Experimental set-up
The 36x100 km transmission distance is demonstrated in a 400 km loop setup which is shown schematically in figure 1. The transmitter generates 40 channels in the C-band at ITU wavelengths from 1530.33 nm to 1561.42 nm with a spacing of 100 GHz. Odd and even channels are modulated separately by two transmitter boards with two cascaded LiNbO 3 Mach-Zenhder modulators. The first modulator impresses NRZ data modulation at 42.657 Gbit/s and the second modulator driven by 21.329 GHz clock converts the NRZ signal into a CS-RZ signal with approximately 50% duty cycle. Odd and even channels are modulated with data and delayed inverted data, respectively. The 42.657 Gbit/s data signal is formed by electrically multiplexing four 10.664 Gbit/s 2 31 -1 PRBS. A RS(255,239) FEC encoding can be enabled or disabled. The even and the odd channels are finally combined with arbitrary polarizations in a wavelength interleaver and sent through a dispersion compensating fiber to obtain the desired -160 ps/nm of pre-compensation. The average channel power into the transmission fiber is -7 dBm.
The loop contains four identical 100 km spans of UltraWaveT Terrestrial dispersion managed fiber [1]. The spans are symmetrical and consist of 35.5 km super large effective area fiber (SLA, dispersion 20 ps/nm/km, effective area 107 µm 2 ) followed by 29 km perfectly slope matched dispersion compensating fiber ("Inverse dispersion fiber", IDF, dispersion -40 ps/nm/km, effective area 31 µm 2 ) followed by additional 35.5 km SLA leading to a span net dispersion of 254 ps/nm. After the four SLA/IDF spans follows additional 28 km IDF to get a net dispersion per loop round trip of about -100 ps/nm corresponding to the dispersion map shown in figure 2a. It was found in computer simulations that this semi-periodic dispersion map has far better transmission properties than traditional dispersion maps where the same basic span is repeated in a completely periodic fashion.
Fig.1. Experimental set-up. (BERT: Bit Error Rate Test-set, CDR: Clock & Data recovery, DGFF: Dynamic gain flattening filter, EMUX: Electrical Demultiplexer, GFF: Gain flattening filter, IDF: Inverse dispersion fiber, RP: Raman Pump, SLA: Super large effective area fiber)
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