Performance analysis of NRZ, RZ, CRZ and CSRZ data formats in 10 Gb/s optical soliton transmission link under the impact of chirp and TOD

This paper presents the performance analysis of non-return-to-zero (NRZ), return-to-zero (RZ), chirped return-to-zero (CRZ) and carrier suppressed return-to-zero (CSRZ) data formats in optical soliton transmission link under the impact of chirp and third-order dispersion (TOD). The performance of these data formats has been analyzed on the basis of certain performance metrics, viz, bit error rate (BER), Q² (dB), OSNR, eye opening, etc. It has been reported here that the performance of CRZ and CSRZ modulation format is better as compared to NRZ and RZ in a soliton transmission link. Further, CSRZ modulation format has been found to deliver optimum performance on the basis of performance evaluation metrics reported in this paper. In case of NRZ and CSRZ, comparatively narrow power spectrum has been observed. Best eye opening, highest value of Q² (dB) of 18 dB and lowest value of BER of the order of 10⁻¹⁶ has been reported in case of CSRZ among the considered data formats. The results have been obtained by varying noise figure from 3.0 to 9.0. No considerable effect of noise was observed. It was observed that at very narrow and ultra short pulse width, OSNR value suffers heavily and reduced to even negative values in dB, thus inducing a high degree of OSNR power penalty. The results were obtained by varying chirp factor from −0.6 to +0.6. Negative chirp resulted in improved OSNR as compared to positive chirp. RZ data format yielded a broader optical spectrum, comparatively low spectral efficiency and poor OSNR thus it was found that RZ format is not suitable for optical soliton transmission under the impact of chirp and TOD.     

40 Gb/s非零色散位移光纤传输系统中四种调制格式的性能比较

介绍了四种调制格式即非归零(NRZ),归零(RZ),载波抑制的RZ(CSRZ)和单边带RZ(SSB-RZ),用计算机仿真方法产生了这四种调制格式的40 Gb/s光信号,比较了其波形和光谱.也对这四种调制格式在非零色散位移光纤(NZDSF)上单信道传输进行了仿真,结果表明:在色散完全补偿情况下,RZ,CSRZ和SSB-RZ抗非线性能力都比NRZ强,其中CSRZ最强, CSRZ能够容忍的入纤光功率比NRZ大10.2 dBm;RZ,CSRZ和SSB-RZ 三种格式抗EDFA噪声能力差不多,但都比NRZ强.     

Performance evaluation of 100 and 200-Gb/s WDM PM-QPSK transmission systems: tolerance analysis to the optical link impairments according to the optical carrier shape

Polarization-multiplexing quadrature phase shift keying (PM-QPSK) has become a key ingredient in the design of 100 and 200-Gb/s dense wavelength-division multiplexed (DWDM) networks. The performance of the system using these formats varies according to the shape of the pulses employed by the optical carrier: non-return to zero (NRZ), return to zero (RZ) or carrier-suppressed return to zero (CSRZ). In this paper, we analyse the tolerance of PM-QPSK to linear and nonlinear optical impairments, including amplified spontaneous emission (ASE) noise, crosstalk, distortion by optical filtering, chromatic dispersion (CD), polarization mode dispersion (PMD) and fibre Kerr nonlinearities. The simulation results show that RZ formats with a low-duty cycle have a higher tolerance to CD, PMD and intrachannel nonlinearities due to the reduction of pulse-to-pulse interaction. Conversely, the PM–NRZ-QPSK format has a higher spectral efficiency (SE) than other options and shows better tolerance to filtering distortion and CD in filterless networks.     

优化调制格式实现2560 km低代价无误码传输

在单级调制器产生非归零码(NRZ)基础上,分析了利用双级调制器产生归零码(RZ)以及载波抑制归零码(CSRZ)的方法和特点。对非归零码,归零码和载波抑制归零码在以掺铒光纤放大器(EDFA)为单一的功率放大、以啁啾光纤光栅(CFBG)为色散补偿器的10Gb/s系统中的传输性能进行了计算机仿真并比较这三种调制码型的传输特性。同时在实际的2560km G.652光纤链路上利用上述三种调制格式以点对点形式进行了8×10Gb/s传输实验,通过适当控制线路的功率分配以及合理安排系统的色散补偿,实现了三种调制格式的无电中继条件下的零误码传输。计算机仿真和实际实验结果进一步表明,载波抑制归零码的采用有利于优化系统的传输性能,降低传输代价,载波抑制归零码在上述配置的实际传输系统中无误码传输2560km功率代价仅为2.5dB。     

Influence of modulation formats performance of the combined modulation in WDM-PON system

Different modulation modes of DPSK and OOK are separately employed in the upstream and downstream link, after the comparison with different modulation formats in the downstream including the codes of non return-to-zero (NRZ), return-to-zero (RZ) and inverse return-to-zero (IRZ), the symmetric rate of 10 Gbps with 20 km transmission is realized without the dispersion compensation. It can be shown that in the combined modulation mode with the downstream of IRZ code, higher extinction ratio in the downstream and better performance of dispersion tolerance in the upstream could be achieved, enhancing the overall property of the transmission system.     

Generation of DQPSK format and its performance against polarization mode dispersion

We propose a novel transmitter and receiver for differential quadrature phase-shift keying （DQPSK） format. The impact of the first-order polarization mode dispersion （PMD） on systems using DQPSK with 100- Gb/s non-return-to-zero （NRZ） or return-to-zero （RZ） format is investigated. Through computing the eye openings of DQPSK formats under different PMD conditions, it is found that NRZ DQPSK, as compared with RZ DQPSK, incurs smaller eye opening due to PMD. Carrier-suppressed return-to-zero （CSRZ） DQPSK format has better tolerance than RZ DQPSK format to PMD for a given bit rate.     

Robustness of NRZ, RZ, CSRZ and CRZ modulation on fiber nonlinearities and amplifier noise at 40 Gbps for (OC-786) long haul link

In this paper, the robustness of NRZ, RZ, carrier-suppressed RZ (CSRZ) and chirped RZ (CRZ) modulation formats at 40 Gbps for (OC-786) long haul link on the amplifier noise figure and fiber nonlinearities has been investigated. The investigations reveals that highest Q²(dB) of the order of [20, 25]; [19, 20]; [18, 19] and [16, 18] has been obtained in case of RZ, CSRZ, CRZ and NRZ modulation formats, respectively, in the presence of fiber nonlinearities and with and without amplifier noise figure of 6 dB. It has been observed that Q²(dB) in case of CRZ fluctuate between 18 and 14 at power variation of −10 to 4 dBm and NF of 6 dB, while it is between 19-9, 20-0 and 16-0 in case of CSRZ, RZ and NRZ. It has been identified that CRZ and CSRZ have shown the robustness on fiber nonlinearity and noise at 40 Gbps up to the transmission distance of 450 km. The wide eye opening in case of CRZ modulation also proved the robustness on fiber nonlinearity and noise.     

40 Gb/s差分相移键控格式抗偏振模色散的性能研究

研究了40Gb/s非归零或归零格式下,差分相移键控和开关键控信号对一阶偏振模色散的影响.比较分析了不同偏振模色散影响下的各种调制格式的眼开度.结果表明:使用非归零和归零格式,在一阶偏振模色散情况下,差分相移键控信号均比开关键控信号有更高的眼开度;与归零差分相移键控格式相比,非归零差分相移键控格式受偏振模色散影响眼开度要小;对于给定的比特率,载波抑制归零差分相移键控格式比归零差分相移键控格式有更好的抗偏振模色散能力.     

Performance evaluation for 160-Gb/s optical phase conjugation systems considering dispersion mapping and third-order dispersion

The impact of third-order dispersion (TOD) is investigated by numerical simulations in 160-Gb/s singlechannel systems incorporated with dispersion mapping and optical phase conjugation (OPC). System performances using retrun-to-zero (RZ) or carrier-suppressed RZ (CSRZ) modulation format are evaluated on the optimized dispersion map. The results indicate that even though TOD has been fully compensated,the intra-channel nonlinearity induced by local TOD would degrade the system performance in nonlinear regime. The scheme with an optimized dispersion map provides a much higher performance and offers a larger tolerance on a variation of pre-compensation. CSRZ modulation format is more robust due to its tradeoff between tolerances on intra-channel nonlinearity and dispersion.     

Investigation of optimum pulse shape for 112 Gbps DP-DQPSK in DWDM transmission

This paper reports the simulative analyses to investigate the impact of different pulse shapes on DP-DQPSK modulation for high-spectral efficient DWDM transmission at 112 Gbps per channel. In the simulation model we have considered three different pulse shapes viz. NRZ, 50% duty cycle RZ (RZ50) and 67% duty cycle RZ (RZ67) in symbol-aligned and symbol-interleaved format. The analysis has been carried out for various linear and nonlinear system impairments where the pulse is subjected to degradation under the influence of amplified spontaneous emission (ASE) noise, group velocity dispersion (GVD), cross-phase modulation (XPM) and polarization mode dispersion (PMD) and thus, limiting the system performance. Results show that the RZ50 pulse shape for DP-DQPSK with symbol interleaving shows the maximum tolerance for the various system degradations in long haul DWDM transmission. Even the system based on the NRZ pulse shape can gain significant improvement from the symbol-interleaving.     

40Gb/s差分相移键控格式抗偏振模色散的性能研究

研究了40Gb／s非归零或归零格式下,差分相移键控和开关键控信号对一阶偏振模色散的影响．比较分析了不同偏振模色散影响下的各种调制格式的眼开度．结果表明：使用非归零和归零格式,在一阶偏振模色散情况下,差分相移键控信号均比开关键控信号有更高的眼开度;与归零差分相移键控格式相比,非归零差分相移键控格式受偏振模色散影响眼开度要小;对于给定的比特率,载波抑制归零差分相移键控格式比归零差分相移键控格式有更好的抗偏振模色散能力．     

Simultaneous all-optical multi-channel RZ and CSRZ to NRZ format conversion

We propose and demonstrate multi-channel all-optical return-to-zero (RZ) and carrier-suppressed RZ (CSRZ) to non-return-to-zero (NRZ) format conversions using a same fiber delay-interferometer (DI). The conversions are based on simultaneous constructive interference induced by the periodical comb-like filtering characteristic of the DI. By using a DI with free spectral range of 40 GHz, 8 channel RZ and CSRZ signals at 20 Gb/s can be converted to corresponding NRZ signals at the same time. Furthermore, a duplicate output can be obtained for multi-channel CSRZ input. Bit error ratio measurements show 4 and 3.5 dB penalties for the proposed multi-channel RZ and CSRZ to NRZ conversions respectively. Further transmission for the converted NRZ signals verifies the good performance of the proposed all-passive multi-channel format converter. The potential of multi-channel RZ signals with mixed duty-cycle to NRZ conversions is also investigated.     

光栅不理想特性对不同调制码型的光传输系统的影响

分析了光纤光栅不理想特性的产生机理，对以啁啾光纤光栅为色散补偿器的10Gb/s光传输系统中，啁啾光纤光栅的不理想特性包括群时延纹波、反射纹波及光栅通带带宽对采用归零码(RZ)、非归零码(NRZ)以及载波抑制归零码(CSRZ)三种调制格式传输系统性能的影响进行了详细的数值分析和比较. 同时进行了基于光纤光栅色散补偿的1500km无误码传输实验，通过对啁啾光纤光栅由于不理想特性的差别而导致对实际传输系统不同信道性能影响的比较，进一步验证了仿真分析的正确性. 关键词： 光传输 啁啾光纤光栅 不理想特性 调制码型     

A novel method for chromatic-dispersion monitoring

A novel method for chromatic-dispersion monitoring based on PM–AM conversion is presented. A nonlinear element (NLE) was used as phase-modulator to improve the monitoring performance. The method was investigated numerically and experimentally for 40-Gbit/s signals in NRZ/RZ and CSRZ formats. The monitoring range was enlarged to 1670 ps/nm, and the monitoring sensitivity was improved to 0.012 dB/(ps/nm) for the NRZ signal. The corresponding values for the RZ50 signal were 680 ps/nm and 0.0046 dB/(ps/nm), respectively, and, for the CSRZ signal, 620 ps/nm and 0.0092 dB/(ps/nm), respectively.     

Performance investigation of suppression of four wave mixing using optical phase conjugation with different modulation format in DWDM soliton communication system

The performance of dense wavelength division multiplexed (DWDM) soliton transmission system for returnto-zero (RZ) and non-return-to-zero (NRZ) modulation formats have been investigated. The main aim of this paper is to estimate and mitigate the four wave mixing (FWM) power by using in-line optical phase conjugator (OPC). The effect of FWM has been estimated using real fiber link having nonlinear and attenuation losses. The FWM power is strongly suppressed by introducing destructive interference between the first and second halves of in-line OPC. It has been indicated that RZ with OPC yields the better performance with FWM power suppression (more than 20 dBm in certain cases) with reasonable bit error rate and Q-factor.     

Impact of optical modulation formats on SPM-limited fiber transmission in 10 and 40 Gb/s optimum dispersion-managed lightwave systems

In this paper, 10 and 40 Gb/s optical systems have been investigated for nonreturn-to-zero (NRZ), return-to-zero (RZ), carrier-suppressed return-to-zero (CSRZ) and RZ-differential phase-shift-keying (RZ-DPSK) data formats. For the range of the optical signal power from −5 to 15 dBm, a maximum self-phase modulation (SPM)-limited transmission distance L_SPM is determined with eye-opening penalty (EOP) >1 dB .The observations are based on the modeling and numerical simulation of optimum dispersion-managed transmission link. Transmission over distances of the order of several hundreds of kilometers has been shown with and without amplified spontaneous emission (ASE) noise of the in-line erbium-doped fiber amplifiers (EDFAs).     

基于偏振度的偏振模色散补偿中检测信号对不同归零码型的响应研究

从理论上数值分析和比较了一阶和二阶偏振模色散对各种光调制码型（RZ、CSRZ、RZ-DPSK、CSRZ-DPSK）的偏振模色散的影响,结果表明:不同码型的偏振度大不相同,RZ码受偏振度影响最大,CSRZ-DPSK码受二阶偏振模色散的影响最小,在补偿系统中更适合缓解偏振模色散.     

Design and performance analysis of various one dimensional codes using different data formats for OCDMA system

In this paper, the design, implementation and performance analysis of various one dimensional codes in an OCDMA system for different data formats is presented. A number of different codes are used with optical CDMA to improve its error performance. Here, three such codes, optical orthogonal codes (OOC), Walsh Hadamard codes and zero cross-correlation (ZCC) codes have been compared using different data formats, NRZ raised cosine, NRZ rectangular, RZ raised cosine and RZ rectangular. It is found that NRZ raised cosine has the best system performance for all the codes used. After that, the three codes have been compared in terms of the BER, eye diagrams and received optical power using NRZ raised cosine modulation format. It is analyzed that ZCC codes have zero cross-correlation property. The simulation results revealed that ZCC codes can provide a better BER compared to the OOC and Walsh Hadamard codes and it is most suitable to be employed in the OCDMA systems.     

PMD对不同线路码型高速光纤通信系统影响的研究

研究了在采用NRZ码、电RZ码、光RZ码及CSRZ码四种不同的线路码型并在接收机不同光滤波器带宽下，研究了偏振模色散(PMD)对40Gbit／s单波道光纤通信系统产生的不可用概率。     

Simulation of high capacity 40 Gb/s long haul DWDM system using different modulation formats and dispersion compensation schemes in the presence of Kerr's effect

In this paper, simulative analysis of 40 Gb/s long haul (500-2000 km) DWDM system with ultra high capacity upto 1.28 Tb/s has been carried out for carrier-suppressed return-to-zero (CSRZ), duobinary return-to-zero (DRZ) and modified duobinary return-to-zero (MDRZ) modulation formats. The DWDM system has been analyzed for the pre, post and symmetrical dispersion compensation schemes for 16 Channels with 25 GHz channel spacing in order to find the optimum modulation format for a high bit rate optical transmission system. The effect of variation in input power and transmission distances is observed in terms of Q value and eye opening for various formats. It is found that symmetrical compensation is superior to pre and post dispersion compensation schemes. It has also been observed that the performance of DWDM system is severely limited by the four-wave mixing (FWM) effect and is determined that MDRZ format seems to be the best choice for the transmission distance beyond 1550 km despite slightly more complex transmitter and receiver configuration. Further, symmetrical compensation scheme has been investigated for 32×40 Gb/s MDRZ format for faithful transmission over 1450 km.