一维光子晶体偏振滤波器通道数的影响因素研究

光子晶体偏振滤波器是利用光子晶体带隙特性来控制信号光偏振状态的一种新型滤波器, 在光纤通信、光学传感测量、光学信息处理等领域均有重要应用。通道数多少是偏振滤波器设计的重要指标, 通道越多则信息容量越大, 越有利于系统的小型化微型化。利用光学传输矩阵法研究了影响一维光子晶体偏振滤波器通道数目的因素, 研究表明：(1）光子晶体缺陷层厚度是影响滤波器通道数目的关键因素, 通道数N与厚度D近似满足线性关系, 在500 ～650 nm波段函数关系为N=0.0035D+0.159; (2）缺陷层折射率nc的变化也会导致通道数改变, 折射率越大通道数越多;( 3）光子晶体单元层数和单元厚度改变不会影响滤波通道数, 但可以调节通道中心波长位置, 同时对偏振度和分离度也有影响。     

Low-Complexity Design of Variable Bandedge Linear Phase FIR Filters With Sharp Transition Band

This paper presents a very low-complexity design of variable bandedge linear phase finite-impulse-response (FIR) filters with fixed sharp transition width. The idea is to first decompose the input signal into several channels in the frequency domain. The channel(s) involved with the transition band of the variable filter due to the variation of the bandedge is (are) shaped to produce the required transition band, and then summed up with the channels involved with the passband of the variable filter to produce the required frequency response. The proposed variable filter has extremely low complexity when the transition band is sharp, if compared with other techniques such as the Farrow structure. It is possible that the computational complexity of the variable filter is even lower than that of a corresponding fixed filter with the same transition width and ripple specifications implemented in its direct form.      

A Design Procedure for Bandpass Channel Multiplexers Connected at a Common Junction

A new general design procedure is presented for multiplexers having any number of Chebyshev channel filters, with arbitrary degrees, bandwidths, and interchannel spacings. The design procedure is developed for bandpass channel filters connected in series at a common junction for narrow-band applications. Commencing with the closed-form expressions for element values in Chebyshev filters, the multiplexer design process modifies all of the elements in each channel filter and preserves a match at the two points of perfect transmission closest to the band edges of each channel filter, while taking into account the frequency dependence across each channel. Examples of several multiplexer are given indicating that the design process is valid for most combinations of contiguous and noncontiguous channels.     

Optimal design of contiguous-band output multiplexers (COMUX)

A general multiplexer design procedure without dummy channels is described. The formulas are applied to the optimal design of practical contiguous or non-contiguous band multiplexers consisting of multicavity filters distributed along a waveguide manifold. All design parameters can be directly optimised. An example of a practical 12 channel, 12 GHz contiguous band multiplexer is presented.<>     

Optimum Modulation and Channel Filters for Nonlinear Satellite Channels

This is a comparative study of three modulation schemes: QPSK, Offset QPSK(OQPSK), and MSK, in nonlinear satellite channels with adjacent channel interference. Two kinds of typical satellite channel models are used for performance evaluation: one is an INTELSAT type narrow band model and the other is a domestic type wide band model. The transmitter filter and receiver filter are optimized for each combination of modulation scheme, channel model, and an input back-off condition for nonlinear amplifiers. All the combinations considered here have the optimum division of the Nyquist shaping between transmitter filter and receiver filter in common. The filters are a wide band sharp cut-off transmitter filter with flat inband response and a gently rolled-off Nyquist receiver filter with an aperture equalizer (x/sin xor1-(2x)^{2}/cos xequalizer). With these optimized filters, comparisons are made with respect to the bit error rate (BER) performance and phase jitter of the recovered carrier. OQPSK and MSK show superior BER performance to QPSK in the wide band model. However, in the narrow band model, QPSK shows the best BER performance among the three modulation schemes. The phase jitter in the recovered carrier is small for all modulation schemes in the wide band model. But, in the narrow band model, the phase jitter in OQPSK and MSK is four times larger than in QPSK. Generally QPSK is the most preferable modulation scheme in the narrow band model: OQPSK and MSK are most preferable for the wide band model.     

航空偏振相机的光学偏振特性实验研究

利用大孔径积分球辐射光源系统对航空偏振相机的偏振特性进行了实验研究,以各偏振工作波段中0°放置的偏振通道为基准,选取航空偏振相机中心视场64×64像素点计算并校正了各偏振通道中偏振片／滤光片的强度透过率差异;并进一步测量了航空偏振相机光学系统自身的起偏度,通过最小二乘法多项式拟合,给出了各偏振工作波段的偏振度随视场角的...     

Design of Sparse Filters for Channel Shortening

Channel shortening equalizers are used in acoustics to reduce reverberation, in error control decoding to reduce complexity, and in communication receivers to reduce inter-symbol interference. The cascade of a channel and channel shortening equalizer ideally produces an overall impulse response that has most of its energy compacted into fewer adjacent samples. Once designed, channel shortening equalizers filter the received signal on a per-sample basis and need to be adapted or re-designed if the channel impulse response changes significantly. In this paper, we evaluate sparse filters as channel shortening equalizers. Unlike conventional dense filters, sparse filters have a small number of non-contiguous non-zero coefficients. Our contributions include (1) proposing optimal and sub-optimal low complexity algorithms for sparse shortening filter design, and (2) evaluating impulse response energy compaction vs. design and implementation stage computational complexity tradeoffs for the proposed algorithms. We apply the proposed equalizer design procedures to (1) asymmetric digital subscriber line channels and (2) underwater acoustic communication channels. Our simulation results utilize measured channel impulse responses and show that sparse filters are able to achieve the same channel energy compaction with half as many coefficients as dense filters.     

一维光子晶体异质结结构偏振带通滤波器

利用一维光子晶体(PC)异质结结构带边峰值叠加的方法设计了一种偏振带通滤波器,在实现p偏振分量带通滤波的同时实现了禁带范同的展宽.给出了设计方法,讨论了这种带通滤波器的通带特性和禁带特性.所设计的偏振带通滤波器具有宽通带、宽禁带、膜层较少、小型化和类矩形通带等特点,制作简单,具有实际应用价值.     

基于偏振光干涉仪的Interleaver解复用器实验研究

为实现更窄信道间隔的密集波分复用 ,提出了一种基于偏振光干涉仪的新型Interleaver解复用器 ,分析了结构组成与基本工作原理 ,对其进行了初步的测试实验 ,该器件所分开的DWDM系统两组波长功率均衡 ,隔离度分别为 1 0 6dB和 1 4 6 4dB ,- 1dB带宽分别为 0 7nm和 0 4nm。     

Eliminating SRS channel depletion in massive WDM systems viaoptical filtering techniques

We demonstrate that the channel depletion due to stimulated Raman scattering in massive wavelength-division-multiplexed (WDM) systems can be eliminated using high-frequency pass filters. These filters, when inserted appropriately into the transmission link, can effectively suppress the SRS power flow from the WDM channels to lower frequency noise. Numerical simulations carried out on WDM systems indicate that the channel depletion penalties can be kept below 0.25 dB even for a total channel power of 2 W     

Flexible waveband optical networking without guard bands using novel 8-skip-0 banding filters

Novel five-band 8-skip-0 band filters realized in silica waveguide planar lightwave circuit technology were successfully used to demonstrate versatile wavelength-division-multiplexed (WDM) optical networking. Forty C-band channels spaced 100 GHz apart grouped in five bands of eight channels each allowed WDM networking without loss of any channel within the available optical bandwidth. We demonstrate simultaneous transport of 10 and 40 Gb/s with rate-appropriate optical add-drop nodes.     

用于波分复用的光子晶体滤波器

本文从光子晶体的光子频率禁带特性出发，提出了用2个或以上的均匀周期结构光子晶体叠加在一起，形成叠层结构光子晶体，以获得窄带滤波特性的设想；利用光学传输矩阵法对这种结构进行了数值计算，结果证实了构思的正确性；设计了信道间隔为8nm的8信道波分复用（WDM）和信道间隔0.8nm的8信道密集波分复用（DWDM）光子晶体滤波器。     

Carrier-density modulation effects in a traveling-wavesemiconductor optical amplifier: communications theory analysis andexperiment

A communications theory equivalent model suitable for analyzing carrier-density modulation effects within a traveling-wave semiconductor optical amplifier is derived by linearizing the amplifier rate equation. This model is used to analyze dual-channel amplification, and it is shown to give results which are in good agreement with those given by nonlinear polarization theory and experimental measurements. The effect of four-wave mixing on the amplification of many optical channels for worst-case operating conditions is studied, and it is shown that the individual channels experience different gains. It is also shown that if the individual channel gains are to be confined to lie within a ±1-dB band when operating the amplifier at high values of unsaturated power gain     

极化轨道上SINR滤波器的通带性能研究

本文研究了非相干、完全极化,单信号-干扰源情况下局部化SINR极化滤波器的通带特性,具体导出了在大圆、小圆极化轨道上SINR滤波器通带的计算公式,分析了滤波器通带性能与电磁环境参数的关系。并给出了一组典型滤波器通带特性曲线。     

Tracking in Wireless Sensor Networks Using Particle Filtering: Physical Layer Considerations

In this paper, a new framework for target tracking in a wireless sensor network using particle filters is proposed. Under this framework, the imperfect nature of the wireless communication channels between sensors and the fusion center along with some physical layer design parameters of the network are incorporated in the tracking algorithm based on particle filters. We call this approach ldquochannel-aware particle filtering.rdquo Channel-aware particle filtering schemes are derived for different wireless channel models and receiver architectures. Furthermore, we derive the posterior Cramer-Rao lower bounds (PCRLBs) for our proposed channel-aware particle filters. Simulation results are presented to demonstrate that the tracking performance of the channel-aware particle filters can reach their theoretical performance bounds even with relatively small number of sensors and they have superior performance compared to channel-unaware particle filters.     

A novel correlation adaptive receiver structure for high speed transmissions in ultra wide band systems with realistic channel estimation

Impulse radio ultra wide band (UWB) communications require robust receivers; typically Rake receivers are required to capture a large number of resolvable paths, (even hundred of paths), so large number of correlators are needed; otherwise, adaptive receivers use complex filters and channel estimation algorithms. Therefore, traditional Impulse radio receivers demand non-practical implementation structures. In this paper we propose a novel correlation-adaptive receiver structure with low complexity for indoor high speed ultra wide band systems. This novel structure combines correlation characteristics from Rake receivers with recursive filters from adaptive receivers. The receiver includes a low complexity recursive channel estimation filter capable of estimating hundreds of channel impulse responses, and a single filter-correlation filter used for coherent bit demodulation. Furthermore, we derive by simulations the bit error rate for high density multipath environments for several impulse radio modulations like TH-PPM, DS-BPSK and TH-BPSK and we compare the performance of the proposed structure with typical Rake receivers.     

Combined Equalization and Demodulation of Chaotic Direct Sequence Spread Spectrum Signals for Multipath Channels

Due to the inherent noise-like characteristic of chaotic signals and their sensitivity to the initial value, chaotic direct sequence spread spectrum (CD3S) signals have the advantages of a low probability of intercept (LPI) and a high level of security. Demodulation of non-cooperated CD3S signals is then a challenging issue. If the signal is sent though multipath channels, it is even more difficult for the receiver to demodulate it blindly. Based on the existing theories and methods, we focus more on signals passing through multipath channels. This paper presents an approach to achieve blind equalization and demodulation of CD3S signals through multipath channels. Multiple unscented Kalman filters (UKFs) are used to equalize and demodulate the CD3S signals for the unknown channel. This method can effectively demodulate the signals without any knowledge of the chaotic transmitter’s parameters, initial value, state equation, or the channel coefficients, even when the signal is severely distorted by the multipath channel. Simulation results demonstrate that this method gives faster convergence and better demodulation performance than existing methods for various channel conditions.     

A robust adaptive DFE receiver for DS-CDMA systems under multipathfading channels

This paper presents a novel receiver design from signal processing viewpoint for direct-sequence code-division multiple access (DS-CDMA) systems under multipath fading channels. A robust adaptive decision-feedback equalizer (DFE) is developed by using optimal filtering technique via minimizing the mean-square error (MSE). The multipath fading channels are modeled as tapped-delay-line filters, and the tap coefficients are described as Rayleigh distributions in order to imitate the frequency-selective fading channel. Then, a robust Kalman filtering algorithm is used to estimate the channel responses for the adaptation of the proposed DFE receiver under the situation of partially known channel statistics. The feedforward and feedback filters are designed by using not only the estimated channel responses but the uncertainties and error covariance of channel estimation as well. As shown in the computer simulations, the proposed adaptive DFE receiver is robust against the estimation errors and modeling dynamics of the channels. Hence, it is very suitable for receiver design in data transmissions through multipath fading channels encountered in most wireless communication systems     

An adaptive maximally decimated channelized UWB receiver with cyclic prefix

The frequency channelized receiver based on hybrid filter bank is a promising receiver structure for ultra-wideband (UWB) radio because of its relaxed circuit requirements and robustness to interference. The uncertainties in the analog analysis filters and the time varying nature of the propagation channels necessitate adaptive methods in practical frequency channelized receivers. Adaptive synthesis filters, however, suffer from slow convergence speed especially when maximally decimated to reduce the analog-digital converter sampling frequency. To improve the convergence speed, the cyclic prefix is applied to the transmitted data. The propagation channel and the channelizer can then be modeled as a circulant matrix and block CM, respectively. Such matrix representation enables the transmitted data to be recovered by two cascaded one-tap equalizers, one of which corresponds to the channelizer and the other to the propagation channel. The cascaded structure is attractive as it allows the estimation of the propagation channel and the channelizer, which vary at vastly different rates, to be updated separately. Adaptive algorithms for both the fractionally spaced equalizer and the symbol spaced equalizer are derived. After initial convergence during startup, the adaptive performance of the channelized receiver to different propagation channels is similar to that of an ideal full band receiver.     

面向毫米波遥感成像的双极化毫米波探测器

针对多极化毫米波遥感成像重大需求,报道了一种高集成度双极化毫米波探测器。探测器采用固态电子学方案,通过喇叭天线接收毫米波信号,利用正交模耦合器进行极化信号分离,采用两级低噪放芯片放大信号,通过肖特基二极管实现功率检测。每支探测器集成两路接收通道,每个接收通道可同时探测水平与竖直两个极化方向信号。经测量,探测器探测频段为W波段(75～110 GHz),平均等效噪声温差达到0.3 K(@10 ms),尺寸不足155 mm×15 mm×20 mm,质量<0.3 kg。利用该探测器实现城市环境双极化毫米波遥感成像,成像结果表明,相比于单极化遥感成像,双极化遥感成像可以获得更多极化信息,可对城市环境下常见物品进行突出显示,这有助于今后进行自动物品识别、轮廓提取与远程物质成分识别。