Nonreturn-to-zero Modulation Format Research Articles

Research of fiber nonlinear effects in WDM-PON based 5G fronthaul networks

In fifth-generation (5G) fronthaul networks, the wavelength division multiplexing passive optical network (WDM-PON) is considered as an important tool to address the advanced transmission requirements. The nonlinear effects occur when multiple wavelengths are transmitted simultaneously in the same optical fiber. In this paper, we investigate the four-wave mixing (FWM) and the cross-phase modulation (XPM) effects by using non-return-to-zero (NRZ), 4-level pulse amplitude modulation (PAM4), and optical duobinary (ODB) modulation formats in WDM-PON-based 5G fronthaul networks. The results show that ODB performs better when it comes to limiting the FWM and XPM effects because of its precoded attribute. Compared to the unpredictable sensitivity penalty based on NRZ and PAM4, the FWM-induced sensitivity penalty using ODB is reduced to 2[Formula: see text]dB. Moreover, the XPM-induced sensitivity penalty is measured as 1[Formula: see text]dB by adopting ODB, which is almost 5[Formula: see text]dB better than NRZ and PAM4 modulation formats.

Performance enhancement of ultra-dense WDM over FSO hybrid optical link by incorporating MIMO technique

Abstract Free-space optical (FSO) communication is a wireless optical data transmission technology with a high data transmission rate. It has received much attention in recent years as it is cost-effective and has license free operation. It is line of sight free-space communication technique where optical signal severely degraded from atmospheric losses especially due to weather conditions; hence it restricts the link range and data carrying capacity. Therefore, a 16-channel ultra-dense wavelength division multiplexing–free space optics (UWDM–FSO) system each having each 10 Gb/s data rate is proposed to enhance the capacity and performance of FSO system. To authenticate the performance of the proposed system, investigation for different modulation formats such as nonreturn to zero (NRZ), return to zero (RZ), carrier suppressed return to zero (CSRZ) and duo binary (DB) are reported. Further, to reduce the atmospheric interference, multiple input multiple output (MIMO) technique is integrated into the proposed system. The outcomes of MIMO–UWDM–FSO link revealed a significant improvement in the bit error rate (BER), eye diagram and Q-factor, under different weather conditions. It is also observed that NRZ modulation formats perform better than RZ, CSRZ and DB formats.

Enhanced NRZ multi-carriers modulation technologies for microresonators in THz technology applications

Abstract Multi-optical carriers suitable for use in an optical communication system have been generated via integrated microring resonators. These carriers were sufficiently stable for travel in either a free space channel or waveguides while experiencing very low dispersion. Multiple carriers were created using the integrated microring resonators, with each carrier possessing a frequency at 193.012, 193.086, 193.186 and 193.268 terahertz (THz). The second part which is the non-return-to-zero (NRZ) modulation has been performed using the microring resonator modulators. The objective of the research is to generate multi-carriers at infrared region and modulate them for the optical communication application using the microring resonators. At the transmitter part, series of microring resonators have been used to generate four different THz frequencies which can be either de-multiplexed and modulated individually using the NRZ modulation format or modulated without de-multiplexing them as these enter a series of microring resonator modulators and microring resonator drop filters. As results, the detection of the four NRZ modulated frequencies has been performed successfully with high signal qualities. Therefore, in this research microring resonators are used for different purposes as to generate optical signals (at the transmitter part), modulate and filter them along an optical transmission link.

Performance Evaluation of Passive Optical Network Using Different Modulation Formats

AbstractIn this paper, the performance of passive optical network is analyzed and compared for different modulation formats such as non-return to zero (NRZ), return to zero (RZ) at 2.5 Gb/s bit rate with 16 optical network units. This system is investigated in terms of quality (Q)-factor, optical received power and eye height at different transmission distances. NRZ achieves maximum transmission distance up to 48 km having Q-factor of 6.18 and RZ achieves the maximum transmission distance up to 41 km having Q-factor of 6.21. Furthermore, it is found that NRZ modulation format is more superior and covers more distance as compared to RZ modulation format.

Comparative Analysis of Inter Satellite Optical Wireless Channel for NRZ and RZ Modulation Formats for Different Levels of Input Power

Abstract Integration of DWDM in Optical wireless communication has undoubtedly revolutionized the satellite communication systems for use in the coming future. Thus OWC systems have become popular due to their outstanding performance uniqueness. This paper looks into the performance of Inter Satellite Optical Wireless Communication system link using DWDM multiplexing technique for long distance transmission. The Inter satellite link has been modeled at a data rate of 10 Gbps for communication range of 5000 kilometers. Furthermore, it demonstrates a comparative analysis of RZ (Return to zero) and NRZ (Non-return to zero) modulation formats by varying the levels of input power.

Performance of RZ and NRZ modulation—Format in 40–160 Gb/s OTDM system demultiplexing

With a symmetric SOA-MZI as a de-multiplexing switch we describe the performance of return-to-zero (RZ) and nonreturn-to-zero (NRZ) modulated signals in all optical demultiplexing of an OTDM channel at data rates up to 160Gb/s. First, the effect of input signal power, control signals power and pattern length on BER and extinction value of demultiplexed channel is investigated for RZ and NRZ signals at different data rates. Second, demultiplexing of 160-Gb/s OTDM signal to the base rate of 40Gb/s was successfully demonstrated with error free operation for both modulation formats. Effect of variation of pulse width on BER has also been analyzed for 160–40Gb/s demultiplexing operation.

Optimizing the FEC Overhead in a 100 GbE PDM-QPSK Digital Coherent Transmission System

The finite electrical bandwidth of digital coherent transceivers together with limited wavelength division multiplexing (WDM) channel spacing constrains the maximum forward error correction (FEC) overhead that can be advantageously applied to fiber optic transmission systems. We investigate through simulations of a 100 GbE system employing coherent polarization division multiplexed quaternary phase shift keying, the impact of these bandwidth constraints on the optimal code rate thereby minimizing the required optical signal-to-noise ratio (OSNR) at the receiver. The optimum FEC overhead is found to increase linearly with available bandwidth and the required OSNR is found to reduce for lower order transponder filters. Fabrication of transmitters with a broader spectral response than their receiver counterpart is found to be advantageous. The optimum electrical bandwidth is found to be approximately half the WDM channel spacing for nonreturn to zero (NRZ) transmission and slightly less for return to zero (RZ). There is shown to be no performance advantage in using RZ over NRZ modulation formats when the optimum FEC overhead and filter bandwidth is employed in each case. Nonlinear simulations demonstrate that transpacific transmission is attainable with a margin that increases as the spectral efficiency is relaxed.

Theoretical Investigation of First-order and Second-order Polarization-mode Dispersion Tolerance on Various Modulation Formats in 40 Gb/s Transmission Systems with FEC Coding

We investigated the polarization-mode dispersion (PMD) tolerance for 40Gb/s non-return to zero (NRZ), duobinary NRZ, return to zero (RZ), carrier-suppressed RZ (CS-RZ), and duobinary-carrier-suppressed RZ (DCS-RZ) modulation formats with a forward error correction (FEC) coding. The power penalty has been calculated as a measure of the system performance due to PMD. After comparison of the PMD tolerance of various modulation formats, our results suggest that RZ signals have the best tolerance against the effect of first-order PMD only. The duobinary NRZ modulation format is most resilient to PMD when both first- and second-order PMD are considered. However, the duobinary NRZ modulation format is the most sensitive to the incident angle of the input signal to a fiber axis in the presence of first- and second-order PMD, leading to incident angle-dependent power penalty. The coding gain by FEC can cope with the power penalties induced by first- and second-order PMD up to a DGD value of 16ps.

PMD Tolerance of 10 Gbps Modulated Signals due to SOA-Induced Chirp in SOA Booster Amplifiers

We investigated how the polarization-mode dispersion (PMD) tolerance was degraded by semiconductor optical amplifier (SOA)-induced chirp for the 10 Gb/s nonreturn-to-zero (NRZ), duobinary NRZ, return-to-zero (RZ), and carrier-suppressed RZ (CS-RZ) modulation formats. The power penalty was calculated as a measure of the system performance due to PMD for a given SOA-induced chirp. Considering only first-order PMD, all modulation formats have a similar PMD tolerance regardless of SOA-induced chirp. On the other hand, when both first- and second-order PMD are considered, the PMD tolerance of all modulation formats with the exception of the CS-RZ modulation format are degraded by SOA-induced chirp. Among all modulation formats considered here, the NRZ modulation format has the PMD tolerance with the highest sensitivity to SOA-induced chirp. When the peak-to-peak chirp induced by SOAs is $0.28{\AA}$ , its PMD tolerance is degraded up to 4 dB for a differential group delay (DGD) of 50 ps. However, the PMD tolerance of the CS-RZ modulation format is largely unaffected by SOA-induced chirp.

Comparison of Cross-Gain Modulation Effect of Manchester-Duobinary, RZ-DPSK, NRZ-DPSK, RZ, and NRZ Modulation Formats in SOAs

Conventional on-off keyed signals, such as return-to-zero (RZ) and nonreturn-to-zero (NRZ) signals are susceptible to cross-gain modulation (XGM) in semiconductor optical amplifiers (SOAs) due to pattern effect. In this letter, XGM effect of Manchester-duobinary, RZ differential phase-shift keying (RZ-DPSK), NRZ-DPSK, RZ, and NRZ signals in SOAs were compared. The experimental results confirmed the reduction of crosstalk penalty in SOAs by using Manchester-duobinary signals

Theoretical investigation of optical wavelength conversion techniques for DPSK Modulation formats using FWM in SOAs and frequency comb in 10 gb/s transmission systems

We have investigated the wavelength conversion techniques for differential phase-shift keying (DPSK) modulation formats in 10 Gb/s transmission systems, compared with the non-return-to-zero (NRZ) modulation format. For the wavelength conversion of DPSK modulation formats, we employed the wavelength converters based on the four-wave mixing (FWM) in semiconductor optical amplifiers (SOAs) and the frequency comb generated by phase modulation. The power penalty at 10/sup -9/ bit error rate was used as a measure of the system performance degraded by the wavelength conversion. Our simulation results show that the DPSK modulation formats have a smaller power penalty than the NRZ modulation format for the wavelength conversion using the FWM effect in an SOA due to a much lower pattern effect. However, as the wavelength conversion uses the frequency comb generated by phase modulation, it has a similar power penalty compared with the NRZ modulation format. It is also shown that the DPSK modulation formats are possible to obtain the power penalty less than 0.4 dB for both wavelength conversion techniques.

Improvement of Power Margin in 10-Gb/s SOA-Boosted Transmission Systems Using Phase-Modulated Duobinary Modulation Formats

We theoretically investigate the performance of 10-Gb/s semiconductor optical amplifier (SOA)-boosted transmission systems using the nonreturn-to-zero (NRZ), conventional duobinary, and phase-modulated (PM)-duobinary modulation formats. NRZ and conventional duobinary modulation formats are based on the intensity modulation. When the NRZ and conventional duobinary modulation formats are used, the nonlinear characteristics of SOA severely distort the signals. On the other hand, the PM-duobinary modulation format is based on differential binary phase-shift-keying modulation. When the PM-duobinary modulation format is employed, the nonlinear characteristics of SOA scarcely affect the signals which maintain a constant intensity in SOAs. Using the PM-duobinary modulation format, we can significantly improve the power margin in SOA-boosted transmission systems.

Performance comparison of standard FEC in 40 Gbit/s optical transmission systems with NRZ, RZ and CS-RZ modulation formats

In this paper, we describe a detailed numerical investigation on performance of standard forward error correction (FEC) in 40 Gbit/s optical transmission systems with nonreturn-to-zero (NRZ), return-to-zero (RZ) and carrier-suppressed RZ (CS-RZ) modulation formats. The results show that FEC performs differently due to the different error distributions for the three formats at different power levels and transmission distances. Furthermore it is found that, with FEC on, NRZ format has a similar tolerance to intersymbol interference (ISI) due to the interactions of dispersion and nonlinearities as RZ and CS-RZ formats without FEC.

Dynamics of the chirped return-to-zero modulation format

We numerically simulated long-distance, high-bit-rate, wavelength division multiplexed (WDM) transmission in dispersion-managed systems. We investigated return-to-zero (RZ) and nonreturn-to-zero (NRZ) modulation formats with amplitude and phase modulation. Consistent with earlier experiments, we find that the chirped return-to-zero (CRZ) modulation format has significant advantages over the NRZ modulation format in WDM systems. We elucidate the physical reasons for these advantages. We then discuss, in detail, the dynamics of the CRZ systems, carefully distinguishing noise effects, single-channel nonlinear effects, and multichannel nonlinear effects. In this way, we provide a physical basis for understanding CRZ systems that should prove useful for future system design. In particular, we find that the pulse evolution is dominated by linear dispersion and that the spread in the eye diagrams is dominated by signal-spontaneous beat noise, just like in linear systems. However, we also find that symmetric dispersion compensation performs better than asymmetric dispersion compensation, due to the effects of nonlinearity. Additionally, we find that interchannel nonlinearities spread the eye diagrams without changing the dynamical behavior. Thus, the system is quasilinear in the sense that its properties resemble those of linear systems, but nonlinearity plays an important role.

RZ versus NRZ modulation format for dispersion compensated SMF-based 10-Gb/s transmission with more than 100-km amplifier spacing

We compared numerically and experimentally the transmission behavior of return-to-zero (RZ) and nonreturn-to-zero (NRZ) modulated signals, 10 Gb/s were transmitted over 2040-km standard single-mode fiber using an alternating dispersion compensation scheme in a recirculating loop with 102 km amplifier spacing. Receiver sensitivities of -33 dBm (NRZ) and -35 dBm (RZ) could be achieved. RZ allows for a simple linear dispersion compensation whereas NRZ suffers from nonlinear signal distortion. NRZ requires under-compensation of the linear chromatic dispersion dependent on signal power and transmission length. Therefore, NRZ makes network design more difficult.

Comparison of resistance to polarisation mode dispersion of NRZ and phase-shaped binary transmission formats at 10 Gbit/s

The purpose of the reported 10 Gbit/s experiments is to compare the resistance to severe polarisation mode dispersion (PMD) exhibited by a link of 63.4 km of conventional fibre, for two different modulation formats: non-return-to-zero (NRZ) and phase-shaped binary transmission (PSBT). It clearly appears that the PSBT format is far more resistant to PMD than the NRZ modulation format.

Calculation of bit-error probability for a lightwave system with optical amplifiers and post-detection Gaussian noise

The author's previously published results (ibid., vol.8, p.1816-23, 1990) which dealt with the bit-error probability of a lightwave communication system whose noise contribution was exclusively attributed to spontaneous emission noise of optical amplifiers are extended. The earlier theory was based on an NRZ (nonreturn-to-zero) modulation format with zero signal power assigned to logical zeros. The extension is based on the same mathematical technique but includes Gaussian noise originating after the signal has been converted to an electrical current. This noise could be thermal noise, shot noise, or a combination of both. It is no longer assumed that the pulse representing a logical one fills its time slot completely. Now, the optical pulses can be much shorter than the bit period (solitons), the power level of logical zeros need not vanish, and the thermal noise of the postdetection electronic circuit is taken into account. >