A field trial of 100-Gbit/s Ethernet over an optical transport network (OTN) is conducted using a real-time digital coherent signal processor. Error free operation with the Q-margin of 3.2 dB is confirmed at a 100 Gbit/s Ethernet analyzer by concatenating a low-density parity-check code with a OTN framer forward error correction, after 80-ch WDM transmission through 6 spans x 70 km of dispersion shifted fiber without inline-dispersion compensation. Also, the recovery time of 12 msec is observed in an optical route switching experiment, which is achieved through fast chromatic dispersion estimation functionality.
Transmitter impairment mitigation for 58-GBaud PM-64QAM with 4×2 WL MIMO embedding preliminary CPR was demonstrated over 100 km SSMF. Q-penalties of 0.1 dB with 14 ps IQ skew and 10 degree phase error were achieved.
High-order modulation formats with high symbol rates are promising candidates for meeting the growing traffic requirements of digital coherent transmission. In using these modulation formats, the impact of transceiver impairment on the signal quality becomes significant. In this paper, we propose an 8×2 widely linear (WL) multiple-input multiple-output (MIMO) equalizer with independent complex filtering on IQ signals to mitigate linear transceiver impairments. Furthermore, we extend the equalizer for digital subcarrier (SC) multiplexing. Accordingly, a 16×4 WL MIMO equalizer is also proposed to mitigate linear transceiver impairments, through application to a pair of SC inputs. Experimental results show that, for transmission of a 58-GBaud polarization-multiplexing 64 quadrature amplitude modulation (PM-64QAM) single-carrier signal, the proposed method effectively compensates for various receiver impairments and also mitigates transmitter (Tx) impairments. Q-penalties of 0.1 dB up to a 10-ps skew, 2.5-dB gain imbalance, 7.2-degree phase error, and -15-dB crosstalk in Tx were achieved for 100-km standard single-mode fiber transmission. Moreover, for a 29-GBaud PM-64QAM dual-SC signal, the proposed 16×4 WL MIMO equalizer shows transceiver impairment mitigation performance similar to that in the singlecarrier case, even though dual-SC transmission is less tolerant of laser phase noise.
SUMMARYWe describe a field experiment of flexible modulation format adaptation on a real-time 400 Gbit/s/ch DSP-LSI. This real-time DSP-LSI features OSNR estimation, practical simplified back propagation, and high gain soft-decision forward error correction. With these techniques, we have successfully demonstrated modulation format allocation and transmission of 56-channel 400 Gbit/s-2SC-PDM-16QAM and 200 Gbit/s-2SC-PDM-QPSK signals in 216 km and 3246 km standard single mode fiber, respectively.
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