Electrical Duobinary Research Articles

Experimental Study on 25 Gbps C-Band PON over up to 25 km SMF Using a 10G-Class DML + APD IM-DD System

In this paper we present an experimental analysis of several modulation formats (pulse amplitude modulation (PAM-2), quaternary pulse amplitude modulation (PAM-4) and electrical duobinary (EDB)) for passive optical network (PON) applications at 25 Gbps bit rate in a C-band 10G-class directly modulated lasers (DML) and avalanche photodiode (APD) intensity modulation and direct detection (IM-DD) system over a single mode fiber (SMF) of up to 25 km, optimizing DML operations and demonstrating that PAM-2 is a promising choice. We also theoretically and experimentally analyzed the channel frequency response of DML and SMF affected by DML chirp and SMF chromatic dispersion.

Optical Power Budget of 25+ Gbps IM/DD PON with Digital Signal Post-Equalization

While infrastructure providers are expanding their portfolio to offer sustainable solutions for beyond 10 Gbps in the access segment of optical networks, we experimentally compare several modulation format alternatives for future passive optical networks (PONs) aiming to deliver 25+ Gbps net-rates. As promising candidates, we consider the intensity modulation direct detection (IM/DD) schemes such as electrical duobinary (EDB) and 4-level and 8-level pulse amplitude modulations (PAM-4/8). They are more spectrally efficient than the conventional non-return-to-zero on-off-keying (NRZ-OOK) used in current 10G PONs. As we move to higher rates, digital equalization enhances the performance by smoothening the systems imperfection. However, the impact that such equalization has on the optical power budget remains unclear. Therefore, in this article, we fairly compare the optical power budget values of a time division multiplexed PON (TDM-PON) exploiting a linear digital signal equalization at the receiver side. We consider the conventional PON configuration (20 km of single-mode fiber (SMF), 1:N optical power splitting) with IM/DD and net-rates above 25 Gbps. Furthermore, we focus on a downstream transmission imposing the bandwidth limitations of 10G components using a digital filter before the detection. The obtained results show that the use of a digital post-equalization with 43 feed-forward (FF) and 21 feedback (FB) taps can significantly improve the signal quality enabling new alternatives and enhancing the optical power budget.

Optimization of Band-Limited DSP-Aided 25 and 50 Gb/s PON Using 10G-Class DML and APD

The increasing demand for network capacity is driving the development of next-generation high-speed Passive Optical Networks (PON) supporting 25 and 50 Gbps. One solution to reduce transceiver cost is reusing the 10G-class optical transmitter (including Directly Modulated Lasers, DML, in O-band) and receiver components in combination with Digital Signal Processing (DSP) techniques to compensate for bandwidth limitations. In this article, by means of both a set of laboratory experiments and a metropolitan field demonstrator, we discuss practical PON solutions at 25 and 50 Gbps per wavelength and per direction. In terms of modulation formats, we compare 2-level pulse amplitude modulation (PAM-2), 4-level PAM (PAM-4), and electrical duobinary (EDB) modulation formats, with feed-forward (FFE) and decision-feedback (DFE) adaptive equalizer at the receiver side. The novelty of our article is manifold. First, we present an optimization in terms of optical receiver band requirements for the 50 Gbps transmission. We show, by means of experimental measurements and numerical simulations, the minimum required bandwidth for DML laser and APD receiver (with appropriate DSP techniques) to realize next generation 25 and 50 Gbps PON transceivers. Second, we discuss also the upstream point of view, with a specific focus on DSP, and in particular, we propose an experimental solution based on a burst mode receiver with memory-aided DSP technique, together with a novel DSP approach to overcome the typical AC coupling distortion due to the burst mode scenario. Finally, we show a coexistence experiment between XGS-PON and 25 Gbps PON on an installed metropolitan field trial.

Experimental Demonstration of FTN-NRZ, PAM-4, and Duobinary Based on 10-Gbps Optics in 100G-EPON

This paper presents an experimental demonstration of 100-Gbps timeand wavelength-division multiplexed passive optical network (TWDM-PON) with 4 × 25-Gbps downstream transmission. We take a comparison of faster-than-Nyquist nonreturn-to-zero (FTN-NRZ), four-level pulse amplitude modulation (PAM-4), electrical duobinary (EDB), and optical duobinary (ODB) on the same transmission link. The use of low-cost 10-Gbps optics in combination with digital signal processing (DSP) makes it feasible for a 25-Gb/s per wavelength transmission over 20-km standard single-mode fiber (SSMF) in a cost-effective way. The spectra efficiency and ISI robustness by going to the higher rate are analyzed theoretically. We achieve link budgets of 33.18 dB for FTN-NRZ, and less than 30 dB budgets for PAM-4, ODB, and EDB in downstream transmission. FTN combination with feedforward equalization (FFE) allows FTN-NRZ to have a 4.18 dB margin in power requirement of PR(x) 30 of 10G-EPON, whereas PAM-4 and ODB with FFE also meet PR(x) 30 with 0.25 dB margin. The results indicate that FTN-NRZ, PAM-4, and ODB can be used for 100G-EPON with 10-Gbps optics, and FTN-NRZ has better performance than other modulations, which is more suitable for next-generation 100G-EPON transmission technique with low cost.

Experimental comparison of 28 Gb/s NRZ and EDB schemes for faster-than-Nyquist PON

In this paper, we experimentally demonstrate 28 Gb/s non-return-to-zero (NRZ) and electrical duo-binary (EDB) schemes over 25-km standard single-mode fiber transmission for faster-than-Nyquist passive optical network (FTN-PON). FTN signaling is a promising technology in the bandwidth-limited PON system. In order to improve the transmission performance, a combination of feed-forward equalization, post-filter and maximum likelihood sequence detection (FFE-MLSD) need to be employed for FTN-NRZ scheme, while only a simple 3-level FFE is needed for FTN-EDB scheme. The simulation results reveal that EDB scheme with 3-level FFE can transmit further fiber length compared with NRZ scheme at same receiver sensitivity. The experimental results show that EDB scheme achieves a power budget of 37.5 dB for 25-km fiber transmission with a pre-amplifier at the receiver, which is ~ 1.7 dB better than the best performance achieved by NRZ scheme. Meanwhile, the computational complexity of EDB scheme with 3-level FFE is 33.3 $$\%$$ lower than that of NRZ scheme based on FFE-MLSD. The EDB scheme with 3-level FFE shows the potential for the future FTN-PON.

Real-time 100 Gbps/λ/core NRZ and EDB IM/DD transmission over multicore fiber for intra-datacenter communication networks.

A BiCMOS chip-based real-time intensity modulation/direct detection spatial division multiplexing system is experimentally demonstrated for both optical interconnects. 100 Gbps/λ/core electrical duobinary (EDB) transmission over 1 km 7-core multicore fiber (MCF) is carried out, achieving KP4 forward error correction (FEC) limit (BER < 2E-4). Using optical dispersion compensation, 7 × 100 Gbps/λ/core transmission of both non-return-to-zero (NRZ) and EDB signals over 10 km MCF transmission is achieved with BER lower than 7% overhead hard-decision FEC limit (BER < 3.8E-3). The integrated low complexity transceiver IC and analog signal processing approach make such a system highly attractive for the high-speed intra-datacenter interconnects.

Upstream dispersion management of 25 Gb/s duobinary and PAM-4 signals to support 0–40 km differential reach

We extensively discuss 25 Gb/s per wavelength capacity in both IEEE and ITU-T standardization to support the increasing bandwidth requirement. In this Letter, we propose to use the optical dispersion compensation technique in an optical line terminal (OLT) combined with a bandwidth-limited electro-absorption modulated laser in an optical network unit to achieve 25 Gb/s capacity for the upstream link. We evaluate the positive and negative dispersion tolerances of 25 Gb/s electrical duo-binary (EDB) and pulse-amplitude modulation (PAM-4) signals. We achieve 39.5 and 31 dB upstream loss budgets for the 25 Gb/s EDB and PAM-4 signals by using −600 and −500 ps/nm optical dispersion compensation in OLT, respectively, both supporting 0–40 km differential reach.

40-Gb/s TDM-PON Downstream Link With Low-Cost EML Transmitter and APD-Based Electrical Duobinary Receiver

We report a cost-effective 40-Gb/s time-division multiplexing passive optical network downstream link using three-level electrical duobinary modulation. The transmitter consists of a compact electroabsorption-modulated laser module. The receiver contains an avalanche photodiode packaged with a transimpedance amplifier, with digitally adjustable gain and bandwidth, followed by a duobinary decoder. Real-time eye diagram and bit-error rate (BER) measurements were performed. At a preforward error correction BER of $10^{-3}$ , a power budget of 23.6 dB in back-to-back conditions is demonstrated. For a dispersion range of −215 to 128 ps/nm, the power penalty does not exceed 3 dB.

Optical Amplified 40-Gbps Symmetrical TDM-PON Using 10-Gbps Optics and DSP

We proposed and demonstrated a symmetrical 40-Gbps time division multiplexed passive optical network (TDM-PON) using low-cost 10-Gbps optical components in the optical network unit, optical amplification at the optical line terminal (OLT), and digital signal processing (DSP), based on four-level pulsed amplitude (PAM-4) modulation in the downstream and electrical duobinary (EDB) detection in the upstream. The use of 10-Gbps components in combination with DSP allows us to increase the serial bitrate beyond 10 Gbps for TDM-PON in a more cost-effective way. The reduced signal-to-noise ratio and the reduced dispersion tolerance by going to the higher rate were investigated for PAM-4 and EDB and optimized using DSP for PON applications. 33-dB power budget and 0–10 km range has been achieved for continuous-mode PAM-4 downstream transfer, and 29-dB power budget and 0–5 km range has been demonstrated for burst-mode EDB upstream transmission at 1537 nm. DSP, in the form of feedforward equalization and decision feedback equalization, compensated for the limited system bandwidth and significantly improved the 10-Gbps class receiver performance for 40 Gbps. Erbium doped fiber amplifiers (EDFAs) were used in the OLT as both booster and preamplifier. DSP techniques were applied to help recover the burst-mode upstream signal and effectively compensate for the amplitude transient effect from EDFAs.

Comparison of cost- and energy-efficient signal modulations for next generation passive optical networks.

Extensive numerical investigations are undertaken to analyze and compare, for the first time, the performance, techno-economy, and power consumption of three-level electrical Duobinary, optical Duobinary, and PAM-4 modulation formats as candidates for high-speed next-generation PONs supporting downstream 40 Gb/s per wavelength signal transmission over standard SMFs in C-band. Optimization of transceiver bandwidths are undertaken to show the feasibility of utilizing low-cost and band-limited components to support next-generation PON transmissions. The effect of electro-absorption modulator chirp is examined for electrical Duobinary and PAM-4. Electrical Duobinary and optical Duobinary are power-efficient schemes for smaller transmission distances of 10 km SMFs and optical Duobinary offers the best receiver sensitivity albeit with a relatively high transceiver cost. PAM-4 shows the best power budget and cost-efficiency for larger distances of around 20 km, although it consumes more power. Electrical Duobinary shows the best trade-off between performance, cost and power dissipation.

25-Gb/s TDM Optical Link Using EMLs for Mobile Fronthaul Network of LTE-A System

We propose and demonstrate a common public radio interface (CPRI)-compliant 25.2923-Gb/s mobile fronthaul network for long term evolution-advanced (LTE-A) systems. In order to meet the CPRI specifications and the stringent latency requirement of the LTE-A fronthaul network cost-effectively, we use the synchronous time-division-multiplexing, forward-error correction, and electrical equalization techniques. To enhance the cost-effectiveness, we also use an electroabsorption-modulated laser and exploit the possibility of using simple modulation formats such as the ON–OFF keying, electrical duobinary, and four-level pulse amplitude modulation. The performance of the proposed network is evaluated experimentally in terms of the tolerances to fiber dispersion and optical reflection.

Comparison of different feedback signals used in one stage PMD compensators for different modulation formats

As PMD compensation has become a very intense subject of research in recent years, the achievement of simple PMD compensators based on a feedback signal is a key issue. As PMD compensation uses a feedback indicator for system performance evaluation, such feedback signals must reproduce the DGD variations with time. In this paper, the correlation between DGD and different feedback signals is studied with a new method. This method is applied for various modulation schemes, leading to well-known results. By applying the method to the electrical and optical duobinary formats, it is shown that for duobinary signals, the DOP feedback signal shows the best correlation with instantaneous DGD value. Such a behavior of duobinary format is very interesting since duobinary modulation schemes are now considered for systems upgrades or mixed architectures (10 Gbit/s-40 Gbit/s on the same link). In such systems, PMD compensation has to be bit-rate independent which is available with the DOP as feedback indicator.

High-speed electrical backplane transmission using duobinary signaling

High-speed electrical data transmission through low-cost backplanes is a particularly challenging problem. We present for the first time a very effective approach that uses the concept of duobinary signaling to accomplish this task. Using a finite-impulse-response filter, we are able to compensate for the phase and amplitude response of the backplane such that the resulting frequency response of the channel is that of an ideal duobinary filter. At the output of the backplane, we use an innovative pseudodigital circuit to convert the electrical duobinary to binary. For 10-Gb/s data transmission, we demonstrate a bit error rate <10/sup -13/ through electrical backplane traces up to 34 in in length on FR4. A full discussion of the concept, system architecture, and measured results are presented. Analysis is presented that compares and contrasts this approach to PAM-4 and standard nonreturn-to-zero signaling.