. To achieve such networks, however, one needs to overcome a number of obstacles that exist at levels from devices to systems. For example, the lack of all-optical memory for storing optical data remains a bottleneck in modern optical information networks.1 There has been substantial progress in addressing this problem using spatial-spectral holography in systems that operate at cryogenic temperatures2 or stored light based on electromagnetically induced transparency, where optical information is impressed upon internal degrees of freedom of an ensemble of atoms or ions.3 Both of these methods, however, are limited to operating at the resonance wavelength of the ions or atoms used. These limitations have recently been partially overcome using a dynamically controlled resonator in which a single optical pulse was stored for ∼100ps.4 We recently presented a different approach: a simple storedlight approach5 in which optical pulse information is transferred onto a slowly moving hypersonic wave (∼1/40,000 of the light speed) in an optical fiber and converted back at a later time through stimulated Brillouin scattering (SBS) as illustrated in Figure 1. In the storage process, optical data pulses (of carrier frequency ν0) interact with a counterpropagating short intense ‘write’ pulse (of carrier frequency ν0 + νB, where νB is the Brillouin frequency shift of the fiber). The optical data pulses become depleted as energy is shifted to a hypersonic wave in the fiber. In the retrieval process, a short intense ‘read’ pulse at the same frequency as the ‘write’ pulse depletes the acoustic wave and releases the data back to the original optical frequency, thereby generating a replica of the incident data pulses. This stored-light approach has advantages such as room-temperature Figure 1. Stimulated Brillouin scattering allows data storage in an optical fiber. In the storage process, (a) optical data pulses interact with a ‘write’ pulse . (b) The optical data pulses become depleted as the information shifts to an acoustic wave in the fiber. To retrieve the data, (c) a ‘read’ pulse depletes the acoustic wave, (d) generating a replica of the original data pulses.5