Multiple Wavelength RZ Pulse Generation
Original Publication Date: 2003-Oct-25
Included in the Prior Art Database: 2003-Oct-25
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In transmission systems with a channel date rate of 40 Gbits/s and higher, the RZ (return-to-zero) data format has many advantages compared to the NRZ (nonreturn-to-zero) data format. However, the RZ pulse generator is more expensive than the NRZ pulse generator. In today's transmission systems, for each channel a RZ pulse source is needed. The RZ pulse source can be realised by either using a special RZ laser (for instance a mode locked fiber ring laser) or alternatively by modulating a CW (Continuous Wave) laser using a gating device (for instance an electroabsorption modulator). Both solutions are not cost effective. A tunable, stable RZ laser is not commercially available up to now. Mode locked fiber ring lasers for instance can be tuned in frequency, but do not have a stable operating point at all frequencies. The electroabsorption modulator can convert a CW signal into a RZ signal, though its working frequency range is limited. A further disadvantage is the dependency of the pulse quality at the output on the frequency. The idea is to feed a pulsed pump signal to a spectral inverter creating a switching window for all input signals. The spectral inverter converts a CW signal to a RZ signal (fig. 1). The wavelength of the RZ signals can be tuned by tuning the CW inputs. Several techniques can be used as spectral inverter: a periodically poled lithium niobate, four-wave mixing in highly nonlinear fiber, etc.