拉曼增强型自相位调制再生技术

自相位调制可用于信号脉冲的整形,可实现归零码(RZ)信号的再生。以高非线性光纤(HNLF)为介质,在高非线性光纤中实现了拉曼集总放大和信号脉冲的自相位调制。从理论上分析了同向拉曼泵浦增强信号的自相位调制,大大降低了所需的信号光强度。论证了在色散长度(LD)远大于HNLF长度(L)时由自相位调制(SPM)导致的频谱展宽,它与脉冲的啁啾无关,频谱的功率密度与脉冲的强度无关。因此在高非线性光纤之后加入偏移载波频率的带通滤波器可实现归零码信号的再生。集中拉曼放大可增强再生性能。     

Performance limitations of an optical heterodyne CPFSK transmission system due to self-phase modulation

A detailed theoretical analysis is presented to evaluate the combined influence of self-phase modulation (SPM) and group velocity dispersion (GVD) of optical fiber on the bit error rate (BER) performance of a heterodyne optical CPFSK system. The power penalty suffered by the system due to the combined influence of GVD and SPM is evaluated from the BER performance results. It is found that the penalty due to SPM at a BER of 10⁻⁹ is significant when the input power exceeds 7 dBm. Further, the CPFSK system with modulation index of 0.5 is less sensitive to the effects of GVD and SPM compared to the system with a modulation index of 1. The theoretical results are in conformity with the experimental results reported earlier.     

Optical wave breaking of high-intensity femtosecond pulses in silicon optical waveguides

We have investigated numerically the propagation of high-intensity femtosecond optical pulses with pulsewidth of 100 fs (half width at 1/e maximum) on the silicon-on-insulator (SOI) optical waveguide when the central wavelength of the pulse locates in the normal dispersion region. Results show that the combined effects of group-velocity dispersion (GVD), third-order dispersion (TOD), self-phase modulation (SPM), and free-carrier dispersion (FCD) can lead to the phenomenon of optical wave breaking that manifests as an asymmetric profile and oscillation near the trailing edge of the pulse. Moreover, the optical wave breaking will be experienced from generation to disappearance during propagation.     

SPM induced limitations for 40 Gbps chirped Gaussian pulses in optical channel

An analysis of self-phase modulation (SPM) induced nonlinearities in a 40 Gbps link with chirped Gaussian pulses of different duty cycles has been reported in this paper. In the present analysis only SPM effect has been considered to control the pulse propagation behavior through the fiber by appropriate selection of pulse width, peak power and channel length to suppress the other channel impairments caused by group velocity dispersion (GVD) and third order dispersion (TOD). The effect of SPM on the Q-factor for the transmission of 40 Gbps chirped pulses with different initial pulse widths and input peak powers has been investigated. It has been observed that a wider pulse having maximum negative chirp can withstand the nonlinear effect of SPM for relatively higher ranges of input peak power.     

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.     

Detailed theoretical investigation on relative intensity noise reduction enhancement based on reflective SOAs

The enhanced performance for relative intensity noise (RIN) reduction based on reflective semiconductor optical amplifiers (R-SOA) has been investigated theoretically by comparison with conventional transmission SOA. The results show that, by selecting appropriate input optical power, as large as >20 dB RIN suppression improvement can be achieved for R-SOA, without sacrificing the noise rejection bandwidth. With increased injection current, the optimized input signal power is decreased and the operation region is extended for the best RIN reduction. For RIN suppression in WDM spectrum slicing, the bandwidth optimization of receiver filter should be performed to avoid the spectral broadening induced by self-phase modulation (SPM) and four wave mixing (FWM). Our derived result is helpful for designing and optimizing the R-SOA in application of noise suppression enhancement.     

Self—Steepening and Thired—Order Dispersion Induced Optical Solitons in Fiber

Usually,one considers only the group velocity dispersion(GVD)-and self-phase modulation(SPM)-induced solitons in optic soliton communication while other higher order effects such as the third-order dispersion(TOD),self-steepening(SS),and stimulated Raman scattering are considered only perturbatively,In this paper,we study the existence of the TOD-and SS-induced soliton solutions.The existence conditions of the TOD-and SS-induced bright and dark solitons are quite different from those of the GVD-and SPM-induced solitons.     

Pilot-based cross-phase modulation compensation for coherent optical orthogonal frequency division multiplexing long-haul optical communications systems

A pilot-based nonlinearity compensator (PB-NLC) is shown in this Letter to be an effective method for compensating cross-phase modulation (XPM) in coherent optical orthogonal frequency division multiplexing (CO-OFDM) systems. An unmodulated pilot tone is transmitted at the center of each OFDM channel to detect phase errors caused by the Kerr effect, which converts intensity fluctuations from all channels to phase errors. The pilots are then used to cancel the XPM phase errors for each OFDM channel at the receiver after each channel's self-phase modulation (SPM) has been compensated, using its intensity waveform to determine its SPM. Numerical simulations of a 58 Gb/s single polarization 2375 km system with inline dispersion compensation show that the signal quality, Q, at the optimal launch power is increased by 2.4 dB if SPM compensation is used before the PB-NLC. This contrasts with only a 0.9 dB improvement if the PB-NLC is used without an SPM compensator for the same link. This shows the PB-NLC can effectively mitigate XPM but not SPM.     

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.     

Performance limit of a multi-frequency probe based coherent optical time domain reflectometry caused by nonlinear effects

The nonlinear effects that limit the performance of the multi-frequency probe(MFP)based coherent optical time domain reflectometry(C-OTDR)are investigated.Based on theoretical analysis and experimental results,compared with conventional C-OTDR,when the probe pulse has power gradient within the pulse width,self-phase modulation(SPM)and cross-phase modulation(XPM)are strengthened in the new C-OTDR scheme.The generation of four-wave mixing(FWM)is dependent on SPM and XPM,and with modulation frequency of phase modulator higher than 40 MHz,the stimulated Brillouin scattering(SBS) threshold can be enhanced by more than 5 dB,which benefits the maximum dynamic range of the MFP C-OTDR.     

200 nm Supercontinuum Generated by Subpicosecond Optical Pulses and its Evolution Process Observation

200 nm superconticnumm (SC) with high flatness (<3 dB) is demonstrated with subpicosecond optical pulses generated by a passively mode-locked figure-eight-laser. The evolution process of SC under different optical pumping power is observed experimentally. Three sequential evolution stages are found: (1) SC spectrum is asymmetrically broadened due to self-phase modulation (SPM) and group velocity dispersion (GVD). (2) When the broadened spectrum exceeds the zero dispersion point, cross phase modulation (XPM) and four wave mixing (FWM) will cause symmetrical spectrum broadening. (3) stimulated Raman scattering (SRS) causes the spectrum to broaden toward long wavelength quickly when pumping power is intense enough.     

Higher-Order Effects Induced Optical Solitons in Fiber

In this paper, we study the existence conditions of the soliton solutions induced by considering the higher-order effects such as the third-order dispersion (TOD), self-steepening (SS), and self-frequency shift arising from stimulated Raman scattering (SRS) simultaneously in optical soliton communication. Based on the Jacobian expansion method, we successfully obtain bright and dark solitons. The results shows that the resultant inclusion is in agreement with Mollenauer et al. [Physical Review Letters 45 (1980) 1095] when the SRS is not considered; while when the SRS is considered, the existence conditions of the higher-order effects induced bright and dark solitons are not only quite different from those of the group velocity dispersion (GVD)-induced and self-phase modulation (SPM)-induced solitons, but also different from those of the TOD- and SS-induced solitons discussed by Mollenauer et al. [Physical Review Letters 45 (1980) 1095].     

200 nm Supercontinuum Generated by Subpicosecond Optical Pulses and its Evolution Process Observation

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窄线宽脉冲光纤激光的自相位调制预补偿研究

自相位调制(SPM)效应会展宽窄线宽脉冲光纤激光的光谱宽度,降低其相干性.通过相位调制对SPM引起的非线性相移进行预补偿,能够使脉冲激光在光纤中进行放大和传输后保持种子激光的光谱特性.基于三波耦合方程开展数值仿真,研究了在对SPM进行"欠补偿","完全补偿"和"过补偿"的情况下,SPM预补偿对受激布里渊散射阈值和激光光谱特性的影响.开展了SPM预补偿实验研究,将脉冲激光的光谱宽度从1.4 GHz压缩到120 MHz.研究内容可以为窄线宽脉冲光纤激光系统的设计搭建提供参考.     

高速光纤通信系统中抑制偏振模色散的新机制

重点研究了偏振模色散、群速度色散、自相位调制三者之间在高速光纤通信系统中的相互作用，从时域角度分析脉冲的演变，从频域角度分析频谱的变化，提出一定条件下，啁啾、色散、自相位调制可以部分补偿偏振模色散的思想。通过对40Gbit／s系统进行偏振模色散、群速度色散和自相位调制共同作用的仿真，从统计意义上验证了它们之间的相互影响，并找到最佳传输方案，对系统设计提供了参考。     

Useful and detrimental aspects of self-phase modulation in fiber optical applications

This paper reviews the features of self-phase modulation (SPM) in single-mode optical fibers and discusses the useful and detrimental aspects of this fiber nonlinearity with respect to fiber optical transmission and device applications. After a short introduction to the physical origin of self-phase modulation in fibers the following topics will be addressed: transmission system limitations due to SPM, soliton propagation, optical pulse compression, modulational instability.     

光纤色散对超连续谱产生的影响

对1550nm波长附近具有不同色散特性的光纤产生超连续谱进行了详细的计算和分析。结果表明，在反常色散区和零散区，由于内脉冲拉曼散射效应和三阶色散效应的影响，不能产生平坦、宽带的超连续谱。而在正常色散区，可以产生平坦光滑的超连续谱。进一步研究表明，具有较小正常色散的色散平坦光纤对于产生平坦、宽带的超连续谱极为有效。通过增强脉冲抽运功率，可以得到谱强起伏小于10dB、带宽达300nm以上的平坦超宽超连续谱。     

基于串行最小频移键控的8进制调制的研究

提出了一种新型的基于串行结构的最小频移键控调制技术,产生了相位连续,频谱宽度窄,每码元时间有两次π/2相移,类似于传统最小频移键控调制信号,给出了该调制方案的理论推导,并将其应用于8进制的多维多阶调制系统中。理论和仿真分析了不同的8进制调制方案在频谱特性,残留色散容限,自相位调制容限的不同,还分析了其受到系统滤波带宽的影响。最后仿真实现了通过350km的色散完全补偿的光纤120Gb/s的数据传输。     

Useful and detrimental aspects of self-phase modulation in fiber optical applications

This paper reviews the features of self-phase modulation (SPM) in single-mode optical fibers and discusses the useful and detrimental aspects of this fiber nonlinearity with respect to fiber optical transmission and device applications. After a short introduction to the physical origin of self-phase modulation in fibers the following topics will be addressed: transmission system limitations due to SPM, soliton propagation, optical pulse compression, modulational instability.     

A narrow-line Erbium-doped fiber laser and its application for testing fiber Bragg gratings

We inspect the spectral features of a diode-pumped Erbium-doped fiber laser (EDFL) with a Fabry-Perot cavity composed of a wavelength-selective coupler in the form of fiber Bragg grating (FBG) and wavelength-insensitive Faraday rotator mirror (FRM). High accuracy for the spectral measurements is provided with the use of an optical heterodyne scheme where the EDFL output is mixed with radiation from a narrow-line semiconductor laser, allowing the detection of the EDFL spectra with a sub-pm resolution. The heterodyne scheme permits precise measurements of the EDFL line-width as a function of the cavity length and pump power. It is worth noticing a narrow-line (a few pm) operation of the EDFL with a short length (<3 m) cavity and low (<5) excess of pump power over the laser threshold. The spectral response of the EDFL to a slow sinusoidal modulation of a physical length of the FBG coupler is analyzed and it is shown that as high as ∼1-nm modulation of the EDFL optical spectrum is attainable at maximal modulation amplitudes. The narrow-line EDFL with a modulated generation wavelength is hereby demonstrated to be a tool for high-resolution measurements of reflection spectra of FBGs, which is to the best of our knowledge a novel application of the EDFL.