Optical Duobinary Signals Research Articles

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.

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.

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.

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.

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.

Optical Duobinary Modulation

Optical duobinary signal has narrow spectrum, tolerance to chromatic dispersion, and resistance to filter distortion. With many early patents from different organizations, optical duobinary modulation was actually invented earlier and described in a thesis by L. C. Blank. The later development of optical duobinary modulation is reviewed, including its applications for retrofitting 40-Gb/s signal into existing 10-Gb/s fiber networks. Keywords: 40 Gb/s, duobinary modulation, fiber communication, lightwave communication, optical networking, wavelength division multiplexing

High-Speed, Low-Driving-Voltage Dual-Drive InP-Based Mach-Zehnder Modulator

We present a dual traveling-wave electrode InP-based Mach-Zehnder (MZ) modulator with an n-i-n waveguide structure. An electrical input/output interface placed on one side of the chip helps us to drive the modulator in a push-pull configuration. This configuration provides the modulator with great advantages such as reduced driving voltage amplitude, chirp-free operation, and the ability to support advanced modulation formats. The fabricated modulator exhibits good performance. A 40Gb/s non-return-to-zero (NRZ) signal is successfully generated with a low driving of 1.3Vpp. In addition, a 10-Gb/s optical duobinary (DB) signal is successfully generated and transmitted over a 240-km single-mode fiber (SMF). We also developed a wavelength tunable transmitter hybrid integrated with a modulator with a wavelength tunable laser. Full C-band 10-Gb/s operation and a 100-km SMF transmission with a low power penalty are confirmed.

107 Gb/s uncompensated transmission over a 470 km hybrid fiber link with in-line SOAs using MLSE and duobinary signals

We experimentally demonstrate uncompensated 8-channel wavelength division multiplexing (WDM) and single channel transmission at 10.7 Gb/s over a 470 km hybrid fiber link with in-line semiconductor optical amplifiers (SOAs). Two different forms of the duobinary modulation format are investigated and compared. Maximum Likelihood Sequence Estimation (MLSE) receiver technology is found to significantly mitigate nonlinear effects from the SOAs and to enable the long transmission, especially for optical duobinary signals derived from differential phase shift keying (DPSK) signals directly detected after narrowband optical filter demodulation. The MLSE also helps to compensate for a non-optimal Fabry-Perot optical filter demodulator.

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.

Surface Mountable 10-Gb/s InP Mach–Zehnder Modulator Module for SFF Transponder

We have developed a small, surface mountable InP-based Mach-Zehnder modulator module. New designs for the electrical ports enable the modulator to be directly mounted on a printed circuit board. We demonstrated a 100-km transmission through single-mode fiber with a 10-Gb/s nonreturn-to-zero signal and a 220-km transmission with a 10-Gb/s optical duobinary signal to confirm the applicability of this device as an ultralong-haul small form factor transponder.

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.

Can 40-gb/s duobinary signals be carried over transparent DWDM systems with 50-GHz channel spacing?

The feasibility of transmitting 40-Gb/s optical duobinary signals over transparent dense wavelength-division-multiplexed (DWDM) systems with a 50-GHz channel spacing and multiple optical add-drop multiplexers (OADMs) is investigated. While the duobinary format is tolerant to passband narrowing, from concatenated filtering by the OADMs, it is very sensitive to the group-delay ripple (GDR) associated with this filtering. We show that GDR must be carefully controlled, e.g., by GDR compensation, before 40-Gb/s duobinary signals can be effectively used in DWDM systems originally designed for 10-Gb/s traffic.

Maximum-likelihood optimal-sampling-phase estimation for ultra-high-sensitivity optically preamplified duobinary receivers

This paper describes the demonstration of a novel method for detecting optical duobinary signals. Oversampling in combination with maximum-likelihood estimation-based data processing of the optical-to-electronic converted signal results in a record sensitivity for an optically preamplified receiver. The concept is investigated at 10 Gb/s and allows data recovery at bit-error rates of 1/spl times/10/sup -9/ and 1/spl times/10/sup -3/ with a receiver sensitivity of better than -39.5 dBm and an optical signal-to-noise ratio (OSNR) of only 7.8 dB, respectively.

On the Use of 2.5-Gb/s Mach–Zehnder Modulators to Generate 10-Gb/s Optical Duobinary Signals

We demonstrate the generation of 10-Gb/s optical duobinary signals from 2.5-Gb/s Mach-Zehnder (MZ) modulators without using duobinary encoders. The absence of the duobinary encoder not only permits the monolithic integration of electrical components but also reduces the required bandwidth of MZ modulators as low as 3 GHz. However, it might induce pattern-length dependency to the signals. Our demonstration, performed with four 2.5-Gb/s MZ modulators obtained from two different vendors, shows that the receiver sensitivity of better than -33.8 dBm is achieved at a pseudorandom bit sequence length of 2/sup 31/-1 when dispersion of 1200 /spl sim/ 1700 ps/nm is applied to the signals. This is 1.6 dB poorer than using an 8.5-GHz bandwidth MZ modulator along with a 3.0-GHz Bessel filter. Therefore, this scheme can be used to implement cost-effective 10-Gb/s optical duobinary transmitters without significant performance degradation.

A Novel 10-Gb/s Duobinary Receiver With Improved Back-to-Back Performance and Large Chromatic Dispersion Tolerance

We demonstrate a receiver, which improves the back-to-back (b-t-b) performance of optical duobinary signals at 10 Gb/s. The required optical signal-to-noise ratio for a bit-error rate of 1/spl times/10/sup -3/ was found to be as low as 10.8 dB in b-t-b operation. We tested the receiver with two commercially available 10-Gb/s duobinary transmitter samples. Excellent chromatic dispersion tolerance was maintained with the novel receiver design.

SSB direct detection scheme in duobinary-carrier-suppressed RZ transmission

A new transmission scheme is proposed that will expand chromatic dispersion tolerance using a novel single-sideband (SSB) direct detection technique. The technique converts a duobinary-carrier-suppressed return-to-zero signal to an optical duobinary signal using spectral filtering in an optical receiver. Enlargement, by both transmission experiment at 43-Gbit/s and numerical simulations, is confirmed.

Signal Shaping for Optical Wideband Transmission Systems Using the Inherent Lowpass Behaviour of Counterpropagating Optical and Electrical Signals in a LiNbO3 Mach-Zehnder Modulator

A new method for signal shaping in optical wideband transmission systems is proposed. Instead of building external electrical filters for spectral shaping of the modulating signal the inherent lowpass property of counterpropagating optical and electrical signals in a LiNbO 3 Mach-Zehnder intensity modulator is used. The presented experimental results for the generating of optical duobinary signals indicate the usefulness of this method.

Receiver optimization for 40-Gb/s optical duobinary signal

The optimized optical receiver for a 40-Gb/s optical duobinary signal is investigated by simulation. It is found, that by optimizing the optical filter and the electrical filter in the receiver, the sensitivity of the optical duobinary can be improved greatly; meanwhile, the high dispersion tolerance nature of the optical duobinary signal will not be degraded.