基于光纤光栅的实时延时技术

光实时延时技术与相控阵技术的融合,解决了传统相控阵雷达的瞬时大带宽受限和波束偏斜问题.文中给出了光实时延时技术的思想,讨论了光实时延时技术出现的背景.分析了应用于光实时延时技术中的光纤光栅的原理,着重讨论了均匀光纤光栅和线性啁啾光栅,分别给出了基于两种光纤光栅的光实时延时的技术方案,在此基础上,讨论了受控于应变和温度的光纤光栅在光实时延时技术中的应用.最后讨论了一些技术上存在的问题.

Abstract：

Optical true time delay technology (OTTD) is the key technology for phase array antennas (PAA).By using OTTD,the beam squint and the restriction of instantaneous bandwidth are resolved.The principles of OTTD are given,the emergence background of OTTD is discussed.The theory of fiber Bragg grating(FBG) used in OTTD is analyzed,especially on uniform fiber bragg grating and linear chirped fiber Bragg grating.Two OTTD schemes based on FBG is presented,then some new kinds of FBG used in OTTD are discussed.Some technique hurdles are analyzed as well.     

一种基于啁啾光纤光栅温度不敏感的应力传感器

提出了一种基于啁啾光纤光栅温度不敏感的应力传感器.这种传感器是以腐蚀后啁啾的Bragg光纤光栅为敏感元件,利用光栅反射功率的变化测量应力的变化,反射功率对温度是不敏感的.利用光功率计检测光栅反射功率的变化.     

Chirped RF Pulse Generation Based on Optical Spectral Shaping and Wavelength-to-Time Mapping Using a Nonlinearly Chirped Fiber Bragg Grating

Chirped radio-frequency (RF) pulse generation based on optical spectral shaping and nonlinear wavelength-to-time mapping in a nonlinearly chirped fiber Bragg grating (NLCFBG) is investigated. In the proposed approach, the spectrum of a femtosecond pulse generated by a mode-locked fiber laser is shaped by an optical filter that has a sinusoidal frequency response. The spectrum-shaped optical pulse is sent to the NLCFBG, to implement nonlinear wavelength-to-time mapping. A chirped electrical pulse with the central frequency and chirp rate determined respectively by the first- and second-order dispersions of the NLCFBG is then obtained at the output of a high-speed photodetector. An approximate model that describes the chirped RF pulse generation is derived, which is verified by numerical simulations. Chirped pulse generation with a pulse compression ratio as high as 450 is demonstrated. The key device in the chirped RF pulse generation system is the NLCFBG, which is investigated in detail with an emphasis on the influence of its group delay ripples on the performance of the pulse generation system. Techniques to design and fabricate the NLCFBG are also discussed. The proposed approach provides a potential solution for the generation of chirped RF pulse with a high central frequency and large chirp rate for applications in pulse compression radar systems.     

Continuous True-Time-Delay System Employing a Novel Tunable Chirped Fiber Grating Delay Line and a Sampled Grating Based Multiwavelength Fiber Laser

A photonics true-time-delay system for phased array antenna beam steering employing a novel tunable chirped fiber grating delay line and a multi-wavelength erbium-doped fiber ring laser source based on a sampled grating filter is proposed. The tunable chirped fiber grating, which act as a continuous time-delay element, is achieved by bending a uniform fiber Bragg grating bonded at a slant onto the lateral surface of a simply supported beam. This technique allows the dynamic control of the chirp rate and spectral width of the grating without center wavelength shift. By adjusting the chirp rate of the fiber grating via bend strain, this kind of tunable chirped fiber grating could achieve very low and adjustable delay times, therefore provides higher angle resolution for scanning microwave beam, even the wavelengths of laser source are fixed and un-tunable. The true-time-delay system using proposed tunable chirped fiber grating delay element and sampled grating based laser source is constructed and demonstrated experimentally.     

基于啁啾相移光纤光栅的多波长滤波器的研究

使用Ⅴ-Ⅰ传输矩阵法分析了相移量、相移点位置以及啁啾系数对啁啾相移光纤光栅透射谱特性的影响,并分析了在啁啾光纤光栅中同时引入多相移时生成的多陷波滤波器的波长间隔,发现其与以同样的位置引入单相移时陷波滤波器的波长偏离间隔基本一致。依据仿真分析结果,可以优化啁啾相移光栅相移数量、位置间隔、啁啾系数和相移量的参数选择,设计出实际需要的多波长滤波器。     

Fourier Transform Ultrashort Optical Pulse Shaping Using a Single Chirped Fiber Bragg Grating

Fourier transform ultrashort optical pulse shaping using a single linearly chirped fiber Bragg grating (LCFBG) is proposed and experimentally demonstrated in this letter. The LCFBG in the system performs three functions: temporally stretching the input ultrashort pulse, shaping the pulse spectrum, and temporally compressing the spectrum-shaped pulse. The impulse response of the entire pulse shaping system is equal to the Fourier transform of the square of the grating power reflectivity function. By appropriately designing the grating reflection response, a temporal optical waveform in the subpicosecond regime can be accurately synthesized. An example to show the synthesis of a triangular optical pulse with a full-width at half-maximum of 2 ps is demonstrated.     

Limitations by Group Delay Ripple on Optical Beam-forming With Chirped Fiber Grating

This paper investigates the effect of group delay ripple on optical beam-formers using chirped fiber grating. Such optical beam-formers were promised to have many advantages over their electrical beam-forming counter-parts. However, mathematical analysis and simulation results have shown that the group delay ripple causes many drawbacks such as the limitation in operation frequency, RF signal bandwidth, and the number of elements. The most advantageous feature of optical beam-formers, which is squint-free operation for wideband, high frequency signals, is severely affected when chirped grating is used.      

布喇格光栅光纤氢浓度传感器的研究

提出了一种基于钯涂层布喇格光栅光纤的氢浓度传感器方案。金属钯在氢环境中能够吸收一定量的氢并使其体积膨胀,而布喇格光栅光纤在应力的作用下其有效折射率和周期发生变化,导致中心波长偏移,两者结合可实现对外界环境中氢的测量。建立了外界环境氢浓度同钯涂层布喇格光纤光栅波长偏移之间的关系,通过数值分析给出光栅光纤氢浓度传感器在不同氢浓度以及温度环境中波长偏移量,并分析了其特点。     

Chirped Microwave Pulse Generation Based on Optical Spectral Shaping and Wavelength-to-Time Mapping Using a Sagnac Loop Mirror Incorporating a Chirped Fiber Bragg Grating

In this paper, we propose and demonstrate an approach to optically generating chirped microwave pulses with tunable chirp profile based on optical spectral shaping using a Sagnac loop filter incorporating a chirped fiber Bragg grating (CFBG) and linear wavelength-to-time mapping in a dispersive element. In the proposed approach, the optical power spectrum of an ultrashort optical pulse is shaped by a CFBG-incorporated Sagnac loop mirror that has a reflection spectral response with a linearly increasing or decreasing free spectral range. The spectrum-shaped optical pulse is then sent to a dispersive element to perform the linear wavelength-to-time mapping. A chirped microwave pulse with the pulse shape identical to that of the shaped spectrum is obtained at the output of a high-speed photodector. The central frequency and the chirp profile of the generated chirped microwave pulse can be controlled by simply tuning the time delay in the Sagnac loop mirror. A simple mathematical model to describe the chirped microwave pulse generation is developed. Numerical simulations and a proof-of-principle experiment are implemented to verify the proposed approach.      

基于叠印啁啾光纤布拉格光栅的宽谱微波光子信道化接收方法

提出了利用叠印啁啾光纤布拉格光栅(S-CFBG)实现宽谱微波信号光子信道化接收的方法。利用一个S-CFBG产生光频梳(OFC),接收的微波信号被强度调制器调制到OFC的各个载波上。第二个S-CFBG对不同的边带进行滤波,利用波分复用(WDM)解复用器进行信道分离,实现对宽谱微波信号频率的实时测量。该方法还可以同时检测不同射频(RF)载波上所携带的数据信息,无需传统的电本振源阵列,简化了系统结构。建立了测量范围为0～20GHz,测量精度为0.5GHz的宽谱微波信号信道化接收仿真系统。实现了不同RF频率上携带信息的实时同步检测,并对接收误码性能进行了分析。     

Optical Generation of Binary Phase-Coded Direct-Sequence UWB Signals Using a Multichannel Chirped Fiber Bragg Grating

A novel technique to generate binary phase-coded, direct-sequence ultra-wideband (DS-UWB) signals in the optical domain is proposed and demonstrated. In the proposed system, the wavelengths from a laser array are modulated by a Gaussian pulse, which is sent to a multichannel optical frequency discriminator, to generate a UWB monocycle or doublet pulse sequence with a predetermined phase-code pattern. By tuning the wavelengths of the laser array, or by tuning the states of polarization of the wavelengths, the generated pulse shape and code pattern can be changed. The key device in the system is the multichannel dispersive chirped fiber Bragg grating (FBG), which functions, in combination with a dispersive fiber, as a multichannel frequency discriminator with a step-increased group-delay response, to ensure the generated UWB sequence to have uniform time spacing among the chips and to compensate for the fiber-induced chromatic dispersion. The proposed scheme is experimentally demonstrated. A multichannel chirped FBG is designed and fabricated. Binary phase-coded DS-UWB signals with different code patterns are experimentally generated.      

啁啾超结构光纤布拉格光栅的一种新研究方法

从耦合波理论出发,利用传输矩阵分析了啁啾超结构光纤光栅,得到了其反射谱的解析式,数值计算结果表明：超结构光纤光栅的光栅总长度、折射率调制深度、占空比、取样周期和啁啾系数等参数都会影响反射谱的峰值和带宽。为超结构光纤光栅的设计提供了理论依据。     

线性啁啾布拉格光纤光栅的色散补偿特性研究

本文将全面分析Ｃｈｉｒｐｅｄ Ｂｒａｇｇ光纤光栅的色散特性，并对色散特性作一定性分析，利用耦合模方程导出ＣｈｉｒｐｅｄＢｒａｇｇ光栅的反射率方程，从而推导出Ｃｈｉｒｐｅｄ Ｂｒａｇｇ光纤光栅的色散计算公式，然后，引入微波领域的“品质因素”概念，从而量化了色散补偿器的补偿能力。     

取样啁啾光纤光栅传输特性的研究

运用传输矩阵理论，对一种新型色散补偿光纤光栅——取样啁啾光纤光栅的传输特性进行了模拟研究。研究了光栅反射谱特性随光栅参数的变化规律。作为应用实例，本文给出了适合于对10Gb／s WDM系统进行色散补偿的8通道取样啁啾光栅的相关参数。     

Mode-Locked Bi-Doped All-Fiber Laser With Chirped Fiber Bragg Grating

We demonstrate a bi-doped fiber laser with dispersion compensation provided by a linearly chirped fiber Bragg grating. Reliable self-starting mode-locking was achieved by using an InGaAsN semiconductor saturable absorber mirror. The all-fiber laser generated short optical pulses with a duration of 1.9 ps at ~ 1165 nm. The large anomalous dispersion of the fiber grating ensured operation in the soliton pulse regime. This in turn enabled us to increase the repetition rate of the output pulse train up to 100.6 MHz via harmonic mode-locking.     

Simulation of Novel Tunable Nonlinear Chirped Fiber Bragg Grating

A novel tunable chirped fiber Bragg grating technology is proposed and simulated numerically by Matlab. If we adhere a uniform fiber grating with super magnetostrictive film and expose them in a non--uniform magnetic field, the period of the grating can be changed with the strain imposed on it by the magnetostrictive effect . The chirped characteristics can be tuned by changing the magnetic filed which is very flexible indesigning.     

相位掩模板接缝相差对光栅时延纹波的影响

电子束刻蚀啁啾相位掩模板采用的是分步啁啾法,而掩模板制造过程中分步之间的接缝误差是啁啾光纤光栅产生时延纹波的一个重要因素。该文以分步步长1 mm,总长度140 mm的相位掩模板为例,理论分析和比较了不同接缝误差对啁啾光纤光栅时延纹波的影响。分析表明,最大相位误差为0.05 rad和0.08 rad时,光栅时延纹波的统计平均分别为14.491 ps和22.38 ps。进行相关试验研究以上相位掩模板写入光栅的时延特性,得出结论与理论分析一致。     

用于相控阵雷达的啁啾光纤光栅延迟技术

为了获得尽可能大的信号带宽和连续可调的时延差,本文设计了一个基于啁啾光纤光栅和多波长激光器的延迟线。通过调制啁啾光纤光栅,实现了33．60ps到45．68ps的连续可调时延差。将此延迟线应用在相控阵雷达中,实现了微波信号在10GHz带宽范围内波束指向角从47．32°到90．00°的连续控制。     

线性啁啾光纤光栅变迹函数的研究

文中利用传输矩阵法对我们构造的四种变迹函数所描述的线性啁啾光纤光栅的光学特性进行了数值计算,并与常用的高斯型变迹线性啁啾光纤光栅的最佳光学特性进行了比较和分析,得出了一些有意义的结论,为设计和制作合适的线性啁啾光纤光栅用作色散补偿器提供了一定的理论依据。     

利用线性啁啾光纤光栅补偿PMD的实验研究

对利用线性啁啾光纤光栅补偿偏振模色散(PMD)进行了实验研究.利用压电陶瓷的压电效应挤压线性啁啾光纤光栅使之产生双折射,用于补偿光通信系统中的偏振模色散.通过改变施加在压电陶瓷上的电压值,可实现对偏振模色散补偿量的线性调谐.实验结果与理论预期基本符合.