Mid-Span Spectral Inversion in an N-WDM System. Monir Morshed1, Bill Corcoran1, Liang B. Du1, Benjamin Foo1, Chen Zhu2, and Arthur J. Lowery1*. 1Centre ...
OECC / ACOFT 2014
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6-10 July 2014
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Melbourne, Australia
Carrier Phase Recovery Aided by Mid-Span Spectral Inversion in an N-WDM System Monir Morshed1, Bill Corcoran1, Liang B. Du1, Benjamin Foo1, Chen Zhu2, and Arthur J. Lowery1* 1 Centre for Ultrahigh-bandwidth Devices for Optical Systems (CUDOS), Department of Electrical & Computer Systems Engineering, Monash University, Clayton, VIC 3800, Australia 2 University of Melbourne, Melbourne, Australia Paper Summary
increase in maximum allowable launch power could support a 20-km increase in span length (between EDFAs) with standard-single mode fiber (S-SMF, attenuation: 0.2 dB/km), thus allowing longer overall transmission distances without increasing the number of inline amplifiers.
We experimentally demonstrate mid-span spectral inversion (MSSI) of a Nyquist wavelength-division multiplexing (N-WDM) 526-Gb/s 16-QAM superchannel over an 800-km link. MSSI improves the robustness of blind carrier phase recovery in the nonlinearity-limited region.
Experimental Setup Figure 1(a) shows the transmitter configuration for the 526-Gb/s system. An external cavity laser (ECL, 193.1 THz) is the light source. The carriers for adjacent NWDM channels are created by overdriving a single intensity modulator at 15.92-GHz RF wave to create nine comb lines (inset (i)), which are then equalized in power with a wavelength selective switch (WSS: Finisar WaveShaper). The comb lines are modulated with a 29.2-Gb/s N-WDM signal, created using 50-tap prefiltering of a 7.3-GBd 16-QAM signal. A 10-GS/s arbitrary waveform generator (AWG) was used for digital to analogue conversion. The N-WDM signal is modulated onto all nine comb lines (inset (ii)) using a complex Mach-Zehnder modulator (C-MZM). The optical signal is then divided into two paths: one path is frequency shifted by 7.96 GHz using a C-MZM before the shifted and un-shifted signals are combined to form a continuous 15.92-GHz wide channel, as shown in inset (iii). A delay of 101.5 ns was used to de-correlate the shifted and un-shifted signals. Fig. 1(a) also shows the receiver configuration [8]. A WSS is used to remove the
(a)
Sig Gen (i) 16 GHz
16 GHz
ECL1 (193.1 THz)
IM
Offline DSP (ii) AWG Q I PM EDFA
8 GHz
50%
C-MZM
τ
RF delay
C-MZM
50% Coupler
WSS PM EDFA
ECL2
(iii)
EDFA Sig Gen 8 GHz
ASE Filter
50% WSS
PBS
50% Coupler
Optical Link
XI XQ YI
DSO Offline DSP
Nyquist wavelength-division multiplexing (N-WDM) has attracted considerable research interest for fiber optic communications due to its high spectral efficiency with an almost-rectangular frequency spectrum [1, 2]. Longhaul and high capacity transmission experiments have used N-WDM successfully [3, 4]. However, fiber nonlinearity is the major limiting factor for all long-distance and spectrally efficient optical communication systems [5, 6]. Additionally, for single-carrier per wavelength systems like N-WDM, the blind carrier phase recovery [7] must be robust against fiber nonlinearities. In this paper, we experimentally demonstrate the first system with MSSI of an N-WDM super-channel. 526Gb/s is transmitted through 10×80-km fiber spans with erbium-doped fiber amplifier (EDFA) amplification. We show that MSSI improves the blind carrier phase recovery [7], extending viable launch powers below FEC limit (BER
