基于Sagnac环可调谐光梳状滤波器特性研究

提出了一种基于Sagnac环干涉结构的光梳状滤波器。该结构利用保偏光纤双折射效应产生梳状滤波响应,通过控制Sagnac环内相位调制器的驱动信号实现光学滤波器陷波深度与滤波波长的独立调谐。利用Jones矩阵对所提出的Sagnac环光滤波器的滤波响应函数进行研究,通过分析得到光滤波器的陷波深度和滤波波长分别与射频信号和直流偏压之间的关系。在此基础上构建实验链路,验证了系统的理论分析,实现了光滤波器陷波深度在0dB~30dB范围内的灵活控制;通过设置直流偏压在0~12V范围内变化,实现了光滤波器滤波波长在一个自由光谱范围(0.5nm)内的连续可调,波长调谐效率为0.043nm/V。     

基于对称结构的光纤谐振环辅助马赫曾德尔干涉仪型梳状滤波器的研究

为了改善常规马赫曾德尔干涉仪(MZI)型滤波器的输出特性, 提出了一种由双耦合器和单模光纤构成的“8”字形谐振环,将该光纤谐振环与一个3 dB光纤方向耦合器相结合,利用光纤谐振环反馈回路引入的相位调节效应,选择合适的谐振环耦合角,设计出一种基于对称结构的光纤谐振环梳状滤波器,具有平坦滤波响应的输出光谱。与普通MZI型梳状滤波器和双级级联MZI型梳状滤波器相比,阻带抑制和过渡带滚降特性明显加强;与不对称结构的光纤谐振环辅助MZI型梳状滤波器相比,在考虑传输损耗的情况下,相干涉的两束光信号不存在幅度差异,降低了传输损耗对梳状滤波器消光特性的影响。     

阵列波导光栅梳状带通滤波器的传输效率

在光波导模场分布高斯近似条件下,根据星形光波导耦合器的耦合特性,推导出了基于累加运算和卷积运算近似表达的阵列波导光栅梳状带通滤波器光谱响应效率的函数表达式。给出了阵列波导光栅梳状带通滤波器光谱响应效率曲线的半最大值全宽度和阵列波导光栅梳状带通滤波器的通道中心波长的光谱响应度与器件参数的关系。在输入信号光谱分布高斯近似条件下,给出了阵列波导光栅梳状带通滤波器信号通道传输效率的计算表达式和输入信号光谱宽度对阵列波导光栅梳状带通滤波器信号通道输出特性的影响。给出了物理意义明确的函数表达式,它们可为快速分析阵列波导光栅梳状带通滤波器的特性提供理论基础。     

基于相位调制和光纤双折射光学倍频法

为实现毫米波信号的光学倍频法产生,利用相位调制器和光纤梳状滤波器,构建了光学倍频系统.其中光纤梳状滤波器由起偏器、双折射光纤和检偏器组成.理论分析表明,在该倍频系统中,通过对梳状滤波器双折射延迟量的选择,可有效地抑制非期望的奇次(偶次)谐波成分;通过对调相指数的优化,可进一步提高期望谐波分量的比例.仿真结果说明,利用该...     

一种结构新颖的高温超导群时延均衡器

本文提出一种平面微带型高温超导微波群时延均衡器，它是由一个3dB混合耦合器和两个单端口反射滤波器构成的全通网络．该群时延均衡器能与不同类型超导微带滤波器级联，实现相位均衡，减小相位失真，改善接收机前端信号群时延特性，提高通信质量．     

梳状波导结构中石墨烯表面等离子体的传播性质

理论上研究了介质/石墨烯/介质梳状波导结构中表面等离子体的传播性质. 波导中表面等离子体模的有效折射率随着石墨烯费米能级的提高而减小, 随着介质折射率的增加而增加. 分析和仿真结果表明, 基于这种梳状波导可以在中红外波段实现新型的纳米等离子体滤波器, 器件的尺度在几百纳米的范围. 通过改变梳状分支的长度, 石墨烯的费米能级, 介质的折射率和波导中石墨烯的层数, 很容易来调节带隙的位置. 另外, 滤波带隙的宽度随着梳状分支数的增加而增加. 这种滤波性质将在可调的高集成光子滤波器件中具有潜在的应用.     

基于法布里-珀罗腔反射光相位特性设计的梳状滤波器

提出了一种用于设计密集波分复用全光网络中梳状滤波器的方法，该器件利用法布里-珀罗腔反射光相位的非线性性质，结合光的相位在一定光程差下随频率呈线性周期变化的特点，通过使这样两束相位匹配的光发生干涉，得到所需滤波特性。运用江膜特征矩阵对模型进行了模拟计算，并分析了计算结果，论证了这种结构的可行性。     

光纤环对非平衡马赫曾德尔干涉仪型波长交错滤波器性能的改善

波长交错滤波器是一种类似于梳状滤波器的无源光子器件，在密集波分复用系统中可以起到复用和解复用器件的作用。如果将一光纤圈加入光纤溶锥型非平衡马赫－曾德尔干涉仪型波长交错滤波器系统中，它的滤波性能将有所改善。改进后的梳状滤波器的透射率形态近似于方波，讨论了新系统的结构和参数选取。     

一种结构新颖的高温超导群时延均衡器

本文提出一种平面微带型高温超导微波群时延均衡器,它是由一个3dB混合耦合器和两个单端口反射滤波器构成的全通网络.该群时延均衡器能与不同类型超导微带滤波器级联,实现相位均衡,减小相位失真,改善接收机前端信号群时延特性,提高通信质量.     

格结构在晶体梳状滤波器设计中的应用

利用数字信号处理中的格滤波器理论,研究了晶体梳状滤波器的设计方法.当传输函数满足对称和功率互补时,分析指出滤波器的阶数是奇数,N阶滤波器只需要(N+1)/2个波片,且所用波片的厚度比为1∶2∶2…2或2∶2…2∶1；提出了对半带滤波器传输函数作谱分解得到光梳状滤波器传输函数的方法.在此基础上总结出根据应用要求设计晶体梳状滤波器传输函数和结构参量的方法,通过设计一个7阶滤波器,表明提出的方法设计过程简单,且设计结果符合梳状滤波特征.     

Toward bias minimization in acoustic feedback cancellation systems

A novel technique for bias suppression within acoustic feedback cancellation systems is proposed. This is achieved based on the use of all-pass filters in the forward part of the hearing aid. The poles of these filters are made time-varying, which results in a frequency response with constant magnitude and varying phase. This is a desired feature of the proposed approach, since the results from human psychoacoustics show that the human ear is not sensitive to moderate phase perturbations. The derivation of the proposed algorithms for the time variation of the location of the poles of all pass filters is based on a rigorous analysis of the phenomenon of bias in acoustic systems. Practical issues, such as the dependence of the steady-state error on the order of the all-pass filter, the number of varying poles, and their standard deviation are examined and strategies for the variation of the poles are introduced. Results obtained from a simulated hearing aid are provided to support the analysis. The quality of the processed audio signals is evaluated through subjective tests.     

多级全通均衡器对介质薄膜滤波器进行色散补偿的探讨

讨论了介质薄膜滤波器的色散特点,并推导了单级全通滤波器的理论色散。比较理论色散曲线与实际测量色散曲线,两者吻合较好。但由于单级全通滤波器的色散带宽及斜率不能满足实际所需的色散补偿曲线,因此提出了多级全通滤波器,通过控制级连的单级全通滤波器的谐振波长及反射率,可以增大色散带宽,改善色散斜率,使之满足实用的要求。文中给出了四级全通滤波器的理论色散曲线。     

Optical all-pass filters for polarization mode dispersion compensation

Polarization mode dispersion (PMD) compensation is addressed by decomposition of a fiber's Jones matrix into amplitude and phase responses, which are then compensated for separately. Cubic and higher-order phase compensation substantially reduce the cumulative probability at a given system penalty over first-order PMD compensation, as demonstrated for a 40-Gbit/s non-return-to-zero signal and a fiber PMD with a differential group delay of 20 ps (rms). Single-stage all-pass filters provide tunable compensation that is comparable to that obtained with a variable-delay line, and multistage all-pass filters are well suited for higher-order phase compensation.     

Dispersion compensation of a 1x N passive optical router with low loss, a flat passband, and low cross talk

A 1xN interferometer-based router with single-stage all-pass filters in the arms has low loss, a flat passband, and low cross talk. However, we show that the router has substantial cubic dispersion over the channel passband, which is identical from channel to channel. For a 1x4 router with a free spectral range of 100 GHz, the average dispersion slope over a 60% passband is -8x10(3)ps/nm(2), and thus a cascade of four routers incurs a significant system power penalty. A three-stage all-pass filter placed on the input arm reduces the dispersion of all channels by a factor of 16. The router is quite insensitive to variations in the all-pass filter design parameters.     

Mechanically switchable photonic crystal filter with either all-pass transmission or flat-top reflection characteristics

We theoretically introduce a new type of optical all-pass filter based on guided resonance in coupled photonic crystal slabs. The filter exhibits near-complete transmission for both on- and off-resonant frequencies and yet generates large resonant group delay. We further show that such a filter can be mechanically switched into a flat-top band rejection filter.     

An analysis on the effect of the equalizer parameters in a direct-modulation optical communication system employing an all-pass filter to combat chirp and dispersion

We consider the effect of the equalizer parameters in the performance of a direct modulated high-bit-rate communication system where the degrading combination of fibre dispersion and source chip is compensated using an all-pass optical filter.     

Further studies on the dual-resonance nonlinear filter model of cochlear frequency selectivity: responses to tones

A number of phenomenological models that simulate the response of the basilar membrane motion can reproduce a range of complex features observed in animal measurements over different sites along its cochlea. The present report shows a detailed analysis of the responses to tones of an improved model based on a dual-resonance nonlinear filter. The improvement consists in adding a third path formed by a linear gain and an all-pass filter. This improvement allows the model to reproduce the gain and phase plateaus observed empirically at frequencies above the best frequency. The middle ear was simulated by using a digital filter based on the empirical impulse response of the chinchilla stapes. The improved algorithm is evaluated against observations of basilar membrane responses to tones at seven different sites along the chinchilla cochlear partition. This is the first time that a whole set of animal observations using the same technique has been available in one species for modeling. The resulting model was able to simulate amplitude and phase responses to tones from basal to apical sites. Linear regression across the optimized parameters for seven different sites was used to generate a complete filterbank.     

All-optical microwave notch filter with flat passband based on semiconductor optical amplifier

An all-optical filter structure for interference mitigation of microwave signals is proposed and demonstrated. The structure is based on a recirculating delay line loop (RDLL) and a fiber Bragg grating. The RDLL is comprised of a semiconductor optical amplifier (SOA) followed by a tunable narrowband optical filter and an optical variable delay line. Negative tap is generated using wavelength conversion based on the cross-gain modulation of amplified spontaneous emission spectrum of the SOA. A negative band-pass filter and a broadband all-pass filter are synthesized to achieve a narrow notch filter with flat passband which can excise interference with minimal impact on the wanted signal over a wide microwave range. Experimental results show the notch rejection ratio of 30 dB, good shape factor and tunability.     

Group delay and dispersion analysis of compound high order microring resonator all-pass filter

In this paper, we propose a novel compound high order microring resonator all-pass filter employing two cascaded microrings and an assistant microring. It improves the dispersion compensation ability and provides a wide bandwidth. The group delay range is effectively extended, which provides flexibility in choosing the geometrical parameters of the microring for technical convenience and bend loss improvement. The careful design of coupling coefficients can optimize the group delay response. This device is able to provide dispersion compensation to systems such as the high speed dense wavelength division multiplexer (DWDM) optical fiber links.     

Dispersion compensation using mismatched multicavity etalon all-pass filter

In this paper, we propose a novel mismatched multicavity etalon (MME) all-pass filter for fixed-value dispersion compensation and dispersion slope compensation. It is a multicavity Gires-Tournois (GT) etalon filter with unequal cavity lengths between adjacent cavities. A theoretical study is presented. Analytical expressions for the group delay and chromatic dispersion are derived to allow device designs to be made. The simulation results show that nearly linear group delay or quasi-flat chromatic dispersion response can be obtained by suitably choosing the reflectances of the reflectors and the cavity mismatch length. The chromatic dispersions and the bandwidth of the quasi-flat-dispersion band can be tailored by changing the reflectances of the reflectors and the mismatched cavity length. The dispersion slope compensation can be obtained by slightly modulating the reflectances of the reflectors. Increasing the number of cavities can enhance the performance and the design flexibility of the dispersion compensator.