Dispersion Compensation Ratio Research Articles

Improvement of three-level code division multiplexing via dispersion mapping

A new dispersion map is designed for three-level code division multiplexing (3LCDM) of a 40 Gb/s $$(2\times 20\, \hbox {Gb/s})$$(2×20Gb/s) over 500 km $$(5\times 100\,\hbox {km})$$(5×100km) standard single mode fiber. The results show that an 87.5 % dispersion compensation ratio was the optimum map for the 3LCDM system. The system performance is improved by 6 dB in optical signal-to-noise ratio, 6 dB in receiver sensitivity and 3 dB in self-phase modulation threshold. Based on these improvements, the 3LCDM performance is comparable to the available multiplexing and modulation techniques while offering simpler transmitter and receiver architecture.

Intra-channel nonlinearity compensation for PM-16QAM traffic co-propagating with 28Gbaud m-ary QAM neighbours

We quantify the benefits of intra-channel nonlinear compensation in meshed optical networks, in view of network configuration, fibre design aspect, and dispersion management. We report that for a WDM optical transport network employing flexible 28Gbaud PM-mQAM transponders with no in-line dispersion compensation, intra-channel nonlinear compensation, for PM-16QAM through traffic, offers significant improvements of up to 4dB in nonlinear tolerance (Q-factor) irrespective of the co-propagating modulation format, and that this benefit is further enhanced (1.5dB) by increasing local link dispersion. For dispersion managed links, we further report that advantages of intra-channel nonlinear compensation increase with in-line dispersion compensation ratio, with 1.5dB improvements after 95% in-line dispersion compensation, compared to uncompensated transmission.

Closed-form expressions for nonlinear transmission performance of densely spaced coherent optical OFDM systems

There has been a trend of migration to high spectral efficiency transmission in optical fiber communications for which the frequency guard band between neighboring wavelength channels continues to shrink. In this paper, we derive closed-form analytical expressions for nonlinear system performance of densely spaced coherent optical OFDM (CO-OFDM) systems. The closed-form solutions include the results for the achievable Q factor, optimum launch power density, nonlinear threshold of launch power density, and information spectral efficiency limit. These analytical results clearly identify their dependence on system parameters including fiber dispersion, number of spans, dispersion compensation ratio, and overall bandwidth. The closed-form solution is further substantiated by numerical simulations using distributed nonlinear Schrödinger equation.

A novel all-optical label swapping based on RZ-DQPSK/IRZ-ASK combined modulation format

A novel all-optical label swapping based on optical return zero (RZ) differential quadrature phase shifted keying/inverse return zero amplitude shifted keying (RZ-DQPSK/IRZ-ASK) combined modulation format scheme is investigated and analyzed theoretically. Internet protocol (IP) packets can be efficiently labeled and processed using this proposed scheme. Numerical simulation is taken to demonstrate the transmission characteristic of the all-optical label swapping based on RZ-DQPSK/IRZ-ASK modulation format. The transmission performance can be affected by the duty cycle of the IRZ pulse, the IRZ-ASK label extinction ratio, the dispersion compensation ratio, received optical power and the coupling coefficient of the coupler. Results show that the IRZ-ASK label extinction ratio is almost infinite and preferable performance is obtained. The proposed scheme is a practical solution to meet the data rate and cost-efficient of the optical links simultaneously in tomorrow's all-optical label swapping.

Performance analysis of AMI-RZ single-sideband signals in 40 Gbit/s transmission systems

The performance of alternate-mark-inversion return-to-zero (AMI-RZ) signalling format with optical sideband suppression (SS) by means of optical filtering is assessed. The optimisation of the settings of the SS filter is performed numerically for three types of SS filters. A minimum level of the suppressed sideband power ratio of 20 dB is required to generate single-sideband (SSB) signals. It is shown that all three filters can generate AMI-RZ-SSB signals by imposing proper SS filter bandwidth and detuning. Transmission performance over different distances revealed that, in a post-compensation scheme, double-sideband (DSB) modulation format shows better transmission performance than the SSB formats, whereas the duobinary format shows the worst performance of the studied formats. In a pre-compensation scheme, the duobinary shows better performance than the SSB formats. However, the optically generated SSB signals nearly triplicate the DSB signal tolerance to group velocity dispersion and dispersion-compensation ratio (DCR) variation. The duobinary proved to have the best DCR tolerance, whereas the SSB formats proved higher tolerance to polarisation-mode dispersion. It is shown that the SSB formats present remarkable robustness to optical filter parameters variation, revealing that the AMI-RZ-SSB format is a good candidate for long-haul transmission systems.

Performance of DCS-RZ single-sideband signal in 40 Gbit/s long-haul transmission systems

Optical sideband suppression (SS) by means of optical filtering is proposed for duobinary-carrier-suppressed return-to-zero (DCS-RZ) coding format. The performance of DCS-RZ with SS format generated using three different SS filters is investigated through numerical simulation. The power of the nonsuppressed sideband to the power of the suppressed sideband ratio (SSPR) is used to categorise the level of sideband suppression. A minimum level of SSPR of 20 dB is required to generate single-sideband (SSB) signals. It is shown that, for all three SS filters, an SSPR higher than 20 dB can be accomplished by choosing properly the SS filter bandwidth and detuning. Hence, the SS filter can generate single-sideband (SSB) signals. Transmission performance over different distances is assessed numerically. Results reveal that a double-sideband (DSB) modulation format shows better performance (Q-factor improvement of ∼3 dB, for optimum input power levels), even after 8 transmission spans of standard single-mode fibre, than the SSB formats. However, the optically generated SSB signals increase the DSB signal tolerance to dispersion compensation ratio variation more than three times, showing remarkable robustness to optical filter parameter variation, revealing that the DCS-RZ-SSB format is a good candidate for long-haul transmission systems.

Influence of transmitter chirp on optimised dispersion managed 10 Gbit/s NRZ installed links

The impact of transmitter chirp on the performance of pre- and post-compensation normalised sections for non-return-to-zero single channel systems was studied by computer simulation. An acceptable dispersion and power margins in typical 10 × 80 and 20 × 80 km-long terrestrial transmission systems were found at 10 Gbit/s. Positive transmitter chirp can remarkably increase the optimised Q-factor of a pre-compensated scheme, increase the acceptable range of the dispersion compensation ratio for a prescribed Q-factor, and shift the optimum power levels toward higher values. However, no significant improvement results from using chirp for the post-compensated scheme. By independently varying the power at the transmission and compensating fibres inputs and the dispersion compensation ratio, the post-compensation scheme shows better performance than the pre-compensation scheme at the expense of stricter parameter tolerance.

The effects of dispersion compensation ratio on the performance of WDM systems with long amplifier spacing

When the transmission signal per channel is a 10 Gbit/s RZ pulse and the amplifier span is over 100 km, proper undercompensation can enhance the nonlinear WDM system performance. Improper undercompensation or overcompensation will degrade the system performance. Cross-phase modulation plays an important role in the nonlinear WDM system. The maximum transmission distance with the XPM effect considered is far smaller than that with the XPM effect isolated. The performance of difference channels in a nonlinear WDM system is dependent on the input power and DCF length. © 1998 John Wiley & Sons, Inc. Microwave Opt Technol Lett 18: 73–78, 1998.

Straight line 10 Gbit/s soliton transmission over 1000 km of standard fibre with in-line chirped fibre grating for partial dispersion compensation

The authors demonstrate a highly practical and robust soliton transmission system with partial dispersion compensation. Error free transmission was obtained for 10 Gbit/s data over 1000 km of standard fibre with nominal dispersion of 17 ps/nm.km. Despite variations in the dispersion compensation ratio and the relatively high UV-induced birefringence of the fibre gratings, the system exhibits BERs < 10–10 for any state of input polarisation provided that the average intra-span dispersion is negative.

Soliton transmission using periodic dispersion compensation

We examine the behavior of solitons in optical fibers where the dispersion is alternated between the normal and anomalous regimes. The periodic nature of the system strongly modifies the shape of the stable soliton (solitary wave) pulses, and increases their energy when compared with solitons in equivalent uniform fibers. Power enhancement factors of up to 70 are numerically observed. This leads to both an increased signal-to-noise ratio (SNR) at the receiver and reduced Gordon-Haus timing jitter. The interaction between pairs of isolated pulses is examined. We also examine implementations including periodic amplification, and show that the energy scalings introduced by the amplification and the dispersion management are independent provided that the periods of the two processes are dissimilar. We show that there is an optimum dispersion compensation ratio which minimizes the received Gordon-Haus jitter. A diagrammatic technique is presented for estimating the performance of dispersion compensated soliton transmission systems.

Optical RZ signal straight-line transmission experiments with dispersion compensation over 5520 km at 20 Gbit/s and 2160 km at 2 × 20 Gbit/s

Through optimisation of a dispersion compensation ratio to balance the effects of timing jitter and waveform distortion, single-channel and two-WDM-channel 20 Gbit/s RZ signals are successfully transmitted over 5520 and 2160 km, respectively, in the anomalous dispersion region.