Duobinary Signal Research Articles

A Low BER DB-PAM4 Adaptive Equalizer for Large Channel Loss in Wireline Receivers

A high-speed serial interface is the core IP of a high-performance computer, data center and interconnection network; its bandwidth and bit error performance restrict the development of the system. With the evolution of high-speed serial interface line rates from 56 G to 112 G in high-end information systems, their bit errors increase sharply, limiting system performance. In order to solve the high-bit-error problem of the 112 Gb/s high-speed serial interface, this paper proposes a low-error Duo-binary PAM4 (DB-PAM) receive equalization technology. This technology utilizes the Duo-binary (DB) signal in which the channel and the transceiving equalizer work together to realize the low-error reception of the 112 Gb/s signal in the high-attenuation channel. To solve the problem of difficulty in generating high-speed DB-PAM4 signals and the complex adjustment of equalization parameters, this paper proposes a two-step progressive equalization technique. In the first step, the technology transmits not-return-to-zero (NRZ) signals at the transmitter (TX) and generates a Duo-binary (DB) signal path at the receiver using the least mean square error (LMS) algorithm. In the second step, the technology sends a precode-PAM4 (pre-PAM4) signal at TX; at the receiving end, the adaptive equalization algorithm is used to adjust the DSP equalization parameters to generate the optimal equalization parameters of the DB-PAM4 signal. This paper uses Cadence’s AMS simulation platform to verify the receive equalizer of DB-PAM4. Simulation results show: when a 112 Gb/s pre-PAM4 signal passes through the 35 dB@28 GHz channel, the receiver (RX) utilizes the adaptive equalizer to generate a 112 Gb/s DB-PAM4 signal, and the receiver bit error rate (BER) is less than 3e-9.

A 5 Gb/s Time-Interleaved Voltage-Mode Duobinary Encoding Scheme for 3-D-Stacked IC

A time-interleaved duobinary encoding scheme for the low-power high-bandwidth memory (HBM) I/O interface is proposed with a 65-nm CMOS process. To reduce power consumption in HBM I/O using multiple through-silicon via (TSV) I/Os, a transmitter (TX) that performs duobinary signaling with a voltage-mode driver is proposed. A small area encoder is implemented to generate duobinary output and an edge-boosted pre-driver is proposed to improve the slew rate and the robustness against the process, voltage, and temperature (PVT) variations of the duobinary voltage-mode driver. To convert the duobinary signal into a non-return-to-zero (NRZ) signal, a one-tap decision feedback equalizer (DFE) is used at the receiver (RX). NRZ signal conversion is proposed using one reference voltage and one PMOS switch to reduce the hardware complexity caused by additional reference voltages. An eight-stacked TSV is emulated in the 65-nm CMOS process, and the emulated capacitance of each stack is 100 fF. The energy efficiency of the proposed transceiver chip is 0.373 pJ/b/pF with a 2 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">7</sup> – 1 pseudorandom binary sequence at 5 Gb/s.

Using duobinary with first‐ and second‐order optical equalisers for extending transmission distance of optical access networks

This study presents the external modulation and direct detection of duobinary signal in optical access networks at 25 and 50 Gb/s with the use of first-order optical equaliser at the transmitter output (pre-equalisation) to compensate the waveform distortion induced by fibre dispersion. The first-order optical equaliser is then replaced by second-order optical equaliser to further improve the bit error rate (BER) performance and extend the maximum transmission distance by compensating the residual dispersion for the first time. The authors explain the enhancement in the BER by analysing the eye diagrams and optical spectra. The authors also investigate non-return-to-zero signal with similar setup parameters for reference.

Terabit Faster-Than-Nyquist PDM 16-QAM WDM Transmission With a Net Spectral Efficiency of 7.96 b/s/Hz

In this paper, we experimentally demonstrate a 1.28 Tb/s faster-than-Nyquist (FTN) wavelength division multiplexing (WDM) system with polarization division multiplexed (PDM) 16-ary quadrature amplitude modulation (16-QAM) signal and coherent detection. Note that intersymbol interference (ISI) and intercarrier interference (ICI) are two major problems in FTN-WDM systems. In our experiment, we use a digital brick-wall filter at the transmitter to reduce the signal bandwidth and fit the FTN-WDM channel spacing. In doing so, the ICI can be mostly suppressed when aggregating the WDM channels. The aggressive filtering induced ISI is compensated based on duobinary signal processing at the receiver. Through numerical simulation, we evaluate the robustness of the receiver-side duobinary signal processing against bandwidth truncation ratio of the digital brick-wall filter, the ICI from neighboring channels, and laser phase noise. The FTN WDM transmission is based on five-channel 32 Gbaud PDM 16-QAM signal with 29 GHz channel spacing. The gross data capacity is 1.28 Tb/s (5 × 256 Gb/s). After 80 km standard single-mode fiber transmission, the bit-error rates of the five WDM channels are all below than 7% hard-decision forward error correction threshold of 4.5 × 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-3</sup> . The net bit rate is 1.15 Tb/s and the net optical spectral efficiency achieves a record of 7.96 b/s/Hz for PDM 16-QAM format. To our best knowledge, our work is the first report of Terabit FTN-WDM system with high-order modulation of PDM 16-QAM signal.

Timing Recovery Algorithm Selection for Duo-Binary Signal Used in Next Generation 25G-EPON

Low complexity and effective symbol timing recovery (STR) algorithm is a serious challenge for high speed NG-EPON system with 25 Gb/s serial bit-rate per channel. In this paper, the frequently used nonlinear function based timing algorithms are compared in 25 Gb/s Duo-binary transmission system through simulation and experiment. Both simulation and experiment results show that absolute-law based STR (AL-STR) algorithm has minimum timing jitter and lowest computational complexity for Duo-binary receiver. The jitter of STR caused by the nonideal Duo-binary signal is also investigated by simulating different bandwidths of the commercial 10G optical devices. Results show that there are only little effect on STR performance when the –3 dB bandwidth changes from 6 to 8.75 GHz. Maximum likelihood sequence estimation (MLSE), linear and nonlinear equalizer are, respectively, performed after STR in 10G optics-based 25 Gb/s Duo-binary receiver. An optical power sensitivity of –25.6 dBm can be obtained with AL-STR and MLSE.

A 5.8-Gb/s Adaptive Integrating Duobinary DFE Receiver for Multi-Drop Memory Interface

This paper describes a 5.8 Gb/s adaptive integrating duobinary decision-feedback equalizer (DFE) for use in next-generation multi-drop memory interface. The proposed receiver combines traditional interface techniques like the integrated signaling and the duobinary signaling, in which the duobinary signal is generated by current integration in the receiver. It can address issues such as input data dependence during integration, need for precursor equalization, high equalizer gain boosting, and sensitivity to high-frequency noise. The proposed receiver also alleviates DFE critical timing to provide gain in speed, and embed DFE taps in duobinary decoding to provide gain in power and area. The adaptation for adjusting the equalizer common-mode level, duobinary zero level, tap coefficient values, and timing recovery is incorporated. The proposed DFE receiver was fabricated in a 45 nm CMOS process, whose measurement results indicated that it worked at 5.8 Gb/s speed in a four-drop channel configuration with seven slave ICs, and the bathtub curve shows 36% open for $10^{-10}$ bit error rate.

25Gbps 광 신호 전송을 위한 광 듀오바이너리 송신기 특성에 관한 연구

본 논문은 마크-젠더 변조기를 사용하여 광 신호를 생성하는 광 듀오바이너리 송신기들의 전송 특성을 이론적으로 분석하였다. 특히 단일 모드 광섬유를 통하여 분산 보상 방법에 대한 고려 없이 1550nm 파장에서 25Gbps 광 듀오바이너리 신호를 전송하는 여러 가지 형태의 송신기들에 대한 성능을 평가하였다. 각 송신기의 특성에 따라 광 듀오바이너리 신호 생성 방법이 다르기 때문에 광 파워 스펙트럼과 광 신호의 눈 열림에 특징이 있었으며 이로 인하여 전송 거리에 따른 분산 내성도 차이를 보였다. 모의실험 결과와 송신기 구조의 복잡성 및 제한 조건을 고려하여 25Gbps 전송에 적합한 송신기를 확인 할 수 있었다. This paper presents a theoretical study of transmission performance for optical duobinary transmitters employed a Mach-Zehnder modulator. Especially, we have investigated the performance of the various transmitters for transmitting 25Gbps optical duobinary signals at a wavelength of 1550nm without any dispersion compensation methods over single mode fiber. Due to the characteristics of generating their duobinary signals, each transmitter has a distinct optical power spectrum and an eye opening shape. By these, there was a difference in the dispersion tolerance. We could find a suitable transmitter for 25Gbps transmission considering the structure complexities and the restricted conditions with the simulation results.

Secure Duobinary Signal Transmission in Optical Communication Networks for High Performance &amp; Reliability

A numerical study is presented in this paper based on semiconductor laser chaos generation which is being used to hide multi-level data signal, i.e., duo-binary message to take the advantage of secure environment & higher data rates at the same time. Duobinary message is generated by using the combination of duobinary precoder, duobinary generator & RZ/NRZ pulse generator. Laser rate equations are used to model chaos generation through semiconductor laser whereas message is made secured by hiding it through chaos masking scheme. Propagation of chaos hiding the multi-format message is studied for long distance communication model. Synchronization between transmitter & receiver is achieved to obtain the acceptable eye-diagrams & quality factor (Q-factor). Q-factor is function of optical signal to noise ratio (OSNR) that gives a qualitative performance of receiver. It provides the minimum SNR to obtain specific bit error rate of signal. A comparison is made with & without deployment of chaos masking scheme on RZ & NRZ duobinary optical system to observe the penalty in terms of Q-factor. In addition, response of amplifier on chaotic signal due to its nonlinearities is investigated by varying the gain of amplifier.

10-Gbps optical duobinary signal generated by bandwidth-limited reflective semiconductor optical amplifier in colorless optical network units and compensated by fiber Bragg grating-based equalizer in optical line terminal

We propose a scheme of optical duobinary-modulated upstream transmission system for reflective semiconductor optical amplifier-based colorless optical network units in 10-Gbps wavelength-division multiplexed passive optical network (WDM-PON), where a fiber Bragg grating (FBG) is adopted as an optical equalizer for better performance. The demodulation module is extremely simple, only needing a binary intensity modulation direct detection receiver. A better received sensitivity of −16.98 dBm at bit rate error ( BER)=1.0×10 −4 can be achieved at 120 km without FBG, and the BER at the sensitivity of −18.49 dBm can be up to 2.1×10 −5 at the transmission distance of 160 km with FBG, which demonstrates the feasibility of our proposed scheme. Moreover, it could be a high cost-effectiveness scheme for WDM-PON in the future.

Research on Dispersion Compensation of 40 GB/s Optical Duo-Binary Coded Transmission System

A 40 Gb/s high speed optical transmission system is designed, and the different dispersion compensation schemes are adopted to realize the transmission of the optical duo-binary (ODB) signals over 120 km optical fiber. Optical duo-binary signals are generated by using a precoder, two low- pass filters (LPF) and one mach-zehnder modulator (MZM). Through combination of dispersion compensation fiber (DCF) and single mode fiber (SMF) in the transmission link, four different dispersion compensation schemes (pre-compensation, post-compensation and hybrid compensation (pre+ post) and hybrid compensation (post+ pre)) were compared. Analyzing Q factor, BER, eye diagrams and receiver sensitivity in several dispersion compensation schemes, the simulation results are: the cut-off frequency of LPF affects the transmission performance, and the hybrid compensation (post+ pre) scheme is the optimal dispersion compensation method.

Transmission of Duobinary Signal in Optical 40 GHz Millimeter-Wave Radio-Over-Fiber Systems Utilizing Dual-Arm LiNbO3 Mach–Zehnder Modulator for Downstream

AbstractIn this paper, for the first time transmission of 2.5 Gb/s duobinary signal is investigated for the downlink direction in 40 GHz optical millimeter-wave generation or up-conversion, utilizing a dual-arm

4 × 40-Gb/s TWDM PON downstream transmission over 42 km and 64-way power split using optical duobinary signals and an APD-based receiver.

We demonstrate downstream transmission of a four-channel 40-Gb/s-per-channel time- and wavelength-division-multiplexed PON over a 42-km, 64-split fiber plant using optical duobinary modulation. At 1550 nm, we obtain a reach of 0-26 km or 16-42 km using two dispersion-precompensation values.

28 Gb/s duobinary signal transmission over 40 km based on 10 GHz DML and PIN for 100 Gb/s PON.

In this paper, we demonstrate the direct modulation and direct detection of 28-Gb/s duobinary signal for the future downstream capacity upgrade in next generation passive optical network (PON). Commercial 10-GHz directly modulated laser (DML) and PIN with a combined modulation bandwidth of ~7 GHz are used as transmitter and receiver respectively. In order to mitigate the chromatic dispersion induced signal distortion, an optical delay interferometer (DI) is employed to narrow down the signal spectrum, thereby realizing 40-km single mode fiber (SMF) transmission in C-band. Besides, the chirp-induced spectral broadening of the directly modulated signal enables a higher launch power than external modulation schemes, which increases the loss budget of the system. As a result, 31-dB loss budget is achieved, supporting 64 users with 40-km reach. Also, as the transceivers in both optical line terminal (OLT) and optical network unit (ONU) are commercial l0-GHz devices, the proposed scheme is compatible with 40-Gb/s time and wavelength division multiplexing passive optical network (TWDM-PON) systems, providing a cost-efficient alternative for the development of 100G PON.

Comparison of Advanced Detection Techniques for QPSK Signals in Super-Nyquist WDM Systems

We compare the performance of detecting quadrature-phase-shift-keying (QPSK) in a super-Nyquist wavelength division multiplexing system as a QPSK and quadrature duobinary (QDB) signal using maximum likelihood sequence estimation (MLSE) and maximum a posteriori (MAP) criterion with both simulations and experiments. Three different detection schemes are studied: 1) QPSK detection with a multitap linear equalizer followed by a MLSE or MAP detector; 2) QPSK detection with only a MLSE or MAP detector; and 3) QDB detection with a MLSE or MAP detector, where a multitap linear equalizer and a delay-&-add operation are placed before the MLSE/MAP detector to convert a QPSK signal to a QDB signal. Our simulations and experiments show that the QDB detection with multitap MLSE does not provide better performance than that with two-tap MLSE, and the QDB detection with two-tap MLSE has better filtering tolerance than the QPSK detection with linear equalization followed by a multitap MLSE/MAP detector.

The generation of optical duobinary signal using electroabsorption modulator for optical access networks

We generate the duobinary signal by utilizing the intensity modulation characteristic of the electroabsorption modulator and the phase characteristic of phase shifter for the high-speed transmission system. In addition, compared to those commercial 10Gbps OOK modulators, lower cost, better performances and easier integration can be achieved by using these duobinary modulators.

Multichannel 25 Gb/s Low-Power Driver and Transimpedance Amplifier Integrated Circuits for 100 Gb/s Optical Links

Highly integrated electronic driver and receiver ICs with low-power consumption are essential for the development of cost-effective multichannel fiber-optic transceivers with small form factor. This paper presents the latest results of a two-channel 28 Gb/s driver array for optical duobinary modulation and a four-channel 25 Gb/s TIA array suited for both NRZ and optical duobinary detection. This paper demonstrated that 28 Gb/s duobinary signals can be efficiently generated on chip with a delay-and-add digital filter and that the driver power consumption can be significantly reduced by optimizing the drive impedance well above 50 Ω, without degrading the signal quality. To the best of our knowledge, this is the fastest modulator driver with on-chip duobinary encoding and precoding, consuming only 652 mW per channel at a differential output swing of 6 Vpp. The 4 × 25 Gb/s TIA shows a good sensitivity of -10.3 dBm average optical input power at 25 Gb/s for PRBS 2 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">31</sup> -1 and low power consumption of 77 mW per channel. Both ICs were developed in a 130 nm SiGe BiCMOS process.

A Low Power 2×28Gb/s Electroabsorption Modulator Driver Array with On-Chip Duobinary Encoding

An integrated 2×28Gb/s dual-channel duobinary driver IC is presented. Each channel has integrated coding blocks, transforming a non-return-to-zero input signal into a 3-level electrical duobinary signal to achieve an optical duobinary modulation. To the best of our knowledge this is the fastest modulator driver including on-chip duobinary encoding and precoding. Moreover, it only consumes 652mW per channel at a differential output swing of 6Vpp.

基于硅基微环的光双二进制

A silicon-based microring modulator and a narrow-band optical Gaussian filter were employed to generate optical duobinary at 10Gbit/s.Performance of the optical duobinary signal was analyzed in terms of laser linewidth,laser operating wavelength,fiber length,and filter bandwidth using Optisystem and Matlab.Simulation results show the optical duobinary signal is sensitive to laser linewidth and wavelength.At the BER of 10-9,the maximum transmission distance of the optical duobinary format can be up to 60km with the optimal Gaussian filter bandwidth of 8GHz.

基于硅基微环的光双二进制

A silicon-based microring modulator and a narrow-band optical Gaussian filter were employed to generate optical duobinary at 10Gbit/s.Performance of the optical duobinary signal was analyzed in terms of laser linewidth,laser operating wavelength,fiber length,and filter bandwidth using Optisystem and Matlab.Simulation results show the optical duobinary signal is sensitive to laser linewidth and wavelength.At the BER of 10-9,the maximum transmission distance of the optical duobinary format can be up to 60km with the optimal Gaussian filter bandwidth of 8GHz.

Improved Quadrature Duobinary System Performance Using Multi-Modulus Equalization

Quadrature duobinary (QDB) signals can be generated from strongly filtered quadrature phase shift keying whose constellation becomes a 9-ary quadrature amplitude modulation. In this letter, the performance of multi-modulus equalization (MMEQ) to suppress noise and crosstalk for this QDB signal is experimentally investigated and compared with that of the constant-modulus equalization (CMEQ) with post filtering, under different filter bandwidth and carrier spacing. The results show that the MMEQ scheme has better performance for noise and crosstalk suppression, resulting in improved filtering tolerance. This improved filtering tolerance is demonstrated in an 8-channel 112-Gb/s wavelength-division-multiplexing experiment with a 25-GHz grid over 2640-km single-mode fiber. Compared with the regular CMEQ with the post filtering scheme, 1-dB optical signal-to-noise ratio improvement at the bit-error-ratio (BER) of $1\times 10^{-3}$ and 32% increased transmission distance at the BER level of $3.8\times 10^{-3}$ for forward-error-correction are obtained for the MMEQ scheme.