基于啁啾光纤布拉格光栅的宽谱光单边带调制方法

提出一种基于啁啾光纤布拉格光栅(CFBG)的宽谱光单边带(OSSB)调制实现方法。光双边带(ODSB)调制信号经过同一CFBG两个相反方向的反射,利用偏振控制器(PC)实现两个方向偏振态的正交。这种双反射CFBG(DR-CFBG)结构可以滤出光载波与其中一个边带实现OSSB调制,同时消除了反射谱内的色散,避免了滤波引起的相位畸变。利用实验制作的线性CFBG搭建了DR-CFBG,实验数据仿真结果表明,本文方法可以实现宽谱基带信号与加载数据信息射频信号的OSSB调制,结果表明传输距离大于6km时,40Gb/s NRZ信号OSSB调制传输有明显优势;加载2.5Gb/s的NRZ信号,OSSB调制传输50km,误码率为10-9时,20GHz射频为载波的功率代价比10GHz低3dB,比40GHz低1.2dB。改进CFBG的边沿斜率可以更好地抑制边带残留,提高OSSB调制信号的传输性能。     

双音调制星间微波光子链路信号噪声失真比优化

建立了包括光源、马赫曾德尔调制器、掺铒光纤放大器和光电探测器的双音调制星间微波光子链路模型。利用贝塞尔函数展开、傅里叶变换/反变换和Graf加法定理,推导出探测器输出信号的严格通用解析解,考虑三阶交调失真的影响,得出信号噪声失真比（SNDR）的表达式。着重分析了在不同调制方式下SNDR、基波和三阶交调信号功率随射频输入功率的变化情况。数值计算结果表明:SNDR、基波和三阶交调信号功率随射频输入功率的增大先增大后减小,存在最优的射频输入信号功率使SNDR达到最大。相同射频输入功率条件下,双边带调制SNDR大于单边带调制,适合星间微波光子链路应用。     

Performance optimization of radio-on-fiber systems employing erbium doped fiber amplifier for optical single sideband signals considering intermodulation distortion

The performances of radio on fiber (RoF) systems with a dual-electrode Mach-Zehnder modulator and an erbium-doped fiber amplifier (EDFA) are optimized by numerical equations including the third order intermodulation (IM3) as well as amplified spontaneous emission (ASE) noise. We investigate a signal-to-noise-and-distortion ratio (SNDR) considering fiber dispersion with respect to an input signal power and an EDFA gain in both noise-dominant and third order intermodulation (IM3)-dominant cases. We also verify that the numerical analysis results are well matched with those of a commercial simulator, VPItransmissionMaker. In the analysis results, the optimum input signal power for the maximum SNDR of a RoF system with EDFA was reduced over 8 dB compared with that without EDFA. The dramatic reduction of IM3 power at a receiver was resulted from this decrement of input signal power. Thus, the maximum SNDR of the system with EDFA was obtained over 17 dB at 40 km fiber compared with that of the system without EDFA. In addition, the results showed that the SNDR was efficiently improved by EDFA in the noise-dominant case, while the SNDR improvement was negligible by EDFA in the IM3 dominant case.     

Optical single-sideband transmitter for various electrical signaling formats

A simple high-speed data transmitter to generate optical single-sideband (OSSB) signals using different electrical signaling formats is presented. The OSSB signal is generated by combining the information signal with the Hilbert transform of that signal, obtained by means of electrical processing. A detailed mathematical model is introduced to evaluate the transmitter performance, considering the generation of OSSB signals with different electrical signaling formats. Two signaling formats are evaluated and compared: nonreturn-to-zero (NRZ) and alternate mark inversion. The optimum transmitter operation conditions, namely bias and drive voltages, are derived according to the signaling format used and confirmed experimentally. Transmission tests conducted using 10-Gb/s OSSB-NRZ signals to assess the improvement obtained by electrical dispersion compensation show a significant mitigation of the dispersion distortion.     

Analysis of CNR penalty of radio-over-fiber systems including the effects of phase noise from laser and RF oscillator

The effect of phase noises from a laser and an oscillator on radio-over-fiber (RoF) systems is analyzed and discussed with a power spectral density (PSD) function. A Mach-Zehnder modulator (MZM) and a phase shifter are employed to externally generate an optical single sideband (OSSB) signal since the OSSB signal is tolerable for power degradation due to a chromatic fiber-dispersion effect. It is shown that a carrier-to-noise ratio (CNR) penalty is deeply related to the bandwidth of a receiver filter and the phase noise from a radio frequency (RF) signal oscillator rather than that from a laser in a small differential-delay environment and a direct detection scheme. The CNR penalty due to the increment of the laser linewidth from 10 to 624 MHz is almost 1.1 dB, while the increase of the RF-oscillator linewidth from 1 to 100 Hz results in about a 20-dB penalty at a 30-GHz 10-km transmission in a standard single-mode fiber (SSMF) with a fiber chromatic dispersion of 17 ps/km/spl middot/nm.     

Spectrally efficient optical label insertion/extraction technique using an optical single sideband filter

A novel label insertion technique, using an adaptive optical single sideband (OSSB) filter, is experimentally shown. The OSSB filter is used to suppress one of the sidebands of the 40-Gb/s payload signal, and a 2.5-Gb/s intensity modulated signal is inserted as a label in the suppressed sideband. Lower label-payload crosstalk is observed using the OSSB filter compared to the absence of sideband suppression, allowing a reduction of 5 dB in the label power without additional penalty. The enhanced tolerance to group velocity dispersion (GVD) of the payload is experimentally assessed and a 5-dB penalty is observed for 136 ps/nm of accumulated dispersion. Additionally, simulation results show the efficient use of electrical dispersion compensation to improve the GVD tolerance, allowing the doubling of the dispersion tolerance.     

基于射频信号2阶零功率的链路色散测量技术

为了适应高速率大色散光纤信道对链路色散的精确补偿要求,研究并提出了一种基于射频信号2阶零功率点的信道色散测量方案。采用信号两边带的位相差来测量光纤链路中的色散值,通过在发射端加载射频信号,可以得到接收端射频信号功率大小随链路色散值的周期性变化关系,从仿真光纤链路色散随射频信号频率的变化曲线获得接收端射频信号2阶零功率点位置。结果表明,基于射频信号2阶零功率的信号测量方案色散测量误差可控制在±10ps/nm范围内。相较于1阶零功率点,基于射频信号2阶零功率点信道色散测量方案可满足高速率、长距离大色散光纤信道对色散值的精确测量需求。     

Subcarrier multiplexing for high-speed optical transmission

The performance of high-speed digital fiber-optic transmission using subcarrier multiplexing (SCM) is investigated both analytically and numerically. In order to reduce the impact of fiber chromatic dispersion and increase bandwidth efficiency, optical single-sideband (OSSB) modulation was used. Because frequency spacing between adjacent subcarriers can be much narrower than in a conventional DWDM system, nonlinear crosstalk must be considered. Although chromatic dispersion is not a limiting factor in SCM systems because the data rate at each subcarrier is low, polarization mode dispersion (PMD) has a big impact on the system performance if radiofrequency (RE) phase detection is used in the receiver. In order to optimize the system performance, tradeoffs must be made between data rate per subcarrier, levels of modulation, channel spacing between subcarriers, optical power, and modulation indexes. A 10-Gb/s SCM test bed has been set up in which 4 × 2.5 Gb/s data streams are combined into one wavelength that occupies a 20-GHz optical bandwidth. OSSB modulation is used in the experiment. The measured results agree well with the analytical prediction     

Optimization of SNDR for amplitude-limited nonlinearities

Many components used in communication systems are nonlinear and have a peak power or peak amplitude constraint. Nonlinearity generates distortions and thus signal-to-noise-and-distortion ratio (SNDR) is an appropriate performance measure. In this paper, we are interested in finding the nonlinear mapping that maximizes the SNDR subject to the peak amplitude constraint. The answer is a soft limiter with gain calculated based on the noise power and the probability density function of the input amplitude. We also investigate a bounding relationship between the SNDR and capacity of the nonlinear channel. The results of this paper can be applied for efficient transmission of high peak-to-average power ratio signals or for optimal linearization of nonlinear devices.     

Optical dispersion eigencompensators for high-speed long-haul IM/DDlightwave systems: computer simulation

This paper proposes what is believed to be the first linear optical dispersion-compensating technique capable of more effectively compensating for dispersively chirped signal than dispersively chirp-free signal. An effective digital eigen-filter approach is introduced for designing optical dispersion eigencompensators (ODECs) for compensation of the combined effects of laser chirp and fiber chromatic dispersion at 1550 nm in high-speed long-haul intensity-modulation direct-detection (IM/DD) lightwave systems. An integrated-optic synthesis of the ODEC using planar lightwave circuit (PLC) technology is proposed to enable high-speed signal regeneration. The proposed eigencompensating scheme is shown to result in the phenomenon of optical power enhancement: the combined effects of laser chirp, fiber chromatic dispersion and ODEC group delay can re-open the receiver eye further than the ideal eye-opening. The eigencompensating approach is shown to compare favorably with the Chebyshev filter technique in both the frequency and time domains     

The Transmission Performance of Non-zero Dispersion Shifted Fiber Communication Systems Using In-line Phase-sensitive Amplifiers

1　ＩｎｔｒｏｄｕｃｔｉｏｎＨｉｇｈ ｓｐｅｅｄｌｏｎｇ ｄｉｓｔａｎｃｅ (ｎｏｎ ｒｅｇｅｎｅｒａｔｉｖｅ)ｔｒａｎｓｍｉｓｓｉｏｎｉｓｔｈｅｍａｉｎｇｏａｌｏｆｏｐｔｉｃａｌｆｉｂｅｒｃｏｍｍｕ ｎｉｃａｔｉｏｎｓ.Ｔｈｅｆａｃｔｏｒｓｌｉｍｉｔｉｎｇｔｒａｎｓｍｉｓｓｉｏｎｓｐｅｅｄａｎｄｄｉｓｔａｎｃｅａｒｅｆｉｂｅｒｌｏｓｓ,Ｇｒｏｕｐ ｖｅｌｏｃｉｔｙＤｉｓｐｅｒ ｓｉｏｎ (ＧＶＤ )ａｎｄｆｉｂｅｒｎｏｎｌｉｎｅａｒｉｔｙ .ＩｔｈａｓｂｅｅｎｓｈｏｗｎｔｈａｔＥｒｂｉｕｍ ｄｏｐｅｄＦｉｂｅｒ…     

Attenuation and fluorescence characteristics of optical signalspropagating in an erbium-doped fiber

For a monochromatic input signal launched into an erbium-doped fiber (EDF), a broadband fluorescence spectrum will be generated with total power approximately 30 dB lower than input signal power. The forward fluorescence power decays slowly at long EDF length due to smaller absorption cross section for wavelength components away from absorption peak. Care must be taken when the conventional cutback method is used to measure the attenuation of the optical signals in an EDF. The backward fluorescence power is saturated to a constant level, and the spectrum does not change for long EDF     

基于NOLM的二元信号功率均衡器研究

为了全光处理具有固定功率差异光信号,本文在详细分析非线性光纤环形镜(NOLM)受不同泵浦作用时输出特点的基础上,设计了将二元功率光信号进行幅度直接均衡的方案.利用光子学仿真软件进行了数值实验,结果显示二元信号经幅度均衡后的输出功率由均衡器输出级探测波功率直接确定,输出脉冲无波长改变,且幅度抖动小.输出脉冲无基座表明该方...     

Analysis of optical phase-conjugate characteristics of picosecondfour-wave mixing signals in semiconductor optical amplifiers

We have analyzed for the first time the optical phase-conjugate characteristics of picosecond four-wave mixing (FWM) signals in semiconductor optical amplifiers (SOAs) using the finite-difference beam propagation method (FD-BPM). We show that the optical phase-conjugate characteristics of the FWM signals are strongly dependent on input pump pulsewidths. As a typical example, we have demonstrated that SOAs act as an ideal phase-conjugator, within the confines of reversing the chirp of optical pulses, for a 10-ps input pump pulse and a ~2.2-ps linearly chirped input probe pulse. When the pulsewidth of pump pulse becomes short, the minimum compressed pulsewidth is obtained by using a fiber shorter in length than the input fiber, but having the same group velocity dispersion as the input fiber. For a much shorter pump pulse such as 1 ps, the short FWM signal can be obtained via the gating characteristics of the FWM. However, only a part of the phase information is copied to the FWM signal due to such gating characteristics. The phase information is also degraded due to the fast nonlinear effect in the SOA. Thus, the pulsewidth is not compressed by propagation through a dispersive medium     

Cross-phase modulation in intensity modulation-direct detection WDMsystems with multiple optical amplifiers and dispersioncompensators

The cross-phase modulation (XPM) effect in intensity modulation-direct-detection (IM)-(DD) optical fiber links with multiple fiber segments with different characteristics and optical amplifiers is investigated theoretically and numerically. A generalized model of the IM induced by an arbitrary number of channels through XPM is derived, compared to simulation results and its validity range is presented. Results show that the XPM-induced IM can be modeled as an intensity modulator driven by the intensity of copropagating waves. The frequency response of the intensity modulator corresponding to each copropagating wave is mainly affected by the walk-off parameter and fiber dispersion. When the walk-off effect is weak the XPM-induced IM is approximately proportional to the square frequency. In single-segment fiber links when the walk-off effect is strong the XPM-induced IM is approximately linearly proportional to the frequency and inversely proportional to the wavelength separation. Both theory and simulation show that the XPM-induced IM in fiber links with multiple optical amplifiers can be enhanced or reduced by properly arranging the dispersion characteristics in each fiber segment. In a nondispersion compensated amplified link and for weak walk-off effect, the total XPM-induced IM increases approximately with the square of the number of fiber segments and of modulation frequency. However, if the dispersion is compensated for within each fiber segment the total XPM-induced IM increases proportionally to the number of fiber segments and to the square frequency. Furthermore, it is shown that in fiber links with a large number of segments placing a single dispersion compensator in the last segment of the link leads to almost the same performance as for non dispersion compensated fiber link and is significantly worse than placing one dispersion compensator in each fiber segment as far as the XPM-induced IM reduction is concerned     

Modeling of four-wave mixing and gain peaking in amplified WDMoptical communication systems and networks

A theoretical model is presented for analyzing the propagation of densely spaced WDM optical signals through a cascade of erbium-doped fiber amplifiers and single-mode optical fibers with nonuniform chromatic dispersion. By combining a numerical solution for the EDFA and an analytical expression for FWM components generated through the cascade, the model allows a realistic system analysis which includes gain peaking effect, amplified spontaneous emission accumulation and the effect of dispersion management on the four-wave mixing efficiency. The FWM power distribution at the end of the multi-amplifier transmission link is computed taking into account the phase relation between FWM light amplitudes generated within different sections of the link. The transmission of many WDM channels, evenly spaced around 1547.5 nm, has been analyzed for various dispersion management techniques and propagation distances. Numerical results point out the importance of such a model for a realistic design of WDM optical communication systems and networks. A proper choice of chromatic dispersion, amplifier characteristics, span length, input signal powers and wavelengths, combined with the use of gain equalizing filters, allows to maximize the transmission distance ensuring acceptable signal-to-noise ratio (SNR) and limited SNR variation among channels     

DCF色散补偿性能的研究

分析了光纤色散和非线性效应。研究了利用色散补偿光纤(DCF)进行色散补偿的三种方案,数值模拟了采用这三种方案对在G.652光纤上传输375 km速率为10 Gb/s和40 Gb/s光信号进行色散补偿时入纤光功率对系统误码性能的影响,并分析了模拟结果,筛选出其中一种最好的方案,给出了具体的入纤光功率的取值范围。     

基于光纤差分相移键控的色散补偿方案的研究

为了研究光差分相移键控(DPSK)调制格式在光纤高速传输系统中的色散补偿, 利用色散补偿光纤(DCF)的色散补偿原理, 对40Gbit/s光纤传输系统进行色散补偿, 分析了40Gbit/s单通道光纤传输系统中3种DPSK调制格式信号的频谱特性; 仿真了3种码型的色散容忍度以及3种调制格式在考虑光纤的非线性下的色散补偿方案。结果表明, 光非归零码差分相移键控(NRZ-DPSK)信号具有最好的色散容忍度, 但其受非线性的影响比较大; 33%归零码差分相移键控(33%RZ-DPSK)信号的色散容忍度差, 但其色散补偿后的效果优于NRZ-DPSK; 而载波抑制归零码差分相移键控信号对色散和非线性效应都有较好的抑制; 3种DPSK调制格式均在对称补偿2方案中色散补偿的效果最佳。此仿真研究对光DPSK信号在光纤中的色散补偿具有参考意义。     

Highly Linear Power Tracking Doherty Amplifierfor WCDMA Repeater Applications

This letter presents a highly linear power tracking Doherty power amplifier (DPA) for wide-band code division multiple access (WCDMA) repeater system. To achieve maximum linearity without extra linearization circuits, the drain bias voltages of the carrier and peaking amplifiers as well as the gate bias voltage of the peaking amplifier are adaptively controlled using the power tracking method according to average power level of the input signal. For experimental verification, a two-way DPA has been implemented at the WCDMA band of 2.11~2.17 GHz and tested using one-tone, two-tone, and four-carrier WCDMA signals. Two-tone and WCDMA test results show the notable cancellation of the IM3 and IM5 components and the significant improvement in adjacent channel leakage ratio over a wide range of output power levels.     

光载毫米波在光纤中传输色散性能研究

提出了并理论分析了一种采用单电极Mach–Zehnder调制器(SD-MZM)产生光载毫米波的方案。采用电混频器将射频信号与基带数字信号混频后再利用单电极调制器产生双边带调制信号并发送至光纤,在基站使用一个交叉复用器(IL)将双边带信号的中心载波与一阶边带信号进行分离,中心载波可用于上行链路的光载波,而一阶边带产生光载毫米波;理论分析了该毫米波的色散特性并在仿真平台上验证了其正确性,研究发现由于光纤色散引起两个一阶边带的延时不同, 从而导致毫米波能量的损失和解调信号的码间干扰,限制了毫米波的最大传输距离。