Ultrafast photonic processing is expected to play a major role in photonic networks and photonic sensing systems. At the bandwidth of 40 GHz or above, electronics imposes severe technology and economic constraints, which ultrafast photonic processing could advantageously remove.
The quasi-instantaneous response of Kerr nonlinearity in fibers makes it the most attractive effect to overcome bandwidth limitations. For simplicity, consider two optical beams of different wavelength copropagating in the same optical fiber; the intensity dependence of the refractive index leads to a large number of interesting nonlinear effects, namely, self-phase modulation (SPM), cross-phase modulation (XPM), and four-wave mixing (FWM). These ultrafast phenomena could be favorably applied to photonic processing. One application is optical multiplexing, which is used as optical switches, multiplexers, and demultiplexers. Another possible application is wavelength conversion, which is to be used in wavelength division multiplexing (WDM) networks. The other application is supercontinuum (SC) generation, which is a promising technique for various applications in photonic networks and sensing systems.
In present photonic networks, there are two primary techniques for multiplexing data signals: optical time division multiplexing (OTDM) and WDM. Optical code division multiplexing (OCDM) is an alternative method for future options. Optical code division multiple access (OCDMA), encoding and decoding of a signal with a kind of temporal waveform (the so-called optical signature code), allows the selection of a desired signal. Different information bits can share nonerror-producing overlaps of time and wavelength. Simultaneous multiple access can thus be achieved without a complex network protocol to coordinate data transfer among the communicating nodes.
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