Showing papers on "Polarization mode dispersion published in 2020"

Deep learning based digital backpropagation demonstrating SNR gain at low complexity in a 1200 km transmission link

Abstract: A deep learning (DL) based digital backpropagation (DBP) method with a 1 dB SNR gain over a conventional 1 step per span DBP is demonstrated in a 32 GBd 16QAM transmission across 1200 km. The new DL-DPB is shown to require 6 times less computational power over the conventional DBP scheme. The achievement is possible due to a novel training method in which the DL-DBP is blind to timing error, state of polarization rotation, frequency offset and phase offset. An analysis of the underlying mechanism is given. The applied method first undoes the dispersion, compensates for nonlinear effects in a distributed fashion and reduces the out of band nonlinear modulation due to compensation of the nonlinearities by having a low pass characteristic. We also show that it is sufficient to update the elements of the DL network using a signal with high nonlinearity when dispersion or nonlinearity conditions changes. Lastly, simulation results indicate that the proposed scheme is suitable to deal with impairments from transmission over longer distances.

Dual Polarization Full-Field Signal Waveform Reconstruction Using Intensity Only Measurements for Coherent Communications

Abstract: Conventional optical coherent receivers capture the full electrical field, including amplitude and phase, of a signal waveform by measuring its interference against a stable continuous-wave local oscillator (LO). In optical coherent communications, powerful digital signal processing (DSP) techniques operating on the full electrical field can effectively undo transmission impairments such as chromatic dispersion (CD) and polarization mode dispersion (PMD). Simpler direct detection techniques do not have access to the full electrical field and therefore lack the ability to compensate for these impairments. We present a full-field measurement technique using only direct detection that does not require any beating with a strong carrier LO. Rather, phase retrieval algorithms based on alternating projections that makes use of dispersive elements are discussed, allowing to recover the optical phase from intensity-only measurements. In this demonstration, the phase retrieval algorithm is a modified Gerchberg–Saxton (GS) algorithm that achieves a simulated optical signal-to-noise ratio (OSNR) penalty of less than 4 dB compared to theory at a bit-error rate of 2 $\;\times 10^{-2}$ . Based on the proposed phase retrieval scheme, we experimentally demonstrate signal detection and subsequent standard 2 × 2 multiple-input-multiple-output (MIMO) equalization of a polarization-multiplexed 30-Gbaud QPSK transmitted over a 520-km standard single-mode fiber (SMF) span.

Design and analysis of a 32 × 5 Gbps passive optical network employing FSO based protection at the distribution level☆

Abstract: A cost efficient and reliable single mode fiber and free space optics based hybrid 32 × 5 Gbps ultra dense wavelength division multiplexed-passive optical network architecture employing optical comb and polarization multiplexing is proposed. The proposed architecture is a step forward towards shifting the next generation wireless network traffic over existing passive optical network to achieve the optimum bandwidth, capacity, quality of service and cost efficiency for mobile subscribers. Self-restorable passive optical networks having fiber based feeder and distribution paths are widely researched in various studies in the past. However, to the best of our knowledge, a self-restorable passive optical network architecture employing free space optics based protection path has not been proposed so-far. The effect of varying polarization mode dispersion from 0.02 to 0.06 ps . km - 0.5 and the refractive index structure parameter of the Gamma-Gamma channel model from 5 × 10 - 16 to 5 × 10 - 12 m - 2 / 3 is evaluated. A techno-economic performance analysis of the architecture for downstream is performed by considering both the distribution and protection paths. It has been shown that the receiver sensitivity for a polarization mode dispersion of 0.06 ps . km - 0.5 is around - 22 dBm and for strong turbulence is around - 20 dBm .

Photonics-based multi-band linearly frequency modulated signal generation and anti-chromatic dispersion transmission.

Abstract: A photonics-based anti-chromatic dispersion transmission scheme for multi-band linearly frequency modulated (LFM) signals is proposed and experimentally demonstrated. In the central station (CS), the key component is an integrated dual-polarization quadrature phase shift keying (DP-QPSK) modulator, of which the up-arm and down-arm are driven by a microwave reference signal and an intermediate-frequency (IF) LFM signal respectively. By properly adjusting the DP-QPSK modulator, optical frequency comb (OFC) and frequency shift lightwave are generated. After polarization coupling and remote transmission, the orthogonal-polarization optical signals are introduced into balanced photodetector for heterodyne detection. Thence, multi-band LFM signals are generated and transmitted to remote base stations (BS) with the largest power for the anti-chromatic dispersion ability. Experiments are conducted to verify the analysis. Multi-band LFM signals at L (1.5 GHz), C (7 GHz), X (10 GHz), Ku (15.5 GHz) and K (18.5 GHz) bands with flatness of 1.9 dB are simultaneously obtained in the CS after 50 km fiber transmission, while the normally double-sideband modulation approach experiences a significant power fading for the fiber dispersion. Tunability of the system is evaluated, and detection performances of the generated signals are also analyzed.

Impact of Polarization- and Mode-Dependent Gain on the Capacity of Ultra-Long-Haul Systems

Abstract: Motivated by the recent interest in single-mode semiconductor optical amplifiers and multimode erbium-doped fiber amplifiers, we present a unified, comprehensive treatment of the effect of polarization- and mode-dependent gain (PDG and MDG) on the capacity of ultra-long-haul transmission systems. We study the problem using simulations of a multisection model, including the effects of PDG or MDG and polarization mode dispersion (PMD) or modal dispersion. We also analytically derive exact expressions for the capacity distribution of PDG-impaired single-mode systems. In agreement with previous work, we find that PDG and MDG cause fluctuations in capacity, which reduces average capacity and may cause outage. We show that the multimode systems studied, with at least $D = 14$ spatial/polarization modes, have sufficient modal diversity and frequency diversity to strongly suppress capacity fluctuations and reduce outage probability so that the outage capacity approaches the average capacity. We show that single-mode systems, by contrast, inherently provide low modal and frequency diversity, making them more prone to outage. To alleviate this problem, frequency diversity can be increased by artificially inserting PMD. Finally, we quantify the PDG/MDG requirements of optical amplifiers to ensure that the average capacity is close (within a 1-2 dB effective SNR loss) to the theoretical optimum. We show that these PDG/MDG requirements are stringent, especially considering the minimum-mean-square error linear equalizers implemented in typical multiple-input multiple-output receivers.

Neural Network Training for OSNR Estimation from Prototype to Product

Abstract: A method for in-service OSNR measurement with a coherent transceiver is presented and experimentally verified. A neural network is employed to identify and remove the nonlinear noise contribution to the estimated OSNR.

Improving FWM efficiency in bi-directional ultra DWDM-PON networking centered light source by using PMD emulator

Abstract: The optical networks provides a high performance data networking and secured way to communicate. New generation optical networks demands high input power and low channel spacing in Wavelength-Division Multiplexing (WDM). Using WDM can lead to some nonlinearities in the system such as Four Wave Mixing (FWM). FWM is a phenomena in which two optical pulses are converted into four pluses after traveling in optical fiber. In this paper Polarization Mode Dispersion (PMD) is used by applying PMD emulator at input to suppress FWM. To analyse the effect of PMD a Dense Wavelength-Division Multiplexing-passive optical network (DWDM-PON) is used with centerlized source over the transemission distance longer than 50 km. System’s performance is carried out on the basis of Q factor, optical signal to noise ratio (OSNR), bit error rate (BER), received power and FWM efficiency. Exhaustive sets of simulations are carried out in “Optisystem” on a eight channel system having 25 GHz spacing, operating at 5 Gbps. Results show 7 dB and 5 dB of improved FWM efficiency in downlink and uplink respectively.

Fiber Nonlinearity and Optical System Performance

Abstract: This chapter aims to provide a comprehensive picture of the impact of fiber nonlinear effects on modern coherent wavelength division multiplexing () systems' performance. First, the main nonlinearity models currently available are introduced and discussed in depth. Then, various specific aspects are addressed, such as the interplay of polarization mode dispersion ()/polarization dependent loss () and nonlinearity, or the dependence of nonlinear effects on modulation format. The important topic of nonlinear effects mitigation is then dealt with. Finally, system performance metrics and capacity are discussed extensively, as to how they are fundamentally influenced and limited by fiber nonlinearity.

Relaxation of the Radio-Frequency Linewidth for Coherent-Optical Orthogonal Frequency-Division Multiplexing Schemes by Employing the Improved Extreme Learning Machine

Abstract: A coherent optical (CO) orthogonal frequency division multiplexing (OFDM) scheme gives a scalable and flexible solution for increasing the transmission rate, being extremely robust to chromatic dispersion as well as polarization mode dispersion. Nevertheless, as any coherent-detection OFDM system, the overall system performance is limited by laser phase noises. On the other hand, extreme learning machines (ELMs) have gained a lot of attention from the machine learning community owing to good generalization performance, negligible learning speed, and minimum human intervention. In this manuscript, a phase-error mitigation method based on the single-hidden layer feedforward network prone to the improved ELM algorithm for CO-OFDM systems is introduced for the first time. In the training step, two steps are distinguished. Firstly, pilots are used, which is very common in OFDM-based systems, to diminish laser phase noises as well as to correct frequency-selective impairments and, therefore, the bandwidth efficiency can be maximized. Secondly, the regularization parameter is included in the ELM to balance the empirical and structural risks, namely to minimize the root mean square error in the test stage and, consequently, the bit error rate (BER) metric. The operational principle of the real-complex (RC) ELM is analytically explained, and then, its sub-parameters (number of hidden neurons, regularization parameter, and activation function) are numerically found in order to enhance the system performance. For binary and quadrature phase-shift keying modulations, the RC-ELM outperforms the benchmark pilot-assisted equalizer as well as the fully-real ELM, and almost matches the common phase error (CPE) compensation and the ELM defined in the complex domain (C-ELM) in terms of the BER over an additive white Gaussian noise channel and different laser oscillators. However, both techniques are characterized by the following disadvantages: the CPE compensator reduces the transmission rate since an additional preamble is mandatory for channel estimation purposes, while the C-ELM requires a bounded and differentiable activation function in the complex domain and can not follow semi-supervised training. In the same context, the novel ELM algorithm can not compete with the CPE compensator and C-ELM for the 16-ary quadrature amplitude modulation. On the other hand, the novel ELM exposes a negligible computational cost with respect to the C-ELM and PAE methods.

Blind optical modulation format identification assisted by signal intensity fluctuation for autonomous digital coherent receivers.

Abstract: A novel and blind optical modulation format identification (MFI) scheme assisted by signal intensity fluctuation features is proposed for autonomous digital coherent receivers of next generation optical network. The proposed MFI scheme needn’t to pre-know OSNR value of incoming signal, even though it is well known that the intensity dependent features of the incoming signal changes as the change of OSNR performance. Here, the proposed scheme firstly utilizes two kinds of signal intensity fluctuation features, Godard’s criterion error and intensity noise variance, to construct a two-dimensional (2D) plane where three different regions which consist of QPSK region, 8QAM region, mixed 16/32/64QAM region can be found. Thus, we can firstly identify QPSK and 8QAM from the 2D plane, and then partition Godard’s criterion error method is introduced to further identify 16QAM, 32QAM and 64QAM in our proposed scheme. The performance of the proposed scheme is firstly verified by a series of numerical simulations in 28GBaud PDM-QPSK/-8QAM/-16QAM/-32QAM/-64QAM coherent optical communication systems. The results show that the lowest required OSNR values to achieve 100% recognition rate for all modulation format signals are even lower than or close to their corresponding theoretical 20% FEC limits (BER = 2.4 × 10−2). Finally, the feasibility is further demonstrated via a series of proof-of-concept experiments among 28GBaud PDM-QPSK/-8QAM/-16QAM, and 21.5GBaud PDM-32QAM systems under back-to-back and long-haul fiber transmission links (from 320 km to 2000km). Experiment results show that the proposed scheme is robust to both linear and nonlinear noise.

Study of burst-mode adaptive equalization for >25G PON applications [Invited]

Abstract: In anticipation of emerging applications such as business services, 5G, and the Internet of Things, research and standardization are working together towards next-generation 25/50 Gbit/s passive optical network access networks. However, the increase in single-channel line rate is limited by the distortion introduced by the low-cost device’s bandwidth limit or the chromatic dispersion in the fiber. Burst-mode electronic distortion/dispersion compensation can be used to mitigate these effects, but requires a burst-mode equalizer (BMEQ) for upstream traffic and introduces many challenges. In this invited paper, the feasibility of single-channel, directly modulated upstream 25 Gbit/s non-return-to-zero transmission is investigated in more detail. By using a linear burst-mode transimpedance amplifier together with an offline BMEQ, specific BMEQ penalties and trade-offs such as limited training time and burst-to-burst phase variation are considered.

Toward Universal Optical Performance Monitoring for Intelligent Optical Fiber Communication Networks

Abstract: Optical performance monitoring (OPM) plays an essential role in the intelligent optical fiber communication networks, which perform dynamic network planning and service deployment based on the knowledge of the real-time conditions of the optical layer. Common parameters estimated by OPM include optical power, optical signal-to-noise ratio, chromatic dispersion, polarization mode dispersion, and so on. To be cost-effective and integrated, a universal OPM for multiple parameters realized on a single hardware platform is highly desirable. Although the sources of distinct impairments are independent, the induced distortions on the signal are mixed together, thus challenging the realization of universal OPM. In this article, the existing OPM methods are reviewed with a focus on those based on spectral analysis. A viable solution of universal OPM based on a double-homodyne scheme with all low-cost components is presented.

Low-loss and ultra-broadband silicon nitride angled MMI polarization splitter/combiner.

Abstract: The property of self-imaging combined with the polarization birefringence of the angled multimode waveguide is used to design a silicon nitride (SiN) polarization splitter (PS) at λ ∼ 1550 nm. The demonstrated PS on a 450 nm thick SiN device layer (with 2.5 µm cladding oxide) has a footprint of 80 µm×13 µm and exhibits nearly wavelength independent performance over the C+L bands. Also, the device can be configured as a polarization combiner (PC) in reverse direction with similar bandwidth and performance. The measured crosstalk (CT) and insertion loss (IL) are respectively <−18 dB (<−20 dB) and ∼0.7 dB (∼0.8 dB) for TE (TM) polarization over the measurement wavelength range of 1525 nm ≤λ ≤ 1625 nm. The measured device parameter variations suggest some tolerance to fabrication variations. Such a device is a good candidate for a photonics integrated chip (PIC) foundry-compatible, SiN PS.

Long-Haul and High-Speed Key Distribution Based on One-Way Non-Dual Arbitrary Basis Transformation in Optical Fiber Link

Abstract: We propose a long-haul and high-speed key distribution based on one-way non-dual arbitrary basis transformation in optical fiber link. The key distribution rate of 277 Kbit/s with free key error rate is demonstrated over 300km.

Polarization Mode Dispersion Effects on Signal Quality and Compensation Methods

Abstract: With the ever-increasing bandwidth demand, high-speed optical systems are currently widely used to transmit various traffic over long distances. The main direction of development of optical communication systems is associated with the increase in the information transmission rate. However, the performance of long-haul high-speed optical systems is severely affected by linear and nonlinear transmission impairments, such as chromatic dispersion, polarization mode dispersion and nonlinear phase noise. In this paper the effects of the polarization mode dispersion on the system performance and its effects along with chromatic dispersion have been evaluated, and compensation methods have been proposed.

Wideband and Dispersion Immune Microwave Photonic Phase Shifter With Tunable Optical Carrier to Sideband Ratio

Abstract: A wideband microwave photonic phase shifter (MPPS) based on a dual-polarization dual-parallel Mach–Zehnder modulator (DP-DPMZM) is proposed and experimentally demonstrated. The proposed system has the features of chromatic dispersion (CD) immunity and tunable optical carrier to sideband ratio (OCSR), which can realize long fiber transmission distance with improved power efficiency. It is realized by carrier suppress double sideband (CS-DSB) plus optical carrier (OC) modulation at two orthogonal polarization states. The phases of output RF signals can be tuned continuously and independently by controlling the phases of the OCs. The experiment results show that the continuous 360° phase shifts of output RF signal over 5–25 GHz are both realized in the cases of back-to-back and fiber transmission. No CD-induced power fading and phase severe shaking of the RF signals appear after the dispersion compensating fiber (DCF) of −331 ps/nm at 1545 nm transmission. By optimizing the OCSR of the system, the output RF power efficiency of the proposed scheme realizes significantly improvement when input RF powers and output optical powers are both fixed. The possibility of generating frequency doubling signal is also verified.

TransLambda: A Multi-Band Transmission System and its Realization, Practical Applications and Use Cases in Optical Networks

Abstract: We focus on the introduction and practical use of TransLambdaTM, a multiband transmission system based on all optical wavelength conversion in optical transport network architectures, and detail its system-level considerations, network applications, and use-cases.

Statistical quantification of nonlinear interference noise components in coherent systems

Abstract: We present and validate a statistical method able to separate nonlinear interference noise (NLIN) into a residual Gaussian (ResN) and a phase noise (NLPN) component. We take into account the interaction of the NLIN with the receiver's DSP, mainly through carrier phase recovery (CPR), by considering the amount of correlation of the NLPN component. This allows obtaining in a straightforward way an accurate prediction of the achievable post-DSP transmission performance. We apply our method on simulated data in different scenarios. For this purpose: (i) several different quadrature amplitude modulation (QAM) and probabilistically shaped (PS) formats are investigated and (ii) simulations with standard single mode fiber (SSMF) and dispersion shifted fiber (DSF) are performed. In all these cases we validate the results provided by our method through comparison with ideal data-aided CPR and a more practical blind phase search (BPS) algorithm. The results obtained are finally compared with the predictions of existing theoretical models and the differences with our approach are pointed out.

Modulation format-independent optical performance monitoring technique insensitive to chromatic dispersion and polarization mode dispersion using a multi-task artificial neural network.

Abstract: We propose and experimentally demonstrate modulation format-independent optical performance monitoring (OPM) based on a multi-task artificial neural network (MT-ANN). Optical power measurements at a series of center wavelengths adjusted using a widely tunable optical bandpass filter (OBPF) are used as the input features for a MT-ANN to simultaneously realize high-precision optical signal-to-noise ratio (OSNR) and launch power monitoring and baud rate identification (BRI). This technique is insensitive to chromatic dispersion (CD) and polarization mode dispersion (PMD). The experimental verification in a 9-channel WDM system shows that for 10 Gbaud QPSK and 32 Gbaud PDM-16QAM signals with OSNR in the range of 1-30 dB, the OSNR mean absolute error (MAE) and root mean square error (RMSE) are 0.28 dB and 0.48 dB, respectively. For launch power in the range of 0-8 dBm, the MAE and RMSE of the launch power monitoring are 0.034 dB and 0.066 dB, respectively, and the identification accuracy for both baud rates is 100%. Furthermore, this technique utilizes a single MT-ANN instead of three ANNs to realize the simultaneous monitoring of three OPM parameters, which greatly reduces the cost and complexity.

Group Delay Measurements of Multicore Fibers with Correlation Optical Time Domain Reflectometry

Abstract: Several multi-core fibers (MCF) were characterized using Correlation Optical Time Domain Reflectometry (C-OTDR) in terms of propagation delay and polarization mode dispersion (PMD). The results show that the propagation delay in the cores depends on the position of the core in the fiber and that the differential delay between the cores varies with temperature.

Record Ultra-High Full-Fill Capacity Trans-Atlantic Submarine Deployment Ushering in the SDM Era

Abstract: A record capacity of 24 Tbps on a 6,644 km trans-Atlantic deployment using 16QAM is enabled by synthesized subcarriers, FEC gain sharing, multi-carrier wavelocking, and large-area, high dispersion fiber. Computer assisted optimization and automated protection facilitate full-fill deployments becoming prevalent as submarine cables enter the SDM era.

Polarization-maintaining optical fiber with an anisotropic core compatible with the SMF-28 standard

Abstract: We present the theoretical study of an all-solid highly birefringent fiber with an anisotropic core fully compatible with SMF-28 fiber and without use of external stress zones or air holes. We propose a fiber with a core composed of interleaved subwavelength layers of silica and germanium-oxide-doped silica. The optimized nanostructured fiber has a phase birefringence of 1.42×10−4, and an effective mode area and numerical aperture similar to SMF-28 fiber. We predict coupling losses of 0.1 dB for bidirectional coupling with the SMF-28 fibers.

The Real Time Implementation of a Simplified 2-Section Equalizer with Supernal SOP Tracking Capability

Abstract: We propose a 2-section equalizer architecture, two adaptive multi-tap 1×1 equalizer updated by proposed joint-CMA, followed by a feedforward 1-tap 2×2 MIMO. We implement it in 10G coherent transceiver and achieve 20Mrad/s SOP tracking speed.

A Robust Reference Optical Spectrum Based in-Band OSNR Monitoring Method Suitable for Flexible Optical Networks

Abstract: The in-band OSNR monitoring methods based on the noise-free reference optical spectrum (ROS) have attracted much attention in the field of optical performance monitoring because they are cost-effective and insensitive to chromatic dispersion and polarization mode dispersion. In this paper, we propose a new ROS based in-band OSNR monitoring method that is robust to the distortions due to non-ideal modulation, the variations of the in-line EDFA gain and the number of filtering elements traversed by the signal. Moreover, this method supports using the standard ROS retrieved by the existing machine-learning technique based optical spectrum identification technique, and thus can remove the need to measure the ROS near the transmitter, which is hard to perform, especially in flexible optical networks. These merits make the method more robust and convenient to use in practice. Extensive numerical simulations are presented to demonstrate the merits of the proposed method with respect to the existing ROS based methods.

Modulation-format-independent in-band OSNR monitoring technique using Gaussian process regression for a Raman amplified multi-span system with a cascaded filtering effect.

Abstract: We propose and experimentally demonstrate an accurate modulation-format-indepen-dent and cascaded filtering effect (CFE) insensitive in-band optical signal-to-noise ratio (OSNR) monitoring technique enabled by Gaussian process regression (GPR) utilizing a widely tunable optical bandpass filter (OBPF) and optical power measurements. By adjusting the center frequency of a widely tunable OBPF and measuring the corresponding output optical power as the input features of GPR, the proposed OSNR monitoring technique is experimentally proven to be transparent to modulation formats and robust to CFE, chromatic dispersion (CD), polarization mode dispersion (PMD), and nonlinear effect (NLE). Experimental results for 9-channel 32Gbaud PDM-16QAM signals with 50GHz channel spacing demonstrate OSNR monitoring with the root mean squared error (RMSE) of 0.429 dB and the mean absolute error (MAE) of 0.294 dB, in the OSNR range of -1∼30 dB. Even better, our proposed technique has the potential to be employed for link monitoring at the intermediation nodes and can eliminate the necessity to know the transmission information.

Impact of Wind Gust on High-Speed Characteristics of Polarization Mode Dispersion in Optical Power Ground Wire Cables

Abstract: Polarization mode dispersion is recognized as a key factor limiting optical transmission systems, particularly those fiber links that run at bit rates beyond 10 Gbps. In-line test and characterization of polarization mode dispersion are thus of critical importance to evaluate the quality of installed optical fibers that are in use for high-speed signal traffics. However, polarization-based effects in optical fibers are stochastic and quite sensitive to a range of environmental changes, including optical cable movements. This, in turn, gives rise to undesired variations in light polarization that adversely impair the quality of the signal transmission in the link. In this work, we elaborate on experimental testing and theoretical analysis to asses changes of polarization mode dispersion in optical fibers that are caused by environmental variations, here wind gusts in particular. The study was performed on commercially harnessed optical fibers installed within optical power ground wire cables, taking into account different weather conditions. More specifically, we showed that changes caused by wind gusts significantly influence the differential group delay and the principal state of polarization in those optical fibers. For this, we experimentally measured a number of parameters to characterize light polarization properties. Measurements were carried out on C-band operated fiber-optic link formed by 111-km-long power ground wire cables and 88 spectral channels, with a test time step of 1 min during 12 consecutive days. Variations in differential group delay allowed for sensitive testing of environmental changes with measured maxims up to 10 ps under the worst wind conditions. Moreover, measured parameters were used in a numerical model to assess the quality of transmitted high-bit-rate optical signals as a function of wind conditions. The analysis revealed a negligible impact of wind on a 10 Gbps transmission, while substantial influence was noticed for higher bit rates up to 100 Gbps. These results show promises for efficient sensing of environmental changes and subsequent monitoring of the quality of recently used fiber-optic link infrastructures.

Advances in Deep Learning for Digital Signal Processing in Coherent Optical Modems

Abstract: We analyze the advances of deep learning in optical coherent modems on the physical layer with respect to modulation design, equalization and signal detection and give an outlook on a combined control and physical layer optimization using neural networks.

Nonlinear Mitigation with TL-NN-NLC in Coherent Optical Fiber Communications

Abstract: We propose a low complexity transfer-learning assisted neural-network nonlinear compensation (TL-NN- NLC) scheme. The experimental results show 1.3-dB quality factor (Q-factor) improvement for 128 Gb/s polarization multiplexed (PM) 16-QAM coherent optical transmission over 800-km SSMF. © 2020 The Author(s)