Precompensation for Narrow Optical Filtering of 10-Gb/s Intensity Modulated Signals

Signals in spectrally efficient optical networks can be distorted by the narrowing of the overall bandwidth that occurs when optical add-drop multiplexers are concatenated. In this letter, it is demonstrated that the performance implications of this bandwidth narrowing can be mitigated by precompensation using arbitrary optical waveform generation. The synthesis of the required voltage waveforms for a dual-drive Mach-Zehnder modulator reduces the penalty in receiver sensitivity due to narrow optical filtering from 6.5 to 1.9 dB. Simultaneous precompensation for fiber dispersion is also demonstrated.     

400-ns Continuously Tunable Delay of 10-Gb/s Intensity Modulated Optical Signal

A continuously tunable optical delay line based on a two-pump parametric process in a highly nonlinear fiber providing 400.5-ns range for a 10-Gb/s optical signal is reported. This record 4005-bit delay used fixed dispersion elements, compatible with requirements for fast delay reconfiguration. The large delay range was made possible by partial dispersion slope cancelation.      

Centralized Lightwave WDM-PON Employing 16-QAM Intensity Modulated OFDM Downstream and OOK Modulated Upstream Signals

We have proposed and experimentally demonstrated a novel architecture for orthogonal frequency-division- multiplexing (OFDM) wavelength-division-multiplexing passive optical network with centralized lightwave. In this architecture, 16 quadrature amplitude modulation intensity-modulated OFDM signals at 10 Gb/s are utilized for downstream transmission. A wavelength-reuse scheme is employed to carry the upstream data to reduce the cost at optical network unit. By using one intensity modulator, the downstream signal is remodulated for upstream on–off keying (OOK) data at 2.5 Gb/s based on its return-to-zero shape waveform. We have also studied the fading effect caused by double-sideband (DSB) downstream signals. Measurement results show that 2.5-dB power penalty is caused by the fading effect. The fading effect can be removed when the DSB OFDM downstream signals are converted to single sideband (SSB) after vestigial filtering. The power penalty is negligible for both SSB OFDM downstream and the remodulated OOK upstream signals after over 25-km standard single-mode-fiber transmission.      

相位调制微波光传输链路特性分析（特邀）

常规的微波光子系统采用强度调制方式实现微波信号的电光转换,由于调制器采用马赫-曾德尔干涉结构(MZI),系统性能不仅受到自身正弦响应特性的制约,而且需要进行偏置点控制,因此存在动态范围受限、系统控制复杂以及3 dB固有损耗带来的效率不足的问题,而采用相位调制可避免该问题。围绕相位调制光传输链路,为了完成相位调制信号的光电解调,文章提出采用薄膜滤波器通过边带抑制与边带选通两种方式实现相位调制到强度调制的转换,并分析了链路射频性能与器件参数之间的映射关系。实测对比了相位调制与常规强度调制链路之间的传输特性,通过分析可知,在相同链路配置条件下,相位调制链路具有更高的传输效率,而且光滤波带来的均衡作用,使得相位调制链路的3 dB带宽比强度调制链路大两倍。     

BPSK Subcarrier Intensity Modulated Free-Space Optical Communications in Atmospheric Turbulence

Free-space optical communications (FSO) propagated over a clear atmosphere suffers from irradiance fluctuation caused by small but random atmospheric temperature fluctuations. This results in decreased signal-to-noise ratio (SNR) and consequently impaired performance. In this paper, the error performance of the FSO using a subcarrier intensity modulation (SIM) based on a binary phase shift keying (BPSK) scheme in a clear but turbulent atmosphere is presented. To evaluate the system error performance in turbulence regimes from weak to strong, the probability density function (pdf) of the received irradiance after traversing the atmosphere is modelled using the gamma-gamma distribution while the negative exponential distribution is used to model turbulence in the saturation region and beyond. The effect of turbulence induced irradiance fluctuation is mitigated using spatial diversity at the receiver. With reference to the single photodetector case, up to 12 dB gain in the electrical SNR is predicted with two direct detection PIN photodetectors in strong atmospheric turbulence.     

Complex Spectrum Analysis of Modulated Optical Signals Using Stimulated Brillouin Scattering

We introduce a novel method for the measurement of the spectral phase of modulated optical signals based on double-pump stimulated Brillouin scattering interaction and direct homodyne detection. This technique is combined with Brillouin high-resolution analysis to achieve a complete characterization of the complex optical spectrum. A 10-Gb/s nonreturn-to-zero signal with a 32-bit pattern modulated with an electroabsorption modulator is measured using this technique and its time-domain information (power and chirp) is obtained by inverse Fourier transform.      

Signal Intensity Estimators for Free-Space Optical Communication With Array Detectors

Estimators motivated by the minimum mean-square estimation (MMSE) criterion are presented for the estimation of the optical signal intensity in free-space optical (FSO) communication systems impaired by atmospheric-induced scintillation. Joint parameter estimators for the estimation of signal intensities across a photodetector array are investigated. Three scenarios are considered. First, it is assumed that the received signal is detected using a p-i-n photodiode array and that the receiver operates under a shot-noise-limited condition. In the second scenario, the received signal is detected using an APD array and the receiver operates under a shot-noise-limited condition. In the third scenario, the received signal is detected using an APD array, but the receiver is impaired by thermal noise as well as shot noise. The mean primary electron count received by the APD is assumed to be large enough to justify the Gaussian approximation. The optical channel is modeled using a log-normal distribution with correlated random signal intensities across the array. With the aid of simulation, it is shown that the proposed estimators outperform the maximum-likelihood estimators for small scintillation indices while providing a performance similar to the maximum a posteriori estimator.     

Weighted Discriminator Function Based Unambiguous Tracking Method for Dual-Frequency Constant Envelope Modulated Signals

The dual-frequency constant envelope modulated (DCEM) signals, represented by alternative binary offset carrier signal, have obvious advantages in code tracking accuracy and anti-multipath performance compared with traditional binary phase shift keying signal, and are attracting more and more attention in the field of global navigation satellite system signal design. However, DCEM signal has a multiple-peaked auto-correlation function, which would lead to the tracking ambiguity problem. To deal with this problem, this paper proposes an unambiguous tracking method based on weighted discriminator function (WDF). This method uses the discriminator functions of noncoherent early minus late power (NELP) and sub carrier phase cancellation (SCPC) to generate a linear WDF without no false-lock points. In addition, a simplified version of the proposed WDF method is also provided for interoperable application. The theoretical code tracking error in thermal noise is derived out and verified. The performance of the proposed WDF is evaluated and compared with SCPC and pseudo correlation function methods with the help of simulation. Results show that our method has a significant improvement in code tracking accuracy. Not only the ambiguity threat is efficiently removed, but also the outstanding performance of DCEM signal is maintained.     

一种混合噪声调制的脉冲多卜勒雷达信号的平均模糊函数

本文研究了随机脉冲位置调制与脉冲之间随机相位调制相结合的脉冲多卜勒雷达信号。首次给出了该随机序列的模糊函数数学表达式，对其推导过程所采用的主要方法作了叙述，并对结果进行了分析。     

强度型光纤传感器的信号处理技术

本文从开发强度型光纤传感器的实用产品出发,根据我们自身的研制工作,提出了采用低噪声的光电探测器——电流放大器电路——半片微机作非线性处理这种三段式的信号处理方案,并希望对研制光纤传感器的同行能提供有益的参考。     

外腔半导体激光器强度调制的小信号分析

本文用小信号分析的方法,研究了外腔半导体激光器的强度调制特性。给出了用外腔改善其调制特性的条件。分析了反馈相位、反馈强度的影响。     

调幅信号的参数循环累量估计

本文利用循环累量讨论讽调幅混合相位信号的参数估计方法。首先给出了调幅信号的基于任意阶循环累量的参数方程。对于调幅混合相位ＡＲ，ＭＡ和ＡＲＭＡ模型，提出了相应的参数估计方法。模拟实验表明了本文方法的有效性。     

Pseudo Optical PAM‐N Signal Using Externally Modulated Lasers

We propose a pseudo optical N‐level pulse‐amplitude modulation (PO PAM‐N) signal using a few externally‐modulated lasers (EMLs) operating at different wavelengths, which is suitable for upgrading the transmission speed over an optical link of ＜ 10 km single‐mode fiber with low‐cost components. To compare a PO PAM‐N signal with that of a standard optical PAM‐N signal, we perform experiments for evaluating the performance of a 51.56‐Gb/s PO PAM‐4 signal and standard 51.56‐Gb/s optical PAM‐4 signal. The receiver sensitivity (at ) of the PO PAM‐4 signal is 1.5 dB better than the receiver sensitivity of a standard optical PAM‐4 signal. We also investigate the feasibility of PO PAM‐N signals operating at 103.12 Gb/s, considering relative intensity noise, timing jitter, extinction ratio (ER) of EMLs, and dispersion. From the results, a PO PAM‐8 signal performs better than PO PAM‐4 and PO PAM‐16 signals at 103.12 Gb/s. Finally, we suggest a timing control method to suppress the effect of dispersion in a PO PAM‐N signal. We show that the tolerance to dispersion of a 103.12‐Gb/s PO PAM‐8 signal can be improved to ±40 ps/nm by applying a proposed scheme.     

Filter-Bank Modulation Based Signal Design and Transmission Techniques for Intensity Modulated MIMO Visible Light Communication Systems

Wireless Personal Communications - Current research in wireless communication undoubtedly points towards the tremendous advantages of using visible light as a spectrum for significantly boosting...     

一种BOC调制信号捕获技术

本文提出一种二阶类BPSK方法,该方法兼顾了运算量和灵敏度,有效消除了BOC调制信号的模糊度,使得接收机能够准确捕获卫星导航新体制信号.经过验证,该方法可以提高信噪比,实现BOC调制信号的高灵敏度捕获.     

Wavelength Conversion of High-Speed Phase and Intensity Modulated Signals Using a Highly Nonlinear Chalcogenide Glass Chip

We report all-optical wavelength conversion of high-speed differential phase-shift keyed (DPSK) and on–off keyed (OOK) signals using the nonlinear Kerr-effect in an optical chip. This was enabled by four-wave mixing (FWM) of the signal with a continuous-wave (CW) pump laser in a 7-cm-long dispersion-shifted planar rib waveguide in highly nonlinear $hbox{As}_{2} hbox{S} _{3}$ glass. Both conversion of 40-Gb/s DPSK and 160-Gb/s OOK signals by 33 and 15 nm, respectively, are shown. These are first demonstrations of signal processing by CW-pumped FWM in a chalcogenide waveguide, highlighting its capability to perform phase-preserving operations at high bit rates in chip-scale devices.      

数字调制通信信号载波频率估计算法

应用修正的ESPRIT算法估计6种数字调制通信信号的载波频率,并且和其他两种算法的性能作了比较。仿真表明,在中等信噪比条件下,ESPRIT算法对载波频率的估计具有均值精确、方差小的特点,表现出较好的实用性和较强的稳健性。     

DPSK-PM调制信号数字解调方法研究

针对卫星USB测控系统中常用的DPSK-PM调制技术，设计了一种简单的数字解调方法。在介绍算法原理的基础上，对解调算法进行了仿真，仿真结果证明了该方法的有效性。该方法对于航天测控链路信息对抗仿真平台的建立具有指导意义。     

漏光环形透镜的光学传递函数

推导了漏光环形透镜的三维(3-D)、2-D和1-D光学传递函数(OTF)公式，给出漏光系数对OTF的影响。模拟计算和分析表明：漏光不改变系统的横向截尾频率，但轴向截尾频率大大增加，由(1-ε^2)／2变为1／2；高ε(遮挡率)系统具有较高的横向成像质量，但轴向信息几乎不能成像；对于高ε系统，中心遮挡区的稍稍漏光对横向成像质量几乎没有影响，但轴向成像质量可显著提高；简单的改变漏光系数，可以获得任意调节的轴向分辨率。     

一种强度调制型光纤传声器的设计研究

提出了一种强度调制型光纤传声器的设计。该设计使用束型光纤用于传送光线和接收反射光线,并提出四点接触式MEMS反射膜片结构,给出了ANSYS仿真结果。该光纤传声器具有较好的光耦合效率,使后续放大电路设计更加简便。