Waveguide Filter for Reducing Crosstalk in All Optical Networks

A novel filter structure which can reduce the crosstalk in cross-connection and switching in all optical networks based on dense wavelength division multiplexing(DWDM) is presented.The filter is constructed by dielectric waveguide with the waveguide boundary or the waveguide itself uncontinuous in transmitting direction.Using the concept of effective refractive index of plane waveguide system, we can get a special index profile along the wave propagation direction by alternatively changing the thickness of waveguide film or its refractive index.Having proved this kind of waveguides with filtering properties, the design principle of an example is given, which will be very useful to reduce the crosstalk in optical cross-connection and switching in all optical networks based on DWDM. This kind of filters can be easily connected with other related component.     

Union self-compensated packaging of FBG strain sensor

To solve the cross-sensitivity to temperature of fiber Bragg grating（FBG）strain sensor,an effective method is firstly proposed for the discrimination of strain and temperature by using a single FBG adopting a special compensated structure,which is based on the thermal stress.The relationship of strain and temperature responses of FBG is analyzed theoretically.The experimental results are in agreement with the obtained theoretical analyses.This sensor structure has excellent characteristics,such as simple structure,easy manufacture and higher strain sensitivity.     

Transmission Characteristics of Sagnac Loop with Fiber Bragg Grating

A transmission filter composed of a Sagnac loop and a fiber Bragg grating is studied in detail.It is found that the transmission spectrum of this filter is the splitting of the reflection spectrum of the fiber Bragg gratings.The filter can behave as a multiple-passband filter when the fiber Bragg grating is strong and as a single-band filter when the fiber Bragg grating is weak.Very narrow transmission filters can be obtained in this way.     

Novel Distributed Fiber Bragg Grating Sensing System Based on M-Z Interferometer

One of the problems in using grating sensors is how to measure a small Bragg wavelength shift accurately. Nowadays demodulation techniques are mainly based on the edge filter, tunable filter, or interferometric scanning methods. Interferometric demodulation is widely accepted as the technology which can provide the high sensitivity. An interrogation system using the interferometric scanning method is presented, in which an unbalanced fiber M-Z interferometer is used as the wavelength scanner for temperature measurement. A novel fiber Bragg grating sensor system based on M-Z interferometric demodulation technique is presented in this paper. The temperature sensitivity measured in the experiment is almost consistent with that obtained from the theoretic calculation.     

2—D Fourier Transform Method for Optical Measurement of 3—D Surface

A emthod of 2-D Fourier transform used in 3-D surface profilometry is proposed,analyzed and compared with 1-D Fourier transform method in theory and practical measuring result.It was proved that the 2-D Fourier transform method has more advantages over 1-D Fourier transform methodd in biggest crook-rate limits,accuracy and sensitivity of measuring.Styudy on measuring object surface details with large crook-rate changing accurately used new higher-power index low-pass filter of spatial frequency domain.A new method of automatic produced reference grating image and error-correcting is proposed.One undeform row of deform grating image is used to extend a complete reference grating image,and some error-correcting method is used to process the result to get accurate surface shape and the deflection of reference surface normal line deviated from the axle of camera.By this new method,one deform rectangle grating image is only used to get the 3-D shape accurately.     

Fiber optic displacement sensor used in railway turnout contact monitoring system

Railway turnout contact monitoring is very important in high-speed rail operation systems. In order to measure the distance between the sharp rail and the basic rail in a switch system, a wide-range, high-precision fiber Bragg grating (FBG) displacement sensor was designed. Because the distance between the sharp and basic rails is always greater than 14 cm, the measurement range width and accuracy of the proposed sensor system are ensured through the use of a long spring and a beam of constant strength. A differential compensation method is used to eliminate temperature effects. Test results show that the resolution of the proposed sensor is 0.040 mm and the measuring range is 0—170 mm. A field test was also carried out to evaluate the performance of the sensors.     

MZI-based wavelength interrogation system with tunable- FBG

We proposed a scheme of fiber Bragg grating (FBG) sensor interrogation system based on all fiber Mach-Zehnder Interfer- ometer (MZI) edge filter and tunable-FBG. The equal power signals from FBG sensor and tunable FBG are coupled into port 1 and port 2 of MZI respectively. The experimental results show that the interrogation precision of the proposed system is 0.02 nm in a range of 1nm. Furthermore, the precision can be improved by adjusting the two interference arms of the filter.     

Photonic crystal ring resonator based add-drop filter using hexagonal rods for CWDM systems

In this paper,theoretical analysis of two-dimensional photonic crystal ring resonator(2D PCRR) based add-drop filter(ADF) is presented for coarse wavelength division multiplexing(CWDM) system to drop a channel at 1511 nm using hexagonal rods that are positioned in the square lattice.The 2D finite difference time domain(2D FDTD) method and plane wave expansion(PWE) method are used for obtaining the filter response and band structure of the filter respectively.Close to 100 dropping and coupling efficiencies at 1511 nm and 16 nm of bandwidth are observed through simulation.This is very well meeting the requirement of ITU-T G.694.2 standard,which is specified for metro access and short haul optical networks.The overall size of the proposed filter is 11.4 μm×11.4 μm.It can also be used in integrated optics.     

Optimization design and realization of Gaussian apodized sample gratings for narrowband wavelength selectivity filters

A sample fiber Bragg grating（SFBG） with Gaussian apodization profile is designed and optimized for the narrowband wavelength filter,and the relevant conclusions provide a guide for the further filter fabrication.With the grating length limited,a narrowband（5 GHz） grating filter used in the radio over fiber（ROF） system is fabricated,which has insertion loss of 3.463 dB,sideband suppression of 24.21dB,3 dB bandwidth of 40 pm,and 20 dB bandwidth of 106.3 pm.     

Counting wavelength demodulation of FBG sensors

Measuring amplitude of signal is the usual method in wavelength demodulation of fiber Bragg grating (FBG) sensors recently. This method is easy to be disturbed and has low precision. In this paper, a novel counting wavelength demodula- tion scheme of FBG sensors using a high birefringent fiber (HBF) loop mirror is reported. This demodulator has simple structure, high precision, cheap price and convenient use. The resolution of the loop mirror device with a HBF of 30 meters long is 0.067 nm. For a center wavelength of FBG of about 1550 nm and a 40 nm shift range of its reflection wavelength, the relative error of measurement is only ± 0.001. This wavelength demodulation device has significance for widespread application of FBG sensors.     

基于非切趾短FBG光栅的小信号测量方法

为解决基于图像传感器的FBG解调系统精细测量的问题,提出了使用非切趾FBG测量弱信号的方法。设计出了非切趾FBG反射谱近似模型,采用对数放大的方法提高非切趾FBG的旁瓣,在较宽的光栅频谱范围内,进行光谱相关解调并给出解调算法。基于蒙特卡洛方法对非切趾光栅测量仿真,并搭建实验系统对非切趾FBG、宽带高斯光栅进行对比测量实验。研究结果表明,基于非切趾FBG的弱信号测量方法可有效提高波长测量精度,通过相关解调,可使测量精度达到宽带光栅的2倍。     

Single-Longitudinal-Mode Erbium-Doped Fiber Ring Laser Based on High Finesse Fiber Bragg Grating Fabry–PÉrot Etalon

We present a simple and stable single-longitudinal-mode (SLM) erbium-doped fiber laser. It consists of an apodized fiber Bragg grating (FBG) and a high finesse FBG-based Fabry-Perot (FP) etalon in the ring cavity. The apodized FBG acts as a wavelength discriminative component selecting a few oscillation modes while the FP etalon serves as narrow bandwidth bandpass filter to further discriminate and select SLM efficiently. Stable SLM laser output at 1.55 m with linewidth about 2.5 kHz is acquired. Furthermore, continuous wavelength tuning over 8 nm is achieved by simultaneously applying strain to the FBG and the FP etalon.     

基于莫尔效应的光纤光栅变迹的研究

从理论上分析了利用莫尔效应进行变迹所引起的光纤光栅反射谱和色散特性的变化 ,指出由于莫尔条纹状的折射率调制使平均有效折射率在光栅区维持不变 ,所以可以实现纯变迹。与此成为对照的是 ,常用的升余弦函数变迹由于存在F P腔效应 ,因此在短波边的边模抑制效果不够满意。利用拉伸和二次曝光法产生的莫尔效应 ,实现了对光纤光栅的纯变迹 ,边模抑制比比相同工艺条件下的未变迹提高了约 6dB。     

Novel FBG triangular filter for interrogating a FBG sensor in dynamic strain measurement

In recent years ,fiber Bragg gratings (FBGs) have at-tracted great considerationsinsensor applications .Inad-dition to the advantages of optical fiber sensors ,e.g.small size and i mmune to electromagnetic interference,FBGs possess flexible multiplexing c…     

All-Fiber Q-Switched Erbium-Doped Fiber Ring Laser Using Phase-Shifted Fiber Bragg Grating

We propose a unique all-fiber Q-switched erbium-doped fiber ring laser. It consists of a phase-shifted fiber Bragg grating (FBG) and an apodized FBG reflector. By using the piezoelectric transducer (PZT) to periodically stretch the apodized FBG and detune it with the phases-shifted FBG, the cavity loss of the fiber ring laser is switched between high and low states to achieve Q-switching. This Q-switched fiber laser has advantages of narrow spectral bandwidth, stable oscillation wavelength, and the repetition rate of the Q-switched pulses can be double of the PZT modulation frequency. A numerical model is developed and presented to simulate and analyze this FBGs-based Q-switched fiber ring laser with consideration of the dynamic response of FBGs during Q-switching. We experimentally demonstrate 10 and 20 kHz Q-switching operation with 10 kHz PZT modulation frequency. The experimental result is similar to the simulation result.     

Fiber Bragg gratings for dispersion compensation in transmission:theoretical model and design criteria for nearly ideal pulserecompression

We propose a transmission-based dispersion compensator employing an apodized, unchirped fiber Bragg grating (FBG). A theoretical model for dispersion compensation in transmission based on the dispersive properties of the periodic structure is developed. A figure of merit is defined for optimization of the grating parameters for maximum recompression of dispersion-broadened optical pulses in long-haul communication systems. Numerical examples confirm that nearly perfect compensation with very low insertion losses can be achieved for many practical cases of interest     

光纤Bragg光栅滤波响应的轴向分布特性研究

为揭示光纤Bragg光栅（FBG）的局部滤波特征,研究和分析了滤波响应沿光栅轴向的空间分布规律。从均匀、切趾和啁啾型等基本光纤Bragg光栅（FBG）类型出发,分析了反射带滤波光场沿轴向的分布规律。结果表明,均匀型FBG中,光场反射多集中在前1/2个光栅长度内,呈现非对称性;切趾型FBG中,光场反射在光栅长度内的均匀性...     

变迹光栅孤子速度与时延特性研究

基于非线性耦合模方程组（NLCME）的解析孤子解, 讨论了均匀布拉格光栅（FBG）中慢光栅孤子（GS）的存在性。利用双曲正切中间变迹光栅中的NLCME, 引入非相对论-绝热-准量子近似法, 将光栅孤子作为一个低速运动且能量守恒的整体进行分析, 得到了孤子的轨迹方程。对反射孤子、低速孤子和静态孤子三种情况下的速度、位移分别进行数值计算, 分析了变迹光栅孤子的速度可控性。对孤子时延进行的数值仿真表明, 50 m的变迹光栅中可产生2000 ns的时延, 平均速度仅相当于均匀光纤中的0.1倍。讨论了光栅参数和脉冲初始参数对速度、位移和时延的影响。研究结果表明：在变迹光栅中, 选取合适的光栅变迹函数和初始脉冲, 可得到速度在0～c/n之间的任意孤子, 产生需要的时延大小, 从而实现孤子光缓存。     

光脉冲色散展宽的光纤光栅透射补偿

分析讨论了利用变迹均匀光纤光栅的透射色散对光纤中传输的脉冲色散展宽进行压缩补偿。给出了啁啾高斯脉冲的补偿原理,计算了相关的曲线和光纤光栅的相应参数。通过选择光纤光栅的不同参数,可以使色散展宽的高斯脉冲经光栅后几乎完全恢复原状或受到进一步压缩。     

光纤光栅滤波器在水下光通信系统中的应用

文章提出了一种基于光纤Bragg光栅(FBG)的用于水下光通信系统接收机前站的滤光方案，并采用耦合模理论分析了FBG的传输特性，数值模拟了Bragg波长为532nm、窄带、高反射率的均匀周期高斯切趾FBG。