Upgrades of Non-Slope Matched Submarine Transmission Systems Using Differential Phase Shift Keying

Abstract

This paper studies the performance of RZ-DPSK at 10, 20 and 40 Gb/s for application on NZDSF based submarine systems. It compares the upgraded performance with respect to the original RZ-ASK modulation and bit rate. OCIS codes: (060.2330) fibre optics communications; (060.5060) phase modulation IntroductionRecent research on higher line rates for undersea transmission systems has mainly focussed on 40 Gb/s transmission, driven by the gaining popularity of OC-768/STM-256 in other segments of the network. Initial work assumed "green field" installations, where systems are built using new line elements such as dispersion managed fibres with low polarisation mode dispersion (PMD) or Raman assisted amplification [1]. Upgrades of existing systems using N×40 Gb/s RZ-DPSK over non-slope matched fibres have also been studied. Even with slope compensating devices at the receiver they did not achieve an increase in total capacity compared to N×10 Gb/s ASK [2,3]. In addition it was found that performance fluctuations were excessive at transoceanic distances, indicating that system power budget requirements would be very hard to meet. By using 40 Gb/s RZ-DQPSK instead of RZ-DPSK the magnitude of the time varying effects was reduced [4], but the mean performance was found to be worse. By polarisation/phase modulating the DQPSK signals the overall system margin was improved, but no significant spectral efficiency improvement was evident.In recent years legacy systems, originally designed for single channel or N×2.5 Gb/s WDM operation, have been successfully upgraded by increasing the bit rate and/or by adding channels. In this paper we address whether and how this can be done for more recent systems designed for N×10 Gb/s. Recent work has shown that 20 Gb/s RZ-DPSK is a promising candidate to perform cost effective overlay upgrades where some of the existing 10 Gb/s ASK channels are left in place [5]. In a continuation of this work we report here further results of our investigations into overlays and whether this bit rate is also suitable for dark fibre upgrades, i.e., where there are no pre-existing channels, and how it compares with 10 Gb/s RZ-DPSK.

Optimisation and statistical analysis of 21.4 Gb/s RZ-DPSK WDM non-slope matched transmission

“…Indeed, supposing an extension of the directly computed BER curves to the region of short distances with either BER(Q A ) or BER(Q el ) as a reference curve, a BER of 10 -9 would relate to a transmission distance of approximately 4500 km for the 33% duty cycle, 5000 km for the 50% duty cycle, and 5000 km for the widest duty cycle. In any case, the results for the three duty cycles studied show that errorfree 21.4 Gbit/s RZ-DPSK transmission at 50 GHz channel separation is feasible beyond the design length of typical installed submarine links with no need for in-band slope compensation of chromatic dispersion, which confirms the experimental observations and theoretical predictions of previous works [5][6][7].…”

“…It has been shown however, that 50 GHz spaced 20Gb/s return-to-zero (RZ) DPSK i.e high spectral efficiency (0.4 bits/s/Hz) is a promising candidate for upgrades of installed submarine systems [6]. The application of DPSK to submarine systems has already been demonstrated in both the 10Gb/s [7], 20Gb/s [2,4] and 40Gb/s [8], all being at the same spectral efficiency. It has also been shown [2,4] that varying the pulse width allows the realisation of quite different transmission regimes.…”

Next generation optical networks based on higher-order modulation formats, coherent receivers and electronic distortion equalization

“…Differential binary phase shift keying (DBPSK) was shown to feature higher robustness against nonlinear effects (Rohde et al, 1999) and $3 dB better noise performance when using balanced detection. High capacity WDM transmission over transatlantic distances was demonstrated using DBPSK for bitrates of 10 Gbit=s (Cai et al, 2004) and 20 Gbit=s (Molle et al, 2007). Modulation formats with auxiliary phase coding, like optical duobinary (ODB), attracted attention due to higher tolerance against CD (Winzer, Essiambre, 2006).…”