Number Of Wavelength Division Multiplexing Channels Research Articles

Nonlinear distortion estimation in dual-carrier PM-QPSK signals for uncompensated fiber links

Abstract Kerr nonlinearity is particularly detrimental in coherent optical communications over long-haul, sub-sea and transatlantic links. The correct and accurate determination of the penalty due to fiber nonlinearity is critical for estimating the link capacity and optical signal to noise ratio margins. Two distinct approaches for calculating the power in the nonlinear field are proposed. The first approach utilizes the nonlinear variance at the decision gate after coherent detection, while the second attempts to extract the electrical field of the nonlinear interference noise. Subsequently, the power spectral density of the nonlinear interference noise is integrated to estimate the nonlinear power within a pre-defined signal-to-nose ratio criterion. Based on the assumptions in this study, a temporal resolution of 16 samples per symbol or (6.25 ps) is required to achieve a signal-to-noise ratio sensitivity of 40 dB on the nonlinear power estimate for a 10 Gbaud signal. Furthermore, a minimum pattern length of 128 symbols is required to obtain an adequate estimate of the nonlinear noise power within 30 dB signal-to-noise ratio for two adjacent wavelength-division-multiplexed (WDM) channels. The influence of the pulse shaping roll-off factor and number of WDM channels on the required pattern length and the nonlinear power estimation is also investigated.

Wavelength division multiplexing of continuous variable quantum key distribution and 18.3 Tbit/s data channels

Quantum key distribution (QKD) can offer communication with unconditional security and is a promising technology to protect next generation communication systems. For QKD to see commercial success, several key challenges have to be solved, such as integrating QKD signals into existing fiber optical networks. In this paper, we present experimental verification of QKD co-propagating with a large number of wavelength division multiplexing (WDM) coherent data channels. We show successful secret key generation over 24 h for a continuous-variable QKD channel jointly transmitted with 100 WDM channels of erbium doped fiber amplified polarization multiplexed 16-ary quadrature amplitude modulation signals amounting to a datarate of 18.3 Tbit/s. Compared to previous co-propagation results in the C-band, we demonstrate more than a factor of 10 increase in the number of WDM channels and more than 90 times higher classical bitrate, showing the co-propagation with Tbit/s data-carrying channels.

Bit Error Rate Performance Limitations Due to Raman Amplifier Induced Crosstalk in a WDM Transmission System

AbstractAnalysis is carried out for a single span wavelength division multiplexing (WDM) transmission system with distributed Raman amplification to find the effect of amplifier induced crosstalk on the bit error rate (BER) with different system parameters. The results are evaluated in terms of crosstalk power induced in a WDM channel due to Raman amplification, optical signal to crosstalk ratio (OSCR) and BER at any distance for different pump power and number of WDM channels. The results show that the WDM system suffers power penalty due to crosstalk which is significant at higher pump power, higher channel separation and number of WDM channel. It is noticed that at a BER 10

Optical Front-Ends to Generate Optical Millimeter-Wave Signal in Radio-Over-Fiber Systems With Different Architectures

We have proposed and experimentally demonstrated three different optical front-ends to implement in wavelength-division-multiplexing (WDM) radio-over-fiber (ROF) networks to minimize the cost of the ROF system. When the number of WDM channels is small, such as smaller than four channels, the simplest front-end to generate WDM optical millimeter (mm)-wave signals is to use only broadband direct-modulation laser (DML) for each WDM channel. In this case, the expensive external modulator can be removed. However, when the number of WDM channels is large, such as larger than four, the frond-end to generate WDM optical mm-wave signals can be realized by using an external modulator to upconvert simultaneously all channels after the WDM channel signals are multiplexed. In this way, the cost of the expensive external modulator will be shared by all channels. For seamless integration of WDM signals that come from the existing backbone with ROF system, a broadband external modulator can be used to upconvert WDM signals.

Upgrading WDM Submarine Systems to 40-Gbit/s Channel Bitrate

The introduction of wavelength division multiplexing (WDM) has triggered a tremendous capacity growth in submarine systems, both by the increase of the number of WDM channels and by the increase of the channel bitrate. Starting from 2.5 Gbit/s in the mid-1990s, the bitrate was upgraded to 10 Gbit/s by the end of the century in commercial products. The next generation of submarine systems will likely be based on a 40-Gbit/s bitrate. However, transmissions at a 40-Gbit/s rate are more challenging than transmissions at 10 Gbit/s. The goal of this paper is to provide an overview of the technologies which could be required or used in next-generation submarine systems. In the first part of this paper, an overview of the history of submarine links is provided. Then the technologies used in current N times 10 Gbit/s systems are described. Eventually, the challenges to overcome are discussed, whether they concern the type of fiber, the type of optical amplifier, or the nature of the modulation format

Analytical Evaluation of the Impact of Four Wave Mixing on the Bit Error Rate Performance of a WDM Soliton Transmission Link

In this paper, an analytical approach is presented tc evaluate the effect of Four Wave Mixing (FWM) in single mode fiber on the bit error rate performance of a multi-channel soliton transmission system with wavelength division multiplexing (WDM). The bit error rate of a WDM soliton transmission link is evaluated at a bil rate of 10 Gbit/s in the presence of FWM. The results show that at 10 Gbit/s the presence of unwanted light signals due to FWM degrades the performance of solitor receiver and the system suffers a penalty in terms of soliton power level. The penalty at BER =10 -9 is found to be 8.7 dB and 9.2 dB respectively for optical filter bandwidth of 40 GHz and 100 GHz when the number of WDM channels is 10 with five amplifiers in cascade for a total fiber length of 250 km.

Output power excursions in a cascade of EDFAs fed by multichannel burst-mode packet traffic: experimentation and modeling

A serious problem facing wavelength-division multiplexed (WDM) networks with fiber amplifier cascades is transient cross-gain saturation or gain dynamics of fiber amplifiers. Attention has been focused primarily on circuit-switched scenarios. When the number of WDM channels transmitted through a circuit-switching network varies, channel addition/removal will tend to perturb signals at the surviving channels that share all or part of the route. Even more serious bit error rate deterioration can arise in WDM packet switched burst mode networks. In this paper, we present experimental and theoretical results demonstrating the effect of fast power transients in erbium-doped fiber amplifiers (EDFAs) on packetized traffic transmitted through a chain of five EDFAs. Traffic of a local-area network has been transmitted over three channels. The effect of EDFA cross-gain saturation due to the burstiness of the traffic has been observed in a continuous-wave monitoring channel. The stabilizing effect of gain clamping of the first EDFA in the cascade has been investigated. The experimental results are extended to eight-channel WDM system using a large signal numerical analysis.

Cross-gain modulation effect on the behaviour of packetized cascaded EDFAs

In this paper, we demonstrate the importance of the number of wavelength division multiplexing (WDM) channels and the network traffic variability on the dynamics of a cascade of erbium-doped fibre amplifiers (EDFAs) fed by packet traffic in burst mode. The dynamics are determined using a numerical model incorporating time variation effects in the EDFA. Calculations are based on the solution of a transcendental equation describing the time evolution of the reservoir, i.e. the total number of excited ions, for each EDFA. Traffic on WDM channels is modelled as statistically independent ON/OFF time-slotted sources. We find that the cross-gain modulation effect depends on the number of WDM channels and also on network traffic variability. As the number of WDM channels increases, and even though each one is highly variable in time, the dynamics of the total input power exhibits less fluctuation, allowing the reservoir to have a more suitable behaviour. In addition, the swings of the reservoir and the total output power decreases when we increase the network utilization factor. This positive effect is not felt on the output power excursion of an individual WDM channel. This is due to the fact that the cumulative effect of the reservoir fluctuations along a cascade will lead to further broadening of any individual channel power probability density function (PDF). Finally, we investigate the effect of gain clamping of the first amplifier in the cascade - by implementing a ring laser and propagating the lasing power through the cascade - on the statistics of several measurable entities.

Design theory of long-distance WDM dispersion-managed transmission system

This paper describes a novel design theory of long distance wavelength division multiplexed (WDM) dispersion-managed optical transmission systems. Assuming that the transmission distance, bit rate, and number of WDM channels are initially known, we investigate the optimum dispersion allocation and input power per channel to achieve the minimum channel spacing. Based on the design guidelines for single-channel and multichannel systems, we establish the optimal design strategy. Details of the design procedure are demonstrated for 2.5-, 5-, and 10-Gb/s 10000 km WDM systems by using computer simulations. Next, we study the impact of the fiber dispersion slope on the usable wavelength span, and show that the attainable capacity of the representative 5-Gb/s 10000 km WDM system employing the postcompensation scheme can not exceed 100 Gb/s. Finally, we propose several techniques to approach the ultimate capacity of the WDM system and show that up to 1 Tb/s (200/spl times/5 Gb/s) 10000 km system can be implemented without utilizing the in-line dispersion slope compensation scheme. We also discuss the 10 Gb/s-10000 km WDM system employing in-line dispersion slope compensation.

Channel sharing in multi-hop WDM lightwave networks: do we need more channels?

A local lightwave network can be constructed by employing two-way fibers to connect nodes in a passive-star physical topology, and the available optical bandwidth may be accessed by the nodal transmitters and receivers at electronic rates using wavelength-division multiplexing (WDM). The number of WDM channels, w, in such a network is technology-limited and is less than the number of network nodes, N, especially if the network should support a scalable number of nodes. We describe a general and practical channel sharing method, which requires each node to be equipped with only one transmitter-receiver pair, and in which each WDM channel is shared in a time-division multiplexed fashion; optical fiber LANs are discussed in particular. We also develop a general model for analyzing such a shared-channel, multi-hop, WDM network. Our analysis yields a counterintuitive result: it is sometimes better to employ fewer channels than a larger number of channels. We explore bounds on the ranges of w which admit queueing stability-using too few or too many channels can lead to instability. We also obtain an estimate for the optimal number of channels that minimizes network-wide queueing delay.