NTT announced the successful field testing of plug-and-play coherent optical transmission technology operating at 40G and 100G over exiting fiber. The coherent technology, which was developed in-house by NTT, enables 100 and 40 Gbps ignals to be configured easily and automatically in 50 ms or less.
NTT said its newly developed digital coherent technology transmits an optical signal with lightwave characteristics (optical phase and polarization) corresponding to ones and zeros of the digital signal. It implements high-speed configuration for the ultra-high-speed signal by applying a new DSP function to the digital coherent technology. A DSP in the optical transmitter first introduces a known digital signal into the transmitted optical signal to measure waveform distortion beforehand, and this is transmitted as a digital coherent optical signal using lightwave characteristics. The receiver then receives optical signal, having been distorted by the unique transmission characteristics of the optical fiber, and it is digitized in real time, as-is, by the receiver DSP, making it available for high-speed digital signal processing. Specifically, the receiver DSP measures the waveform distortion added to the received optical signal directly and accurately by extracting the known signal from it, and later removes this measured waveform distortion from the received signal. The new technology measures the waveform distortion quickly and reduces configuration time to allow high-speed removal of the distortion.
For the trial, 11 wavelengths with 100 or 40 Gbps signals per wavelength were transmitted under over 1,000 different artificially-created transmission conditions, in field tests spanning 580 km. The results confirmed extremely stable automatic configuration in all cases.
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