2R Regeneration Research Articles

Impact of RoPP in Wavelength Conversion Inducing Nonlinearity and All-Optical 3R Regeneration for DWDM Networks

Impact of RoPP in Wavelength Conversion Inducing Nonlinearity and All-Optical 3R Regeneration for DWDM Networks

Hybrid amplifier placement in mesh DWDM networks using integer linear programming models

Hybrid erbium-doped fiber (EDF)/Raman amplifiers (HFAs) can be utilized to improve the performance of specific fiber spans in dense wavelength division multiplexing (DWDM) networks, aiming to extend the reach and/or increase the capacity of optical channels, thereby reducing the total number of line interfaces required to satisfy a given set of traffic demands. However, HFAs are costlier than simpler EDF amplifiers (EDFAs) since they include Raman pumps in addition to an EDFA. Consequently, it is paramount to place them only at selected fiber spans of the network so as to maximize their impact while keeping their number limited. It has been shown that HFA placement can be a complex task in mesh DWDM networks in view of optical channel diversity, with each fiber span traversed by multiple channels with different source and destination nodes. Building on the approximation that noise adds up incoherently along the transmission path, this paper proposes optimal methods to solve the problem of placing hybrid amplifiers in mesh networks. Particularly, it describes two integer linear programming models, one to determine the minimum number and location of HFAs required to reach a target set of feasible optical channels (i.e., without intermediate 3R regenerators) and another to maximize the number of feasible optical channels given a limited number of HFAs to be deployed. A comprehensive set of network simulations using three reference optical network topologies is reported, providing insight into the effectiveness of the proposed models when compared to existing approaches.

Performance analysis of a cross-gain modulation (XGM) utilization in bulk-semiconductor optical amplifiers (SOAs) based all-optical 2R regeneration scheme

Performance analysis of a cross-gain modulation (XGM) utilization in bulk-semiconductor optical amplifiers (SOAs) based all-optical 2R regeneration scheme

DRAMA+: Disaster Management With Mitigation Awareness for Translucent Elastic Optical Networks

Elastic optical networks (EONs) have emerged as attractive candidates to satisfy the dramatic growth of demand in 5G and cloud applications. EONs promise to provide high spectrum utilization due to flexibility in resource assignment. In translucent EONs, the spectrum efficiency can be further improved by deploying regenerators. Because of their extremely high flexibility, developing efficient mechanisms and strategies to ensure the survivability of translucent EONs is a challenging problem. In this paper, we consider disaster mitigation in translucent EONs. We propose a new approach to disaster management by introducing the concept of mitigation zone, which identifies a region surrounding the disaster zone wherein lightpaths may be reconfigured with degraded service (with a penalty) in order to improve overall performance. We formulate an integer linear program (ILP) to minimize the penalty due to service degradation after a disaster, and present a heuristic algorithm named Disaster Management Algorithm with Mitigation Awareness and 3R regenerators (DRAMA+). Simulation results demonstrate that the proposed algorithms have a better performance in terms of total penalty and blocking ratio than conventional disaster recovery algorithms.

All-optical 2R regenerator based on similariton-induced spectral broadening

We numerically investigated an all-optical high-bit-rate 2R-regenerator based on similariton-induced spectral broadening of the optical signal spectrum. The proposed configuration incorporates two cascaded regeneration stages. Active and passive generation of similariton pulses in a highly nonlinear photonic crystal fiber and a comb-like dispersion decreasing fiber are used for the first and the second stages, respectively. The study of the static behavior of the regenerator linking the design to their nonlinear power transfer functions reveals the operating conditions under which the regenerator is able to reduce amplitude noise and improve the signal extinction ratio. Furthermore, the potential of the proposed configuration is evaluated to regenerate an optical signal at 40 Gbit / s, and the 2R-regenerator is then assessed in a long recirculating fiber loop to investigate its cascadibility. The ability of the 2R-regenerator to enable operating at high-bit rates up to 160 Gbit / s is also investigated. The results demonstrate the high potential of similariton pulses for all-optical 2R-regeneration in future high-speed and long-haul transmission systems.

Impact of Amplification and Regeneration Schemes on the Blocking Performance and Energy Consumption of Wide-Area Elastic Optical Networks

This paper studies the physical layer’s impact on the blocking probability and energy consumption of wide-area dynamic elastic optical networks (EONs). For this purpose, we consider five network configurations, each named with a network configuration identifier (NCI) from 1 to 5, for which the Routing, Modulation Level, and Spectrum Assignment (RMLSA) problem is solved. NCI 1–4 are transparent configurations based on all-EDFA, hybrid Raman/EDFA amplifiers (with different Raman gain ratio $\Gamma _{R}$ ), all-DFRA, and alternating span configuration (EDFA and DFRA). NCI 5 is a translucent configuration based on all-EDFA and 3R regenerators. We model the physical layer for every network configuration to determine the maximum achievable reach of optical signals. Employing simulation, we calculate the blocking probability and the energy consumption of the different network configurations. In terms of blocking, our results show that NCI 2 and 3 offer the lowest blocking probability, with at least 1 and 3 orders of magnitude of difference with respect to NCI 1 and 5 at high and low traffic loads, respectively. In terms of energy consumption, the best performing alternatives are the ones with the worst blocking (NCI 1), while NCI 3 exhibits the highest energy consumption with NCI $2\,\,\Gamma _{R}=0.75$ following closely. This situation highlights a clear trade-off between blocking performance and energy cost that must be considered when designing a dynamic EON. Thus, we identify NCI 2 using $\Gamma _{R}=0.25$ as a promising alternative to reduce the blocking probability significantly in wide-area dynamic EONs without a prohibitive increase in energy consumption.

Verification of All-Optical Regeneration with Hybrid Modulation and with On-Off Keying Modulation with Return to Zero and Non-Return to Zero Coding

In this work we study the non-linear effects through the analysis of the operating results of three alloptical 3R regeneration (re-amplifying, re-shaping and re-timing) under the effects of cross-phase modulation (XPM) and four-wave mixing (FWM), being a system with hybrid modulation and two other communication systems with modulation on-off keying (OOK) with return to zero (RZ) and non-return to zero (NRZ) coding. The main part of the 3R regeneration system proposed here is a Mach-Zehnder interferometer (MZI) composed of an acousto optical filter (AOF) and a highly nonlinear photonic crystal fiber (HNL-PCF), so the system proposed here was named 3R-MZIAOF regenerator. The comparison of the system results occurred through the variation of the input power variation from -10 dBm to 10 dBm for the link length of 121.3 km and transmission rate 10 Gbps. The results showed that the regeneration 3R scheme OOK-NRZ with AOF presented excellent values of bit error rate (BER) equal to 10-21 and quality factor (Q-Factor) equal to 9.4, when compared to a system with OOK-NRZ 3R regeneration and hybrid modulation.

Numerical analysis of the performance of a Mach–Zehnder interferometer based on acousto-optic filter for signal regeneration

In this work we performed a numerical analysis of the performance of an all-optical 3R regenerator based on four wave mixing through a communication system Mach–Zehnder interferometer (MZI) with acousto-optic filter (AOF) and photonic crystal fiber. The frequency difference between the input signal and the pump was used as a figure of merit for comparing minimum bit-error-rate (min. BER), maximum quality factor (max. Q-factor) and optical spectrum results. In this case the non-linear Schrodinger equation was solved by the split step Fourier method. Simulation and performance analysis of the 3R-MZI-AOF regenerator were performed using OptiSystem software for systems with different frequency spacings. Therefore, with the 3R regeneration proposed here, a significant improvement in system performance was achieved, where max. Q-factor was equal to 9 and min. BER was equal to 1 × 10−19 for the 600 GHz frequency spacing and 10 Gb/s transmission rate.

All-optical 3R regeneration for DPSK signal based on a semiconductor optical amplifier scheme.

This paper presents experimental demonstration of an all-optical 3 R (re-amplification, re-shaping, re-timing) regeneration scheme for differential phase-shift keying (DPSK) signals, which consists of a clock recovery module and a phase-regeneration module. The clock recovery module is based on a mode-locked fiber laser, and the optical clock is extracted with low timing jitter of 29 ps from a degraded 10 Gb/s DPSK signal. The phase regenerator consists of a one-bit delay interferometer demodulation stage and a semiconductor optical amplifier in which cross-phase modulation and nonlinear polarization rotation occur simultaneously. The results show that, after 3 R regeneration, the receiver sensitivity is improved by more than 1.6 dB for a bit error rate of 1 E-9.

Simulation of Fiber-Optic Buffer Loop Memory with All-Optical 2R Regeneration

Structure of the fiber-optic recirculating loop memory with periodic 2R-regeneration of information flow in the optical range is designed. The modified optical fiber loop mirror for 2R-regeneration of wavelength division multiplexed return-to-zero signals is proposed. On the basis of the proposed mathematical model, using numerical modeling, the efficiency of the restoration of optical information pulses using a nonlinear optical loop mirror (NOLM) is shown. The dependences of the restoration of the signals to the required values in duration and power on the variable parameters of the NOLM (the gain of the fiber-optic erbium amplifier and the length of the nonlinear optical fiber) are obtained for 10 Gbit/s wavelength channels.

BER-Adaptive RMLSA Algorithm for Wide-Area Flexible Optical Networks

Wide-area optical networks face significant transmission challenges due to the relentless growth of bandwidth demands experienced nowadays. Network operators must consider the relationship between modulation format and maximum reach for each connection request due to the accumulation of physical layer impairments in optical fiber links, to guarantee a minimum quality of service (QoS) and quality of transmission (QoT) to all connection requests. In this work, we present a BER-adaptive solution to solve the routing, modulation format, and spectrum assignment (RMLSA) problem for wide-area elastic optical networks. Our main goal is to maximize successful connection requests in wide-area networks while choosing modulation formats with the highest efficiency possible. Consequently, our technique uses an adaptive bit-error-rate (BER) threshold to achieve communication with the best QoT in the most efficient manner, using the strictest BER value and the modulation format with the smallest bandwidth possible. Additionally, the proposed algorithm relies on 3R regeneration devices to enable long-distances communications if transparent communication cannot be achieved. We assessed our method through simulations for various network conditions, such as the number of regenerators per node, traffic load per user, and BER threshold values. In a scenario without regenerators, the BER-Adaptive algorithm performs similarly to the most relaxed fixed BER threshold studied in blocking probability. However, it ensures a higher QoT to most of the connection requests. The proposed algorithm thrives with the use of regenerators, showing the best performance among the studied solutions, enabling long-distance communications with a high QoT and low blocking probability.

Performance Comparison of Dynamic Elastic Optical Networks with Optical Regeneration

We have investigated optical regeneration issues and application in elastic optical networks that are capable of providing dynamically optical paths with flexible bandwidths. We have analyzed the impact of optical regeneration in elastic optical networks and clarified various usage scenarios. We have then evaluated and compared the performance, in terms of the overall blocking probability and the total accommodated traffic volume, of three possible network scenarios with regeneration capability including (i) no regeneration, (ii) 3R regeneration, and (iii) 4R regeneration for practical network topologies. Numerical simulation proved that deployment of optical regeneration devices can exploit elastic optical networking to enhance the network performance for provisioning dynamically bandwidth-flexible lightpath services. It is also demonstrated that using re-modulation function while regenerating optical signals (4R regeneration) can further improve the network performance. However, due to the high cost of optical regeneration devices, especially all-optical ones, and more functional regenerators, the trade-off between the performance enhancement and the necessary number of regenerating devices needs to be carefully considered.

All-Optical Function Based on Self-Similar Spectral Broadening for 2R Regeneration in High-Bit-Rate Optical Transmission Systems

All-Optical Function Based on Self-Similar Spectral Broadening for 2R Regeneration in High-Bit-Rate Optical Transmission Systems

All-optical 2R-regeneration and continuous wave to pulsed signal wavelength conversion based on fiber nonlinearity

In this paper, we propose a novel all-optical 2R (re-amplification and re-shaping) regenerator based on inducing nonlinear chirp over a continuous wave probe. The regenerator also performs continuous wave to pulsed wavelength conversion. The chirp is induced in a highly nonlinear fiber by the data modulated pulsed signal that is to be regenerated. Offset filtering is employed at the output of the highly nonlinear fiber to extract the frequencies generated as a result of chirping. The regenerator performance has been evaluated with the help of bit-error-rate plots and eye diagrams at different values of optical signal to noise ratios. Apart from re-shaping and re-amplification, inclusion of the regenerator results in better resilience to amplified spontaneous emission noise.

All-optical two-channel 2R regenerator for time-interleaved PAM signals

Abstract All-optical multi-channel regeneration of advanced modulation signals is necessary for high-speed larger-capacity optical communication networks in the future from the cost point of view. As for the Mach–Zehnder-interferometer (MZI)-based pulse-amplitude-modulation (PAM) regenerator, we put forward the delay-complementary transmission scheme to avoid the crosstalk of cross-phase modulation (XPM) between two channels. The proposed scheme can ensure the optical power transfer performance required for multi-channel regeneration of time-interleaved PAM signals, regardless of differential group delay of available high nonlinear fibers. All-optical two-channel 2R regenerator for dual-wavelength RZ PAM-4 signals is established by simulation and the noise reduction ratios are up to 9.05 dB and 9.17 dB, respectively.

All-Optical 3R Regeneration Based on an Acousto Optical Filter with Q-Factor Improvement

All-Optical 3R Regeneration Based on an Acousto Optical Filter with Q-Factor Improvement

Optimized Hybrid Raman/EDFA Amplifier Placement for DWDM Mesh Networks

The minimization of the number of expensive 3R regenerators required at intermediate nodes is a key task when planning long-haul optical transport networks. Combining Raman amplification with Erbium-doped fiber amplifiers (EDFAs) is one of the strategies that can be exploited to achieve this objective, especially in the presence of long fiber spans. Given that hybrid Raman/EDFA amplifiers are more expensive than EDFAs, their deployment should also be minimized. However, determining the number and location of these amplifiers in a mesh optical network is a complex problem because of the overlap of lightpaths with different source and destination nodes at each link. A method to optimize the placement of hybrid Raman/EDFA amplifiers in mesh optical networks is described in this paper. The proposed method analyzes the network as a whole and determines where to introduce Raman amplification such that the 3R regenerator count is minimized while also keeping the number of hybrid Raman/EDFA amplifiers at a minimum. It is shown that, in a reference mesh optical network, the proposed method clearly outperforms the simpler placement approach based solely on fiber span attenuation.

Simultaneous wavelength exchange and 2R regeneration for two optical time division multiplexing signals by a single highly nonlinear fiber

The simultaneous wavelength exchange and 2R regeneration between two degraded optical time division multiplexing (OTDM) signals is experimentally demonstrated. By exploiting the self-phase modulation effect and offset filtering in a single highly nonlinear fiber (HNLF), it achieves 2R optical regeneration. Meanwhile, it realizes wavelength exchange using a bidirectional configuration. Optical wavelength exchange and 2R of 20- and 50-Gbit/s OOK signals at 1557.3 and 1552.3 nm is implemented with a power penalty of ∼0.5 dB at a bit-error rate of 10−9. The results show that the crosstalk is negligible for both channels in opposite directions. This bidirectional configuration exhibits excellent performance for simultaneous wavelength exchange and 2R regeneration between two degraded OTDM signals with different wavelengths.

Characteristics of all-optical 3R regenerators using cascaded second-order nonlinear effect in quasi-phase matched lithium niobate devices

We numerically show that quasi-phase matched (QPM) lithium niobate (LN) devices employing the cascaded second-order nonlinear effect of second harmonic generation (SHG) and difference frequency mixing (DFM) have all-optical decision gate characteristics. The decision gate function is realized by a parabolic transmittance for a low-power region and a limiting characteristic for a high-power region. The limiter function is attributed to the large group-velocity mismatch between the fundamental and second harmonic pulses. This operation principle differs from those of other all-optical 2R (reamplification and reshaping) or 3R (2R and retiming) regenerators that have been proposed in the past. Furthermore, we show that an initial time offset between the signal and clock pulses can improve the output signal power or the switching efficiency of the device. Based on the numerical results, we propose a method for designing all-optical 3R regenerators using the cascade of SHG and DFM in the QPM-LN devices. Following the design method, all-optical 3R operation at the bit rate of 200 Gbps can be achieved using a 1-cm-long waveguide device.

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