Simultaneous chromatic dispersion, polarization-mode-dispersion and OSNR monitoring at 40Gbit/s

A novel method for independent and simultaneous monitoring of chromatic dispersion ( CD), first-order PMD and OSNR in 40Gbit/s systems is proposed and demonstrated. This is performed using in-band tone monitoring of 5GHz, optically down-converted to a low intermediate-frequency (IF) of 10kHz. The measurement provides a large monitoring range with good accuracies for CD (4742 +/- 100ps/nm), differential group delay (DGD) (200 +/- 4ps) and OSNR (23 +/- 1dB), independently of the bit-rate. In addition, the use of electro-absorption modulators (EAM) for the simultaneous down-conversion of all channels and the use of low-speed detectors makes it cost effective for multi-channel operation. (C) 2008 Optical Society of Americ

Experimental Demonstration of Geometrically-Shaped Constellations Tailored to the Nonlinear Fibre Channel

A geometrically-shaped 256-QAM constellation, tailored to the nonlinear optical fibre channel, is experimentally demonstrated. The proposed constellation outperforms both uniform and AWGN-tailored 256-QAM, as it is designed to optimise the trade-off between shaping gain, nonlinearity and transceiver impairments

Candidate technologies for high-capacity optical communication systems

The practicalities in designing high-capacity optical communication systems are described. With a given perspective on the present and future technologies, we cover the transceiver design and optical amplifier technologies to maximize optical fiber capacity. OCIS codes:

Nanosecond channel-switching exact optical frequency synthesizer using an optical injection phase-locked loop (OIPLL)

Experimental results are reported on an optical frequency synthesizer for use in dynamic dense wavelength-division-multiplexing networks, based on a tuneable laser in an optical injection phase-locked loop for rapid wavelength locking. The source combines high stability (50 dB), narrow linewidth (10 MHz), and fast wavelength switching (<10 ns)

Inter-Channel Interference in Non-Linear Frequency-Division Multiplexed Networks on Fibre Links with Lumped Amplification

There has been some interest in the Non-linear Frequency-Division Multiplexing (NFDM) in optical fibre communication systems, because it promises interference-free or weak-interference between channels in an optical routed network. NFDM scheme uses Non-linear Fourier Transform (NFT) to bring a time-domain signal into the non-linear frequency domain (NFD), where the spectra evolve in a linear manner during signal propagation in the fibre channel. The successful application of NFT relies heavily on the "channel's integrability" that is only fulfilled by an ideal distribution-Raman amplification. However, most of the optical fibre links are amplified by Erbium-doped fibre amplifiers (EDFAs). The impact of the non-integrability in NFDM networks is unclear. In such a network, one key device is the Non-linear Add-drop Multiplexer (NADM) that adds or drops channels in the NFD. Simulating such device that processes many channels simultaneously is still difficult due to a high complexity and inaccuracy of the current INFT-NFT algorithm. To get around this difficulty, we adopt a different approach to estimate the inter-channel interference (ICI) in NFDM networks

Achievable rate degradation of ultra-wideband coherent fiber communication systems due to stimulated Raman scattering

As the bandwidths of optical communication systems are increased to maximize channel capacity, the impact of stimulated Raman scattering (SRS) on the achievable information rates (AIR) in ultra-wideband coherent WDM systems becomes significant, and is investigated in this work, for the first time. By modifying the GN-model to account for SRS, it is possible to derive a closed-form expression that predicts the optical signal-to-noise ratio of all channels at the receiver for bandwidths of up to 15 THz, which is in excellent agreement with numerical calculations. It is shown that, with fixed modulation and coding rate, SRS leads to a drop of approximately 40% in achievable information rates for bandwidths higher than 15 THz. However, if adaptive modulation and coding rates are applied across the entire spectrum, this AIR reduction can be limited to only 10%

Physical layer transmitter and routing optimization to maximize the traffic throughput of a nonlinear optical mesh network

This paper investigates the physical layer optimization as a means of improving the utilization of limited network resources. A transparent optical network operating in the nonlinear transmission regime using coherent optical technology is considered. A physical layer model is described that allows the transmission signal quality to be included in the optimization process. Initially a fixed power, route-adapted modulation format approach is taken using integer linear programming to solve the static route allocation problem. It is shown that for the 14-node, 21-link NSF mesh network adaptation of the modulation formats leads to increases in data throughput of 17%. Optimization of the individual transmitter launch powers and spectral channel allocation results in a SNR margin of 2.3 dB, which is used to further increase the overall network traffic throughput exceeding the fixed PM-QPSK modulation format by as much as 50%. Compared to other work this paper highlights that increased gains in network throughput can be achieved if nonlinear interference is included in the routing and spectral assignment algorithm and individual transmitter spectral assignment and launch power is optimized to minimize nonlinear interference

MB2.1 - Coherent Technologies for Passive Optical Networks (Invited)

To date, optical access networks have been exclusively based on intensity modulation with direct detection. However, recent advances in coherent transceivers offer the potential to overcome the many limitations of these systems. This work reviews such candidate technologies for low complexity coherent optical access networks

Combining Optical Phase Conjugation and Volterra Equalisation: a Novel Nonlinearity Compensation Scheme

A novel nonlinearity compensation scheme combining optical phase conjugation and Volterra equalisation is proposed and assessed. This hybrid approach outperforms both Volterra and optical phase conjugation schemes, individually applied, by over 4 dB in EDFA-amplified fibre links