Chromatic Dispersion Pre-compensation Research Articles

Neural network-based electrical dispersion pre-compensation for a 56 Gb/s PAM-4 over an 80 km fiber in intensity-modulation and direct-detection systems.

A neural network (NN)-based electrical dispersion pre-compensation (pre-EDC) scheme in intensity-modulation and direct-detection (IM/DD) systems is proposed and experimentally demonstrated in this Letter. The scheme enables 56 Gbit/s four-level pulse amplitude modulation (PAM-4) generation at a transmitter over an 80 km single-mode fiber (SMF) transmission in the C-band. The NN is utilized to better fit nonlinear phase-amplitude transformation due to the chromatic dispersion (CD) in IM/DD systems, in place of the existing Gerchberg-Saxton (GS) iterative algorithm and linear GS-based finite impulse response (GS-FIR) non-iterative compensation schemes. The experimental results show that the measured bit error ratio (BER) can be reduced to below the 7% hard-decision forward error correction (HD-FEC) threshold of 3.8 × 10-3 with 0 dBm receiver optical power (ROP) by the NN-based non-iterative pre-EDC scheme, which also saves up to 81% of computational complexity compared to the GS-based scheme. The results indicate that our proposed scheme is promising for the CD pre-compensation at the transmitter.

Low-complexity clustered polynomial nonlinear filter-based electrical dispersion pre-compensation scheme in IM/DD transmission systems.

A polynomial nonlinear filter (PNLF)-based electrical dispersion pre-compensation (pre-EDC) scheme assisted with Gerchberg-Saxton (GS) algorithm is proposed to compensate the chromatic dispersion (CD) for intensity-modulation and direct-detection (IM/DD) optical transmission systems, where PNLF is utilized to fit the nonlinear transfer function of the iterative GS algorithm-based pre-EDC scheme to realize a low-complexity non-iterative CD pre-compensation. The capability of PNLF to fit the nonlinear iterative process enables the PNLF-based pre-EDC scheme to compensate for CD-induced linear distortions and address CD-induced nonlinear distortions, which are typically captured through iterative approaches. Additionally, to further reduce the computational complexity, we also introduce the k-means clustering algorithm to eliminate the weight redundancy and propose a lower-complexity clustered PNLF-based pre-EDC scheme. Simulation results show that PNLF-based and clustered PNLF-based pre-EDC schemes save 76.0% and 97.5% complexity with only 0.3 dB receiver sensitivity penalty at 20% forward error correction (FEC) threshold, compared with GS-based pre-EDC scheme in C-band 56 GBaud 80-km on-off keying (OOK) system. Furthermore, the effectiveness of PNLF-based and clustered PNLF-based pre-EDC schemes is also evaluated through the experimental demonstration. Experimental results show that under C-band 32 GBaud 80-km OOK system, bit error ratio (BER) satisfying 20% FEC threshold is achieved by applying PNLF-based and clustered PNLF-based pre-EDC schemes, which save 78.3% and 94.2% complexity with only 0.4 dB receiver sensitivity penalty compared with GS-based pre-EDC scheme, respectively. The research results indicate that the (clustered) PNLF-based pre-EDC scheme has the great application potential for CD compensation in high-performance and low-cost IM/DD optical transmission systems.

Modified Gerchberg-Saxton Algorithm Based Electrical Dispersion Pre-Compensation for Intensity-modulation and Direct-detection Systems

In intensity-modulation and direct-detection (IM-DD) communication systems, electrical chromatic dispersion (CD) compensation cannot be directly applied in the transceivers due to the absence of phase information. Gerchberg-Saxton (GS) algorithm has been utilized to iteratively solve for real-valued CD pre-compensated signal in an IM-DD system. In this scheme, the amplitude information at the transmitter and phase information before the direct detection receiver are treated as the degree of freedoms (DoFs) and jointly optimized. In this paper, a modified GS algorithm is proposed and experimentally demonstrated for CD pre-compensation in a 28-GBaud PAM-4 system over 80-km single mode fiber (SMF) transmission. Compared with the basic GS electrical dispersion pre-compensation (pre-EDC) scheme, the amplitude information of received samples at the <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">T/2</i> position is regarded as DoFs as well, in order to reduce the error. Besides, to accelerate the convergence speed, two error reversing factors associated with the phase error at the transmitter and amplitude error at the receiver are introduced. The experimental results show that the bit error rate (BERs) of 56-Gbps PAM-4 signal over 80-km SMF transmission without CD compensation and with 10 iterations of basic GS pre-EDC scheme are 2.35×10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">−1</sup> and 5.13×10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">−2</sup> , respectively, when a 21-taps feedforward equalizer (FFE) is equipped at the receiver side. While the BER can be reduced to below the hard-decision forward error correction (HD-FEC) threshold of 3.8×10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">−3</sup> by the proposed scheme with the iterative number of 10. The results reveal that the proposed scheme is a promising solution for 50-Gbps class 80-km metro optical communication links based on the IM-DD structure.

High-speed PON downstream transmission based on pre-configured KK scheme with CD pre-compensation and direct detection

In this paper, the pre-configured Kramers–Kronig (Pre-KK) scheme combined with the chromatic dispersion pre-compensation (CDPC) has been proposed and studied to reduce the complexity of DSP and hardware implementation at the optical network unit (ONU) side for passive optical network (PON), avoiding the use of KK receiver. For further analysis and verification, 100 Gb/s/λ PON downstream transmissions with 4-level pulse amplitude modulation (PAM-4) signal based on the Pre-KK scheme and KK receiver have been implemented and compared on a unified optical system platform. The results show that the Pre-KK requires 1-bit resolution lower than KK receiver for ADC, and achieves a power budget of 29 dB after 20 km fiber transmission at the strong FEC threshold of 1 × 10−2. By increasing the launch power, the maximum power budget of 33.2 dB can be achieved due to the fiber nonlinearity. The effectiveness of CDPC in Pre-KK scheme has also been investigated and demonstrated over 20 and 50 km transmission. Besides, the computational complexities of two schemes are analyzed and discussed in detail. Hence, the Pre-KK scheme joint with CDPC can be a promising solution for the high-speed PON downstream transmission.

Real-time reception of 106 Gbps PAM-4 transmission over an 80 km SSMF link enabled by CD pre-compensation.

In this study, we report, to the best of our knowledge, the first experimental demonstration of the real-time reception of a 106 Gbps PAM-4 transmission over an 80 km dispersion uncompensated standard single-mode fiber (SSMF) link. In the transmitter, a chromatic dispersion (CD) pre-compensation, aided by an optical IQ modulator, is implemented. The optimization guideline of driver signal amplitudes and bias voltages is proposed to enable optimal CD pre-compensation. In the receiver, a real-time PAM-4 module including simple feed-forward equalization (FFE) is used. After the transmission, the required optical signal-to-noise ratio (OSNR) at a bit error rate (BER) below 3.8 × 10-3 is determined to be 35 dB for 106 Gbps PAM-4 signals. The better BER of 6.9 × 10-4 is achieved successfully compared to the previously reported off-line reception. The demonstration confirms the feasibility of 80 km DCI based on CD pre-compensation under real-time reception.

Influence of EEPN and P2A noise with CD pre- and post-compensation in optical SSB transmission and Kramers-Kronig receiver system.

We present a comparative study of equalization-enhanced phase noise (EEPN) and phase to amplitude (P2A) noise with chromatic dispersion (CD) pre- and post-compensation in single side-band (SSB) transmission and direct-detection (DD) systems, respectively. We analyze the interplay of laser phase noise and fiber dispersion on an optical SSB Nyquist shaped four-level pulse amplitude modulation (PAM-4) signal in a Kramers-Kronig (KK) receiver. Our main results show that the EEPN in a DD-KK receiver dominates the system noise with the relaxed signal-to-noise ratio (SNR). The P2A noise in CD post-compensation scheme is relaxed due to the complex filed recovery with KK receiver. The numerical simulations are implemented to illustrate the interplay of laser linewidth and fiber dispersion in both CD pre- and post-compensation scenarios. Compared with CD pre-compensation, 3-dB reduction of power spectral density (PSD) of P2A noise at the peak is alleviated with CD post-compensation. The laser linewidth has ~1 MHz release with CD post-compensation for a 56-Gbaud PAM-4 signal over 100-km standard single-mode fiber (SSMF) transmission.

Complexity analysis of flexible transmitter digital signal processing for terabit (40 × 50G) four‐level pulse amplitude modulation transmission

The authors propose a transmitter digital filter for joint optimisation of signal pulse shaping and chromatic dispersion pre-compensation, providing a detailed analysis of the architecture complexity. Experimental transmission of 40 × 50G channels (28 Gbaud four-level pulse amplitude modulation) over up to 110 km uncompensated standard single mode fibre with low-bandwidth hardware is demonstrated.

Enabling High-Capacity Long-Reach Direct Detection Transmission With QAM-PAM Stokes Vector Modulation

We introduce a three-dimensional modulation format using a Stokes-vector direct-detection system, where a pulse amplitude modulation (PAM) signal is polarization multiplexed with a quadrature amplitude modulation (QAM) signal. The phase reference of the PAM signal enables the retrieval of the phase information of the QAM signal using a Stokes vector receiver (SVR). A dual-polarization in-phase–quadrature modulator is employed to generate QAM-PAM optical signals with chromatic dispersion precompensation. We show direct detection of dual-polarization 16QAM-PAM2 and 16QAM-PAM4 signals delivering 280 and 336 Gb/s (net bit rate 233 and 280 Gb/s) below the soft-decision forward error correction threshold of 2 $\times$ 10 $^{-2}$ at 320 and 80 km, respectively. In addition, we study system performance at different modulation formats and symbol rates. Our findings indicate that increasing the order of modulation formats of the QAM signal is better than increasing that of the PAM signal to achieve the same bit rate. Finally, the performance of a 56 Gbaud 16QAM signal with PAM2 modulation on one polarization and a 56 Gbaud 16QAM signal with a pilot carrier on the orthogonal polarization detected with an SVR is experimentally investigated.

Transmission Performance Comparison for 100-Gb/s PAM-4, CAP-16, and DFT-S OFDM With Direct Detection

Metro network, as a medium distance transmission system, poses a special challenge of transmission capacity and cost. In this paper, we present a detailed comparison of applying three advanced modulation formats including pulse amplitude modulation-4 (PAM-4), carrierless amplitude and phase modulation-16 QAM (CAP-16), and discrete Fourier transform spread orthogonal frequency division multiplexing (DFT-S OFDM) with low-cost direct detection for 100-Gb/s/λ metro optical transmission systems. These modulation formats are all experimentally demonstrated with similar digital signal processing algorithms. Three kinds of chromatic dispersion (CD) compensation ways named CD precompensation method, single sideband (SSB), and dispersion compensating fiber (DCF) are also compared. Two types of modulators including an IQ modulator and a dual-drive Mach–Zehnder modulator are employed to generate SSB or CD precompensated signals in this experiment and their transmission performance is also evaluated. To the best of our knowledge, this is the first time that the performance of single-wavelength 100-G signal transmission based on direct detection is evaluated over 480 km of standard single mode fiber with PAM-4, CAP-16, and DFT-S OFDM modulation formats.

Nonlinear Look-Up Table Predistortion and Chromatic Dispersion Precompensation for IM/DD PAM-4 Transmission

In this paper, we propose and experimentally demonstrate 10 GBaud intensity modulation direct detection pulse amplitude modulation 4 transmission over 48-km single mode fiber (SMF). Look-up table predistortion and chromatic dispersion precompensation are employed to mitigate channel bandwidth constraint and nonlinear impairment. At the receiver side, decision-directed least mean square and cascaded multimodule algorithm are employed to improve the decision precision. By combining these techniques, link budgets of 5.3 and 4 dB are achieved at bit error rate of 1 × 10−3 for the back-to-back case and after transmission over 48-km SMF, respectively.

Impact of Chromatic Dispersion Compensation in Single Carrier Two-Dimensional Stokes Vector Direct Detection System

We experimentally demonstrate, aided with mathematical analysis, two methods for chromatic dispersion (CD) compensation for two-dimensional Stokes vector direct detection (2D-SV-DD) system. Results show that the better CD compensation method is dependent on transmission distance and operating symbol rate relative to the digital-to-analog converter (DAC) sampling rate. When 84 GBd 16 QAM signal is generated using an 84 GSps DAC, the bit error rate (BER) after 640 km propagation is $\sim1.67\times 10^{-2}$ and $\sim2\times 10^{-2}$ using CD post- and precompensation, respectively. When 64 GBd 16 QAM signal is generated at the same DAC sampling rate, the BER at 960 km is $\sim1.61\times 10^{-2}$ and $\sim9.8\times 10^{-3}$ using CD post- and precompensation, respectively. In addition, our findings reveal that CD precompensation allows for transmission distances greater than 1000 km at which CD postcompensation is no longer viable due to the required training. Finally, enabled by CD precompensation, we report the highest capacity-times-distance products of 591 360 (Gb/s) $\cdot$ km and 614 400 (Gb/s) $\cdot$ km in 2D-SV-DD system using QPSK modulation format and symbol rates of 84 and 64 GBd, respectively. Also, we can achieve 300G transmission for distances below 320 km using 84 GBd 16 QAM signal with BER below hard decision forward error correcting threshold of $\sim3.8\times 10^{-3}$ .

336 Gb/s in Direct Detection Below KP4 FEC Threshold for Intra Data Center Applications

We demonstrate direct detection of single polarization and dual polarization PAM4 signals delivering 168 and 336 Gb/s below the KP4 FEC threshold of $2.2\times 10^{{ {-4}}}$ . The 84 Gbaud 2 bits and 4 bits per symbol transceivers operate at a bit error rate (BER) that is compliant to the RS(544, 514) FEC encoding for error-free operation, as considered for next generation PAM4 400GBase Ethernet standard targeting data center applications. For the DP-PAM4 format, we show that the BER is independent of the state of polarization of the optical signal. To the best of our knowledge, this is the first experimental demonstration of a single carrier delivering 336 Gb/s in direct detection at a BER compliant to the physical coding sublayer of 400GBASE interfaces. Finally, using an intensity modulator in series with a phase modulator, we demonstrate chromatic dispersion pre-compensation of 84 Gbaud PAM4 signals, producing a 40-fold BER improvement after 10 km of single-mode fiber.

Record 500 km unrepeatered 100 Gb s−1 transmission

In this work we experimentally demonstrate 500 km unrepeatered transmission of a single-channel 100 Gb s−1 dual polarization quadrature phase shift keyed (DP-QPSK) signal. Such long distance transmission is achieved through the use of an advanced configuration of remotely pumped optical amplifiers (ROPAs), chromatic dispersion pre-compensation and ultra-low-loss Corning® SMF-28® ULL optical fiber. Excellent long-term bit error ratio (BER) performance is observed. To the best of our knowledge this is the longest unrepeatered 100 Gb s−1 transmission reported to date.

Comparison of Passive Chromatic Dispersion Compensation Techniques for Long Reach Dense WDM-PON System

The maximum reach of the DWDM-PON system can be severely limited by chromatic dispersion (CD). This paper contains the investigation of long-reach high speed 16-channel DWDM-PON system with efficient CD pre-compensation and post-compensation methods. It is shown that CD compensation has a crucial role for guaranteed downstream optical link performance and maximum link length of high speed long-reach DWDM-PON system. The results show that usage of additional 7 km long dispersion compensating fiber (DCF) placed in central office (pre-compensation configuration) improves the DWDM-PON network reach by 19.3% (from 57 km up to 68 km), but if additional 2 km long DCF fiber is used in remote terminal (post-compensation configuration) link length can be extended up to 5.3% (from 57 km to 60 km). It was found that usage of fiber Bragg grating (FBG) in central office (pre-compensation configuration) improves network reach up to 26.3% (from 57 km up to 72 km), but using this FBG for CD post-compensation in remote terminal network reach can be improved by 15.8% or 9 km in length – from 57 km to 66 km. Basis on the results authors recommend to use FBG as the best solution for CD compensation in pre-compensation configuration (before SMF line) in future high speed long-reach DWDM-PON systems.DOI: http://dx.doi.org/10.5755/j01.eee.122.6.1112

Joint nonlinearity and chromatic dispersion pre-compensation for coherent optical orthogonal frequency-division multiplexing systems

This paper introduces a joint nonlinearity and chromatic dispersion pre-compensation method for coherent optical orthogonal frequency-division multiplexing systems. The research results show that this method can reduce the walk-off effect and can therefore equalize the nonlinear impairments effectively. Compared with the only other existing nonlinearity pre-compensation method, the joint nonlinearity and chromatic dispersion pre-compensation method is not only suitable for low-dispersion optical orthogonal frequency-division multiplexing system, but also effective for high-dispersion optical orthogonal frequency-division multiplexing transmission system with higher input power but without optical dispersion compensation. The suggested solution does not increase computation complexity compared with only nonlinearity pre-compensation method. For 40 Gbit/s coherent optical orthogonal frequency-division multiplexing 20×80 km standard single-mode fibre system, the suggested method can improve the nonlinear threshold (for Q > 10 dB) about 2.7, 1.2 and 1.0 dB, and the maximum Q factor about 1.2, 0.4 and 0.3 dB, for 2, 8 and 16 ps/(nm·km) dispersion coefficients.

360-Gb/s Optical Transmitter With Arbitrary Modulation Format and Dispersion Precompensation

This letter introduces a versatile data-rate and modulation format transparent optical transmitter for 360-Gb/s transmission based on optical arbitrary waveform generation (OAWG) techniques. An experimental implementation of static OAWG, or line-by-line pulse shaping, with a silica arrayed-waveguide-grating pair waveform shaper, demonstrates creation of repetitive time-domain waveforms representing data packets in on-off keying and differential phase-shift-keying modulation formats with optional precompensation for fiber chromatic dispersion (CD). Transmission of repeated 9-bit 360-Gb/s data packets occupying 680 GHz of total optical bandwidth, with CD precompensation over a 10-km single-mode fiber link, indicates the potential for terabit-per-second operation. These data packets have a spectral efficiency of 0.53 b/s/Hz.