级联光子晶体Mach-Zehnder干涉仪的可调谐滤波特性

基于液晶的电控双折射特性和光子晶体自准直特性,在二维光子晶体引入复合缺陷提出一种可调谐Mach-Zehnder 干涉(MZI)滤波器结构,应用液晶系统的自由能理论,推导了外加电压与液晶有效折射率的关系,并结合MZI 相位调制原理和光子晶体等效折射率理论,得到液晶的电控双折射特性与MZI 滤波器的输出光谱间的数学关系,运用时域有限差分法(FDTD)对滤波器的输出进行仿真模拟,并根据仿真结果对结构进行一级级联的优化设计。结果表明:通过控制外加电压的大小可以改变输出端的透射波长,达到可调谐滤波的效果,并且一级级联后的滤波效果比级联前有很大的改善,滤波的半波带宽从20 nm 减小为7 nm,可调谐范围从15 nm 增大为40 nm,因此可以通过进一步级联的方式使滤波器结构更加的优化,以便运用到光波分复用系统中。     

S波段GaAs PHEMT宽调谐比可重构滤波器芯片设计

基于单片微波集成电路技术设计了一款S波段频率可调谐滤波器芯片,该可调谐滤波器芯片采用信道化结构,通过选择不同通道实现宽调谐比。其中每个通道采用多级放大器与无源滤波网络级联的形式提高该滤波电路的选择性,通过在无源滤波网络引入变容二极管实现通道频率的连续调谐,该结构可在滤波器具备较高选择性的前提下实现宽调谐比。采用0.25 μm GaAs 赝配高电子迁移率晶体管(PHEMT)工艺设计了一款S波段双通道信道化可重构滤波器,仿真结果表明,在0~3 V控制电压范围下,该滤波器中心频率调谐范围为2.5~4 GHz,带宽变化范围为420~650 MHz,调谐比达到60%,滤波器芯片尺寸为3 mm×3.1 mm。该设计为片上可重构射频滤波实现宽频率调谐比提供了一条技术途径。     

纤内马赫-曾德尔结构优化光纤环镜滤波器研究

在单模光纤(SMF)上拉出级联对称缓锥,形成马赫 -曾德尔干涉仪(MZI)结构,将其置入光纤环镜中, 理论和实验研究了它对滤波器特性的改善。环镜滤波器的透射谱由MZI和Sagnac干涉 结合的非相干叠加而成,调谐MZI能实现可调谐滤波。实验表明,滤波器在自由 谱60nm(1425～1485nm)范围内可提高梳状滤波 器的滤波器特性,实现了可调谐滤波。本文结构输出波形稳定, 调制深度大于20dB,优化了光纤环镜滤波特性。     

一种频率与带宽可调的可重构射频滤波器芯片

本文基于0.25μm砷化镓赝晶高电子迁移率晶体管工艺设计实现了一款频率与带宽皆可调的有源可重构滤波器芯片。该滤波器采用了双通道信道化拓扑结构,每个通道由两级可调谐振器与三级宽带放大器交叉级联构成,通过对通道内各级谐振器频率的同步和异步控制,实现对滤波器的频率与带宽的调谐,通过不同工作频段的通道间切换组合,实现了频率的宽范围调谐。为了验证该设计的有效性,完成了该滤波器的流片,其尺寸为3.1 mm×3.0 mm。经实测,该滤波器通带中心频率可在2.52 GHz～3.92 GHz之间进行调谐,频率调谐比达到了54%,通道内带宽可实现350 MHz～1 080 MHz之间的变化,相对带宽可调范围为12%～33%,同时具备了频率和带宽的宽范围调控能力。     

基于液晶材料的带宽可重构毫米波滤波器

根据液晶材料在毫米波段良好的介电特性和调谐能力,设计了一款基于液晶材料的毫米波带宽可重构宽带带通滤波器。滤波器使用一个高通滤波器和一个低通滤波器级联实现带通效果;在低通部分加载液晶材料,通过调谐液晶材料的等效介电常数改变低通滤波器的响应频率,实现带宽的可重构。仿真结果表明,当调谐液晶介电常数从2.4变化到3.8时,滤波器的高频截止频率从52 GHz下降至48 GHz,相对带宽从84.9%变为78.3%。     

基于MMI滤波器的可调谐连续光全光纤OPO

在连续光全光纤光学参量振荡器（FOPO）中,目前主要利用可调滤波器（TBPF）等高插入损耗的滤波器件进行边带光输出波长的调谐,这种方式所引起的高环形腔损耗限制了FOPO输出性能的进一步提升。为解决此问题,提出了基于多模干涉（MMI）滤波器的低腔损耗可调谐连续光FOPO。通过选取不同长度和纤芯尺寸的多模光纤制作级联单模-多模-单模光纤（SMS）作为滤波器件,使其在选定波长处的插入损耗小于1 dB,FOPO环形腔的总损耗不大于5 dB,并通过对SMS器件施加轴向拉力的方式调节滤波器件的透射谱,实现了1 494~1 501 nm和1 638~1 629 nm范围内的双边带可调谐连续光输出。     

可调谐窄带宽的负系数微波光子滤波器

针对负系数微波光子滤波器很难用正系数的光学抽头来实现,提出了一款基于色散器件级联的可调谐、窄带宽、负系数微波光子滤波器。利用整形后的多波长光纤激光器的输出信号作为滤波器的抽头光源,将单模光纤与F-P光纤环级联作为延迟单元,实现滤波器的频率选择性。利用相位调制器和级联的色散器件共同作用,实现负系数的微波光子滤波器。实验得到了波长间隔为0.34 nm的多达37个激光信号的稳定输出,进而基于此实验结果仿真研究了F-P光纤环中C2、C3的耦合系数r、不同长度的可调谐光纤延迟线（TODL）和延迟单元中不同长度的单模光纤等参数对微波光子滤波器性能的影响。     

基于高双折射光纤环镜的可调谐光滤波器

为了得到具有全光纤结构和中心波长可调谐的光滤波器,采用3阶高双折射光纤环镜,提出了一种电磁力的悬臂调谐单元构成的新型可调谐光滤波器,对环镜传输过程和悬臂调谐单元原理进行了理论分析,通过控制悬臂调谐单元的输入电流,实现了滤波器通带的调谐。结果表明,该滤波器具有调谐灵活、输出光谱精细等特点,可应用于不同波长光波的选频输出。     

中红外可调谐量子级联激光器研究进展

量子级联激光器(QCL)是中红外波段重要的激光光源,其中,可调谐中红外量子级联激光器具有单纵模、频率可调谐的优点,成为目前研究的热点。可调谐中红外量子级联激光器主要通过分布反馈(DFB)光栅、分布布拉格反射(DBR)光栅、外腔衍射光栅等方法实现。本文介绍了中红外量子级联激光器的基本原理,分别归纳、总结了近年来DFB、DBR可调谐量子级联激光器以及外腔可调谐量子级联激光器的研究进展,讨论了各种可调谐方法的优缺点。最后,对可调谐量子级联激光器的发展趋势进行了展望。     

基于重构等效啁啾超结构光纤光栅的可调谐微波光子滤波器的仿真研究

提出了一种新型的基于重构等效啁啾(REC)超结构光纤光栅的可调谐微波光子滤波器的结构。根据REC技术, 利用同一块均匀相位掩模板可以灵活地设计制作出具有不同斜率的线性群时延的光纤光栅。作为有限冲击响应(FIR)滤波器的抽头延时单元, 不同光纤光栅之间群时延的差值决定了滤波器的自由频程(FSR)。通过改变可调谐激光器的输出波长来选择不同的抽头间时延差从而达到调谐FSR目的。仿真结果表明, 该滤波器可以实现中心频率从21 GHz到33 GHz的连续可调。事实上, 由于REC技术的灵活性, 在理论上对于任意给定的频段和调谐范围, 这种新型的滤波器结构都能够实现。     

A tunable polarization-independent liquid-crystal Fabry-Perotinterferometer filter

The authors propose a simple structure for a tunable polarization-independent wavelength-selective filter. This successfully fabricated filter consists of a liquid crystal Fabry-Perot interferometer, a γ/4 plate, and a mirror. The input light is divided into a transmitted light and a reflected light. The polarization of this reflected light is rotated 90° by the γ/4 plate and the mirror and then this light is input again into the filter. The bandwidth is 0.48 nm and the tuning range is 50 nm. Fiber-to-fiber loss is approximately 3.9 dB and polarization dependence of the loss is approximately 0.3 dB     

有源光纤环形腔滤波器优化

本文引入输入光线宽因子,利用多光束干涉理论,给出了有源光纤环形腔滤波器输出光谱密度等公式。利用这些公式可以对腔的结构和参数方便地进行理论分析和优化设计,当使该有源滤波器工作在锁定状态时,可得到窄线宽光输出。     

Wavelength conversion using a light injected DFB-LD and aMach-Zehnder filter with a ring resonator

Wavelength conversion using a light injected DFB-LD and a Mach-Zehnder filter with a ring resonator (r-MZ) is described. It utilizes frequency modulation of the DFB-LD induced by an external light and the FM/IM conversion function of the r-MZ filter. Owing to a unique characteristic of the r-MZ filter, the converter has good tolerance for input signal level and an effect of suppressing signal fluctuation, compared with a conversion scheme using a conventional MZ filter     

Wavelength conversion with self wavelength selection using Mach-Zehnder filter and DFB-LD

Wavelength conversion with a self wavelength selecting function is described. The convertor utilises the FM/IM conversion function of a Mach-Zehnder filter and the light injection induced frequency shift in a DFB laser diode. Frequency-modulated light is converted to another wavelength which can be tuned by a wavelength selection signal contained in the original input light.<>     

1.5 μm phase-shift-controlled distributed feedback wavelengthtunable optical filter

A 1.5-μm phase-shift-controlled distributed feedback wavelength tunable optical filter is studied. This wavelength tunable optical filter controls the transmissivity (gain) and the transmission wavelength independently by current injection. During wavelength tuning, the submode suppression ratio is large and a wavelength tuning range as wide as 120 GHz (9.5 Å) with 24.5-dB constant gain is achieved. An 18-channel wavelength selection with less than -10 dB crosstalk is expected with this filter. The effect of the light input, whose wavelength is in the sidelobe, on the transmission spectrum shape is shown     

Wavelength conversion for frequency-modulated light using opticalmodulation to oscillation frequency of a DFB laser diode

A technique for wavelength conversion for frequency-modulated (FM) light is described. It utilizes the light-injection-induced frequency shift of a distributed-feedback (DFB) laser diode and the frequency-modulated-to-intensity-modulated (FM-IM) conversion function of the Mach-Zehnder (M-Z) optical filter. Input FM light is converted into IM light by the M-Z filter. The IM light is injected into the DFB-LD oscillating at another wavelength, modulating its oscillation frequency. The output from the DFB-LD has an FM signal identical to the input FM light. Thus, wavelength conversion for FM light is achieved. The characteristics of the frequency shift induced by this optical injection were experimentally studied using a λ/4 phase-shift DFB-LD. A wavelength conversion experiment was performed. In the experimental demonstration, FM light at 1.534 μm was converted into FM light at 1.550 μm     

A Tunable Lyot Birefringent Filter With Variable Channel Spacing and Wavelength Using Nonlinear Polarization Rotation in an SOA

We experimentally demonstrate a tunable fiber-optical Lyot birefringent comb filter with independent tuning of the channel spacing and wavelength. The filter configuration is based on sandwiching a fiber-optic programmable differential group delay line (DGDL) and a semiconductor optical amplifier (SOA) between two polarizers. The channel spacing of the filter can be tuned by adjusting the programmable DGDL. Using the nonlinear polarization rotation effect in the SOA, the phase shift between the transverse electric and the transverse magnetic components of the input probe beam can be adjusted by varying the power of the pump light, and hence fast and continuously wavelength tuning of the filter can also be achieved. The wavelength tuning range is up to 50% of the channel spacing when the pump power is increased from ${-}$10 to 17 dBm.      

基于光纤环的可调谐微波光子滤波器

设计了2种基于光纤环和啁啾光栅（CFBGs）的无源可调谐微波光子滤波器的新颖结构。这两种结构的滤波器可通过改变输入光波长来实现滤波器自由频程（FSR）的调谐,其所需的FSR可通过光纤环中CFBs的写入位置来控制。研究结果表明,2种滤波器的结构是有效和可行的,在微波和毫米波光纤系统中有着潜在的应用价值。     

两种接收机结构的等效性证明

现行的各种通信原理教材中,最佳接收机框图里其输入端均无带通滤波器,而凡是使用低通滤波器的接收机框图里其输入端都有带通滤波器。针对学生提出的低通滤波器型接收机输入端是否一定需要带通滤波器的疑问,本文着重对无带通滤波器的低通型接收机的误码性能进行了推导,理论证明了无带通滤波器接收机结构与有带通滤波器接收机结构的等效性。     

Fast orthogonalization networks

A numerically efficient and stable algorithm is developed to adaptively filter multiple input channels into desired multiple output channels. The algorithm is a type of adaptive lattice filter that employs a fast orthogonalization network (FON) algorithm for numerical efficiency. Past researchers have concentrated on developing efficient lattice algorithms to process stationary input channels; i.e., the input covariance matrix is Toeplitz in form. The algorithm developed herein is designed to adaptively filter nonstationary input channels. Various implementations of the FON algorithm are given.