Duobinary Transmission Research Articles

Half-Rate Duobinary Transmitter Architecture for Chip-to-Chip Interconnect Applications

For a high speed duobinary transmitter clock frequency defines the transmission limit. A conventional duobinary transmitter needs a clock frequency equal to the data rate. In this work we propose a duobinary transmitter that uses a clock frequency half of the output data rate and hence achieves double the transmission rate for a given clock frequency as compared to a conventional duobinary transmitter. In the proposed transmitter the duobinary precoder is integrated into the last stage of a tree structured serializer to combine two NRZ data streams at half the transmission data rate. Two modes for the precoder have been incorporated into the design. The first mode is applicable for data transmission over copper whereas the second mode is suitable for wavelength division multiplexed optical transmission. A DLL based clock multiplier unit is employed to produce the high frequency clock with 50% duty cycle needed for the precoding operation. It incorporates a clock generation logic with integrated duty cycle control. A charge pump with dynamic current matching and a high resolution PFD are employed to reduce static phase error in locking and hence achieves improved jitter performance. A new delay cell along with automatic mode selection is proposed. To cover a wide range of data rate, the DLL is designed for a wide locking range and maintains almost 50% duty cycle. The design is implemented in 1.8-V, 0.18 μm Digital CMOS technology with an f T of 27 GHz. Simulations shows that, the duobinary transmitter circuit works up-to 10 Gb/s and consumes 60 mW of power.

Dispersion Tolerance for Optical Duobinary Transmitters based on a Mach-Zehnder Modulator and an Optical Filter

We theoretically investigated dispersion tolerance of an optical duobinary transmitter employed a Mach-Zehnder modulator and an optical filter. Compared to the optical transmitter based on a Mach-Zehnder modulator and an optical delay interferometer by optimizing the applied voltage for improving the dispersion tolerance, the demonstrated duobinary transmitter provides improved receiver sensitivity and higher dispersion tolerance while maintaining narrow spectral bandwidth.

A Duobinary Signaling for Asymmetric Multi-Chip Communication

Duobinary signaling has been introduced into asymmetric multi-chip communications such as DRAM or display interfaces, which allows a controlled amount of ISI to reduce signaling bandwidth by 2/3. A x2 oversampled equalization has been developed to realize Duobinary signaling. Symbol-rate clock recovery form Duobinary signal has been developed to reduce power consumption for receivers. A Duobinary transmitter test chip was fabricated with 90-nm CMOS process. A 3.5dB increase in eye height and a 1.5 times increase in eye width was observed.

Active‐terminated transmitter and receiver circuits for high‐speed low‐swing duobinary signaling

SUMMARYIn this work, we propose transmitter and receiver circuits for high‐speed, low‐swing duobinary signaling over active‐terminated chip‐to‐chip interconnect. In active‐termination scheme port impedance of transmitter and receiver is matched with characteristic impedance of the interconnect. Elimination of the passive terminators helps in reducing the transmitted signal level without degrading the 0signal detectability of the receiver. High‐speed current‐mode receiver and transmitter circuits are designed, so that the input port impedance of the receiver and the output port impedance of the transmitter are matched with characteristic impedance of the link. These Tx–Rx pair is used to validate the proposed active‐termination scheme. We also propose a duobinary precoder architecture suitable for high‐speed operation and a low‐power broadband equalizer topology for compensating the lossy long interconnect. The duobinary transmitter and receiver circuits are implemented in 1.8 V, 0.18 µm Digital CMOS technology. The designed high‐speed duobinary Tx/Rx circuits work up to 8 Gb/s speed while transmitting the data over 29.5 in. FR4 PCB trace for a targeted bit error rate (BER) of 10−15. The power consumed in the transmitter and receiver circuits is 42.9 mW at 8 Gb/s. Copyright © 2010 John Wiley & Sons, Ltd.

Single-Sideband Differential Phase-Shift Keying Asynchronous Carrier-Suppressed Return-to-Zero – A Novel Signaling Format Optimized for Long-Haul UDWDM Systems

<para xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> In this paper, a novel single-sideband differential phase-shift keying asynchronous carrier-suppressed return-to-zero (SSB-DPSK-ACS-RZ) format is proposed for long-haul ultradense wavelength-division multiplexing (UDWDM) systems with 43 Gbit/s/channel and 50 GHz of channel spacing. The time delay between the DPSK and clock signals is optimized to achieve higher eye-opening and improved group velocity dispersion tolerance. Furthermore, the tight SSB filtering performed by the multiplexer is used to convert the DPSK-ACS-RZ signal from phase- to amplitude-shift keying, allowing using a lower-cost direct-detection receiver and improving its spectral efficiency. The single-channel and UDWDM transmission performance of the novel format is numerically investigated and compared to the SSB duobinary carrier-suppressed RZ, bandwidth-limited duobinary, phase-modulated duobinary transmission, and bandwidth-limited DPSK formats. The SSB-DPSK-ACS-RZ format shows similar Q-factor and tolerances to pre- and in-line dispersion compensations and fiber nonlinearity to the ones of other investigated direct-detection formats. Significant total residual dispersion tolerance improvement is achieved by the SSB-DPSK-ACS-RZ format relative to the other formats due to the signal chirp. Moreover, the SSB-DPSK-ACS-RZ format shows higher Q-factor than the one of the bandwidth-limited DPSK for long-haul UDWDM transmission systems. In ultra-long-haul UDWDM transmission systems, SSB-DPSK-ACS-RZ and bandwidth-limited DPSK formats show similar performance. </para>

Improved dispersion tolerance of an optical duobinary transmitter based on a Mach–Zehnder modulator and an optical delay interferometer

We present a method for improving the dispersion tolerance of an optical duobinary transmitter based on a dual-arm Mach–Zehnder (MZ) modulator and an optical delay interferometer without electrical low-pass filters. Since such a duobinary modulator using a standard 1-bit delay cannot provide high dispersion tolerance, we investigated the impact of the modulator driving voltages and the bit delay in the interferometer to improve the transmitter’s dispersion tolerance.

Performance Comparison of Duobinary Formats for 40-Gb/s and Mixed 10/40-Gb/s Long-Haul WDM Transmission on SSMF and LEAF Fibers

Duobinary formats are today considered as being one of the most promising cost-effective solutions for the deployment of 40-Gb/s technology on existing 10-Gb/s WDM long-haul transmission infrastructures. Various methods for generating duobinary formats have been developed in the past few years but to our knowledge their respective performances for 40-Gb/s WDM transmission have never been really compared. In this paper, we made an extensive numerical evaluation of the robustness of these different types of duobinary transmitter to accumulation of ASE noise, chromatic dispersion, PMD but also to single-channel and WDM 40-Gb/s transmission impairments on standard single-mode fiber. A numerical evaluation of the ability of duobinary format for mixed 10/40-Gb/s WDM long-haul transmission with 50-GHz channel spacing is also led, on both standard single-mode and LEAF fibers, and compared to DQPSK format. In order to clearly identify the limiting transmission effects on each of these two fiber types, the assessment of the performance of a 50-GHz spaced WDM 40-Gb/s long-haul transmission using either duobinary or DQPSK channels only is implemented at last.

Full C-Band Tunable DFB Laser Array Copackaged With InP Mach–Zehnder Modulator for DWDM Optical Communication Systems

We fabricated a compact 10-Gb/s-wavelength tunable laser module by integrating a tunable DFB laser array and an InP-based n-i-n Mach-Zehnder modulator in one package. We developed a multichip assembly technology to realize high optical coupling efficiency and achieved a continuous-wave output power of +6.5 dBm. We demonstrated a full C-band 10-Gb/s optical duobinary transmission with a constant modulation voltage of 2.4 V <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">pp</sub> . And we achieved a 200-km single-mode-fiber transmission with a power penalty of less than 1.0 dB over the entire C-band range.

39.4-Gb/s Duobinary Transmission Over 24.4 m of Coaxial Cable Using a Custom Indium Phosphide Duobinary-to-Binary Converter Integrated Circuit

We show, for the first time, duobinary transmission of 39.4-Gb/s data over a 24.4-m-long 5.2-mm-diameter coaxial cable with SMA connectors, enabled by the design of a custom 40-Gb/s HBT indium phosphide duobinary-to-binary converter integrated circuit (IC). We achieve a bit error rate better than 3 times 10-12 with a 215- 1 b sequence, using clock recovery. The transmission experiment and design of the duobinary-to-binary converter IC are discussed in detail.

Performance Analysis of Optical Transmitters with the Non-ideal Mach-Zehnder Modulator

This paper presents the performance analysis of 10[Gb/s] optical duobinary transmitters with the non-ideal Mach-Zehnder modulator which does not have exactly 50/50 splitting/combining ratios by computer-simulations. For driving voltage ratios(=driving voltage/switching voltage) with smaller than 100[%], the transmission performance has been greatly affected by extension of LPF bandwidths. Nevenheless, the performance has been degraded when the driving voltage ratio is 100[%]. The smaller driving voltage ratios has, the more sensitivity improves by extension of LPF bandwidths under the asymmetry condition. But the driving voltage ratio with 80[%] has better bit error rate(BER) than those with 50[%] and 25[%].

Partial bit delay correlative modulation used to improve the dispersion tolerance of an optical duobinary system

Phase effect of the optical duobinary (ODB) modulation on the chromatic dispersion (CD) tolerance is more important than the ODB modulation-induced bandwidth effect. To show this, we evaluate, respectively, the filter bandwidth effect and the phase effect of the partial bit delay correlative modulation (PBDCM) on the CD tolerance. Due to the cancellation between the CD-induced and the PBDCM-induced phase effects, the PBDCM method can increase the CD-limited transmission to 2 ??? 3 times of that using standard 1-bit delay modulation, while the optimized filter bandwidth method can increase the transmission by 50% or less, depending on the input signal format. The PBDCM can be physically realized by adjusting the delay time of the delay-and-add circuit in the conventional duobinary transmitter (without lower-pass filter). These conclusions are also valid for systems having non-negligible polarization-mode dispersion (PMD) and polarization dependent loss (PDL).

20-Gb/s PolDM Duobinary Transmission Over 350-km SSMF Supported by a Polarization Stabilizer and an Optical Dispersion Compensator

A 20-Gb/s transmission over 350-km standard single-mode fiber exploiting duobinary dispersion robustness and polarization-division multiplexing has been demonstrated. The system performance is evaluated employing an automatic endless polarization stabilizer and a suitably designed transmitter-side optical dispersion compensator.

Asymmetry Effects on Optical Duobinary Transmitters

We have theoretically investigated the asymmetry effects on 10[Gb/s] optical duobinary transmitters from the viewpoint of the driving voltage ratios by computer simulations. For driving voltage ratiost(=driving voltage/switching voltage) with smaller than 100[%], the transmission performance has been greatly affected by the asymmetry of the bandwidth of LPFs than that of the Mach-Zehnder Modulator driving voltage. On the other hand, for driving voltage ratios with 100[%], the transmission performance has been degraded by the asymmetry of the driving voltage and is not sensitive to that of the bandwidth of LPFs. For the transmission performance within 1[dB] power penalty under the asymmetry condition, the driving voltage ratio with 100[%] has performed better than the low driving voltage ratios.

Pattern dependency comparison of four different 40-Gb/s optical duobinary transmitters using low-bandwidth modulators

We investigate the pattern dependency of the 40-Gb/s optical duobinary signals generated by a 10-Gb/s-rated Mach–Zehnder modulator with four different configurations. These configurations correspond to all possible combinations of a 15-GHz-bandwidth low-pass filter and a 0.24-nm bandwidth optical filter used to shape up the duobinary signals. We compare through experiment the back-to-back sensitivities and transmission performances of the duobinary signals for pseudorandom bit sequence lengths of 2 7–1 and 2 31–1. The results show that the combination of the 10-Gb/s-rated modulator and the 0.24-nm optical filter exhibits the best performance in terms of both the receiver sensitivity and pattern dependency owing to the good frequency response of the optical filter.

Comparison of RZ Versus NRZ Pulse Shapes for Optical Duobinary Transmission

This paper presents an experimental study and comparison of return-to-zero (RZ) versus nonreturn-to-zero (NRZ) pulse shapes for optical duobinary systems. Surprisingly, and contrary to the case of on-off keying, we find the NRZ pulse shape to be superior, compared with RZ, for duobinary transmission in all the cases that were studied, including systems that are limited by amplified-spontaneous-emission noise, fiber chromatic dispersion, and self-phase modulation.

Tailoring the Electrooptic Response and Improving the Performance of Integrated $\hbox{LiNbO}_{3}$ Modulators by Domain Engineering

Domain inversion (DI) is applied to traveling-wave integrated electrooptic (EO) LiNbO3 modulators to achieve predefined EO frequency response and improved performance with respect to standard single-domain (not domain-inverted) counterparts, including lower driving voltages and larger modulation bandwidths. In particular, when an appropriate poling (DI) is performed along the interaction length, two novel configurations are envisaged. 1) An apodised longitudinal poling profile is used in non-velocity-matched (NVM) modulators to achieve a desired EO response, such as amplitude modulation with intrinsic third-order Bessel-type optical filtering for duobinary transmission. 2) Two- section longitudinal poling is used to counteract the detrimental microwave loss effect in VM modulators and to increase the bandwidth to driving voltage ratio, achieving a value up to 50% larger than that of single-domain (unpoled) structure.

Effects of filter bandwidth and driving voltage on optical duobinary transmission systems

This work demonstrates how electrical driving voltage of a Mach–Zehnder modulator and the bandwidth of electrical low-pass filters (LPFs) affect optical duobinary signals. The fact that a 100% driving voltage does not necessarily yield optimal results in duobinary systems is established both numerically and experimentally. Various filter bandwidths correspond to respective optimum driving voltages. In a 10 Gbps duobinary system, compared with the conventional condition of using a 2.5 GHz electrical LPF, a 2.5 dB sensitivity improvement is obtained by employing a 3 GHz LPF with an 88% driving voltage of fully driving.

Chirp-Managed Directly-Modulated DFB Laser

We review recent patents on a chirp managed transmitter comprised of a DML and the subsequent optical bandpass filter. Large dispersion tolerance of this transmitter is realized by chirp control through the phase correlation between adjacent bits for the destructive interference in order to erase the power of “0” bits and enhance the extinction ratio. The reach of this transmitter without dispersion compensation is superior to the best reported DML-based and duobinary transmitters. The results show that this is a promising solution to meet the size, power, capacity and cost requirements of the optical links simultaneously in the today and tomorrows metro and access networks. Keywords: External modulator, directed modulated laser, dispersion compensation, distributed feedback laser, chirp, optical fiber, metro optical network, long haul optical network, single mode fiber, telecommunication

Impact of uncompensated dispersion on non-Gaussian statistics in duobinary transmission

We show through numerical simulation of 10.7- Gbits/s dense wavelength-division multiplexed DWDM duobinary transmission over 800 km of nonzero-dispersion- shifted fiber that uncompensated dispersion can introduce significant departures from Gaussian statistics in the re- ceiver current. © 2007 Society of Photo-Optical Instrumentation Engineers.

Dispersion-tolerant 10-gb/s duobinary system employing heterodyne detection and MLSE

We experimentally demonstrate a 10.7-Gb/s duobinary transmission system operating over a chromatic-dispersion range of /spl sim/12 000 ps/nm. Heterodyne detection and maximum-likelihood sequence estimation are employed to achieve this result.