50/100GHz AWG型光学梳状滤波器的设计与制备

以Si基SiO2平面光波导为基础,设计并制备了50/100GHz AWG型光学梳状滤波器.制备得到的AWG型光学梳状滤波器可以覆盖1520～1585nm的波长范围,共有160个信道.功率输出不均匀度＜0.5dB,插入损耗＜8dB,相邻通道的串扰＞13dB,在距离中心频率最远的信道,输出频率偏离ITU标准15GHz.分析了影响器件串扰和信道频率偏移的原因,并提出了相应的解决办法.     

50/100GHz AWG型光学梳状滤波器的设计与制备

以Si基SiO2平面光波导为基础,设计并制备了50/100GHz AWG型光学梳状滤波器．制备得到的AWG型光学梳状滤波器可以覆盖1520～1585nm的波长范围,共有160个信道．功率输出不均匀度＜0.5dB,插入损耗＜8dB,相邻通道的串扰＞13dB,在距离中心频率最远的信道,输出频率偏离ITU标准15GHz．分析了影响器件串扰和信道频率偏移的原因,并提出了相应的解决办法．     

热膨胀机制产生窄带激光声信号的方法研究

为压缩激光声信号的带宽,基于热膨胀激光致声理论提出了一种采用高重频激光脉冲串产生窄带声信号的方法(重频法),推导了最优重复频率的计算过程,并通过实验测量对重频法进行了验证。以声信号在中心频率处的功率谱密度为参考标准,将重频法与长脉冲法产生窄带声信号的性能进行了比较。理论分析与实验结果表明,激光器在最优重复频率下产生的声信号窄带特性最好;最优重复频率与激光波长、光束半径以及观测角有关;激光脉冲数大于10时,重频法的性能优于长脉冲法;脉冲数为100时,在中心频率处重频法的功率谱密度比长脉冲法高9.3dB。     

SOI基微环谐振可调谐滤波器

采用电子束光刻和ICP刻蚀等工艺制作出基于SOI纳米线波导微环谐振滤波器。滤波器微环半径为5μm左右,波导截面尺寸为(350nm～500nm)220nm不等。测试结果表明,波导宽度为450nm时器件性能最为理想,其自由频谱宽度为16.8nm,1.55μm波长附近的消光比为22.1dB。通过对微环滤波器进行热光调制,在21.4℃～60℃温度范围内实现了4.8nm波长范围的可调谐滤波特性,热光调谐效率达到0.12nm /℃。同时,研究了基于单环和双环的多通道上下载滤波器,实验结果表明多通道滤波器的信号传输存在串扰,主要是不同信道之间的串扰,尤其在信号上载时,会在相邻信道产生较大串扰。     

基于Interleave和微谐振环的32信道波分复用器特性

对结合interleave滤波器的1×32信道垂直耦合双环谐振波分复用器件的传输特性进行了研究,得到了器件的光学传递函数公式,对器件的参数、光谱响应、分波光谱、插入损耗以及信道间的串扰进行了数值模拟和优化.分析结果表明,通过在微环谐振波分复用器件的前端增加interleave滤波器,使信道间的串扰降低了14 dB,并且改善了器件的输出光谱形状,提高了器件的信道复用密度;同时,由于采用了在同一基片上集成,保证了器件的低插入损耗.通过参数优化,得到了中心波长为1 550 nm、波长间隔为0.4 nm、3 dB带宽为0.21 nm、插入损耗低于1.1 dB和串扰低于-32 dB的32信道密集波分复用器(DWDM).     

新型Christiansen滤波器的设计

针对一种新提出的新型Christiansen滤波器,进行了理论计算、仿真分析和实验,其功率透射谱和理论数据吻合.结果表明:通过对输出谱、峰值功率、邻道串扰、3 dB带宽以及光阑孔径进行数值分析和比较,设计出峰值损耗低于4 dB,3 dB带宽低于2 nm的器件.并且对比一阶至四阶sinc函数滤波器的仿真功率透射谱发现,越高阶的滤波器,其功率透射谱越理想,性能越好.     

一种基于正交向量的极化相关衰减效应消除方法

针对双极化通信场景下正交极化信号串扰导致的解调性能恶化问题,提出了一种基于正交向量的极化相关衰减效应消除方法. 该方法通过对发送信号进行设计,利用一组正交向量分别在发射端和接收端对极化信号进行处理,达到消除极化间串扰的目的,同时在发送端利用估计的信道参数处理发送信号,进一步消除非理想信道影响. 在不改变噪声功率的基础上,实现正交极化信号的无串扰接收,有效提高接收端信号解调性能. 理论分析和仿真结果表明,极化状态调制信号的解调误码率逼近高斯信道下的理论值,相比于预补偿方法和迫零矩阵法有更好的误码率性能,仿真结果与理论推导具有较好的一致性. 本文方法能有效解决无线信道中正交极化信号间串扰,提高接收端信号解调性能.     

3G-ALE短波信号信道化接收机高效设计

快速选频建链对提高短波通信系统的接通率和通信质量至关重要,针对第三代自动链路建立（3G-ALE）短波信号频率较低、信道带宽窄、信道个数多的特点,设计了一种基于加权叠接相加（WOLA）滤波器组的射频直采信道化接收机,同时,提出了信道组内有效信道全覆盖的方式,能够使建链时间缩短为单路接收时的1/511。在高斯白噪声信道下进行了仿真,当SNR低至-9dB时同步捕获概率甚至可以达到100%,当SNR高于24dB时误码率为0,与单路接收相比该信道化接收机不会因为并行接收而降低信号接收质量。     

波长转换对光交叉连接节点中串扰的影响

针对具有波长转换功能的节点共享型和链路共享型光交叉连接(OXC)节点,分析了相干串扰和非相干串扰引起的功率代价并进行了仿真计算.结果表明,相干串扰引起的功率代价远远大于非相干串扰,尤其当时间延迟小于激光器的相干时间并小于码型周期时,串扰引起的功率代价最大.为达到一定的系统性能,分析了WDM光网络对器件的要求,并比较了波长转换器的加入对OXC节点串扰的影响,结果发现,加入波长转换器后,系统的功率代价有一定的改善,相同条件下波长转换器的加入对器件的隔离度要求降低2 dB.     

MIMO—OFDM系统的半盲迭代接收机

针对存在多载波窄带干扰的多输入多输出正交频分复用系统，本文提出了基于马尔可夫链蒙特卡罗方法的迭代接收机．该方法不仅可以精确地估计出信道脉冲响应，还可以估计出噪声方差以及脉冲噪声发生的位置，这样接收机能够对窄带干扰区别对待，从而有效提高系统性能．该方法的另一个优点是，易于和软输入软输出译码结合，从而完成Turbo接收．仿真结果表明，在慢衰落信道下，与理想信道状态信息下的接收算法仅有3dB差别.     

采用小波进行频带分割的脉冲压缩方法

针对因频带分割滤波器的不理想产生的频谱混叠、幅度以及相位失真导致子带脉压误差较大的问题,提出了一种采用小波设计的正交镜像滤波器组进行频带分割的子带脉压方法.借助小波及多分辨分析理论,利用最优频域准则设计频带分割滤波器组,消除或减小混叠失真、幅度及相位失真后,对信号进行频域分解,实现子带脉冲压缩.仿真结果表明,和传统的子带脉压方法相比,所提的脉压方法在主副瓣比方面提高了约12 dB,最大脉压误差减小了约7 dB,验证了该算法的正确性和有效性.     

DQPSK: When Is a Narrow Filter Receiver Good Enough?

In this paper, we investigate experimentally and via simulation the pros and cons of a narrow filter receiver for differential quadrature phase-shift keying based on a single optical filter and eschewing the conventional asymmetrical Mach-Zehnder interferometer structure. We quantify the performance differences between the two receivers, allowing system designers and operators to determine when the less complex narrow filter receiver might be the appropriate choice. We numerically optimize the 3-dB bandwidth and center frequency of the narrow filter and show it is more robust to carrier frequency detuning than the conventional solution. We show that the narrow filter receiver is more tolerant to chromatic dispersion (CD) than the conventional one, and equally tolerant to first-order polarization-mode dispersion. We show the impact of the 3-dB bandwidth on the receiver performance when CD accumulates. Finally, we show via experiments and simulations that the 3 dB advantage of the conventional receiver vanishes when the nonlinear impairments are fiber nonlinearities; comparing the two receivers at the optimum launch power for a 25 times 80 km system, the difference in optical SNR margin is reduced to ~1.6 dB. Experiments are conducted at 42 Gb/s using a commercially available narrow filter for reception.     

Observation of coherent interchannel interference in themultiwavelength operation of an acoustooptic filter

Wavelength-division multiplexing using acoustically tuned optical filters offers narrow channel spacing, wide tuning range, and the capability for multiple-wavelength switching. It is shown that a coherent source of interference can arise in multiwavelength switching, due to the simultaneous interaction of several acoustic waves with even a single optical channel. Bit-error-rate studies have been performed on an integrated-optic version of the acoustooptic filter and a crosstalk penalty of ~2 dB due to dual channel interference has been observed. The theoretical origin of this crosstalk is described and it is shown that a modest relaxation of channel spacing can effectively eliminate and crosstalk penalty     

A wavelength-tunable semiconductor amplifier/filter for add/drop multiplexing in WDM networks

Reconfigurable channel drop in a wavelength-division multiplexed system is demonstrated using a packaged semiconductor amplifier/filter. The filter is electrically tunable over 9.0 nm with a 0.9-nm width and is used with an optical circulator to demultiplex three 5.0-Gb/s WDM channels spaced by 2.25 nm. A receiver sensitivity improvement and low optical crosstalk is observed over a dynamic range of nearly 10 dB.     

Tunable polymer optical add/drop filter for multiwavelength networks

We present a polymer optical add/drop filter with a channel cross-talk of -18.5 dB, a free spectral range of 12.8 nm and a channel spacing of 400 GHz (4 channels) as well as a tunable optical filter with a free spectral range of 50 nm. Both filter designs are based on a synthesis which provides the minimum number of filter stages for a given channel crosstalk and number of channels. Wavelength tunability over the entire free-spectral range (FSR) is demonstrated with applied heating powers of 500 mW. For the narrow bandwidth filter we used a fluorinated high temperature stable polymer as the waveguiding material, which has proven to exhibit losses as low as 0.25 dB/cm at a wavelength of 1.55 /spl mu/m.     

Methods for crosstalk measurement and reduction in dense WDMsystems

We propose a scheme for the monitoring and reduction of crosstalk arising from the limited stop-band rejection of optical bandpass filters in dense WDM systems. The optical carrier at each wavelength is modulated with a subcarrier tone unique to that wavelength. The level of crosstalk from a given channel can be determined by measuring the power of the corresponding tone. Crosstalk from other channels can be cancelled in a linear fashion by weighting and summing the photocurrents of the desired channel and several adjacent interfering channels. Alternatively, in nonlinear crosstalk cancellation, decisions are made on the interfering signals, and these decision are weighted and summed with the photocurrent of the desired channel. For example, assuming an optical filter having a Gaussian passband, the channel density can be increased from 20 to 30%, depending on the number of adjacent channels detected. The signal-to-interference ratio can be increased by 10-20 dB and the system can achieve a BER<10^-9 under conditions where, without interference cancellation, the signal-to-interference ratio would be less then 10 dB     

The effect of crosstalk and phase noise in multichannel coherentoptical DPSK systems with tight IF filtering

Results for two-channel differential-phase-shift-keying (DPSK) systems using finite integrator and raised cosine response IF filters are presented. The sensitivity of an optical receiver in a two-channel DPSK system is studied. The results are compared with previous work in the limit of no phase noise and it is shown that the agreement is good. The penalty due to crosstalk for different linewidths and filter shapes is computed, and it is shown that the minimum channel spacing is a few bit rates for an ideal integrator IF filter and is larger for an IF filter with a raised cosine impulse response. The penalty is increased somewhat by phase noise     

Comparison of MC-CDMA with DS-CDMA using frequency domain and time domain RAKE receivers

In this paper a multicarrier CDMA (MC-CDMA) system with a soft decision differential phase shift keying (DPSK) frequency domain RAKE receiver is described. We compare a MC-CDMA system with a direct sequence CDMA system using RAKE receivers. In contrast with previous MC-CDMA systems, guard intervals are not used and the carriers are spaced at the reciprocal of the bit rate, optimising the usage of the bandwidth. In this way a comparison can be made between the multicarrier CDMA system described and a direct sequence (DS-CDMA) system with the same bandwidth. The results presented are received bit error rates from Monte Carlo simulations. The simulations are conducted in a multipath channel with Rayleigh fading and 300 Hz Doppler spectrum with additive white Gaussian noise. It is shown that the multicarrier CDMA matched filter receiver performs favourably compared to the direct sequence CDMA matched filter receiver for 1 -path fading. For a single user at a receive bit error rate of 1×10^–3 in the 4-path fading channel the multicarrier RAKE receiver requires no knowledge of the channel delay spread and performs 3 dB worse than the DS-CDMA RAKE receiver simulated. The performance of the MC-CDMA RAKE receiver for a single user increases with increasing channel dispersion. The performance of the DS-CDMA RAKE receiver for multiple user is superior to that of the MC-CDMA RAKE receiver.     

Crosstalk investigation of laser-diode pairs

The crosstalk between the lasers of different laser-diode pairs has been investigated experimentally in the frequency domain. The mutual crosstalk of two lasers diodes monolithically integrated on a single transmitter chip and separated by 100 μm was measured to be about -50 dB up to a modulation frequency of 100 MHz. At higher frequencies, it rises linearly with the frequency to -40 dB at 1 GHz. Measurements and calculations indicate that the origin of this crosstalk is the leakage current in the chip and inductive coupling of the bond wires. With these crosstalk values, digital data transmission at high bit rates is possible without significantly reducing the receiver sensitivity     

WDM transmission system performance: influence of non-Gaussiandetected ASE noise and periodic DEMUX characteristic

This paper presents the first unified wavelength division multiplexing (WDM) transmission model for systems incorporating cascaded optical amplifiers and a realistic demultiplexing (DEMUX) characteristic with periodic transfer function. The bit error ratio (BER) is evaluated accounting in rigorous form for the influence of non-Gaussian detected amplified spontaneous emission (ASE) noise, noise correlation between stochastic noise samples in the receiver, the bandwidth of the electrical receiver noise filter, the gain tilt and effective noise figure of optical amplifiers (with as well as without optical ASE noise filtering), channel crosstalk, signal extinction ratio and a one-or two-stage DEMUX implementation. The model is compared to the Gaussian receiver model in realistic design cases providing important information as to the validity of the Gaussian model. Practical design results indicate the link budget dependence on the DEMUX design and the ASE noise filtering