All-optical data format conversions and reconversions between the wavelength and time domains for dynamically reconfigurable WDM networks

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Abstract
We demonstrate all-optical error-free 2 Gb/s data format conversions and reconversions between the wavelength and time domains. Conversion between these two domains is accomplished by performing single-stage TDM-to-WDM and WDM-to-TDM conversions. We also perform the function of converting back all-optically to the original domain by performing both WDM-to-TDM-to-WDM and TDM-to-WDM-to-TDM reconversions. All conversions and reconversions are realized by using the cross gain compression mechanism inherent in semiconductor optical amplifiers (SOA's). We first demonstrate our TDM-to-WDM converter by simultaneously time demultiplexing and wavelength shifting a four-channel 2 Gb/s TDM data stream into four 500 Mb/s WDM channels. Moreover, we extend this single-stage approach by demonstrating a two-stage TDM-to-WDM converter consisting of two cascaded single-stage TDM-to-WDM modules. This two-stage converter selectively time demultiplexes and wavelength shifts a four-channel 2 Gb/s TDM data stream into two 500 Mb/s WDM channels after the second stage. Furthermore, we demonstrate a WDM-to-TDM converter by simultaneously time multiplexing and wavelength shifting the data from two 1 Gb/s WDM channels into one 2 Gb/s TDM signal. Finally, we demonstrate reconversion between the wavelength and time domains for two channels by performing both WDM-to-TDM-to-WDM and then TDM-to-WDM-to-TDM reconversions. In order to demonstrate system robustness, we use 80 km of fiber and three EDFA's between the conversion and reconversion stages. We show that reconverting back to the TDM data format requires an interstage WDM channel wavelength range less than /spl sim/4 nm, due to the power penalty induced by the interstage relative phase shift between the channels. This constraint limits the operation of the TDM-to-WDM-to-TDM reconverter to data rates up to 10 Gb/s and interstage distances to /spl sim/100 km. All demonstrated conversion and reconversion processes are accomplished with low power penalties. These conversion and reconversion schemes could be useful in WDM switching nodes and may serve as key building blocks for all-optical WDM networks.