Channel Spacing Values Research Articles

Quadruple impact of SPM, XPM, FWM and SRS nonlinear impairments on the performance of DWDM-PON

Recently, dense wavelength division multiplexing passive optical networks (DWDM-PONs) have become a considerable choice for 5G and beyond fronthaul implementations. Formerly, we have proposed a full-duplex bidirectional DWDM-PON architecture convenient for those implementations and analyzed the combined dual impact of four-wave mixing (FWM) and stimulated Raman scattering (SRS) nonlinear impairments on the proposed architecture. Meanwhile, a detailed literature analysis showed us that the combined quadruple impact of self phase modulation (SPM), cross phase modulation (XPM), FWM and SRS on the performance of bidirectional DWDM-PONs have never been researched up to now. In this paper, quadruple impact of SPM, XPM, FWM and SRS on the performance of both uplink channels (ULCs) and downlink channels (DLCs) of the formerly proposed DWDM-PON has been analyzed with simulations. Simulations have been performed in O-band region for ULCs and in C-band region for DLCs of 2 × 15- and 2 × 63-channel DWDM-PONs having 12.5 GHz, 25 GHz, 50 GHz, 100 GHz equally-spaced channels. The quadruple impact of optical nonlinear impairments on the DWDM-PON performance has been analyzed with signal-to-crosstalk ratio (SXR) simulations performed under varying channel input powers and channel lengths. Results show that under the quadruple nonlinear impact reliable bidirectional transmission with an SXR over 23 dB can be achieved for channel input powers below 0.58 mW and 0.16 mW in 2 × 15- and 2 × 63-channel DWDM-PONs, respectively, for all channel spacing values and 25 km transmission lengths. Moreover, results also imply that variations in channel lengths do not significantly affect SXR at both ULCs and DLCs of 2 × 15- and 2 × 63-channel DWDM-PONs for lengths exceeding 50 km. The thorough analysis presented in the paper will give a new insight for analysis of conventional and next generation PONs.

Combined impact of SRS, FWM and ASE noise in UDWDM/DWDM long-haul communication systems using EDFAs

In this paper, the combined impact of SRS, FWM and ASE noise in center channels of 7-, 15-, 31- and 63-channel UDWDM/DWDM long-haul multi-span optical fiber communication systems using different numbers of EDFAs has been analyzed with simulations. UDWDM/DWDM systems with varying system parameters, i.e. channel input powers, channel spacing values, multi-span fiber lengths and numbers of EDFAs, have been taken into account in simulations. Comparative OSNR simulation results satisfying a minimum 23 dB OSNR criterion under the combined impact of SRS, FWM and ASE noise have been presented and evaluated. OSNR vs channel input power simulation results show that FWM becomes the most dominant effect with respect to SRS and ASE noise in UDWDM systems. Therefore, OSNR values decrease as channel input powers increase in multi-span UDWDM systems having 3.125 GHz and 6.25 GHz channel spacing values. However, both ASE noise and SRS become more dominant with respect to FWM in DWDM systems with 100 GHz channel spacing values. OSNR values increase as the channel input powers increase in those multi-span DWDM systems. Simulation results for OSNR vs channel spacing values show that OSNR values obtained in multi-span UDWDM systems increase as channel spacing values increase in the 3.125 GHz–6.25 GHz range. This is due to the decrease in FWM crosstalk, which has a dominant effect in UDWDM systems, with increasing channel spacing values in those UDWDM systems. However, OSNR values obtained in multi-span DWDM systems decrease as channel spacing values increase in the 12.5 GHz–100 GHz range. This is due to the increase in ASE noise, which has a dominant effect in DWDM systems, with increasing optical filter bandwidths of those DWDM systems. OSNR vs channel length simulation results show that OSNR values generally decrease with increasing total fiber lengths and inter-amplifier fiber lengths in both UDWDM and DWDM multi-span systems. This is due to the FWM crosstalk and the ASE noise, which become more dominant with respect to the SRS as the total fiber length and inter-amplifier fiber lengths increase. Simulation results for OSNR vs number of EDFAs show that OSNR values obtained in multi-span UDWDM systems having 3.125 GHz channel spacing values decrease with increasing numbers of EDFAs. However, OSNR values in multi-span UDWDM/DWDM systems having 6.25 GHz-100 GHz channel spacing range increase with increasing numbers of EDFAs. Simulation results provide important clues for the design and implementation of reliable long-haul UDWDM/DWDM systems.

Performance enhancement of Raman + EYDFA HOA for UD-WDM system applications

Abstract In this work, we study and analyze the performance of Raman + Erbium-Ytterbium codoped fiber hybrid optical amplifier (HOA) for an ultradense wavelength division multiplexing (UD-WDM) system having 100 channels. The system has been investigated considering initial values of channel spacing and data rate of 0.1 nm (12.5 GHz) and 100 GB/s, respectively. Initially, the two important WDM system parameters—wavelength and channel spacing—have been selected and then optimization of the proposed HOA has been performed in terms of EYDFA length, pump power and Er+ concentration to achieve higher values of average gain, Q-factor and lower gain variation ratio. The optimized configuration of the HOA results in the achievement of higher value of average gain, Q-factor and gain variation ratio of 47 dB, 14 and 0.14, respectively, which confirms its viability for UD-WDM system applications.

Thermal–hydraulic efficiency management of spiral heat exchanger filled with Cu–ZnO/water hybrid nanofluid

In this paper, the effect of different channel spacing in spiral heat exchanger filled with Cu–ZnO–water hybrid nanofluid was investigated to find the optimum thermal–hydraulic performance. The hot water flow enters into the test section from central aperture of heat exchanger, and the cold hybrid nanofluid flow enters into the test section from the outer aperture of the heat exchanger. The effects of different flow velocities, nanoparticles φ and channel spacing values have been analyzed. Results have been presented on Nusselt number, outlet temperature, pressure drop and PEC. According to the obtained results, channel spacing decrease in constant flow velocity values is more effective than volume fraction increase on outlet temperature improvement. Also, an increase in inlet flow velocity leads to lower heat transfer between cold and hot channels, but the growth of volume fraction can improve the thermal efficiency of the heat exchanger at high velocities. On the other hand, the reduction in channel spacing leads to more pressure drop penalty. Especially for the hot water flow, this behavior reduces the hydraulic performance of heat exchanger. The less the channel spacing, the more the pressure drop. The highest average Nusselt number occurs at a velocity of 0.45 (m s−1) and φ = 4% at a channel spacing of 35 mm. The maximum value of the pressure drop occurs at b = 2.5–5 mm. Besides considering the PEC value, 2% volume fraction is recommended for the spiral heat exchanger.

Investigation of EDFA Performance in DWDM Transmission Systems Under Different Operating Conditions

Abstract The article investigates dependence of EDFA performance on its operating conditions. First of all, the impact of changes in channel spacing on the quality of the amplifier signal and on the desired EDFA configuration is observed – three different values of channel spacing are considered – 37.5 GHz, 50 GHz and 100 GHz. Afterwards, the impact of EDFA positioning on the quality of the amplified signal and the desired configuration is assessed. Three different EDFA positioning scenarios are considered – when the EDFA is used as a power booster, as an in-line amplifier and as a preamplifier. In all cases, such configuration of the EDFA is found that can ensure bit-error ratio (BER) values below 1·10−9 in all channels of the system. To assess the performance of the amplifiers, power penalty values are obtained in respect to identical transmission systems but without amplification.

Effect of Channel Spacing on the Design of Mixed Line Rate Optical Wavelength Division Multiplexed Networks

Abstract The ever increasing heterogeneity and growing traffic volume has resulted in significant innovations and paradigm shifts within the telecom backbone networks. In order to cost-effectively respond to the diverse variety of traffic requirements having heterogeneous service demands, wavelength division multiplexed (WDM) optical networks have adopted the mixed line rate (MLR) strategy. In MLR networks, many wavelength channels with various line rates can co-exist within the same fiber which, however, raises many important design issues; one of them being the choice of the channel spacing. The quality of signal is affected by the channel spacing in terms of the bit-error rate (BER), which in turn affects the maximum optical reach of the lightpaths that depends on the line rates. In regard to the aforementioned, different methods can be adopted in order to set the width of the channel spacing, viz., (a) choice of a 50 GHz uniform fixed channel spacing specified by the ITU-T grid, (b) exploring various channel spacing values for different line rates so as to optimize the usage of the fiber spectrum, or (c) seek for an optimal value of the channel spacing which results in the minimum network cost. In the current work, we evaluate the MLR network cost for various channel spacings; hence, we find an optimal value of the channel spacing that leads to the minimum MLR network cost. The simulation results reveal that, for a MLR network, even with the assumption of uniform channel spacing, optimal values of the channel spacing for a minimum cost network can be identified.

Parallel channels' fracturing mechanism during ice management operations. Part II: Experiment

During ice management operations, cutting parallel channels with narrow spacing in the ice using icebreakers can effectively reduce the size of ice floes reaching the protected vessel/structure. A narrow channel spacing width generates smaller ice floes. However, a spacing that is too narrow can lead to excessive or even impractical ice management operations. Therefore, it is beneficial to establish a theoretical model that correlates the channel spacing width with the frequency of ice fracturing events and the reduction of managed ice floe sizes. This is achieved in the current study with two sequential papers, i.e. Papers I and II. In Paper I, a theoretical model involving an ‘edge crack model’ was formulated to predict the following conditions for an ice management operation: 1) the maximum ice floe with size LMCD that can be produced; 2) the maximum channel spacing width hmax beyond which long cracks will not develop between the channels; and 3) the required force to initiate long cracks between parallel channels. In this paper (Paper II), we describe two dedicated ‘parallel channel tests’ conducted separately on September 26th and 29th in 2015 during an expedition to the Arctic Ocean (around 82°N and 16°E) with the icebreakers Oden and Frej. The tests had ‘well-controlled’ channel spacing in each test run. Several different channel spacing values were tested with the Oden and the consequent fracturing information was documented by camera images. Image processing enabled us to extract information, such as maximum floe sizes and floe size distributions, given different channel spacing widths. In addition, the ship's data, such as ship velocity and propulsion history, enabled us to validate the theoretical model's capability to predict the onset of long cracks between two parallel channels. Despite uncertainties (e.g., non-uniform ice thickness, fracture properties of sea ice, etc.) involved in the tests, favourable comparisons between the experimental results and the theoretical predictions were achieved. Both the theoretical model and experimental results help clarify the parallel channel fracturing mechanism.

SRS VE FWM OLAYLARININ DWDM-GPON SİSTEMLERİN AŞAĞI YÖNLÜ KANAL PERFORMANSLARI ÜZERİNDEKİ BİRLEŞİK ETKİSİ

In this paper the combined impact of stimulated Raman scattering (SRS) and four-wave mixing (FWM) on the downlink channel performance of dense wavelength division multiplexed-gigabit passive optical networks (DWDM-GPONs) has been compared with the single impact of FWM via signal-to-crosstalk ratio (SXR) simulations performed on center downlink channels of 7-, 15- and 31-channel DWDM-GPON systems. Simulation results show that SRS compensates negative impacts of FWM and compensation significance enhances with increasing channel numbers and channel spacing values. At high channel spacing values of 50 GHz and 100 GHz, variation of SXR can display a strong oscillatory behavior in very short channel length variations of 0.5 km. The combined impact of SRS and FWM enhances the maximum oscillation amplitude of SXR variation with respect to the single impact of FWM at those channel spacing values. It has been observed that Raman gain exhibits an approximately linear variation with channel input powers in 0.1-5 mW range and it increases with increasing fiber lengths, channel spacing values and channel numbers. Results of this research emphasize the significant difference between the combined impact of SRS and FWM and the single impact of FWM on DWDM-GPON systems and give important hints for current DWDM-GPON implementations.

On the Performance of MLR Optical WDM Network Based on ITU-T Conforming Fibers in the Presence of Dominant Physical Layer Impairments

The tremendous and consistent increase in the volume and heterogeneity of traffic has resulted in major innovations in the telecommunication networks. In regard to the optical networks, existing studies have shown that by adopting a mixed line rate (MLR) strategy, the wavelength division multiplexed optical networks can cost-effectively respond to the diverse variety of traffic requirements which have heterogeneous service demands. Unlike existing studies which focus on various MLR network issues by considering deployment of the standard single mode fiber only within the network, in the current work, we investigate the signal quality deterioration due to the combined effects of dominant physical layer impairments for an MLR optical network conforming to the various ITU-T compliant fibers and also considering the optical frequency grid based on ITU-T Recommendation G.692. The main aim of our current study is to identify, for a given fiber, the modulation format configuration which provides the highest performance. We conduct extensive simulations on the considered MLR system using the obtained optimum channel spacing values between the single and mixed line rates. Our results show that the existence of 10 Gbit/s line rate has a detrimental effect on the 40 Gbit/s and/or 100 Gbit/s line rate; however, the 40 Gbit/s and/or 100 Gbit/s line rate’s effect on a 10 Gbit/s line rate is not so detrimental, as well as between the similar line rates. Overall, our results clearly show that choice of the line rate of both, the central channel and its adjacent channels, has a major effect on the MLR network performance.

Analysis of the four-wave mixing impact on the most heavily affected channels of dense and ultra-dense wavelength division multiplexing systems using non-zero dispersion shifted fibers

In this paper, the impact of four-wave mixing (FWM) phenomenon on the system performance has been analyzed via focusing on effects of FWM products falling into the center channels, i.e. the most heavily affected ones among all, of equally spaced 9-, 11-, 13- and 15-channel DWDM systems having channel spacing values of 12.5GHz, 25GHz, 50GHz and 100GHz, and UDWDM systems having 6.25GHz channel spacing value. DWDM and UDWDM systems using four different single-span commercially available NZDSFs, i.e. TeraLight™, LEAF®, TrueWave®-Reach and TrueWave®-RS, have been considered in simulations. Results show that for all NZDSF types, input powers even as low as 1mW do not satisfy a minimum 23dB signal-to-crosstalk ratio (SXR) criterion in UDWDM and DWDM systems using 6.25GHz and 12.5GHz channel spacing values, respectively. Furthermore, for all DWDM and UDWDM systems, the lowest and the highest FWM crosstalk values belong to the TeraLight and the TrueWave-RS fibers, respectively, at all input powers, channel numbers and channel wavelengths while the minimum and the maximum SXR variations with varying channel wavelengths are obtained in the TrueWave-Reach and the LEAF fibers, respectively.

On the effect of channel spacing, launch power, and regenerator placement on the design of mixed-line-rate optical networks

Due to the increasing heterogeneity and the growing volume of traffic, telecom backbone networks are going through significant innovations. Wavelength-division multiplexed (WDM) optical networks can now cost-effectively support the growing heterogeneity of traffic demands by having mixed line rates (MLR) over different wavelength channels.The coexistence of wavelength channels with different line rates, e.g., 10/40/100Gbps, in the same fiber brings up various design issues: in this study, we focus on (1) choice of channel spacing; (2) choice of launch power; and (3) regenerator placement. Channel spacing affects the signal quality in terms of bit-error rate (BER), and hence affects the maximum reach of lightpaths, which is a function of line rates. Various approaches to set an opportunistic width of the channel spacing can be considered, viz., (i) uniform fixed channel spacing specified by the ITU-T grid (typically 50GHz); (ii) different channel spacing for different line rates; or (iii) optimal value of channel spacing for all line rates that leads to minimum cost.The launch optical power of a signal is another important parameter that affects the network cost. Adjacent channels on different line rates, especially 10Gbps and 100Gbps, may exhibit serious degradation of signal quality and optical reach for both the channels due to cross-phase modulation (XPM) between them. Launch power plays a role in such a scenario as it governs the BER by affecting both the signal power and the noise power due to XPM. Moreover, intelligent choice of launch powers on different line rates can significantly reduce the number of regenerators required in the network. The tradeoff between placement of regenerators and choice of launch power is an important problem to address for MLR network design.In this work, we investigate the effects of channel spacing and launch optical power by evaluating the cost of a MLR network for different values of these parameters. We also study the interplay between regenerator placement and launch power. Our results show that (a) it is possible to identify optimal values of channel spacing for a minimum-cost MLR network design, and (b) controlling the power of 10Gbps and 100Gbps channels shows maximum sensitivity to the network cost.

Investigation of four wave mixing effect with different number of input channels at various channel spacing

In this paper the design, implementation and performance analysis of four wave mixing (FWM) in optical communication system for different number of input channels is presented using various values of channel spacing. Here, all the input channels have been spaced evenly at various values like 6.25GHz, 12.5GHz, 25GHz, 40GHz, 50GHz with the different number of channels at the input i.e. with 2, 4, 6, 8, 12 input channels. The simulation results reveal that the four wave mixing is minimum when the channel spacing is maximum i.e. 50GHz with minimum number of channels i.e. 2 input channels. It is observed that on increasing the channel spacing, the interference between the input frequencies decreases and hence the four wave mixing also decreases. Also, on increasing the number of input channels/users, the interference between the input frequencies increases and thus, the four wave mixing also increases.

FWM minimization in WDM optical communication systems using the asymmetrical dispersion-managed fibers

Four wave mixing (FWM) induced power penalty is investigated theoretically for asymmetrical dispersion-managed fibers in wavelength division multiplexing (WDM) systems. The power penalty in these fibers is analyzed for various values of channel spacing, maximum dispersion and number of sections in different channels. Using numerical simulations, it is illustrated that the FWM induced power penalty is minimized for the case of two fiber sections with unequally special lengths and symmetrical dispersion values.

Impact of Channel Dynamics, Combined Nonlinearities and ASE Noise on Transmission Performance of all Optical Star WDM Networks

For all optical Wavelength Division Multiplexing (WDM) network based on G.653 fibers, we investigate the quality factor deterioration due to combined nonlinear effects and Amplified spontaneous emission (ASE) noise for system parameters based on ITU-T Recommendation G.692. The investigation: (a) emphasizes on stimulated Raman scattering (SRS) and four wave mixing (FWM) effects which are the dominant nonlinearities known to limit WDM system performance and (b) accounts for beating between nonlinearities and beating between ASE noise and nonlinearities. Using the proposed model, performance of the worst affected channels due to SRS and FWM is compared and the results indicate that the worst affected channel due to SRS performs better and hence must be preferred for reliable and efficient transmission over the worst affected channel due to FWM. Further, the results suggest that to achieve a desired error rate (quality factor); there exists an optimal value of channel spacing for a given number of channels. The proposed theoretical model is also validated through extensive simulations over Rsoft OptSimTM simulator and the two sets of results are found to match, indicating that the proposed model accurately calculates the quality factor of the all optical WDM network.

SOA nonlinearities in 4 × 25 Gb/s WDM pre-amplified system for 100-Gb/s Ethernet

A simulation analysis of the impact that the nonlinear response of a semiconductor optical amplifier (SOA) has in a four-channel WDM pre-amplified transmission system is presented in the framework of the recently proposed extended-reach (40-km, 4 × 25 Gb/s) 100 Gb Ethernet link. Channel spacing values ranging from 200 to 800 GHz, and fiber losses between 0 and −20 dB are considered. A maximum power penalty of 4.5 dB is predicted for short fiber lengths and for the tightest channel plan. For short fiber lengths, the penalty drops by about 0.8 dB when moving from 400 to 800 GHz; whereas for long fiber lengths, the penalty increases by 0.2 dB, provided that an average dispersive fiber is utilized. The widely spaced channel plan then represents the best choice in terms of the analyzed physical effects to implement the next-generation 100 GbE link. Further, our numerical investigation includes a discrimination analysis that confirms cross-gain modulation as the main overall SOA nonlinear impairment in the analyzed architecture, and establishes ultra-fast carrier heating-induced FWM as responsible for the system performance difference observed as a function of channel spacing. The difference practically vanishes for fiber lengths above 30 km. Finally, the proposal of an equation that fits the simulated power spectrum density of the first-order four-wave mixing-generated product as a function of channel spacing is presented as an aid to validate our numerical results.

Characterization of wavelength interleaving in radio-over-fiber systems employing WDM/SCM

A radio-over-fiber (RoF) distribution system incorporating both sub-carrier multiplexing and wavelength division multiplexing (WDM) technologies is presented. This signal is directly modulated onto three high-speed lasers. Bragg filters are employed at the receiver base station in order to both demultiplex the required optical channel, and ensure that the detected signal is single side band (in order to overcome dispersion limitations of the link). System spectral efficiency is optimised by wavelength interleaving. The channel spacing between the WDM channels is varied and the system performance for different values of channel spacing and spectral efficiencies is investigated. The results show that wavelength interleaving is a reliable technique that could be used to increase the spectral efficiency of RoF systems.