Generation and distribution of a wide-band continuously tunable millimeter-wave signal with an optical external modulation technique

A new technique to generate and distribute a wide-band continuously tunable millimeter-wave signal using an optical external modulator and a wavelength-fixed optical notch filter is proposed. The optical intensity modulator is biased to suppress the odd-order optical sidebands. The wavelength-fixed optical notch filter is then used to filter out the optical carrier. Two second-order optical sidebands are obtained at the output of the notch filter. A millimeter-wave signal that has four times the frequency of the microwave drive signal is generated by beating the two second-order optical sidebands at a photodetector. Since no tunable optical filter is used, the system is easy to implement. A system using an LiNbO/sub 3/ intensity modulator and a fiber Bragg grating filter is built. A stable and high spectral purity millimeter-wave signal tunable from 32 to 50 GHz is obtained by tuning the microwave drive signal from 8 to 12.5 GHz. The integrity of the generated millimeter-wave signal is maintained after transmission over a 25-km standard single-mode fiber. Theoretical analysis on the harmonic suppression with different modulation depths and filter attenuations is also discussed.     

可调谐光纤F-P线性滤波器的设计与分析

光纤滤波器在光纤通信和光纤传感领域发挥着重要的作用。本文基于光学薄膜干涉理论设计了一种用于光纤传感的可调谐F-P线性滤波器,该滤波器由两端面相对的入射光纤与出射光纤构成,两光纤端端面分别镀有反射光纤薄膜。该F-P干涉腔改善了传统F-P腔的透射率响应特性,有助于提高滤波器的线性度和线性范围。本文采用光学薄膜干涉矩阵分析法对该滤波器的透射率响应关系进行了计算与分析,并得出该FP滤波器的结构参数。设计结果表明,这种新型线性滤波器具有线性度好、线性范围宽和线性区间可调的优点。     

入射角度不敏感型石英光双折射滤波器

为了实现石英光滤波器中心波长随角度变化不敏感的目的,利用石英光滤波器绕着平行于或垂直于石英光轴的方向旋转时,石英光滤波器输出中心波长漂移方向不同的原理,提出了一个新型的两级改进型的Lyot石英光滤波器滤波的方法,并进行了相关理论分析和实验验证。结果表明,当入射角小于18时,这个新型的光滤波器的中心输出波长的确对入射角度的变化不敏感。该结论与相关的实验结果是相符合的。     

两种不同类型的滤光片式彩色亮度计性能比较

显示器的色度和亮度可以通过彩色亮度计进行测量。小视场滤光片式彩色亮度计因其低成本在生产线上应用广泛,而近来出现的影像式彩色亮度计虽然也属滤光片式,但是由于其探测器不同而具有大视场,且结构、原理和性能与前者都有差异。量化比较这两类滤光片式彩色亮度计的性能,可以为影像式彩色亮度计的质量评估提供依据。文章分别选取两类滤光片式彩色亮度计中的代表型号,通过进行原理分析和实验验证进行对比分析。结果表明,影像式彩色亮度计的性能不低于小视场滤光片式彩色亮度计。     

超窄带宽可调光滤波器的研究

为了降低可调光滤波器的带宽,采用双光栅结构和基于微机电系统的反射镜相结合的方法,构建了具有波长连续可调谐的超窄带宽滤波器,并进行了理论分析和实验验证,取得了滤波带宽小于0.4nm的数据。结果表明,双光栅结构的光滤波器具有性能稳定、重复性优良的性能特点,并且很好地满足了带宽需求。这种结构显著降低了可调谐光滤波器的滤波带宽,提高了系统的稳定性。     

二维多项式位相光瞳滤波实现超分辨望远成像

为了对望远光学系统实现横向超分辨成像,设计了一种高斯特列尔比的二维多项式函数形式的位相型光瞳滤波器,分析了其对光学系统焦点附近光强分布的有益影响。理论分析表明,加入滤波器之后,与无滤波器时相比系统横向光学分辨率提升了1.33倍,同时斯特列尔比为无滤波器时的0.75倍。给出了该种滤波器与典型的三区型、四区型和一维多项式位相型光瞳滤波器的对比,从对比结果可知,二维多项式型滤波器的斯特列尔比为几种滤波器中的最优,且其横向分辨倍率仅次于四区型滤波器,但四区型滤波器的斯特列尔比过低,不适合应用于望远系统。研究了入射光视场角对应用该种滤波器的望远光学系统成像效果的影响,视场角不大于4时,具有较佳的超分辨效果。     

On the cascade of incoherent discrete-time microwave photonic filters

In this study, a theoretical analysis leading to the derivation of the overall incoherent transfer function of a microwave photonic filter composed of the cascade of two optical structures is developed. Two cases that are more common in practice are considered, i.e., 1) a filter illuminated by a single optical source and 2) a compound filter illuminated by an optical source array. In both cases, the conditions on which the overall incoherent transfer function can be expressed as the product of the individual incoherent transfer functions of each of the optical structures that compose the filter are investigated. In other words, the conditions where the end-to-end electrical linearity is preserved when cascading incoherent optical structures are studied. These results are of importance for the design of complex incoherent filter structures aiming to provide high Q or single resonance performance.     

A New Optical Fiber Line Testing Function for Service Construction Work That Checks for Optical Filters Below an Optical Splitter in a PON

In this paper, we propose a new function for construction work undertaken to install optical fiber lines for services in a passive optical network (PON). This paper describes a novel measurement technique designed to check for optical filters located in front of an optical network unit in branched optical fiber regions in PONs with outside optical splitters. The purpose is to determine whether an optical fiber is ldquoliverdquo or ldquounused.rdquo The features of our proposed technique are the use of test lights operating at two different wavelengths and a nondestructive macrobending technique. By comparing the difference between the reflected powers of the two wavelengths, we can determine the presence of a filter at the end of a fiber line. Furthermore, we describe an enhanced estimation analysis method that uses two photodetectors installed symmetrically in the detection part and an analysis procedure for detecting only a test light reflected from the fiber end. We also demonstrate the performance of the enhanced analysis method experimentally and confirm that it can be employed to detect an optical filter installed at the end of an optical fiber line.     

A band-pass microwave photonic filter based on Lyot-Sagnac filter and cascaded optical structures

A band-pass microwave photonic filter（MPF）based on Lyot-Sagnac filter and two cascaded optical structures is demonstrated.In the experiment,a stabilized and tunable multi-wavelength optical source is obtained by slicing the broadband optical source（BOS）with a Lyot-Sagnac filter.A standard single-mode fiber（SMF）and a fiber ring resonator are cascaded to improve the mainlobe-to-sidelobe suppression ratio（MSSR）and Q-factor of the filter.The analysis shows that MSSR and Q-factor are improved by reducing the split ratio of the coupler or increasing the length of fiber in fiber ring resonator.The results have significant guidance for MPF design by choosing appropriate devices and parameters.Based on the analyses,a band-pass filter with MSSR of 53.54 dB and Q-factor of 4048 is achieved by choosing the split ratio of0.01,the length of SMF of 30 km and the length of fiber in fiber ring resonator of 152.27 cm.     

Optical Millimeter-Wave Up-Conversion Employing Frequency Quadrupling Without Optical Filtering

This study presents two optical frequency quadrupling techniques for generating high-purity millimeter-wave signals with optical carrier suppression. To our best knowledge, this investigation demonstrates for the first time that a frequency quadrupling system requires only a single integrated Mach–Zehnder modulator without an optical narrowband filter to remove undesired optical sidebands. Since no optical filter is needed, fast frequency tuning is straightforward and this approach is particularly attractive for the optical up-conversion in the wavelength-division-multiplexing radio-over-fiber systems. This study provides both theoretical analysis and experimental demonstration. The generated optical millimeter-wave signals are of very high quality with optical carrier and undesired harmonic distortion suppression ratio of more than 36 dB.      

Optical Millimeter-Wave Signal Generation Using Frequency Quadrupling Technique and No Optical Filtering

This letter demonstrates a novel method to generate high-purity optical millimeter-wave signals with carrier suppression by using a frequency quadrupling technique. To the authors' knowledge, this is the first time that a frequency quadrupling system requires only a single integrated Mach-Zehnder modulator without a narrowband optical filter to remove undesired optical sidebands. Since no optical filter is needed, fast frequency tuning is straightforward and this approach will be particularly attractive for optical up-conversion in wavelength-division-multiplexing radio-over-fiber systems. This letter provides both theoretical analysis and experimental demonstration. The generated optical millimeter-wave signals have very high quality with an optical carrier and harmonic distortion suppression ratio of more than 38 and 36 dB at 40 and 72 GHz, respectively.     

利用光学微分预处理的强度光学相关

本文把采用菲涅耳全息滤波器的强度光学相关识别系统与光学微分预处理系统相结合,通过对输入图像进行边缘增强预处理,强度相关器的鉴别能力得到了改善。给出了理论分析和实验演示的结果。     

Design and analysis of a novel tunable optical filter

In this paper, an improved design of a tunable optical filter device which is driven by a piezoelectric actuator is proposed. The device can be used either as a tunable optical filter for discrete wavelength alignment or as a dynamic optical filter. The tunable filter is electrostatically driven and consists of three main parts: The electromechanical stage, the suspension and the thin film optical filter. The electromechanical stage and the suspension were designed using graph presentation methods, studied numerically using the finite element method (FEM). The thin film optical filter was designed by a thin film design software. The electromechanical stage was integrated with the suspension and tested as an angular driver of thin-film tilt interference filter for dense-wavelength division demultiplexing system applications.     

基于应变的多模光纤可调谐光纤滤波器设计

可调谐光纤滤波器技术是波分复用系统的关键技术之一,对于发展全光通信网络和光纤传感具有极其重要的意义。提出了一种基于大芯径的多模光纤可调谐带阻滤波器,其制作方法是将包层/纤芯直径为125/105μm的特种多模光纤通过单模光纤接入光纤系统,实现单模-多模-单模(SMS)光纤结构,并使一端单模光纤与多模光纤熔接,另一端只是共轴对接而不焊接。在多模干涉原理的基础上,利用该结构对应变的敏感性实现可调谐光滤波。该可调谐滤波器的调制和解调借助于放大自发辐射(ASE)宽谱光源和光谱分析仪(OSA)实现。详细给出了该滤波器的理论仿真分析,并实验证实了该方案的有效性。     

A figure of merit for iso-index filter materials

A discussion of materials for dispersive birefringent filters which simultaneously exhibit extremely narrow bandwidths (< 1 Å) and wide fields of view (geq +45degacceptance angle) will be presented in this paper. Two specific types, the iso-index filter and the dispersive birefringent Lyot filter are considered. First, a figure of merit for the filter material is derived. Then the figure is related to the optical properties of the material. From this analysis the dependence of the filter bandwidth on crystal birefringence and optical bandedge characteristics is obtained.     

A comparison between optical SSB transmitter-filter in a full-duplex radio-on-fiber transport system

We present the investigation of the fiber Bragg grating (FBG) filter as an optical single sideband (SSB) filter at the receiving site. A comparison is made with an alternative optical SSB generation technique using optical SSB transmitter. The function of the optical SSB filter is employed to replace the optical SSB transmitter, not only to select the appropriate wavelength but also to suppress the fiber dispersion effect. Using simple FBG filter as an optical SSB filter in full-duplex radio-on-fiber (ROF) transport systems is a very attractive option, as it is passive and potentially low cost.     

腔体为单轴晶体的F-P滤光片光学性质仿真研究

为了计算腔体为单轴晶体的F-P滤光片的光学性质,采用理论分析的方法,对垂直入射到光轴在入射面内的单层单轴晶体薄膜的寻常光与非寻常光在两界面处的电磁场量的边界条件和薄膜两界面处电场量的相位关系进行了分析,得到了单层晶体薄膜反射率与透射率的计算方法,并将其应用于腔体为单轴晶体的F-P滤光片光学特性的仿真,取得了滤光片透射率随光轴方向变化的数据。结果表明,光轴旋转角对F-P滤光片的透射峰有明显影响。     

Performance of optically preamplified receivers with Fabry-Perotoptical filters

A technique is presented for evaluating the probability of error for an optically preamplified receiver with a fiber Fabry-Perot optical filter of arbitrary bandwidth between the preamplifier and photodiode. The technique permits simultaneous consideration of the distortion due to modulator chirp and fiber dispersion, the optical filter and the baseband electrical filter. The optical filter is characterized by a Lorentzian passband response, and the quadrature noise processes due to the amplified spontaneous emission are represented by Karhunen-Loeve expansions. For an arbitrary optical filter bandwidth, the evaluation of the probability of error depends explicitly on the details of the Karhunen-Loeve expansion. The solution procedure is general and consequently can, in principle, be applied to other filter passband responses. The influence of the bandwidths of the optical and electrical filters on the performance of a 10 Gb/s system is assessed     

光谱精确可控Sagnac环滤波器及其在ASE光源中的应用

研究了一种结构新颖光谱特性可精确控制的Sagnac环滤波器,这种滤波器通过在传统Sagnac环中插入两段高双折射光纤和一个偏振控制器构成。利用等效光路和传输矩阵法理论研究了该滤波器的滤波特性,研究结果表明,固定两段高双折射光纤参数,仅通过调整偏振控制器的状态,便可精确控制Sagnac环滤波器的滤波光谱特性。将Sagnac环滤波器用于掺铒光纤（EDF）放大的自发辐射（ASE）光源的光谱平坦滤波,通过调节偏振控制器三个波片的倾斜角度,实验获得了光谱平坦的宽带ASE激光。     

Analysis of signal distortion and crosstalk penalties induced by optical filters in optical networks

The design of optical communication networks with network switching elements operating in the optical domain requires careful system analysis and potentially stringent component requirements. We consider here network elements such as transparent optical cross-connects that demultiplex WDM signals, optically switch individual channels, and then multiplex the wavelengths together again before transmission into the next span. Network element optical impairments that can significantly degrade signal quality are in-band (same wavelength) crosstalk and signal distortion from filter concatenation effects. We examine tradeoffs between accumulated crosstalk and filter distortion in the context of the optical filters used in the network elements and demonstrate the balance that must be struck in the design of the filters and network system. As an example, we study a 10-Gb/s network with 50-GHz channel spacing, examining both nonreturn-to-zero (NRZ) and return-to-zero (RZ) modulation formats. In both cases, we find optimal filter bandwidths that minimize the total signal degradation measured in terms of Q penalty, including filter misalignment statistics and signal laser frequency offset. A model is developed to treat the statistical nature of filter misalignment and its effect on filter-generated in-band crosstalk. The optical node penalties suffered by RZ signals can be significantly higher than that of NRZ signals and must be considered when estimating overall system reach.