Polarization dependent distortion in AM-SCM video transmissionsystems

The second-order intermodulation distortion product, namely composite second-order (CSO) distortion, of an AM-SCM video transmission system can be caused by the optical isolators, cascaded fiber amplifiers, or the fiber transmission cable employed. Moreover, the absolute distortion value depends on the polarization angle of light input to the optical isolators, cascaded fiber amplifiers, and fiber transmission line. The degraded distortion values are measured and their mechanisms are clarified     

Polarization dependent gain in erbium doped-fiber amplifiers

Measurement of polarization hole burning is reported for an erbium doped fiber amplifier. This effect produces a dependence of gain, measured with a weak probe, on the polarization of the saturating signal; the maximum gain occurs for probe polarizations orthogonal to the signal. The pump also contributes to the gain dependence on polarization. Reduction of the degree of polarization of both pump and signal below 10% reduces the polarization dependent gain substantially     

Polarization insensitive frequency conversion of a 10-channel OFDMsignal using four-wave-mixing in a semiconductor laser amplifier

Four-wave-mixing based on ultrafast nonlinear gain dynamics in a semiconductor laser amplifier was applied for wavelength conversion of a 10-channel OFDM signal with a channel spacing of 9 GHz and a modulation rate of 140 Mb/s per channel. Conversion over 275 GHz was realised. BER measurements revealed no severe system degradation due to polarisation fluctuations or cross-talk     

Polarization dependent loss in polymeric rib channel waveguide

Large polarization dependent loss (PDL) as high as 15 dB was observed in the rib-type channel waveguide fabricated using a birefringent polymer. The PDL mechanism was explained by the mode-mode coupling between the TM mode of a rib and the TE mode of a slab waveguides. This TM-TE mode conversion is due to nonuniform off-diagonal component of the dielectric susceptibility tensor which is generated by a thermal stress during the curing process.     

钛合金粗糙表面的偏振光及变温BRDF特性

基于红外光谱椭偏仪测得钛合金TC4在298~773 K范围的光学常数,结合Monte Carlo射线跟踪法对钛合金随机粗糙表面的双向反射分布函数(BRDF)进行了研究.分析了不同表面粗糙度、入射光偏振态及温度对钛合金表面BRDF分布的影响.结果表明:偏振光入射下钛合金的BRDF分布随入射角度及表面粗糙度的变化趋势与非偏振光相同;入射平面内粗糙钛合金表面的BRDF随光源偏振态变化与光滑平板具有相同趋势;TE波入射时的BRDF反射峰值大于TM波入射;钛合金粗糙表面的BRDF镜反射峰值随温度升高有下降趋势;在所研究的温度范围内(298~773 K),峰值变化在10.2%以内,温度变化对TM波下钛合金BRDF分布特性的影响大于TE波,且在入射角度增大时影响增大.     

Polarization dependent loss induced gain ripple statistics inerbium-doped fiber amplifiers

A Monte-Carlo model is used to simulate the wavelength-dependent polarization dependent loss (PDL) statistics and PDL induced gain-ripple statistics for a chain of concatenated optical elements in an erbium-doped fiber amplifier (EDFA). Simulations indicate that unlike polarization-mode dispersion (PMD), the quadrature sum of PDL overestimates the mean of the PDL distribution. We show that EDFA total PDL variance scales linearly with the individual component PDL variance. Moreover, the relative impact of PDL on the gain ripple is reduced in the presence of the PDL independent gain ripple in the EDFA     

Polarization mode dispersion and polarization dependent loss for apulse in single-mode fibers

Polarization mode dispersion (PMD) and polarization dependent loss (PDL) for a pulse in optical fibers are calculated with a model of two concatenated fibers. Each of the two fibers has both elliptical birefringence and PDL. The results show that the PMD and PDL for a short pulse can be very different from those for a narrow-band pulse in optical fibers. Two anomalous results are reported: (1) the effective PDL for a pulse can be smaller than the PDL difference of the two fibers and (2) the effective PMD for a pulse can be either larger than the sum of the differential group delays (DGDs) of the two fibers or less than the DGD difference of the two fibers, depending on the input pulsewidth. The pulse distortions when the pulses are launched into the two principal states of polarization (PSPs) are discussed     

Phase locking via Brillouin-enhanced four-wave-mixing phaseconjugation

We show that it is possible to control with good accuracy the relative phase of several conjugate beams for a properly designed Brillouin-enhanced four-wave-mixing phase conjugation system. Three geometries, two that utilize two Brillouin cells and another that requires only one Brillouin cell, that achieve conjugate phase control are studied and many properties of each system are examined. We show that for our high-power laser application the one-cell geometry performs as well as or better than the other geometry. Phase control is shown to be useful for beam combination, vector phase conjugation, and optical path selection. A laser system that utilizes the one-cell geometry to enhance its performance is built and examined     

Polarization dependent gain in erbium-doped fiber amplifiers:computer model and approximate formulas

A computer model for polarization dependent gain (PDG) in Er-doped fiber amplifiers (EDFA) is presented. The model assumes that each erbium ion possesses an ellipsoidal gain surface and that all ion orientations are equally likely. By dividing the ions into subsets based upon orientation and computing the inversion of each subset in the presence of polarized pump and signal waves, the model predicts the dependence of the PDG induced by this polarization hole-burning (PHB) on the design of the EDFA, the signal degree and state of polarization (SOP), and the pump SOP. For moderate gain amplifiers (made from the same fiber) with the same gain peak wavelength and the same compression level, the magnitude of the PDG is nearly independent of the EDFA gain. Internal and random fiber birefringence are included to model real fibers. In fibers which cause the signal SOP to walk rapidly around the Poincare sphere, the PDG is reduced by a factor of 2/3 when compared with a linear polarization-maintained signal. Scrambled signals and partially-polarized saturating tones are also considered. Simple rules are derived for predicting the PDG of a given EDFA     

Polarization dependent loss vector measurement in a system with polarization mode dispersion

A polarization dependent loss (PDL) vector equation of motion in Stokes space was derived in a system interacting with polarization mode dispersion (PMD). A new PDL measurement method based on the PDL vector equation was proposed and validated by numerical simulation and experiment.     

Polarization crosstalk dependence on length in silica-basedwaveguides measured by using optical low coherence interference

We describe a powerful method for precisely measuring polarization crosstalk dependence on length for birefringent waveguides which uses optical low coherence interference between excited and orthogonally coupled light waves. This method is applied to 10-m long silica-based waveguides with the total polarization crosstalks of 8.9×10^-3 and 7.5×10^-3. The spatial resolution is 10 cm and the measurement error for a waveguide part longer than 1 m is ⩽10%. A comparison of measured and theoretical crosstalk curves for the waveguides enables us to confirm that the bends in the waveguides are the main origin of the crosstalk. The polarization crosstalk per bent section is ~4×10^-5     

Polarization dependent loss in a Ti:LiNbO/sub 3/ polarization scrambler/controller

We have investigated the polarization dependent loss (PDL) of a waveguide-type polarization scrambler/controller consisting of a half-wave plate (HWP) and a quarter-wave plate (QWP) in series fabricated in x-cut/z-propagating Ti-diffused LiNbO/sub 3/ optical waveguides. Based on the polarization dependences of both the propagation loss coefficient and mode-mismatch loss with fiber at 1.55 /spl mu/m combined with a numerical analysis, the PDL of the fabricated device is estimated to be 0.063 dB. It is shown that the low PDL is a direct consequence of a special anisotropy relation between the propagation loss and waveguide-fiber mode-mismatch loss.     

极化调制假目标干扰的鉴别

采用数字射频存储器(DRFM)技术的转发式假目标干扰对雷达构成了日益严重的威胁,利用极化信息对真、假目标进行鉴别进而剔除假目标,是对抗假目标干扰的一种有效途径.目前的极化鉴别方法只对脉内极化恒定的假目标干扰有效,为此,本文专门研究了真实目标和脉内极化调制假目标的鉴别方法.首先设计了一种对来波极化矢量进行张量积接收的处理方式,目标回波矢量经此处理后,汇聚于四维复空间中一点,而假目标干扰则无规律地散布在该空间中,利用这种差异,以矩阵间的散度作为鉴别统计量设计了鉴别算法.仿真实验结果及分析结论表明,本文方法对真实目标和脉内极化调制假目标均具有较高的鉴别率.     

Numerical analysis of four-wave-mixing based multichannei wavelength conversion techniques in fibers

We numerically investigate four-wave-mixing （FWM） based multichannel wavelength conversion for amplitude-modulated signals, phase-modulated signals, together with mixed amplitude and phase modulated signals. This paper also discusses the influence of stimulated Brillouin scattering （SBS） effects on high-efficiency FWM-based wavelength conversion applications. Our simulation results show that DPSK signals are more suitable for FWM-based multichannel wavelength conversion because the OOK signals will suffer from the inevitable data- pattern-dependent pump depletion. In future applications, when the modulation format is partially upgraded from OOK to DPSK, the influence of OOK signals on the updated DPSK signals must be considered when using multi-channel wavelength conversion. This influence becomes severe with the increase of OOK channel number. It can be concluded that DPSK signals are more appropriate for both transmission and multichannel wavelength conversion, especially in long haul and high bit-rate system.     

雷达极化问题和铁氧体变极化技术

描述了雷达极化问题的基本概念,提出了两类铁氧体全(变)极化器的机制。从理论上解决了这种器件的收发功能,并介绍了它在极化雷达中可实现极化扫描和接收的功能。     

Numerical analysis of four-wave-mixing based multichannel wavelength conversion techniques in fibers

We numerically investigate four-wave-mixing (FWM) based multichannel wavelength conversion for amplitude-modulated signals, phase-modulated signals, together with mixed amplitude and phase modulated signals. This paper also discusses the influence of stimulated Brillouin scattering (SBS) effects on high-efficiency FWM-based wavelength conversion applications. Our simulation results show that DPSK signals are more suitable for FWM-based multichannel wavelength conversion because the OOK signals will suffer from the inevitable datapattern-dependent pump depletion. In future applications, when the modulation format is partially upgraded from OOK to DPSK, the influence of OOK signals on the updated DPSK signals must be considered when using multichannel wavelength conversion. This influence becomes severe with the increase of OOK channel number. It can be concluded that DPSK signals are more appropriate for both transmission and multichannel wavelength conversion,especially in long haul and high bit-rate system.     

Wide-band polarization-free wavelength conversion based on four-wave-mixing in semiconductor optical amplifiers

Wide-band polarization free wavelength conversion based on four-wave mixing in semiconductor optical amplifiers (SOAs) subject to two pump beams has been studied in detail. With equalized forward and backward pump power, polarization independence of the converted signal was experimentally achieved when the wavelength detuning was larger than 1.24 nm. This is independent of the SOA bias current. When the wavelength detuning between the signal and one pump beam was fixed at 1.6 nm, the amplitude of the converted signal was nearly constant over a 58-nm wavelength range. A new theoretical analysis allows for signals of arbitrary polarization state to be considered. The experimental results are in good agreement with the theory developed here.     

长波红外偏振图像及其误偏振信息分析

给出了长波红外偏振图像融合的结果,对融合的偏振图像进行了定性分析和定量评价.研究表明,偏振图像的融合方法有多种,能产生多种图像融合结果.融合后的长波红外偏振图像凸显了目标的形状,细节更加清楚,边缘更突出,立体感更强.与原始红外图像比较,长波红外偏振图像灰度均值提高168％、灰度标准差提高194％,梯度提高468％.处理后的偏振图像和原始的红外图像比较说明了长波红外偏振成像能明显提高目标和背景之间的对比度,更加有利于目标的识别.和中波红外偏振图像相比,给出了长波红外偏振图像误偏振信息的来源,这些误偏振信息在后续的偏振信息处理中是要消除的,说明了中波红外偏振成像的效果好.     

Polarization dependent loss and temperature fluctuations effect on degree of orthogonality in polarization multiplexed arrayed waveguide grating based distribution networks

We analyze the effect of arrayed-waveguide grating (AWG) polarization dependent loss (PDL) on the orthogonality between polarization multiplexed channels in a cascaded AWG-based access network topology. For a single AWG, with 0.5-dB PDL, we find an experimental degradation in polarization multiplexing orthogonality to be a maximum of 0.9/spl deg/, in good agreement with theory. In addition, experimental, and numerically simulated maps of orthogonality degradation versus input states of polarization (SOP) are investigated and found to agree well. Consequently, we analyze the effect of cascaded AWGs and again find that the experimental result of maximum 2.9/spl deg/ degradation in polarization multiplexing orthogonality closely matches theoretical predictions. Thermal variations are also found to have similar effects for all SOPs, with a measured degradation in orthogonality of up to 2.5/spl deg/ for a temperature range between 20/spl deg/C and 55/spl deg/C. Overall, this indicates the robustness of polarization multiplexing, making it applicable for appropriate deployment in bandwidth/user-enhanced access networks based on cascaded AWGs.