Dispersion Supported Transmission Research Articles

Laser Optimization Guidelines for Dispersion Supported Transmission Systems Operating at Arbitrary Bit Rates

Laser guidelines for the performance optimization of dispersion supported transmission (DST) systems operating at arbitrary bit rates, not exceeding 40 Gbit-s <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-1</sup> , are presented. These laser guidelines are derived by numerical simulation for 40 Gbit-s <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-1</sup> and analytically validated for other bit rates. The laser guidelines are settled in order to accomplish two DST system goals: maximizing the back-to-back sensitivity and the total dispersion tolerance, with fixed laser bias and modulation currents, thus avoiding the usual DST laser current tailoring to the fiber length. The laser optimization guidelines are expressed in terms of the intrinsic laser response parameters as in the following. The -3 dB intensity modulation (IM) bandwidth normalized by bit rate must be about 0.7; the zero of frequency modulation response normalized by bit rate must be about 0.75; the damping ratio of IM response must be about 0.7; the steady-state frequency deviation normalized by bit rate must be about 0.55; and the extinction ratio must be about 5.5. Numerical results show that these rules hold for lasers with parasitics with a cutoff frequency as low as 30% of bit rate, as well as for different current pulse shapes, laser gain, and compression models, and receiver electrical filters.

Laser optimisation for dispersion supported transmission systems

Ideal single-mode laser intrinsic parameters that optimise the performance of dispersion supported transmission (DST) systems are investigated. Laser parameter optimisation is performed to accomplish two goals: maximising the back-to-back sensitivity (BBS) and the total dispersion tolerance (TDT), with fixed laser bias and modulation currents, thus avoiding the usual DST laser current tailoring to the fibre length. Extensive numerical simulations reveal that significant improvement of DST system performance can be achieved by optimising simultaneous, independently and without restrictions, four laser intrinsic parameters; namely, linewidth enhancement factor (α), photon lifetime, gain parameter and gain compression factor (ɛ). The optimised laser shows good robustness of BBS and TDT to variations of those laser intrinsic parameters and a remarkable improvement in BBS and the TDT in comparison with the non-optimised DST system is achieved. It is shown that, to achieve the best DST performance at 20 Gbit/s using fixed laser currents, lasers with low α (α≃0.8) and high ɛ (ɛ≃10 × 10−23 m3) are required. The physical feasibility of the optimal laser intrinsic parameters is discussed from the standpoint of current laser technology. It is shown that a suboptimal set of laser intrinsic parameters consistent with strained multi-quantum well laser technology gives improved system performance.

Improving the Spectral Efficiency of DWDM-DST Systems through Line Coding and Optimized FBGs

In this contribution we show that by using the dense wavelength division multiplexing (DWDM) and the dispersion supported transmission (DST) techniques, together with compressed bandwidth data formats and optimized fiber Bragg grating (FBG) filters, it is possible to implement optical fiber communication systems with very high spectral efficiencies and long fiber spans. This is achieved by using fiber gratings with a Gaussian apodization together with a non-uniform average index perturbation, acting simultaneously as optical demultiplexers and group velocity dispersion compensators. For a be 32 x 20 Gsymbol/s WDM-DST system, we demonstrate spectral efficiencies of 0.7 bit/s/Hz for the binary and duobinary data formats, at distances of 65 km and 100 km, respectively, over standard single-mode fiber. Using 4-level coding, 1.28 Tbit/s (32 x 40 Gbit/s) can be packed in approximately 10 nm of optical bandwidth, corresponding to a spectral efficiency of 1 bit/s/Hz, and transmitted over a fiber span with 45 km.

Dispersion supported transmission technique: comparison of performance in anomalous and normal propagation regimes

Through semi-analytical simulation, the feasibility of an application of the dispersion-supported transmission (DST) technique in the normal propagation regime is investigated and its performance compared with that in the anomalous propagation regime. It is shown that, in the normal propagation regime, the DST technique operating at 20 Gbit/s can improve the maximum system sensitivity by about 7 dB relative to the anomalous propagation regime. However, a reduction of the maximum transmission distance and a greater dispersion dependence of system sensitivity around its maximum value are observed. The influence of laser adiabatic and transient chirps on the DST performance in both propagation regimes is investigated. It is shown that in the normal propagation regime, the presence of laser transient chirp can be beneficial, improving the system performance by opening the eye diagram at system output. Contrarily, in the anomalous propagation regime, its presence can strongly degrade the system performance, by closing the eye diagram at system output.

Small-signal analysis for nonlinear and dispersive optical fibres and its application to design of dispersion supported transmission systems with optical dispersion compensation

The exact general analytical solution of the small-signal analysis for nonlinear and dispersive optical fibre is derived and discussed. Exact solutions in case of particular situations are also presented, and compared with other authors' results. An approximated solution obtained from the physical description of fibre nonlinearity effect on the small-signal conversions is derived, numerically compared with the general solution, and shown to be less accurate for larger fibre nonlinearity effect, larger modulation frequencies and/or fibre dispersion. It is shown quantitatively that, at low-medium frequencies and for moderate optical powers at fibre input, the fibre nonlinearity affects the intensity modulation fibre transfer function (IM-FTF) primarily through the IM-IM conversion. Furthermore, it is shown that the fibre nonlinearity can provide perfect compensation of IM-FTF distortion in case of an external modulator with positive chirp parameter. The performance of various optical dispersion compensation (DC) configurations in dispersion supported transmission systems is compared and discussed using the IM-FTF, from the viewpoint of amplitude and delay distortion and bandwidth available. It is shown that under- and post-optical DC leads to an equalised IM-FTF with smaller amplitude and delay distortions and larger bandwidth.

Estimation of multiple-quantum-well laser parameters for simulation of dispersion supported transmission systems at 20 Gbit/s

In this paper, a set of multiple-quantum-well (MQW) laser parameters is proposed for simulation of optical transmission systems at 20 Gbit/s. The parameters have been estimated by joint fitting of a small signal intensity modulation (IM) response model to five measured IM response curves of a strained layer MQW laser, using the Levenberg–Marquardt method. Good agreement between theoretical and experimental curves was obtained. Using these laser parameters, we have assessed the performance of dispersion supported transmission systems at 20 Gbit/s incorporating an erbium doped fibre amplifier (EDFA) or a semiconductor optical amplifier (SOA) as a booster amplifier. It is shown that the use of a SOA, with an unsaturated gain of 20 dB, improves the system performance for link lengths ranging from 8 to 20 km of standard single-mode fibre (SMF) due to partial chirp compensation in the SOA, and degrades the system performance between 1.2 and 2.5 dB for link lengths ranging from 30 to 50 km. The increase of the unsaturated gain of the SOA from 20 to 25 dB is only advantageous for link lengths ranging from 8 to about 12.5 km where a small performance improvement, less than or equal to 0.8 dB, is observed. The influence on the system performance of an increase of the laser line width enhancement factor from 2 to 3 is also investigated.

Dispersion supported transmissionwith a binary optical signal at the receiver

A novel modulation scheme for dispersion supported transmission (DST) is proposed. Instead of the binary frequency modulation of the transmitter laser a linear frequency modulation along with the differential Manchester coding is used. It is shown that it gives greater values of the extinction coefficient as compared to the previous research in the range of 100km<L<200km.

Letter: Impact of double cavity FP demultiplexers on the performance of WDM dispersion supported transmission

AbstractThis paper discusses the impact of double cavity Fabry‐Perot demultiplexers on the performance of wavelength division multiplexing (WDM) systems with dispersion supported transmission (DST) of three 10 Gbit/s channels separated 1 nm. For performance assessment, a suitable simulation methodology has been used which combines signal simulation with noise analysis in optically amplified multichannel direct detection systems. Simulation results show an improved system performance if a double cavity Fabry‐Perot filter is used as demultiplexer, resulting in WDM transmission with a crosstalk penalty less than 1 dB in the region of small linear increase of dispersion penalty of the DST method. The robustness of the multichannel DST method against data pattern dependencies is investigated.

Performance implications of three-mirror Fabry-Perot demultiplexers for 10-Gb/s WDM dispersion-supported transmission with 0.5-nm channel spacing

This letter assesses the performance of dispersion-supported transmission (DST) for three 10-Gb/s WDM channels separated 0.5 nm, using a three-mirror Fabry-Perot demultiplexer. It is shown that the use of three-mirror demultiplexers reduces the crosstalk penalty to less than 1 dB in the region of small linear increase of dispersion penalty of the DST method, while double-cavity Fabry-Perot demultiplexers are less suitable to operate at this channel spacing. Compared with published performance studies for WDM-DST systems with 1 nm of channel spacing, these results indicate the channel spacing may be cut in a half, if a three-mirror filter is used as demultiplexer.

Influence of laser phase noise on dispersive optical fiber communication systems

Noise from semiconductor lasers in dispersive optical communication systems can give rise to a BER floor. Due to frequency-to-intensity noise conversion, the impact of laser phase noise increases with the fiber length. It is shown that the maximum transmission distance for dispersion-supported transmission obtained in laboratory experiments is mainly determined by the laser phase noise.

Performance assessment of two-channel dispersion-supported transmission systems using single- and double-cavity Fabry-Perot filters as demultiplexers

This letter presents a theoretical performance assessment assuming that single- and double-cavity Fabry-Perot filters are used as demultiplexers in two-channel dispersion supported transmission systems operated at 10 Gb/s. A suitable simulation methodology has been used that combines signal simulation with noise analysis in optically amplified multichannel direct detection systems. The results obtained show an improved system performance if a double-cavity Fabry-Perot filter is used as a demultiplexer, resulting in a WDM transmission with a crosstalk power penalty within 1 dB in the region of low dispersion penalty of the DST method, for a channel spacing of 1 nm. The robustness against dependencies on data patterns is verified.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Field experiments at 10 Gbit/s over 80, 160 and 240 km of standard singlemode fibre installed between Sesimbra and Lisbon using dispersion supported transmission technique

10 Gbit/s dispersion supported transmission (DST) experiments over up to 240 km of installed standard singlemode fibre (SMF) have been carried out using the existing fibre infrastructure between Sesimbra and Lisbon in Portugal, which is a part of the CPRM terrestrial fibre network. These experiments demonstrate the robustness of DST under real operating conditions.

10 Gbit/s dispersion supported transmission field trial over 123 km standard singlemode fibre for HDTV studio interconnection

A bidirectional studio interconnection system operating at 10 Gbit/s over 123 km installed standard singlemode fibre is presented. Uncompressed HDTV programme channels are transmitted in STM-format without an in-line repeater, using the dispersion supported transmission (DST) method.

Dispersion-supported transmission at 20 Gbit/s over 53 km standard singlemode fibre

The optical transmission of 20 Gbit/s signals over a record distance of 53 km standard nondispersion-shifted singlemode fibre (SMF) without optical dispersion compensation has been demonstrated successfully using a directly modulated MQW DFB laser operating at 1544 nm.

Limitations of dispersion supported transmission over standard single-mode fiber

Dispersion supported transmission (DST) is a new technique which combines intensity modulation (IM) and optical frequency modulation (OFM) to allow transmission spans beyond the usual dispersion limit. Using computer simulation, DST limitations are evaluated and optimum values for the frequency deviation and receiver bandwidth are determined. Finally, the maximum transmission distance is estimated for a power penalty of 1 and 2 dB. >

Impact of residual amplitude modulation on the performance of dispersion-supported and dispersion-mediated nonlinearity-enhanced transmission

The authors investigate the impact of nonvanishing residual amplitude modulation on the improvement in length which is achievable with dispersion-mediated nonlinearity-enhanced transmission over simple dispersion-supported transmission. The results reveal the feasibility of an increase in length by a factor of 1.5 for a 10 Gbit/s standard-fibre transmission, even when conventional direct modulation is used, allowing more than 300 km to be bridged.

10-Gb/s optical transmission up to 253 km via standard single-mode fiber using the method of dispersion-supported transmission

Using the new method of dispersion-supported transmission, 10 Gb/s signals at 1.53 /spl mu/m wavelength are transmitted on standard single-mode fiber with zero dispersion at 1.3 /spl mu/m via the record length of 253 km without in-line regeneration. Detailed experiments with a directly modulated laser demonstrate the system performance for different fiber lengths ranging from 0 up to 253 km. >

Operating principle of in-line amplified dispersion-supported transmission

Dispersion supported transmission (DST) has been presented as a linear scheme to extend the linear chromatic-dispersion limit. Although such a scheme is possible, the Letter clarifies that the recently demonstrated DST 10Gbit/s transmission over 252km is definitely predicated on fibre nonlinearities.