Multi-pump Raman Amplifier Research Articles

Four wave mixing, average amplified spontaneous emission, and channel spacing effects on the optical transceiver systems based on multi pumped Raman amplifiers

Abstract This study has clarified the four-wave mixing, average amplified spontaneous emission, and channel spacing effects on the optical transceiver systems based on multipumped Raman amplifiers. The employed spectral width is applied in the fiber core from 1450 nm to 1650 nm through the subgroups in the fiber link. The optical loss and fiber dispersion effects are demonstrated with the spectral wavelength band with different pumping levels. The optical loss is clarified in relation to different laser pumping levels and different number of links per fiber core channel at 1550 nm. As well as the dispersion factor is demonstrated in relation to different laser pumping levels and different number of links per fiber core channel at 1300 nm. Extended fiber length, amplifier gain, and repeater spacing are clarified with different laser pumping levels and different number of links variations per fiber core channel at 1550 nm. The data rate transmission is studied against different laser pumping levels and different number of links variations per fiber core channel at both 1550 nm and 1300 nm. The optimum fiber coupled power is demonstrated against different laser pumping levels and different number of links variations per fiber core channel at 1550 nm. The fiber coupling efficiency is studied and demonstrated against different laser pumping levels and different number of links variations per fiber core channel at 1550 nm.

Numerical achievement of high and flat gain using Er-Yb co-doped fiber/Raman hybrid optical amplifier

A novel hybrid optical amplifier is proposed for 100 × 10 Gb/s dense wavelength division multiplexed (DWDM) system. The amplifier consists of a combination of Er-Yb co-doped fiber amplifier (EYDFA) with backward-propagating multi-pump Raman amplifier. A flat gain of >26 dB is achieved, over a wavelength range of 1545–1565 nm. The scheme works at 1 mW optimum input power per channel. Gain ripple of 1.37 dB and noise figure (NF) of <4.5 dB is observed. Anyhow, for higher input powers up to 10 mW, an increase in gain ripple up to 7.59 dB and NF up to 12.04 dB is observed. The effects of varying various parameters, like EYDFA pump wavelength, EYDFA length, Er/Yb concentrations and Raman length are also investigated. The obtained high and flat gain, along with the low NF, lesser bit error rate and high Q-factor, justifies the usefulness of proposed amplifier for applications in long-haul DWDM systems.

Performance Analysis of Flat Gain Wideband Raman Amplifier for S+C and C+L Band DWDM System

Raman amplifier is an open area of research in telecommunication field. This paper discusses the performance of 64 channels of 10 Gbps WDM systems with backward multipump Raman amplifier. The main goal of this paper is the optimization of Raman amplifier to minimize its gain variation without using any gain flattening techniques. To increase the transmission capacity of DWDM system, Raman amplifier with backward multipump configuration is implemented. The optimized parameters such as pump power and frequencies are used to deliver both ground and excited state absorption for amplification in S+C and C+L band region. The pump power and frequencies are optimized through multitarget and multiparameter optimization tool available in OptiSystem software. Gain ripple was achieved &lt;0.5 dB for this simulation setup. The maximum flat gain achieved is 8.6 dB and noise figure of &lt;8 dB was achieved for this wide bandwidth without using gain flattening techniques. This amplifier design will be helpful for CATV applications and telecommunication networks.

Optimization of Raman-assisted wavelength-division-multiplexing system with arbitrary input signal power spectrum

We analyze the method to uniform the output signal power spectrum for a long-haul wavelength-division-multiplexing (WDM) system using backward multipump Raman amplifiers with arbitrary initial input signal power spectrum. A genetic algorithm is used to optimize the output signal power. The theoretical results show that using variable pump wavelengths is better than using fixed pump wavelengths to decrease the spectral maximum power difference. An experiment is conducted based on the theoretical analysis. The results agree well with the numerical calculations.

Performance Analysis of Backward Multipumped Raman Amplifier in DWDM System

In this paper to increase the capacity of Dense wavelength division multiplexing system (DWDM) system, a C band ranging from 1530-1625.4nm is designed. The performance of the system is analysed in terms of input power, output power, Gain, Noise figure and Quality factor, the coverage distance found is 50km SMF and 20km Raman amplifier. The system is designed with 10Gbps data rate non return to zero modulation formats. It offers high gain is about 53.3 dB and less noise figure is 9dB.The Quality factor for equal spacing at 10km SMF is 16.6 and BER is 1.4e-62.

A correction method for the analytical model in Raman amplifiers systems based on energy conservation assumption

This paper presents a modification for the already consolidated analytical model that calculates the gain and ripple in multi-pump Raman amplifiers by considering energy conservation. The original analytical model precisely computes the pump-pump interaction to the C- and L-band for a WDM input signal. However, when this method is used to amplify a large bandwidth, as the entire C and a part of the L band, the increase in the number of pump lasers impacts the obtained results. The error, if compared with results obtained by a numerical method, becomes significant. An analysis in terms of energy is proposed to minimize the discrepancy between analytical and numerical results. An improvement is observed to the gain results.

Performance analysis and comparison of multipump Raman and hybrid erbium-doped fiber amplifier + Raman amplifiers using nondominated sorting genetic algorithm optimization

This paper presents a performance analysis and comparison of optimized multipump Raman and hybrid erbium-doped fiber amplifier (EDFA) + Raman amplifiers, operating simultaneously at conventional (C) and long (L) bands, using multiobjective optimization based on evolutionary elitist nondominated sorting genetic algorithm. The amplifiers performance was measured in terms of on–off gain, ripple, optical signal-to-noise ratio (OSNR) and noise figure (NF), after propagating over 90 and 180 km of single-mode fiber (SMF). Numerical simulation results of the first analysis show that only three pumps are necessary to generate optimal gains in both amplifiers. Comparing the results of the second performance analysis, we conclude that, after 90 km SMF, the two amplifiers has the same on–off gain, if the total pump power (1807.1 mW) of the Raman amplifier is approximately double (100+994.7 mW) of the hybrid amplifier, when the EDFA is operating at 1480 nm with 5 m of doped fiber. Furthermore, the Raman amplifier needs a single laser with at most 741.1 mW, against 343.9 mW of the distributed Raman amplifier (DRA) pump in the hybrid system. Finally, the results of the last analysis, which considers only the EDFA + Raman amplifier, shows that with on–off gain of 26.14 dB, ripple close to 1.54 dB over a bandwidth of 66 nm and using three pumps lasers in the DRA the achieved OSNR was 39.6 dB with an NF lower than 3.3 dB, after 90 km of SMF.

Fast optimization of multipump Raman amplifiers based on a simplified wavelength and power budget heuristic

We report a simple budget heuristic for a fast optimization of multipump Raman amplifiers based on the reallocation of the pump wavelengths and the optical powers. A set of different optical fibers are analyzed as the Raman gain medium, and a four-pump amplifier setup is optimized for each of them in order to achieve ripples close to 1 dB and gains up to 20 dB in the C band. Later, a comparison between our proposed heuristic and a multiobjective optimization based on a nondominated sorting genetic algorithm is made, highlighting the fact that our new approach can give similar solutions after at least an order of magnitude fewer iterations. The results shown in this paper can potentially pave the way for real-time optimization of multipump Raman amplifier

A TWDM-PON with Advanced Modulation Techniques and a Multi-Pump Raman Amplifier for Cost-Effective Migration to Future UDWDM-PONs

Dense wavelength-division multiplexing passive optical networks and ultra-dense wavelength-division multiplexing passive optical networks are strong candidates to future next-generation passive optical network stage 3 access networks in order to satisfy increasing bandwidth demand, but their deployment is still a great challenge for telecommunication operators. Time and wavelength division multiplexed PON (TWDM-PON) has already been chosen by ITU-T as one of the best architectures in brownfield contexts to allow the reuse of the optical distribution network. Our proposal exploits the advantages of TWDM in order to reach a balance between coexistence with legacy systems and gradual and cost-effective migration towards pure wavelength division multiplexed PON (WDM-PON). In order to fulfill this aim, with reference to downstream traffic enhancement, two main novelties are presented: 1) the use of a multi-pump Raman amplifier (MRA) to satisfy the future necessity of large gain bandwidth; 2) the introduction of advanced modulation techniques to increase spectral efficiency and the future number of user channels (a less than 7 GHz-wide channel bandwidth providing 10 Gb/s bitrate has been demonstrated). A coherent system has been also proposed and its main impairments have been evaluated. The MRA has been accurately optimized to minimize power consumption without compromising performances. In the upstream direction, a semiconductor optical amplifier has been considered. The performances of the proposed TWDM-PON have been predicted through numerical simulations based on a system-level commercial CAD software.

Design methodology for multi-pumped discrete Raman amplifiers: case-study employing photonic crystal fibers

This paper proposes a new design methodology for discrete multi-pumped Raman amplifier. In a multi-objective optimization scenario, in a first step the whole solution-space is inspected by a CW analytical formulation. Then, the most promising solutions are fully investigated by a rigorous numerical treatment and the Raman amplification performance is thus determined by the combination of analytical and numerical approaches. As an application of our methodology we designed an photonic crystal fiber Raman amplifier configuration which provides low ripple, high gain, clear eye opening and a low power penalty. The amplifier configuration also enables to fully compensate the dispersion introduced by a 70-km singlemode fiber in a 10 Gbit/s system. We have successfully obtained a configuration with 8.5 dB average gain over the C-band and 0.71 dB ripple with almost zero eye-penalty using only two pump lasers with relatively low pump power.

Design of a flat-gain multipumped distributed fiber Raman amplifier by particle swarm optimization

The pumping scheme of multipumped distributed fiber Raman amplifiers is optimized by a powerful method called particle swarm optimization. By use of particle swarm optimization, we optimize both pump powers and frequencies of multipumped Raman amplifiers with a high number of pumps. Particle swarm optimization is a fast and effective method, and it surpasses other optimization methods, such as the genetic algorithm, for optimizing fiber amplifiers. It is shown that the computational efficiency of particle swarm optimization is significantly better than that of the genetic algorithm, reducing the time of computation to one third, and its implementation is more straightforward. A gain bandwidth of 92.1 nm and a gain variation of 0.49 dB in the range of 1524.5-1616.6 nm are obtained by this method, using ten backward pumps in a 60-km-long amplifier. The gain variation reduction is due to the inclusion of pump frequencies in the optimization process.

Optimization of Raman gain spectrum using Lagrangian multiplier method

Based on Lagrangian multiplier method (LMM), the gain spectrum of distributed multi-pump Raman amplifier (DMRA) is optimized. Beside of governing rate equations in Raman amplifiers, we consider two applicable constrains on cost function for optimizing the gain spectrum. Because of more accurate and controllable designing of DMRAs, a maximum power for each input pump wave is considered as well as average gain value as two constrains. LMM reduces the optimization problem with constrains to solve a two-point boundary value problem for each solution. This method is applied to minimizing gain ripple of full bandwidth (60 nm) a 100 Km Raman amplifier for different number of pumps.

NUMERICAL COMPARISON OF MULTI-PUMP RAMAN AMPLIFIERS BASED ON PHOTONIC CRYSTAL FIBER AND STANDARD SINGLE MODE FIBER

This paper presents a numerical analysis and comparison on the performance of multi-pump gain-flat Raman amplifiers based on triangular photonic crystal fiber and conventional fiber. It is demonstrated that the extra 5.93 dB Raman net gain can be achieved in the L-band when PCF acts as Raman gain medium. The noise performance of the two amplifiers are also calculated and compared. Comparison with the data of published literature was also carried out to verify our analysis. The results showed that PCF is the appropriate candidate for high gain Raman amplifiers.

Fast and Effective Analysis Methods for Fiber Raman Amplifiers

A series of new single-step methods and their corresponding algorithms with automatic step size adjustment for model equations of fiber Raman amplifiers are proposed and compared in this paper. On the basis of the Newton–Raphson method, multiple shooting algorithms for the two-point boundary value problems involved in solving Raman amplifier propagation equations are constructed. A verified example shows that, compared with the traditional Runge–Kutta methods, the proposed methods can increase the accuracy by more than two orders of magnitude under the same conditions. The simulations for Raman amplifier propagation equations demonstrate that our methods can increase the computing speed by more than 5 times, extend the step size significantly, and improve the stability in comparison with the Dormand–Prince method. The numerical results show that the combination of the multiple shooting algorithms and the proposed methods has the capacity to rapidly and effectively solve the model equations of multipump Raman amplifiers under various conditions such as co-, counter- and bi-directionally pumped schemes, as well as dual-order pumped schemes.

Optimization for various schemes of distributed fibre Raman amplifiers

A fast and stable numerical method for solving the model equations of distributed fibre Raman amplifiers is proposed. This method can increase the computing speed by more than five times compared to the classical Dormand?Prince method. In this paper, on the basis of the proposed method and genetic algorithm, the signal gain spectrum and corresponding optical signal-to-noise ratio (OSNR) for counter-?and bi-directional multi-pump Raman amplifiers are optimized and compared. The optimized results show that (1)?bi-directionally pumping configurations with proper forward pump diodes can effectively decrease the gain ripple and the OSNR ripple and equalize the OSNR tilt in comparison with pure backward pumping configurations; (2)?the gain spectrum and noise performance can be availably improved by means of increasing the pump number. The simulations demonstrate that, when optimizing bi-directional multi-pump configurations, (1)?there are multiple global or near-global maxima for the signal gain spectrum; (2)?different bi-directional pump schemes have different gain ripple and noise performance.

Optimization and Comparison for Different Raman AmplifierConfigurations

Gain spectra and corresponding optical signal-to-noise ratio (OSNR) forbi-directional multi-pump Raman amplifiers are optimized and compared.Numerical results exhibit that, for optimizing bi-directionalmulti-pump configurations, there are multiple global maxima forsignal gain spectra, and different bi-directional pump cases havedifferent gain ripple and noise performance. Bi-directionally pumpingschemes with suitable pump spectra can obviously decrease the gainripple and equalize the OSNR tilt in comparison with pure backwardpumping schemes.

Efficient algorithm and optimization for broadband Raman amplifiers

A hybrid genetic algorithm (HGA) assisted by stochastic perturbation and the adaptive technique is proposed. Compared with our previous reports, the proposed HGA can exploit better solutions and greatly shorten the amount of run time. An example shows that the design of multipump Raman amplifiers involves the multimodal function optimization problem with multiple variables. With the new HGA, relationships of the optimal signal bandwidth with the span length and the ON-OFF Raman gain are obtained. A movie demonstrates the detailed interaction in pump-to-signal and signal-to-signal procedures. The corresponding optical signal-to-noise ratio of optimal results is obtained.

Optimal Design of Fiber Raman Amplifier Based on Hybrid Genetic Algorithm

A hybrid genetic algorithm (GA) based on the clustering fitness sharing and the elite replacement is proposed. Our proposed GA can effectively solve the multimodal optimization in the distributed multipump Raman amplifier (DMRA). The optimal results show that, under the conditions of the ON-OFF gain of > 10 dB, the relative gain flatness of < 0.1 and the fiber length of 80 km, the bandwidth of > 100 nm can be designed from DMRA with five pumps after the optimization of our GA. There are four schemes to realize the required setup parameters in our simulation.

Optimizing gain profile and noise performance for distributed fiber Raman amplifiers

Raman gain spectrum, noise performance and corresponding nonlinear impact for co-, counter- and bi-directional multi-pump Raman amplifiers are optimized and compared in this paper. A fast numerical method, which can shorten the computing time more than 4 times by comparison to the classical fast method, for solving Raman amplifier propagation equation is proposed. Based on the geometry compensation technique, multiple shooting algorithms and hybrid genetic algorithm, an effective and fast algorithm for optimizing the design of various structures of multi-pump Raman amplifiers is proposed. The optimized results demonstrate that (1) the optimal efficiency and speed are increased significantly by using the proposed algorithm and method (2) although pure forward pumping scheme can improve more than 3-dB optical signal-to-noise ratio (OSNR) in comparison with pure backward pumping scheme, the latter costs less total power of input pumps and has great less nonlinear impact; (3) bi-directionally pumping configurations with proper forward pump source can obviously decrease the ripples of both gain and OSNR and equalize the OSNR tilt by comparing to pure backward pumping configuration; (4) there are multiple global or near-global maximums for signal gain spectrum in each pumping scheme and different global maximum in any pumping scheme has different OSNR performance; (5) different bi-directional pump schemes have different gain ripple and noise performance.

Optimal Bandwidth for Distributed Multi-Pump Raman Amplifier Basedon Hybrid Genetic Algorithm

Based on a hybrid genetic algorithm, the bandwidth for distributedmulti-pump Raman amplifier (DMRA) is optimized. Optimal results showthat signal bandwidth Δλ can be evidently broadened by means ofincreasing the number of pumps, Δλ decreases with the increase ofRaman gain and with the improvement of flatness property, and the hybriderbium-doped fibre amplifier and DMRA can availably overcome theweakness of pure DMRA.