All-optical parallel-to-serial conversion by holographic spatial-to-temporal frequency encoding.

The bandwidth and the efficiency of fiber-optic communication systems exceed those of electrical cable systems. However, currently we are far from realizing the potential performance of optical networks. Electronic devices and systems connected to optical networks may reach bit rates in the range of gigabits per second. In contrast, the maximum bit rate of a photonic network may exceed 1 Tbitys, limited by the performance of the optical fiber. The 3-order-ofmagnitude mismatch between fiber and device capacity can be exploited to increase the speed, security, and reliability in the data transmission. Several alloptical methods exploiting this bit-rate mismatch have been investigated for controlling data streams in communication channels so that this bandwidth can be used more eff iciently. – 8 The principle of spectral holography has been used for optical pulse shaping. The combination of spectral holography with conventional spatial Fouriertransform holography permits the conversions of temporal signals into spatial signals and vice versa. – 5 Dynamic spectral holography or spectral nonlinear optics can realize these conversions in real time, thus providing the possibility for all-optical time-division multiplexing and demultiplexing of broadband data streams. Dynamic time-to-space conversions of ultrashort light pulses (all-optical serial-to-parallel conversion) based on this principle have been demonstrated with four-wave and three-wave interactions. In this Letter we analyze and experimentally demonstrate this principle with a holographic optical processor that permits parallel-to-serial (i.e., space-to-time) optical signal conversion. Moreover, by combining our technique with existing serial-to-parallel conversion methods we demonstrate experimentally the possibility of transmitting parallel optical signals over long-distance optical fiber networks. The all-optical parallel-to-serial conversion processor is shown schematically in Fig. 1(a). The processor consists of two independent optical channels for carrying temporal signals and spatial signals. The temporal information-carrying channel consists of a pair of gratings and a 4-F lens arrangement. The incident pulses are transformed by the input ref lecting grating and the first lens into a temporal frequency spectrum distributed in space of the focal plane, while the second lens and the output ref lecting grating are performing the inverse transformation of the temporal