Effective Area Fiber Research Articles

Impact of Fiber Attenuation and Effective Area on Spectrum Efficiency of Elastic Optical Networks

The ultra-low-loss optical fibers becoming available now offer large effective areas with much better transmission performance than conventional standard single-mode fibers (SSMFs). However, how low the attenuation should be and how large the effective area has to be to benefit the transmission performance of a fiber-optic system have been open questions until now. In the context of an elastic optical network (EON), this paper evaluates for the first time the extent to which both fiber attenuation and effective area impact the network capacity. We first present an optical signal-to-noise ratio (OSNR) model to evaluate the performance of a lightpath considering various optical transmission impairments. We also propose different service-provisioning approaches based on this OSNR model. Simulation studies show that a spectrum-dependent provisioning scheme that considers different levels of cross-channel interference (XCI) requires minimum spectrum resources when provisioning incremental demands, and a margin-reservation scheme that considers different alternate routes shows the lowest bandwidth blocking probability (BBP) when provisioning dynamic lightpath demands. We also estimate optimal launch powers needed by lightpaths for different fiber attenuations and effective areas. Under different launch powers, it is found that lowering fiber attenuation and increasing fiber effective area demonstrate saturation in performance improvement, i.e., initially decreasing fiber attenuation and increasing effective area can significantly improve the network service provisioning performance, but the improvement is much less when the fiber attenuation and effective area are lower than 0.165 dB/km and greater than 110 μm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> , respectively. This implies that it is not necessary to fabricate a fiber with extremely low attenuation and large effective area for the best cost-to-performance ratio.

Guided acoustic Brillouin scattering measurements in optical communication fibers.

Guided acoustic Brillouin (GAWBS) noise is measured using a novel, homodyne measurement technique for four commonly used fibers in long-distance optical transmission systems. The measurements are made with single spans and then shown to be consistent with separate multi-span long-distance measurements. The inverse dependence of the GAWBS noise on the fiber effective area is confirmed by comparing different fibers with the effective area varying between 80 µm2 and 150 µm2. The line broadening effect of the coating is observed, and the correlation between the width of the GAWBS peaks to the acoustic mode profile is confirmed. An extensive model of the GAWBS noise in long-distance fibers is presented, including corrections to some commonly repeated mistakes in previous reports. It is established through the model and verified with the measurements that the depolarized scattering caused by TR2m modes contributes twice as much to the optical noise in the orthogonal polarization to the original source, as it does to the noise in parallel polarization. Using this relationship, the polarized and depolarized contributions to the measured GAWBS noise is separated for the first time. As a result, a direct comparison between the theory and the measured GAWBS noise spectrum is shown for the first time with excellent agreement. It is confirmed that the total GAWBS noise can be calculated from fiber parameters under certain assumptions. It is predicted that the level of depolarized GAWBS noise created by the fiber may depend on the polarization diffusion length, and consequently, possible ways to reduce GAWBS noise are proposed. Using the developed theory, dependence of GAWBS noise on the location of the core is calculated to show that multi-core fibers would have a similar level of GAWBS noise no matter where their cores are positioned.

Scaling properties of guided acoustic-wave Brillouin scattering in single-mode fibers.

We investigate guided acoustic-wave Brillouin scattering (GAWBS) in single-mode optical fibers. By treating the discrete GAWBS spectrum as a continuum, we propose a closed-form formula to evaluate the GAWBS variance due to radial modes, showing its dependence on the inverse of the fiber effective area. The formula is checked against an experimental validation at variable signal power. The almost flat experimental results with power suggest that GAWBS dominates stimulated electrostriction. We also compare GAWBS with the Kerr effect showing their common grounds and their main differences. The phase noise characteristics of the nonlinear interference induced by GAWBS is investigated, showing that in ultra-long links GAWBS can be safely taken as a circular white noise. The theoretical results can be used for quick estimations of the GAWBS penalty with any fiber effective area. In particular, we estimated a GAWBS penalty on the signal-to-noise ratio (SNR) of 0.5 dB after 6000 km with fibers of effective area 150 μm2.

Complex-Valued Neural Network Design for Mitigation of Signal Distortions in Optical Links

Nonlinearity compensation is considered as a key enabler to increase channel transmission rates in the installed optical communication systems. Recently, data-driven approaches - motivated by modern machine learning techniques - have been proposed for optical communications in place of traditional model-based counterparts. In particular, the application of neural networks (NN) allows improving the performance of complex modern fiber-optic systems without relying on any a priori knowledge of their specific parameters. In this work, we introduce a novel design of complex-valued NN for optical systems and examine its performance in standard single mode fiber (SSMF) and large effective-area fiber (LEAF) links operating in relatively high nonlinear regime. First, we present a methodology to design a new type of NN based on the assumption that the channel model is more accurate in the nonlinear regime. Second, we implement a Bayesian optimizer to jointly adapt the size of the NN and its number of input taps depending on the different fiber properties and total length. Finally, the proposed NN is numerically and experimentally validated showing an improvement of 1.7 dB in the linear regime, 2.04 dB at the optimal optical power and 2.61 at the max available power on Q-factor when transmitting a WDM 30 × 200G DP-16QAM signal over a 612 km SSMF legacy link. The results highlight that the NN is able to mitigate not only part of the nonlinear impairments caused by optical fiber propagation but also imperfections resulting from using low-cost legacy transceiver components, such as digital-to-analog converter (DAC) and Mach-Zehnder modulator.

Phase-sensitive inverse four-wave mixing in optical fibres

ABSTRACT Inverse four-wave mixing (IFWM) is a nonlinear self-action effect also known as self-parametric amplification (SPA) which manifests itself as narrowing the optical spectrum of the pump wave propagating along the optical fibre. This paper aims to accurately model the IFWM process in various optical fibres including large effective-area fibre (LEAF) and highly nonlinear fibre (HNLF). Here, the coupled amplitude equations for the IFWM are derived based on the relative phase difference of interacting waves and impacts of the initial phase difference, pump and fibre parameters on the gain spectrum of the IFWM are examined. Results show that the maximum gain is obtained when the initial phase difference of the input waves set at and by increasing the initial phase to the gain is decreased to its minimum.

Impact of fiber parameters on EDFA and/or Raman amplified high-spectral-efficiency coherent WDM transmissions.

The impact of fiber properties is investigated for coherent systems employing polarization-division multiplexed high-level quadrature amplitude modulation, wavelength-division multiplexing, and erbium-doped fiber amplifier and/or distributed Raman amplification. This is done by comparing the performances of fiber links of various attenuation coefficients and effective areas via experimentally verified analytical methods. Results show that the excess noise, which originates at amplifiers compensating for the losses of filters and switches located between fiber spans, can weaken or even diminish the performance enhancement brought about by lowering the fiber attenuation coefficient, especially if distributed Raman amplification is employed. This leads to the difference in the link performance assessment between our analytical results and some previously published figures of merit (FOM). On the other hand, increasing the fiber effective area results in the same amount of performance improvement regardless of the amplification scheme or the excess noise, which agrees with the FOMs. Since the larger effective area causes poorer pumping efficiency for systems employing distributed Raman amplification, a tradeoff between high performance and low power consumption needs to be determined for such systems.

Parametric Analysis of Self-Phase Modulation in Single-Tone RoF System

Abstract Self-phase modulation (SPM) is one of the major non-linear effect in single-tone radio over fiber system which limits the long-distance transmission as it leads to the broadening of pulse spectrum. In this paper, the mathematical and parametric analysis was carried out to understand the origination and upgradation of SPM and based on results achieved, a rigorous evaluation has been conducted to decrease the impact of SPM. The effect of SPM has been evaluated in terms of optical spectrums, eye diagrams, eye-opening and Q-factor by utilizing four important parameters specifically launched power, fiber effective area, bit rate and fiber attenuation using OptiSystem simulator which reveals insight information for the elimination of non-linear effects.

Estimation of Signal-to-Cross Talk Ratio of Stimulated-Raman-Scattering-Induced Cross Talk in Wavelength-Division-Multiplexing-Based Radio-over-Fiber Links

Abstract This paper evaluates the signal-to-cross talk ratio (SXR) of cross talk induced by stimulated Raman scattering (SRS) in radio-over-fiber (RoF) systems based on wavelength-division multiplexing. The reported study has modeled the relations of SXR to modulation frequency, optical power, transmission length, and effective area of fiber for various values of the walk-off parameter. The summary of experimental results reveals that SXR decreases with increases in channel input power and transmission distance and increased with increases in fiber effective area and modulation frequency. Results showed that increasing the walk-off parameter from 13.6 to 81.6 ps/km increased the SXR by almost 6 dBm. Furthermore, various fibers, including standard single-mode fiber (SMF), Corning LEAF, and Alcatel TeraLight were tested for their capacity to mitigate SRS-induced cross talk. These tests demonstrated that standard SMF suppressed SRS cross talk effectively and offered values of SXR 3 dBm and 6 dBm higher than the values exhibited by Alcatel TeraLight and Corning LEAF, respectively.

Lowering backward Raman and Brillouin scattering in waveguide Raman wavelength converters

BackgroundLiquid filled hollow core fiber Raman wavelength converters are devices enabling to red-shift the wavelength of laser beams delivered by either fixed wavelength or tunable lasers. Most of the reported converters operate in a pulsed regime with pulse durations comprised between a few hundreds of picoseconds and up to a few nanoseconds, and energy of a few micro-Joules. However, and depending on the pulse duration, the optimization of Raman converters turns to be rather challenging since the desired forward Raman scattering may compete with counter-propagating nonlinear effects like Raman and Brillouin back-scatterings. The Brillouin back-scattering is especially hard to cancel since the Brillouin gains are usually larger than the Raman gains. Techniques have already been investigated but are not fully satisfactory. Our aim in this paper is to propose a technique to optimize the Raman forward scattering and to minimize these back-scattering effects.MethodsWe compare the interaction lengths in the forward and backward directions in the above-mentioned temporal regimes. If the fiber length is higher that the backward effective length of interaction then the backward effects should decrease at the benefit of the forward Raman scattering. Numerical simulations enable to estimate more precisely how long the fiber should be to get large Raman conversion efficiency and negligible Brillouin scattering.Results and discussionTo validate this technique we build two identical Raman converters differing only by the fiber lengths (0.5 m and 1.5 m). We present the experimental setup. The experimental results are confronted to the numerical simulations. As expected increasing the fiber length strongly decreases the Brillouin scattering.ConclusionsWe have proposed a simple and efficient solution to minimize Brillouin back-scattering in Raman wavelength converters by optimizing the fiber length. The experimental demonstration was conducted with low energy (≈ 6 μJ) but the energies should scale with the fiber effective area if more energy is needed, without affecting the conversion efficiencies.

Quasi-Single-Mode Fiber Transmission for Optical Communications

The transmission of a single fundamental mode in a fiber with cutoff wavelength above the transmission band is studied as a means of allowing a larger fiber effective area and reducing fiber nonlinearity. The reduction of nonlinear impairments is achieved at the expense of a potential new linear impairment in the form of multipath interference (MPI). We use a power-coupled-mode formalism to analyze the growth of MPI, and the effects of fiber and cable attributes on its magnitude and the required complexity of digital signal processing to combat the MPI. Hybrid fiber spans comprised partially of a quasi-single-mode fiber are also analyzed using a modification of the Gaussian noise model of coherent systems to predict optimal configurations, and results from transmission experiments are presented that demonstrate very high spectral efficiencies and performance surpassing that of a purely single-mode fiber system.

400 G Transmission of Super-Nyquist-Filtered Signal Based on Single-Carrier 110-GBaud PDM QPSK With 100-GHz Grid

We experimentally demonstrate a coherent transmission system with a high symbol rate using up to 110-GBaud PDM-QPSK signals. Super-Nyquist-filtering technology is used to narrow down the bandwidth of a single channel on a 100-GHz grid. The performance of the high baud rate electronic time division multiplexed-based super-Nyquist-filtered signal is also studied under the aggressive optical filtering elements in multiple reconfigurable optical add-drop multiplexers (ROADMs) nodes during transmission. We successfully transmit 100-GHz-grid, 20 channel single-carrier 440-Gb/s super-Nyquist 9-QAM-like signal over 3600-km ultralarge effective-area fiber (ULAF) at a high net SE of 4 b/s/Hz (after excluding the 7% hard-decision FEC overhead). The highly filtering tolerant performance of the 9-QAM liked super-Nyquist signal is also experimentally demonstrated. Using this scheme, we then successfully transmit ten channel 440-Gb/s signal over 3000-km ULAF and ten cascaded 100-GHz-grid ROADMs based on the 110-GBaud QPSK. Such signal is coherently detected and processed after a real-time oscilloscope at 160-GSa/s sampling rate with 65-GHz bandwidth.

Evaluation of effective area of erbium doped fibers

The effective area of an Er3+ doped fiber of 3% erbium concentration was studied experimentally by the transverse shift measurement method for the excitation of 980 and 1480 nm wavelengths and at the amplification range of 1520–630 nm. Based on experimental results, the fiber effective area was calculated. A comparative analysis and estimation of the results for different wavelengths of an Er3+ doped fiber are given.

Evaluation of effective area of erbium doped fibers

The effective area of an Er3+ doped fiber of 3% erbium concentration was studied experimentally by the transverse shift measurement method for the excitation of 980 and 1480 nm wavelengths and at the amplification range of 1520–630 nm. Based on experimental results, the fiber effective area was calculated. A comparative analysis and estimation of the results for different wavelengths of an Er3+ doped fiber are given.

Dispersion-flattened designs of the large effective-area single-mode fibers with ring index profiles

Two kinds of the large effective-area fibers with the ring index profiles named RI and RII type were proposed. In view of the impossibility to deduce the expression of waveguide dispersion directly due to the complexity of the characteristic equations, a feasible approach to calculate waveguide dispersion was established successfully. The influences made by the geometric parameters and optical parameters on the waveguide dispersion and cutoff characteristics of low order modes were analyzed. The calculated results indicate that the dispersion-flattened and large effective-area performances can be achieved simultaneously by adjusting the geometric and optical parameters in a region of wavelengths. A dispersion-flattened fiber design with the total dispersion of about 4.5 ps/nm/km, dispersion slope of below 0.006 ps/nm 2/km and the effective areas from 95 to 118 μm 2 in the spectral range of 1540–1620 nm was presented and its tolerance analysis and bending loss characteristics at 1550 nm were also examined.

Optical fibers with low nonlinearity and low polarization-mode dispersion for terabit communications

Refractive-index nonlinearities have negligible effect on the performance of short-haul fiber-optic communication links utilizing electronic repeaters. However, in long links, nonlinearities can cause severe signal degradations. To mitigate nonlinear effects, a new generation of fibers, referred to as large effective-area fibers, have been introduced in recent years. This paper reviews the latest research and development work on these fibers conducted by several research groups around the world. Attention is focused on a class of large effective-area fibers that are based on a depressed-core multiple-cladding design. Another important issue in long-haul and high capacity fiber optic systems is the polarization-mode dispersion (PMD) which has been recognized as a serious limiting factor. In this paper, an improved fiber design is proposed which, in addition to providing large effective-area and low bending loss, eliminates PMD due to elliptical deformation in the single-mode wavelength region. Furthermore, this design is allowed to provide a small chromatic dispersion about few ps/ nm km , in order to overcome four-wave mixing effects.