EDFA Research Articles

Compensation of the Distorted WDM Signals by Symmetric Dispersion Map with Nonuniform Zero-Crossing Place of Accumulated Dispersion in Midway-OPC System

The nonlinear Kerr effect and chromatic dispersion are the fundamental causes of optical signal degradation in single-mode fiber (SMF) and erbium-doped fiber-amplification (EDFA)-based wavelength division multiplexing (WDM) transmission. Dispersion management combined with a midway optical phase conjugator among the technologies for compensating for such optical signal distortion is known to not be limited by the modulation format and multiplexing technology. Optimization of the dispersion map can partially alleviate the capacity and maximum transmission distance limitations of the SMF and EDFA system. In this paper, we propose various types of symmetric dispersion maps in which the position of zero-crossing place of the cumulative dispersion is not constant, and analyze the effect of each dispersion map configuration on 40 Gb/s × 24-channel WDM signal distortion compensation. When designed with the residual dispersion per span (RDPS) around 400 ps/nm, it is confirmed that most of the proposed dispersion maps are more effective in compensating the distorted WDM signal than conventional dispersion map. In particular, we confirm that, among the proposed dispersion maps, the dispersion map in which the RDPS is designed uniformly for all fiber spans can increase the power margin of WDM channel and expand the range of the total residual dispersion in the dispersion-managed link.

Hybrid-Pumped Few-Mode Erbium-Doped Fiber Amplifier for Gain Equalization

Hybrid-Pumped Few-Mode Erbium-Doped Fiber Amplifier for Gain Equalization

A Distributed Acoustic Sensor with a 120-km Sensing Range Based on a Phase-Sensitive Optical Time-Domain Reflectometer and a Remotely Pumped Erbium-Doped Fiber Amplifier

A Distributed Acoustic Sensor with a 120-km Sensing Range Based on a Phase-Sensitive Optical Time-Domain Reflectometer and a Remotely Pumped Erbium-Doped Fiber Amplifier

Short-pulsed Q-switched fiber laser using graphene oxide quantum dots based as saturable absorber

In this work, we report the experimental study of a Q-switched optical fiber laser based on graphene oxide quantum dots (GOQDs) as saturable absorber (SA). GOQDs are fabricated by carbonization and exfoliation electrospun polyacrylonitrile (PAN) fibers. The results of Fourier Transform Infrared Spectroscopy (FTIR) showed bands caused by the CHs and CO groups associated with the GOQDs. The Raman spectrum showed the typical G and D bands of GOQDs. The size of the GOQDs, calculated by Transmission Electron Microscopy (TEM) was 6 nm; additionally, by high resolution TEM (HRTEM), an interplanar distance of 0.19 nm corresponding to the (002) direction of the graphene oxide was calculated. The SA was achieved using the photodeposition technique of the GOQDs onto the core of a single-mode optical fiber. The nonlinear characterization (NLC) of the GOQDs was carried out using the P-scan technique with a high-gain erbium-doped fiber amplifier (EDFA) at a wavelength of 1550 nm. The obtained results showed a saturable absorption behavior with a value of β=−1.178x10−6(m/W) and a non-linear susceptibility of Im(χ(3))≈−1.573x10−7(esu). The experimental results of the SA, based on GOQDs as a switching device in a fiber laser, showed a typical behavior of a Q-switched laser by generating a pulsed emission at a wavelength of 1599 nm, a frequency from 2 to 16 kHz, and a maximum average output power of 1.3 mW.

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.

High-power, low noise, high gain few-mode fiber amplifier

The few-mode erbium-doped fiber amplifier (FM-EDFA) is a necessary component for high-capacity long-haul mode-division multiplexing (MDM) fiber optic communication systems. In this paper, an all-fiber few-mode amplifier based on erbium-ytterbium co-doped double-clad fiber is designed and demonstrated. We have developed a fiber-optic pump beam combiner and a few-mode isolator. Combined with the two-stage cascade method, an all-fiber few-mode fiber amplifier with high-power, high-gain and low-noise is realized. Simultaneous amplification of 6 modes (LP01, LP11a, LP11b LP21a, LP21b and LP02) are achieved in the 1535–1565 nm range with average modal gain greater than 40 dB, maximum saturated output power up to 29.5 dBm, differential modal gain (DMG) of ∼3 dB and minimum noise figure (NF) of 4.69 dB.

Observation of the extracavity propagation of amplified bound-state soliton pulses emitted from a SWNT mode-locked fiber laser

We have experimentally investigated the extracavity propagation of amplified bound-state soliton pulses from a passively single-wall carbon nanotube mode-locked fiber laser. Under proper configuration of pump power and state of polarization, bound-state pulses exhibit a modulated optical spectrum. Except for the two main center wavelengths of 1557.3 and 1560.5 nm, additional five sidelobes centered at 1548.9, 1552.8, 1565.5, 1569.0 and 1573.1 nm are observed. Besides, the propagation after the extracavity erbium-doped fiber amplification is also investigated. It is demonstrated the significant change of the pulse separation is experimentally obtained when adjusting the extracavity PC before the autocorrelator, which is attributed to the coherent nonlinear soliton-soliton interaction. In addition, when different lengths of single-mode fiber after extracavity amplifier is removed or added, the significant change of the pulse separation is also observed, which matches well with the simulated evolution of pulse separation with respect to the SMF length. The pulse separation change of amplified bound soliton pulses is experimentally and theoretically investigated. These results provide further physical understanding of the generation and extracavity propagation of bound-state soliton pulses.

Enhancing signal quality in dense wavelength division multiplexed systems by eliminating crosstalk with cascaded optical bandpass filters

Non-orthogonal wavelength division multiplexing (WDM) channels are crucial in achieving significantly higher capacity and spectral efficiency than conventional schemes. Additionally, conventional schemes face challenges in electrical processing of wide-bandwidth signals. To suppress crosstalk in non-orthogonal WDM channels, the use of cascaded bandpass filters with suitable transmissivity and bandwidth is investigated for effective channel separation of large-capacity and multiplexed optical signals. This study employs the bandwidth ratio as a parameter, which is defined as the ratio of the channel spacing to the signal bandwidth, to quantify the extent of signal overlapping, and uses optical bandpass filters to filter non-orthogonal signals with a bandwidth ratio ranging from 1.0 to 0.75. The non-overlapping portion is set as the transmission bandwidth of the filter, and the crosstalk is maximally reduced with two-stage filters using Nyquist, super Gaussian, and Butterworth shaped filters. According to the analysis, the combination of Gaussian N = 1 and Gaussian N = 5 exhibits the lowest error vector magnitude (EVM) performance within a bandwidth ratio of 0.8 to 1.0. Simulations showed that a two-stage OBPF with a combination of Gaussian N = 1 and Gaussian N = 5 provides the best EVM performance at a bandwidth ratio between 0.85 to 1.0 within the combination of filter shapes and their orders we used. Additionally, the study includes an analytical investigation of the impact of amplified-spontaneous-emission noise associated with the Erbium-doped fiber amplifier (EDFA) and frequency resolution tolerance of the LCOS filter. The results demonstrate that cascaded EDFAs can be achieved down to OSNR of 10 dB at a minimum resolution of 4 GHz. Finally, the optimal filter shape is analyzed for different bandwidth ratios. The investigation shows that the optimal filter shape is independent of the function used and remains consistent across all bandwidth ratios. The tolerance of the filter is primarily affected by the −0.5 dB transmittance bandwidth between subchannels, which varies depending on the bandwidth ratio. Furthermore, a high tolerance is observed in the −20 dB transmittance bandwidth.

Effect of Rayleigh backscattering on the multiwavelength random fiber laser bandwidth

We investigated the effect of Rayleigh backscattering on the bandwidth of a multiwavelength random fiber laser (MWRFL). This MWRFL is based on an erbium-doped fiber amplifier (EDFA) as the gain medium and a Lyot filter as the wavelength-selective device. A high number and stable lasing line is generated with the assistance of a nonlinear polarization rotation effect induced by highly nonlinear fiber (HNLF) and optimized by a polarization controller. Longer single-mode fiber (SMF) produces wider multiwavelength bandwidth as compared to shorter SMF lengths, as 10 km, 3 km, and 0.1 km obtained 6.24 nm, 5.76 nm, and 2.75 nm wavelength bandwidth, respectively. When the SMF is removed from the setup, no Rayleigh backscattering is provided in the cavity, which led to a narrower multiwavelength bandwidth of 2.69 nm. Subsequently, the alteration of EDFA power, half-wave plate (HWP) angle, and quarter-wave plate (QWP) angles affected the degradation of multiwavelength performance. The best output spectrum is achieved at an EDFA power of 18 dBm, a HWP angle of 60°, and a QWP angle of 105°. The laser stability over a period of 120 min was excellent with a peak power deviation of 1.33 dB.

Improved QoT estimations through refined signal power measurements and data-driven parameter optimizations in a disaggregated and partially loaded live production network

Accurate quality of transmission (QoT) estimations are essential enablers for future low-margin dynamic optical network operations. However, physical parameter measurement uncertainties and other intractable signal propagation effects degrade the accuracy of QoT estimation, especially in live production networks. The recent trend of network disaggregation further exacerbates the issue, and a vendor-agnostic accurate QoT estimator is much needed. In this paper, we study Gaussian-noise-model-based QoT estimation in a large-scale disaggregated and partially loaded live production network with monitored physical layer data spanning across 8 months. We first propose refining the signal power measurements by combining the inline amplifier and optical channel monitor (OCM) power measurements, followed by estimating the gain and noise power profiles of each inline amplifier, which in turn improves QoT estimation accuracy. We further introduce an optical multiplex section and frequency bias to the analytical model to incorporate intractable location-specific and spectral effects in the network and proposed data-driven parameter optimizations to learn the biases as well as erbium-doped fiber amplifier noise figures. The (mean, standard deviation) of the QoT estimation errors were reduced from (−0.1043, 0.6037) dB using average amplifier power and (−0.7875, 0.6337) dB using OCM power to (−0.0964, 0.4649) dB after input parameter refinements and were further reduced to (0.0046, 0.2377) dB with data-driven parameter optimization. The proposed methodologies are simple procedures that network operators can adopt to optimize analytical-model-based QoT estimators and/or serve as feature engineering procedures preceding machine-learning-based QoT in realistic disaggregated live production networks.

Numerical Investigation of Polarization-Dependent Ultrashort Pulse Amplification in Erbium-Doped Fluoride Fibers

We have theoretically investigated the polarization-dependent ultrashort pulse amplification in erbium-doped fluoride fibers. The numerical model is based on the coupled generalized nonlinear Schrödinger equations and the rate equations. It is found that the Raman effect can be weakened by converting the seed polarization from linear to circular. Compared with the linearly polarized seed pulses, amplification of the circularly polarized seed pulses can generate Raman solitons with a larger pulse energy of the same central wavelength, although more pump power is needed. Furthermore, the amplification dynamics when no pulse splitting occurs have also been investigated. We demonstrate that amplification of the circularly polarized seed pulses allows the main pulse to accumulate more energy while maintaining a single-pulse profile. It is predicted that sub-two-cycle laser pulses at 2.8 μm with megawatt peak power and hundreds of nanojoules pulse energy can be directly generated from the erbium-doped fluoride fiber amplifiers. The investigations conducted in this paper can provide guidelines for the design of Raman-soliton-based tunable fiber laser systems and high-power few-cycle fiber laser systems.

Stable Triple-Wavelength Random Fiber Laser Based on Fiber Bragg Gratings

We demonstrate a generation of three lasing wavelengths with the assistance of Rayleigh backscattering as the stabilizer of peak power variations. The proposed laser consists of a combination of the semiconductor optical amplifier (SOA) and erbium-doped fiber amplifier (EDFA) as the amplifying media. Three fiber Bragg gratings are employed as the selective wavelength selectors at 1544, 1547 and 1550 nm. At 110 mA SOA current and 18 dBm EDFA output power, a flattened output spectrum with 0.9 dB peak power variation is attained. In terms of stability, the maximum peak power fluctuation for the individual laser is 0.24 dB within 120 minutes observation period. Without the Rayleigh backscattering effect, the peak power flatness is severely degraded. This shows that the weakly distributed photons can be utilized as peak power stabilizers in fiber laser systems.

Flexible optical fiber channel modeling based on a neural network module.

Optical fiber channel modeling, which is essential in optical transmission system simulations and designs, is usually based on the split-step Fourier method (SSFM), making the simulation quite time-consuming owing to the iteration steps. Here, we train a neural network module termed NNSpan to learn the transfer function of a single fiber (G652 or G655) span with a length of 80 km and successfully emulate long-haul optical transmission systems by cascading multiple NNSpans, which gives remarkable prediction accuracy, even over a transmission distance of 1000 km. Even when trained without erbium-doped fiber amplifier (EDFA) noise, NNSpan performs quite well when emulating the systems affected by EDFA noise. An optical bandpass filter can optionally be added after EDFA, making the simulation more flexible. Comparison with the SSFM shows that NNSpan has a distinct computational advantage, with the computation time reduced by a factor of 12. This method based on NNSpan could be a supplementary option for optical transmission system simulations, thus contributing to system designs as well.

Open EDFA gain spectrum dataset and its applications in data-driven EDFA gain modeling

Optical networks satisfy high bandwidth and low latency requirements for telecommunication networks and data center interconnection. To improve network resource utilization, machine learning (ML) is used to accurately model optical amplifiers such as erbium-doped fiber amplifiers (EDFAs), which impact end-to-end system performance such as quality of transmission. However, a comprehensive measurement dataset is required for ML to accurately predict an EDFA’s wavelength-dependent gain. We present an open dataset consisting of 202,752 gain spectrum measurements collected from 16 commercial-grade reconfigurable optical add–drop multiplexer (ROADM) booster and pre-amplifier EDFAs under varying gain settings and diverse channel-loading configurations over 2,785 hours in total, with a total dataset size of 3.1 GB. With this EDFA dataset, we implemented component-level deep-neural-network-based EDFA models and use transfer learning (TL) to transfer the EDFA model among 16 ROADM EDFAs, which achieve less than 0.18/0.24 dB mean absolute error for booster/pre-amplifier gain prediction using only 0.5% of the full target training set. We also showed that TL reduces the EDFA data collection requirements on a new gain setting or a different type of EDFA on the same ROADM.

The influence of Kerr nonlinear effect on the signal and pump intensities in parabolic and triangular index EDFAs

Erbium-doped fiber amplifiers (EDFAs) is an integral part of all-optical communication system. Intensities of pump and signal within EDFAs is one of the significant parameters in its application perspective. Nonlinear effect on pump and signal may affect the performance aspect of EDFAs. In this work, we study intensity profile of pump and signal at different wavelengths of interest in EDFAs for the first higher order (LP11) excited mode considering the nonlinear impact. In this comparative analysis, EDFAs made up of some parabolic-index and triangular-index fibers of several V-numbers have been chosen. Our study involves the power series expression of the LP11 field prescribed by Chebyshev’s technique. A short computation is needed for achieving the objective by this method. Outcomes of this exercise are in superb conformity with those derived through the cumbersome finite element method (FEM) proving reliability of the Chebyshev’s method. The analysis is important in the context of use of dual mode optical fiber in EDFAs. The impact of Kerr nonlinearity on the performance of EDFAs involving dual mode optical fiber is also investigated. This analytical exercise through a handy and reliable mathematical instrument may be a dependable option for photonic EDFAs designers in practical realization of nonlinear EDFAs.

Channel power equalization based on joint optimization of EDFA and ROADM configuration in open optical network.

Deterioration of the signal-to-noise ratio (SNR) is an important challenge in ultra-long multi optical line system (OLS) optical transmission systems. The non-uniform gain and cascading of the Erbium-doped fiber amplifier (EDFA) lead to SNR deterioration in transmission systems. In this paper, we propose two channel power equalization methods based on joint optimization of EDFA and Reconfigurable optical add-drop multiplexer (ROADM) configurations: 1) reinforcement learning (RL)-based channel power equalization (RL-PE) and 2) covariance matrix adaptive evolution strategy (CMA-ES) channel power equalization (CMA-PE). The simulation results indicate that the power equalization effect was improved by 1.9 dB through the CMA-PE method, while the RL-PE method led to a 1.5 dB improvement in an ultra-long 80-channel 7-OLS transmission system.

A novel active continuous-wave FLRD strain sensor based on frequency-shifted interferometry

ABSTRACT An active continuous-wave fiber loop ringdown strain sensor based on frequency-shifted interferometry is presented and experimentally investigated. By measuring the decay rate of the continuous light in the ringdown loop (RDL), the sensor achieves strain measurement without optical pulsation and rapid detection. A bidirectional erbium-doped fiber amplifier is embedded in the loop to form an active fiber RDL, to compensate the inherent loop loss. The strain sensor head was built by splicing a segment of normal graded index multimode fiber (MMF) into the RDL composed of single-mode fiber. In this configuration, the core-cladding mode conservation and insertion loss of the MMF changes with the strain applied, making it possible to detect different levels of strains. The proposed device was tested with the strains in the range from 0 to 2.25 mϵ, which exhibits a linear response with a sensitivity of 0.29 km-1·mϵ-1, with a measurement resolution of 22 mϵ.

Spectral power profile optimization of a field-deployed wavelength-division multiplexing network enabled by remote EDFA modeling

We propose a technique for modeling erbium-doped fiber amplifiers (EDFAs) in optical fiber networks, where the amplifier unit is located at a distant node outside the laboratory. We collect data on an optical point-to-point link with the amplifier as the only amplification stage. Different amplifier operating points are modeled using probe signals and by adjusting the settings of the amplifier through a control network. The data are used to train a machine learning algorithm integrated within a physical EDFA model. The obtained mathematical model for the amplifier is used to model all amplifiers of a network and links with multiple amplification stages. To confirm the modeling accuracy, we thereafter predict and optimize launch power profiles of two selected links in the network of 439.4 km and 592.4 km lengths. Maximum/average channel optical signal-to-noise ratio prediction errors of 1.41/0.68 dB and 1.62/0.83 dB are achieved for the two multi-span systems, respectively, using the EDFA model trained on the single span system with margin-optimized launch power profiles. Up to 2.2 dB of margin improvements are obtained with respect to unoptimized transmission.

Capacity Expansion in Submarine Cable Systems With Bidirectional Transmission Using 4-Core-or-More MCF and MC-EDFA

Bidirectional transmission in a multicore fiber (MCF) reduces core-to-core crosstalk, changing optimal MCF design and multicore submarine cable systems, compared with conventional unidirectional transmission systems. We first demonstrate analytically the increase in capacity with bidirectional transmission in submarine systems. From the perspective of the capacity of one MCF, we show that bidirectional transmission enables an optimum design based on a 6-core MCF with a standard cladding diameter, taking advantage of the reduction of XT. For multicore submarine cable systems, we demonstrate that 6-core MCF systems with bidirectional transmission offer the highest cable capacity for regional Asian systems in the range of 3,000 km. We further discuss a multicore erbium doped fiber amplifier (MC-EDFA) system even for bidirectional transmission to improve the energy efficiency in submarine systems, and we show that 6-core MCF systems offer the highest capacity up to 6,000 km because of MC-EDFA. We also show a 10 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$\%$</tex-math></inline-formula> larger capacity for a 3,000 km 6-core MCF system, and 43 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$\%$</tex-math></inline-formula> larger capacity for a 9,000 km 4-core MCF system in bidirectional transmission with MC-EDFA, compared with the conventional repeater amplifier in FIFO devices. In addition, we investigated the potential increase in the cable capacity with the future cable system assumption, especially concerning cable supply voltage.

Ultra-Long-Span U-Band Transmission Enabled by Incoherently Pumped Raman Amplification

We demonstrate U-band Raman amplification in non-zero dispersion shifted fibre, exploiting the amplified spontaneous emission of an erbium-doped fibre amplifier as a broad-bandwidth, incoherent pump for low-noise amplification. By doing so, we achieve a high overall gain of ∼22 dB over a 3-dB bandwidth of ∼2.6 THz and obtain noise figures better than 4.3 dB and 5 dB in a 40km-long, discrete amplifier configuration, in forward pumped and backward pumped scenarios, respectively. The performance of the U-band Raman amplification is also studied through transmission of a coherent signal over a 285-km point-to-point link. This work represents, at the time of writing, the longest-reach single-span U-band transmission demonstrated.