Experimental Set-up
A. Transmitter
Figure 1 shows the CSRZ-DPSK transmitter. The transmitter takes a 231-1 PRBS at 9.95 Gbit/s from a pattern generator and performs EFEC encoding to generate a 10.7 Gbit/s data signal which is multiplexed to get a 42.8 Gbit/s data signal. This signal is sent to the 40G DPSK precoder built from 50G logic, more precisely an AND gate and a T-flip-flop rather than the conventional XOR/one-bit-delay solution [14]. The output signal from the precoder is amplified in a high power driver delivering about 10Vpp ( » 2Vp ) voltage swing to the single drive x-cut (zero chirp) LiNb03 Mach-Zehnder modulator (MZM) biased at transmission minimum. Using an x-cut modulator to generate the DPSK phase modulation contributes to the good transmitter performance by virtually eliminating unwanted chirp. A z-cut LiNb03 Mach-Zehnder modulator also biased at transmission minimum and push-pull driven by a 21.4G clock subsequently carves CSRZ pulses to generate the CSRZ-DPSK signal. Two transmitters are used to modulate the 20 even and 20 odd channels that are interleaved with arbitrary polarizations to get forty 100 GHz spaced channels in the C-band from 1530.33 nm to 1561.42 nm. The average launch power into the transmission fiber is -11 dBm per channel.
Fig. 1. Schematic of the CSRZ-DPSK transmitter including the 40G DPSK precoder. "PPG": pattern generator.
Fig. 2. Schematic of the loop set-up including the four 100 km spans of Raman amplified dispersion managed fiber. The first three spans have a dispersion of 122 ps/nm, and the fourth span has a dispersion of -276ps/nm. -1100 ps/nm of precompensation is used.
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