Field-Trial of an All-Optical PSK Regenerator/Multicaster in a 40 Gbit/s, 38 Channel DWDM Transmission Experiment

Abstract

The performance of future ultra-long haul communication systems exploiting phase-encoded signals is likely to be compromised by noise generated during signal transmission. One potential way to mitigate such noise is to use Phase Sensitive Amplifiers (PSAs) which have been demonstrated to help remove phase as well as amplitude noise from phaseencoded signals. Recently, we showed that a PSA-based signal regenerator based on degenerate four-wave mixing can be implemented in a network-compatible manner in which only the (noisy) signal is present at the device input (black-box operation). The developed regenerator was also able to perform simultaneous wavelength conversion and multicasting, details/analysis of which are presented herein. However, this scheme was tested only with artificial noise generated in the laboratory and with the regenerator placed in front of the receiver, rather than in-line where even greater performance benefits are to be expected. Here, we address both theoretically and experimentally the important issue of how such a regenerator, operating for convenience in a multicasting mode, performs as an in-line device in an installed transmission fiber link. We also investigate the dispersion tolerance of the approach.

All-Optical Regeneration of Phase Encoded Signals

“…A field transmission experiment which made use of the wavelength conversion/multicasting feature of the regenerator was carried out [58]. A conceptual outline of the network and its practical implementation are shown in Figure 16 a and b respectively.…”

“…In order to facilitate placing the regenerator at the mid-point of the network and to operate at twice the transmission distance that was physically available, a wavelength shift was incorporated in the regeneration process, Figure 16 b. Obviously, conversion of the wavelength would not normally be required in most transmission applications, nevertheless, it serves to illustrate another useful functionality of the technology (wavelength conversion/multicasting) as previously reviewed [57,58]. 37 channels (excluding ITU Channel 23) were sent down the dark fibre link (part of the UK JANET Aurora Network) that extends from Southampton to London and back again (400 km dispersion-compensated transmission distance, 6 inline flat-gain EDFAs with maximum input/output powers of -5/15 dBm, operated in automatic gain control mode with a nominal gain of 20 dB).…”

“…The maximum total power launched into the link was 7 dBm with a maximum power along the link of 15 dBm. The detailed configuration is shown in [58]. At its output, ITU Channel 27 was converted to Channel 23 [Copy -1] (either with or without regeneration) and sent through the link again together with all the remaining channels.…”

“…Constellation diagram analysis , Figures 14a and 14b, show that the regenerator is capable of reducing the phase noise fluctuations even in the presence of some residual dispersion (80 ps/nm in the diagrams shown) albeit at the expense of increased amplitude stability. This influences the BER as shown in Figure 14c (taken from [58]), where it can be seen that the regenerator can cope well with residual dispersion corresponding to residual dispersion accumulated in about 2 km of SMF-28, but gives no advantage for dispersion accumulated in an SMF-28 length of 8 km. More discussion regarding this topic can be found in [58].…”

“…This influences the BER as shown in Figure 14c (taken from [58]), where it can be seen that the regenerator can cope well with residual dispersion corresponding to residual dispersion accumulated in about 2 km of SMF-28, but gives no advantage for dispersion accumulated in an SMF-28 length of 8 km. More discussion regarding this topic can be found in [58].…”