Mitigation Of Nonlinear Effects Research Articles

Dynamic mitigation of nonlinear effects in a silicon photonic add-drop filter.

Nonlinear effects limit the maximum amount of optical power that can be handled by silicon photonic integrated circuits (PICs). This limitation is particularly tight in resonant devices such as microring resonator (MRR) filters, suffering from a power-dependent resonance spread due to intracavity power enhancement. In this Letter, we present an automatic control system that can dynamically mitigate the nonlinear spectral distortion of silicon MRR filters by thermally controlling each MRR. The benefit of the proposed scheme is demonstrated on the spectral response of a polarization-transparent coupled-MRR filter operating on a 200 Gbit/s signal. The proposed technique, which does not require a priori information on the PIC topology and functionality, is scalable to more complex architectures and can be employed to compensate for generic nonlinear effects in different photonic platforms.

Mitigation of Nonlinear Effects using Machine Learning in Coherent Optical Access Networks

Introduction/Context: The use of coherent detection jointly with high-level modulation formats such as 16 and 64-QAM seems to be a convenient strategy to increment capacity of future optical access networks. However, coherent detection requires high complexity digital signal processing to mitigate different impairments. Objective: Mitigate signal distortions using nonsymmetrical demodulation techniques based on Machine Learning (ML) algorithms. Methodology: First, a single channel Nyquist m-QAM system at 28 and 32 Gbps was simulated in VPIDesignSuite software. Then, different signals modulated at 16 and 64-QAM were generated with different laser linewidth, transmission distances and launch powers. Two ML algorithms were implemented to carry out the demodulation of the generated signals. The performance of the algorithms was evaluated using the bit error rate (BER) in terms of different system parameters as laser linewidth, transmission distance, launch power and modulation format. Results: The use of ML allowed gains up to 2 dB in terms of optical signal-to-noise ratio at a BER value of for 16-QAM and 1.5 dB for 64-QAM. Also, the use of ML showed that it is possible to use a lower cost laser (100 kHz linewidth vs 25 kHz) with a better BER performance than using conventional demodulation. Conclusions: We showed that the use of both algorithms could mitigate nonlinear effects and could reduce computational complexity for future optical access networks.

Diode-pumped triple-clad fiber MOPA with an output power scaling up to 4.67 kW.

In this Letter, we have demonstrated a triple-cladded fiber (TCF)-based master oscillator power amplifier (MOPA), with an output power scaling up to 4.67 kW, an optical-to-optical efficiency of 78%, and a beam quality factor ${{\rm M}^2}$M2 of 1.57. The MOPA output power was limited by stimulated Raman scattering (SRS) of which our design yielded a 31.2 dB suppression ratio at the 4.67 kW output power. Such a unique design of a TCF-based structure allows a wide range of flexibility over fiber parameters, mitigation of nonlinear effects, low-loss splice integration, reliable high-power pump guiding in turn, and an ease in overall thermal management at multi-kW output power levels. Together with direct diode-pumping configuration, TCF-based designs promise thermally and mechanically robust, compact, and highly efficient MOPA systems of a superior beam quality.

Nonlinear Feature Normalization for Hyperspectral Domain Adaptation and Mitigation of Nonlinear Effects

Domain adaptation in remote sensing aims at the automatic knowledge transfer between a set of multitemporal and multisource images. This process is often impaired by nonlinear effects in the data, e.g., varying illumination conditions, different viewing angles, and geometry-dependent reflection. In this paper, we introduce the Nonlinear Feature Normalization (NFN), a fast and robust way to align the spectral characteristics of multiple hyperspectral data sets. NFN employs labeled training spectra for the different classes in an image to describe the corresponding underlying low-dimensional manifold structure. A linear basis for data representation is defined by arbitrary class reference vectors, and the image is aligned to the new basis in the same space. This results in samples of the same class being pulled closer together and samples of different classes pushed apart. NFN transforms the data in its original domain, preserving physical interpretability. We use the continuous invertibility of NFN to derive the NFN Alignment (NFNalign) transformation, which can be used for domain adaptation, by transforming one data set to the domain of a chosen reference. The evaluation is performed on multiple hyperspectral data sets as well as our new benchmark for multitemporal hyperspectral data. In a first step, we show that the NFN transformation successfully mitigates nonlinear effects by comparing classification of the linear Spectral Angle Mapper on original and transformed data. Finally, we demonstrate successful domain adaptation with NFNalign by applying it to the task of hyperspectral data preprocessing. The evaluation shows that our approach for alignment of multitemporal data produces high-spectral similarity and successfully allows knowledge transfer, e.g., of classifier models and training data.

Mitigation of Nonlinear Effects with Volterra and Wiener Hammerstein Electrical Equalizer in LDPC Coded Coherent Optical OFDM System

Mitigation of Nonlinear Effects with Volterra and Wiener Hammerstein Electrical Equalizer in LDPC Coded Coherent Optical OFDM System

Mitigation of Non Linear Effects Using Non Linear Transform in Dispersion Managed Coherent Optical OFDM Systems

It is very important to compensate the dispersion and non linearity present in the optical backhaul so that it is compatible with upcoming technologies. Optical Frequency Division Multiplexing (OFDM) is a physical layer, Multicarrier Modulation Technique (MCT) which is being widely used to design Back Bone (BB), Back Haul (BH) and Cognitive Optical Networks (CONs). Fiber nonlinearity present in dispersion managed links limits the capacity of an OFDM link, as it gets enhanced by high Peak to Average Power Ratio (PAPR) value of the transmitted signal. This work aims to decrease the PAPR value and hence in turn reduce the non linear impairments present in the coherent OFDM optical fiber link. In this work L2-by-3 non linear transform has been implemented to mitigate various fiber non linear effects through PAPR reduction.

Digital Signal Processing of 400 Gbps CO-QPSK-WDM System Over Optical Wireless Channel for Carrier Phase Estimation

High bandwidth, low cost and small size has made Inter satellite optical wireless communication a promising and advance technology with an alternative to current microwave satellite systems. In this paper, advantages of coherent-detection quadrature phase shift keying (CO-QPSK) with DSP are investigated for the mitigation of non-linear effects. The technique of carrier phase estimation has been used to prolong the transmission range to several thousand kilometers. Further, 400 Gbps WDM-QPSK system has been analyzed for different distances with 30 dB transmitting power and 11 dB LO power. At last, system has been investigated at narrow channel spacing of 50 GHz and a brief comparison has been made with system having channel spacing of 100 GHz.

A Direct Formula for Ultra-Large Effective Area Fibers Design With Top-Hat Intensity Profile

In this paper, we present a new refractive index profile, in simple easy to use equation form, which allows the design of large mode area (LMA) single mode (SM) optical fibers with the special property of supporting “perfect top-hat” mode profiles. The few parameters of this formula define the refractive index profile of such fibers. We show the effect the parameters of the refractive index profile have on the desired mode field. By applying this direct formula, we avoid the use of complex inverse refractive index reconstruction methods, or time-consuming iterative design processes. We demonstrate this formula with a number of example designs of LMA SM optical fibers with perfect flat-top electric field profile and an effective mode area (Aeff) size that in some cases exceeds the 4800 μm 2 . We expect such LMA SM top-hat fiber design to be useful for the mitigation of non-linear effects and catastrophic optical damage, as well as for achieving uniform intensity deposition on the target (material, biological tissue, and so on) in high-power applications. The results presented here are testing the validity of the refractive index profiles for non-ideal designs so as we can determine the tolerance to manufacturing such fibers.

Mitigation of Nonlinear Effects on WDM QAM Signals Enabled by Optical Phase Conjugation With Efficient Bandwidth Utilization

We present nonlinear impairment mitigation of wavelength division multiplexed signals, through optical phase conjugation (OPC). We conduct our experiments on a 400-km-long installed fiber link equipped with erbium-doped fiber amplifiers, with the OPC placed close to the middle of the link. Our OPC configuration realizes efficient reuse of the signal bandwidth, avoiding the loss of half of the spectral band typical of most phase conjugating schemes. We demonstrate the operation of the system using both 16- and 64-quadrature amplitude modulation (QAM) signals and report Q-factor improvements up to 0.5 and 2.5 dB for 16- and 64-QAM, respectively.

Design of Arbitrary Shape Higher Order Mode Electric Field in Optical Fibers for High Power Applications

In this paper, we present a new and efficient technique for the exact reconstruction of large mode area (LMA) higher order mode (HOM) optical fibers by using arbitrary shape HOM electric field profiles. One known strategy to achieve LMAs for high power optical applications is by using optical fibers supporting multimode operation, and engineering these fibers such that they operate on just a single transverse mode. Although the fundamental mode is preferred in most circumstances, there is an increasing interest in operating on a single HOM instead since these can have interesting dispersion characteristics and also significantly higher ability to scale mode areas. An issue with the use of HOMs in high power applications is that often they demonstrate regions of high field intensity across the core. This leads to problems with optical damage at lower values of effective area than might otherwise be expected. In order to avoid this problem, we offer designs of optical fibers supporting mode-flattened HOM electric fields. We develop a new inverse transmission line technique for calculating directly and accurately the refractive index profiles of such fibers from knowledge of the desired HOM electric field. We demonstrate this algorithm with a number of example reconstructions of LMA HOM optical fibers supporting prescribed mode-flattened electric field profiles with ultralarge effective mode areas We expect such fiber designs to be useful in the mitigation of nonlinear effects and in thermal and damage management.

Mitigation of nonlinear effects through frequency shift free mid-span spectral inversion using counter-propagating dual pumped FWM in fiber

We propose and numerically verify a scheme of frequency-shift free mid-span spectral inversion (MSSI) for nonlinearity mitigation in an optical transmission system. Spectral inversion is accomplished by optical phase conjugation, realized by counter-propagating dual pumped four-wave mixing in a highly nonlinear fiber. We examine the performance of MSSI due to critical parameters such as nonlinear fiber length, pump and signal power. We demonstrate the near complete nonlinearity mitigation of 40 Gbps DQPSK modulated data transmitted over 1000 km standard single mode fiber using our method of MSSI. We perform simulation of bit-error rate as a function of optical signal to noise ratio to corroborate the effect of frequency-shift free MSSI.

Coherent beam combining with an ultrafast multicore Yb-doped fiber amplifier.

Active coherent beam combination using a 7-non-coupled core, polarization maintaining, air-clad, Yb-doped fiber is demonstrated as a monolithic and compact power-scaling concept for ultrafast fiber lasers. A microlens array matched to the multicore fiber and an active phase controller composed of a spatial light modulator applying a stochastic parallel gradient descent algorithm are utilized to perform coherent combining in the tiled aperture geometry. The mitigation of nonlinear effects at a pulse energy of 8.9 µJ and duration of 860 fs is experimentally verified at a repetition rate of 100 kHz. The experimental combining efficiency results in a far field central lobe carrying 49% of the total power, compared to an ideal value of 76%. This efficiency is primarily limited by group delay differences between cores which is identified as the main drawback of the system. Minimizing these group delay issues, e.g. by using short and straight rod-type multicore fibers, should allow a practical power scaling solution for femtosecond fiber systems.

Mitigation of nonlinearities using conjugate data repetition.

We investigate a time-domain implementation of generalized phase-conjugated twin waves which we call conjugate data repetition. A theory based on time-domain perturbation analysis explaining the mitigation of nonlinear effects is provided, and the concept is evaluated using numerical simulations. Compared to PM-QPSK at the same channel bit rate, the single-channel transmission reach in a conventional system with standard single-mode fiber of conjugate data repetition-QPSK is increased by approximately a factor of 2.

Dispersion Compensation and Mitigation of Nonlinear Effects in 111-Gb/s WDM Coherent PM-QPSK Systems

We carried out an extensive simulative analysis to investigate in depth the potential of electronic dispersion compensation (EDC) in amplified multispan 111-Gb/s wavelength- division-multiplexed systems based on polarization-multiplexed quadrature phase-shift keying modulation with coherent detection, also in the presence of substantial fiber nonlinearity. For typical single-mode and nonzero dispersion-shifted fibers, our results show that the use of inline optical dispersion management is always suboptimal versus using EDC at the receiver.

Kalman filter application for mitigation of nonlinear effects in multicarrier communication systems

The extension of Bussgang's theorem for multicarrier signals states that the effect of a memoryless band-pass nonlinearity consists in an attenuation of the input signal and its corruption by additive nonlinear noise. In spite of the fact that before the fast Fourier transform (FFT) block at the receiver nonlinear noise is non-Gaussian, the Kalman filter is applied (which is known to provide the minimum mean-square estimate when the informative Gaussian signal is corrupted by additive Gaussian noise). In doing so the structure of the useful signal is taken into account as well as the relationship between the powers of the useful signal and nonlinear noise. It turns out that the procedure of Kalman filtering, as applied to the above problem, consists in the simple multiplication of the received samples by the ‘Kalman gain’. This gain can be calculated in advance because it depends only on the input signal power and the transfer characteristic of the nonlinearity. If the communication system is operated in an additive white Gaussian noise (AWGN) channel, the noise characteristics should also be taken into account when the above gain is calculated. The theoretical analysis and simulation results show that this simple procedure decreases the noise variance before the decision device and thus improves the performance of the system.