Dispersion Tolerance Research Articles

Four-amplitude shift keying-single sideband millimeter-wave signal generation with frequency sextupling based on optical phase modulation

We have proposed and demonstrated a scheme to generate a frequency-sextupling amplitude shift keying (ASK)-single sideband optical millimeter (mm)-wave signal with high dispersion tolerance based on an optical phase modulator (PM) by ably using the−4th-order and +2nd-order sidebands of the optical modulation. The ASK radio frequency signal, superposed by a local oscillator with the same frequency, modulates the lightwave via an optical PM with proper voltage amplitudes, the +2nd-order sideband carries the ASK signal with a constant slope while the −4th-order sideband maintains constant amplitude. These two sidebands can be abstracted by a wavelength selective switch to form a dual-tone optical mm-wave with only one tone carrying the ASK signal. As only one tone bears the ASK signal while the other tone is unmodulated, the generated dual-tone optical mm-wave signal has high dispersion tolerance.

Precoded APPM Modulated Short Reach Optical System Based on Two-Dimensional Cyclic Iterative Coding

This paper proposes and demonstrates a novel coded amplitude and pulse position modulation (APPM) scheme based on 2-D cyclic iterative coding (TDCIC) for short-reach optical systems. By adopting the precoding, better performance can be obtained because of the bits correlation. An experiment with 150-Gb/s TDCIC coded APPM signal is successfully reached after 22.5-km transmission. The demonstration also shows that the precoded APPM format provides superior performances to the conventional APPM and pulse amplitude modulation formats on chromatic dispersion tolerance and launched optical power.

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.

Dispersion and rheological behaviors of laponite in 2-acrylamido-2-methylpropanesulfonic acid solution

Previous studies of Laponite (Lap) in electrolyte solution have revealed a fast aggregation or gelation due to reduced electrostatic repulsion between Lap layers. In this work, the dispersion and stability of Lap in 2-acrylamido-2-methylpropanesulfonic acid (AMPS) solution were explored. Lap in low concentration of AMPS (<2.0wt%) were likely to generate aggregation because the formation of electrostatic bonds. In high concentration of AMPS (≥2.0wt%), Lap layers were gradually damaged due to the leaching out of magnesium ions and more likely converted into amorphous silica. So the mutual attraction force between particles was weakened and the phenomenon of aggregation gradually disappeared. However, aging process may convert a well-dispersed fluid into a gel due to electrostatic interaction between sulfonate groups of AMPS absorbed onto Lap and magnesium ions leached out from Lap when the concentration of AMPS range from 2.0wt% to 5.0wt%. Besides, rheological tests indicated that Lap/AMPS dispersions changed from pseudoplastic fluids to Newton fluids as the concentration of AMPS increased to 6.0wt%. The addition of AMPS could also improve the salt tolerance of Lap dispersion.

NRZ versus RZ over Absolute Added Correlative coding in optical metro-access networks

This paper comparatively investigates the transmission performance of absolute added correlative coding (AACC) using non-return-to-zero (NRZ) and return-to-zero (RZ) pulse shapes with a binary intensity modulation direct detection receiver in 40Gb/s optical metro-access networks operating at 1550nm. It is shown that, for AACC transmission, the NRZ impulse shaping is superior in comparison to RZ in spectral efficiency, dispersion tolerance, residual dispersion and self-phase modulation (SPM) tolerance. However, RZ-AACC experiences a ~1–2dB advantage in receiver sensitivity over NRZ-AACC for back-to-back configuration as well as after 300-km single-mode fiber delivery.

Comparison Study of Long-haul 100-Gb/s DDO-OFDM and CO-OFDM WDM Systems

In this paper, for the first time, the transmission performances of long-haul 100-Gb/s direct detection optical OFDM (DDO-OFDM) and coherent optical OFDM (CO-OFDM) wavelength division multiplexing (WDM) systems are compared by simulation. It provides specific guides for system parameter selection to get a high-performance and cost-effective OFDM WDM system. Specifically, the comparison involves three aspects: launched power is investigated to achieve better system performance; laser linewidth is numerically investigated to choose cost-effective laser; system dispersion tolerances with different laser linewidths are analyzed to further reveal the advantages and disadvantages of these two detecting methods, direct detection and coherent detection, in long-haul OFDM WDM system.

Evaluation of Real-Time 8 × 56.25 Gb/s (400G) PAM-4 for Inter-Data Center Application Over 80 km of SSMF at 1550 nm

Leveraging client optics based on intensity modulation and direct detection for point-to-point inter-data center interconnect applications is a cost and power efficient solution, but challenging in terms of optical signal-to-noise ratio requirements and chromatic dispersion tolerance. In this paper, real-time 8 × 28.125 GBd dense wavelength division multiplexing four-level pulse amplitude modulation (PAM-4) transmission over up to 80 km standard single mode fiber in the C-Band is demonstrated. Using a combination of optical dispersion compensation and electronic equalization, results below a bit error rate of 1e−6 are achieved and indicate sufficient margin to transmit over even longer distances, if an forward error correction (FEC) threshold of 3.8e-3 is assumed. Moreover, single channel 28.125 GBd PAM-4 is evaluated against optical effects such as optical bandwidth limitations, chromatic dispersion tolerance, and optical amplified spontaneous emission noise.

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.

Research on Transmission Performance of Different Modulation Formats Based on Re-modulation WDM-PON

Abstract Dispersion and nonlinear effects will increase the effect on the system when the optical information transmits in high speed and long distance. The new optical modulation technology can reduce the attenuation caused by transmission procedure. In this paper, OptiSystem and Matlab were combined to set a model by comparing the dispersion tolerance and nonlinear effect of different code modulation formats. After that, the better performance code of IRZ (Inverse Return-to-Zero) and DQPSK (Differential Quadrature Phase Shifted Keying) will be used to study their properties in 10Gbit/s re-modulation WDM-PON access model. The DQPSK was used in downlink, IRZ modulation was used in uplink adopts the IRZ modulation was used in 10 Gbit/s re-modulation WDM passive optical network access model uplink on the basis of the above method. A simulation analysis is also made between the different duty ratios of the DQPSK and IRZ. Compared with the NRZ type, the IRZ has a better anti-dispersion property, channel crosstalk suppression ability and higher spectrum efficiency although it costs 3 dB powers. At the same time, it simplifies the structure of the ONU on the premise of not increasing the power and the cost. So, it fits the large capacity requirements between user stations and the central office in the future.

Silicon Microring Modulator for Dispersion Uncompensated Transmission Applications

We report an investigation of the negative-chirp characteristics of an overcoupled silicon microring modulator with carrier-depletion p-n junction for 10-Gb/s transmission over single-mode fiber up to distances of 100 km. The modulator exhibits over 15 dB extinction ratio for an approximately 5 V peak-to-peak driving voltage. The on/off chirp α -parameter is estimated to be less than −1 for an optimally designed device. This negative chirp leads to a robust dispersion tolerance which is verified by bit error rate measurements. The results show that the device can support transmission with a negative power penalty up to 50 km, while the power penalty at 100 km is as low as 2.5 dB.

Assessment of absolute added correlative coding in optical intensity modulation and direct detection channels

The performance of absolute added correlative coding (AACC) modulation format with direct detection has been numerically and analytically reported, targeting metro data center interconnects. Hereby, the focus lies on the performance of the bit error rate, noise contributions, spectral efficiency, and chromatic dispersion tolerance. The signal space model of AACC, where the average electrical and optical power expressions are derived for the first time, is also delineated. The proposed modulation format was also compared to other well-known signaling, such as on-off-keying (OOK) and four-level pulse–amplitude modulation, at the same bit rate in a directly modulated vertical-cavity surface-emitting laser-based transmission system. The comparison results show a clear advantage of AACC in achieving longer fiber delivery distance due to the higher dispersion tolerance.

Polarization division multiplexed-duobinary modulation format for long-reach passive optical network

We propose and demonstrate the increased dispersion tolerance with an improvement in spectral efficiency for long reach passive optical networks, with the use of polarization division multiplexing (PDM) and optical duobinary (ODB) modulation format. We investigate the stimulated Brillouin scattering threshold for data in PDM–ODB format through experiments. Improvement in power budget with PDM ODB format is demonstrated experimentally.

System Performance and Limits of Optical Modulation Formats in Dense Wavelength Division Multiplexing Systems

In this paper we investigate in OptSim software environment the system performance of intensity and phase modulation formats for different network scenarios and dense wavelength division multiplexing grids. OptSim employs the Time Domain Split Step method to implement the signal distribution equation in a fiber. We investigate intensity formats, such as Non Return to Zero, Return to Zero, Carrier-Suppressed Return to Zero and DuoBinary, and phase modulation formats like Differential Phase-Shift Keying and Differential Quadrature Phase-Shift Keying. The main goal is to compare these formats in terms of bit error rate, Q-factor, optical reach and grid limitations for transmission rates 10, 40 and 100 Gbps per channel and discuss the possibilities of increasing their spectral efficiency. We also focus on other advanced solutions such as the polarization division multiplexing combined with phase modulations, coherent detection and advanced digital signal processing which mainly benefits in spectral efficiency, optical signal to noise ratio and chromatic dispersion tolerances. DOI: http://dx.doi.org/10.5755/j01.eie.22.2.9599

Equalization of Dispersion-Induced Crosstalk in Optical Offset-QAM OFDM Systems

In discrete-Fourier-transform-based offset quadrature amplitude modulation (QAM) orthogonal frequency division multiplexing (OFDM), the orthogonality between the inter-carrier interference (ICI) and the signal is broken as dispersion increases, which in turn limits the dispersion tolerance. The ICI on a subcarrier is only from its adjacent two subcarriers, but its influence depends on the frequency of the subcarrier. We find that it is the high-frequency subcarriers that limit the dispersion tolerance and thus propose to equalize these dominant subcarriers to improve the performance. Simulations of 112-Gb/s offset-4QAM and 224-Gb/s offset-16QAM OFDM are performed to verify the analysis. We also experimentally demonstrate the transmission of a 38-Gb/s offset-16QAM OFDM signal over 1200-km single-mode fiber without cyclic prefix (CP). The bit error rate (BER) is reduced from $10^{-3}$ to $10^{-4}$ at $\sim 16$ -dB optical signal to noise ratio by equalizing only the high frequency half of the subcarriers. This is in contrast to conventional OFDM which cannot realize a BER of $10^{-3}$ at 400 km when CP is not applied.

Investigations of high-speed optical transmission systems employing Absolute Added Correlative Coding (AACC)

A novel multilevel modulation format based on partial-response signaling called Absolute Added Correlative Coding (AACC) is proposed and numerically demonstrated for high-speed fiber-optic communication systems. A bit error rate (BER) estimation model for the proposed multilevel format has also been developed. The performance of AACC is examined and compared against other prevailing On–Off-Keying and multilevel modulation formats e.g. non-return-to-zero (NRZ), 50% return-to-zero (RZ), 67% carrier-suppressed return-to-zero (CS-RZ), duobinary and four-level pulse-amplitude modulation (4-PAM) in terms of receiver sensitivity, spectral efficiency and dispersion tolerance. Calculated receiver sensitivity at a BER of 10−9 and chromatic dispersion tolerance of the proposed system are ∼−28.3 dBm and ∼336 ps/nm, respectively. The performance of AACC is delineated to be improved by 7.8 dB in terms of receiver sensitivity compared to 4-PAM in back-to-back scenario. The comparison results also show a clear advantage of AACC in achieving longer fiber transmission distance due to the higher dispersion tolerance in optical access networks.

Symmetrical 25-Gb/s TDM-PON With 31.5-dB Optical Power Budget Using Only Off-the-Shelf 10-Gb/s Optical Components

Increasing the serial bitrate beyond 10 Gb/s in time division multiplexed passive optical network (TDM-PON) is difficult. The reduced chromatic dispersion tolerance and the reduced signal-to-noise ratio's at higher rates make it much more challenging to achieve the needed optical power budget, especially in a cost-effective way. To combat these challenges, we investigated and demonstrated a 25-Gb/s TDM-PON, with optical amplification at the optical line termination (OLT), based on PAM-4 modulation in the downstream and Duobinary modulation in the upstream. Described in this paper is a first demonstration of a symmetrical 25-Gb/s TDM-PON with 31.5-dB class N2 power budget over 0–20 km at 1556 nm using only cost-effective off-the-shelf 10-Gb/s optical components at the ONU and OLT side. We used small form factor erbium doped fiber amplifiers as booster and preamplifier at the OLT. We also applied low-cost dispersion compensating schemes to increase chromatic dispersion tolerance, a simple predistortion scheme based on optimization of electroabsorption modulated laser bias voltage and a simple fiber dispersion supported transmission scheme. We obtained a power budget of 31.5 dB with 0–20 km of standard single mode fiber, which we doubled to 0–40 km using dispersion compensating fiber at 1556 nm (BER = 10 −3).

Simulation and Analysis of Radio over Fiber (RoF) Systems using Frequency Up-Conversion Technique

Radio-over-Fiber (RoF) technology is an integration of microwave and optical networks [1]. RoF technology uses optical fiber as a backend technology due to the enormous advantages offered by it. SCM-WDM RoF systems (Subcarrier based Wavelength division multiplexing RoF system) improves spectral efficiency with high dispersion tolerance [7]. The data to be transmitted is electrically modulated with an IF (Intermediate frequency)or a RF (Radio frequency) carrier and electrically multiplexed using a multiplexer these signals are further optically modulated using an optical modulator and multiplexed using WDM to exploit the high bandwidth offered by the optical fiber. A comparison between IF over fiber and RF over has been analyzed in terms of quality factor and BER (Bit error rate) in a RoF system. In which the IF over fiber shows better performance than RF over fiber in terms of BER and Quality factor. IF signals are up-converted using HBT (Hetero-junction bipolar transistor) electronic mixer in the remote antenna units to the RF frequencies with the help of LO (local oscillator) and transmitted wirelessly [27]. General Terms Wireless communication systems, Optical fiber communication, Subcarrier multiplexing, Wavelength division multiplexing, Radio-over fiber systems.

Q-factor analysis of nonlinear impairments in ultrahigh-speed Nyquist pulse transmission.

We present detailed analytical and numerical results of the dispersion and nonlinear tolerances of RZ and Nyquist optical pulses in ultrahigh-speed TDM transmissions. From a Q-map analysis, i.e. by numerically calculating the Q-factor distribution as a function of transmission power and fiber dispersion, we found that Nyquist TDM transmission has a substantially larger Q margin as regards both dispersion and optical power thanks to ISI-free overlapped TDM. We also show that the optimum transmission power for Nyquist pulses is 2 dB lower than for RZ pulses. An analytical model is provided to explain the overlap-induced nonlinear impairments in Nyquist TDM transmission in a high power regime, which agrees well with numerical results.

All optical up-converted signal generation with high dispersion tolerance using frequency quadrupling technique for radio over fiber system

A novel all optical up-converted signal generation scheme with optical single-sideband (OSSB) technique for radio over fiber (RoF) application is presented and experimentally demonstrated using low-bandwidth devices. The OSSB signal is generated by one low-bandwidth intensity LiNbO3 Mach-Zehnder modulator (LN-MZM) under frequency quadrupling modulation scheme and one low-bandwidth LN-MZM under double sideband carrier suppressed modulation (DSB-CS) scheme. The proposed all OSSB generation scheme is capable of high tolerance of fiber chromatic dispersion induced power fading (DIPF) effect. Benefiting from this novel OSSB generation scheme, a 26GHz radio frequency (RF) signal up-conversion is realized successfully when one sideband of the optical LO signal is reused as the optical carrier for intermediate frequency (IF) signal modulation. The received vector signal transmission over long distance single-mode fiber (SMF) shows negligible DIPF effect with the error vector magnitude (EVM) of 15.7%rms. In addition, a spurious free dynamic range (SFDR) of the OSSB up-converting system is measured up to 81dBHz2/3. The experiment results indicate that the proposed system may find potential applications in future wireless communication networks, especially in microcellular personal communication system (MPCS).

Simplified DSP-Based Signal–Signal Beat Interference Mitigation Technique for Direct Detection OFDM

Short- and medium-haul links in interdata center, access, and metro networks require cost-effective direct-detection wavelength-division multiplexing transceivers offering energy efficiency, high information spectral density (ISD), and dispersion tolerance. Single-sideband orthogonal frequency-division multiplexing (SSB-OFDM) with direct detection is a potential solution; however, it suffers a penalty from signal–signal beat interference (SSBI) caused by the square-law photodetection. In this paper, a novel DSP-based SSBI mitigation technique, with lower complexity than previously proposed methods, is proposed and assessed through numerical simulations for the first time. The performance improvement is quantified by simulations of 9 × 112 Gb/s 16-QAM SSB-OFDM signal with a net optical ISD of 2.1 (b/s)/Hz. The performance is shown to be similar to that of the more complex receiver-based iterative SSBI compensation technique. Simulations predict an 8.7 dB reduction in the required OSNR at the 7% overhead HD-FEC threshold, and increases up to 100% in maximum reach over uncompensated standard single-mode fibre using the proposed simplified SSBI compensation technique.