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1.
Optical Generation and Detection of Ultrasound   总被引:2,自引:0,他引:2  
Abstract: This is a review of the optical generation and detection of ultrasound on work carried out in different optical detection techniques at the Strathclyde University. We start by pointing out some limitations of conventional ultrasonic transducers and show how the use of optical-based transducers can overcome them. After explaining how laser generation of ultrasound works, we will describe and compare the advantages and disadvantages of three optical detection techniques. Finally, we describe applications in which optical ultrasound techniques appear to have a promising future.  相似文献   

2.
A fibre axial strain sensor based on a phase modulated microwave photonics filter (MPF) with dual-passband is proposed and experimentally demonstrated. According to the phase-modulation to intensity-modulation (PM-IM) conversion in the MPF, dual-passband can be generated by utilizing two cascaded fibre Bragg grating Fabry-Perot (FBG-FP) filters. The fibre axial strain will change the wavelength of the FBG-FP, and resulting in the frequency variation in the passband. Thus, with one FBG-FP serving as the sensing element and the other acting as the reference element, a highly sensitive strain sensor can be realized simply by monitoring the frequency difference variation between the two passbands. The result shows that the passband frequency changes linearly in response to the strain with a sensitivity of 1.40 × 108 Hz/με. The sensor reveals the advantages of highly sensitive, small hysteresis and good stability, providing great potential for practical applications.  相似文献   

3.
In this work, a theoretical study was conducted on temperature sensing in Ge–Sb–Se multimode fibre Bragg grating (MM-FBG). The sensing characteristics of the designed MM-FBGs with different fibre parameters and operating wavelengths were calculated using a coupled model method. The temperature sensitivity of this MM-FBG was found to improve significantly by shifting the operating wavelength from telecom range to mid-infrared (MIR) and utilizing the wide transmission range of Ge–Sb–Se glasses. The temperature sensitivity of the proposed Ge–Sb–Se MM-FBG was calculated to be 0.0758 nm/°C at 1550 nm, which is 7.58 times higher than silica FBGs at 1550 nm, and the temperature sensitivity was calculated to be more than 0.16 nm/°C at 3390 nm, which is 2.2 times higher than that at 1550 nm. In addition, the proposed MM-FBGs provided multi-peak information, and the sensitivity of each peak was calculated to be comparable to the single-mode FBG. The proposed Ge–Sb–Se MM-FBG has great potential for temperature sensing in MIR because of its advantages of simple preparation, high coupling efficiency, multi-peak information and wide working window.  相似文献   

4.
提高光纤Bragg光栅波长测量精度的方法   总被引:5,自引:1,他引:5  
利用一对固定Bragg波长的光栅作为参考,在锯齿波电压驱动下,可调谐滤波器输出的窄带光分别扫描传感光栅和参考光栅,使用高斯寻峰算法计算出参考光栅反射峰值波长对应的驱动电压。在参考波长区间,利用参考光栅的波长准确性高的特点,对滤波器输出波长进行校准,建立滤波器调谐波长与扫描电压的关系。传感光栅的Bragg波长可以通过线性插值求取。温度传感实验中,利用质心法、微分法和高斯拟合法计算光栅反射峰值波长,分别获得±1℃、±0.5℃和±0.3℃测量精度,对应着±10pm、±5pm和±3pm的波长误差。实验结果表明,波长校准和选择好的寻峰算法分别减小了可调谐滤波器波长输出非线性性及波长扫描精度低带来的测量误差。  相似文献   

5.
从光纤Bragg光栅(FBG)反射中心波长随碳纤维增强塑料复合材料(CFRP)拉伸试件表面应变变化敏感特性的角度,详细研究了拉伸过程中FBG中心波长的拉伸变化速率(即CFRP的宏观弹性模量)与复合材料内部断裂饱和状态的相关性和断裂瞬间试件表面的应变波响应特性,即:在拉伸过程中,CFRP拉伸试件的宏观弹性模量随着内部断裂的发生而不断减小,且在试件出现明显应力松弛状态前趋于平稳;应力松弛状态出现时,断裂区域表面接收的应变波响应略大于其他区域。通过设计相应排布形式,将FBG与CFRP断裂监测相结合,提出了一种基于FBG传感的CFRP断裂分阶段监测方法。该方法中传感探头直接与CFRP试件耦合,测量及传导光路全光纤化,可实现对CFRP断裂状态的绝对监测。  相似文献   

6.
    
ABSTRACT

We experimentally demonstrate the first VCSEL-based all-optical wavelength reuse technique with reconfigurable fibre Bragg grating add and drop multiplexer. EDFA gain saturation and Bragg trans-reflection effect on a single FBG are respectively, adopted for full-duplex reference frequency and data transfer. A 1550 nm energy-efficient VCSEL is modulated with 1.7?GHz clock signal and transferred downstream over 26.6?km fibre OLT attain a phase noise stability of ?54.01 dBc/Hz at 10?kHz offset frequency. A saturated EDFA is exploited to optically reduce the peak-to-peak voltage of the incoming downstream RF, allowing for wavelength reuse with 10?Gbps upstream data. A 1.57 dB transmission penalty is incurred over the transmission fibre. An all-passive OADM is developed exploiting Bragg trans-reflection at 1549.45?nm. The reflected wavelength is routed over another 24.7?km fibre network attaining an extinction ratio of 6.1?dB and a SNR of 5.8?dB. This work provides an all-optical technique for routing and spectral management in flexible networks.  相似文献   

7.
    
《Journal of Modern Optics》2012,59(20):1973-1978
ABSTRACT

Current optical interconnects are dominated by electrical wavelength converter module technologies which are not only power consuming but also bandwidth limited. We experimentally demonstrate a technique to maximize network robustness, flexibility and efficiency through combined adoption of energy-efficient VCSELs, distributed forward Raman, all-optical wavelength conversion and reuse. The precise wavelength selectivity of a fibre Bragg grating (FBG) is exploited to realize all-optical wavelength switch at 10 Gbps directly modulated 1549.60 nm VCSEL channel. The 6.2 dB flat gain of a forward Raman amplifier is exploited to achieve a 25.25 km downstream transmission of the switched channel incurring a 1.23 dB transmission penalty. Gain saturation of an Erbium-doped fibre amplifier (EDFA) is incorporated to achieve real-time all-optical data erase/rewrite. The 1549.62 nm VCSEL channel is further reused for upstream transmission of 8.5 Gbps data incurring a maximum penalty of 0.83 dB. Our concept is key for adoption in dynamic wavelength routing for spectral utilization in optical interconnect.  相似文献   

8.
J. Molimard  S. Vacher  A. Vautrin 《Strain》2011,47(Z2):364-373
Abstract: Optical fibre Bragg gratings (FBG) provide accurate and non‐intrusive strain and temperature local measurements. FBG sensors can be embedded into fibrous preforms to monitor the flow and the cure of the resin and deliver real‐time information on the ongoing process. The paper concentrates on the utilisation of the strain‐induced birefringence of the FBG to derive information on the effective stress–strain state of the composite at the end of the process cycle (Vacher 2004, Optical fiber sensors to monitor the processing and the mechanical characterization of composites. PhD thesis). During the cooling phase, the reflection spectrum from the FBG splits into two peaks because of the birefringence of the glass fibre owing to the residual stress. The paper shows that this effect can be utilised to estimate the residual stress and strain in composites manufactured by Liquid Composite Moulding technologies. The birefringence effect arising from the cooling of a [06,903]S CFRP laminate is first characterised, and then the determination of the strains along the principal axes inside the laminate is completed by modelling the local stress–strain state because of the interaction of the optical fibre and its environment within the framework of orthotropic thermo‐elasticity and the Classical Laminated Plate Theory.  相似文献   

9.
Test control is traditionally performed by a feedback signal from a displacement transducer or force gauge positioned inside the actuator of a test machine. For highly compliant test rigs, this is a problem since the response of the rig influences the results. It is therefore beneficial to control the test based on measurements performed directly on the test specimen. In this paper, fibre Bragg grating (FBG) and Digital Image Correlation (DIC) are used to control a test. The FBG sensors offer the possibility of measuring strains inside the specimen, while the DIC system measures strains and displacement on the surface of the specimen. In this paper, a three‐point bending test is used to demonstrate the functionality of a control loop, where the FBG and DIC signals are used as control channels. The FBG strain control was capable of controlling the test within an error tolerance of 20 µm m?1. However, the measurement uncertainty offered by the FBG system allowed a tolerance of 8.3 µm m?1. The DIC displacement control proved capable of controlling the displacement within an accuracy of 0.01 mm.  相似文献   

10.
This paper reports the measurement of the surface topology of optical fibres containing a fibre Bragg grating (FBG) using an atomic force microscope (AFM). The AFM observation was made on FBGs fabricated via the phase mask technique in germanium–boron codoped optical fibres, in hydrogen-loaded germanium–boron codoped fibres and in standard telecommunications optical fibres. The surface images reveal that a spatial corrugation pattern was induced by the UV-irradiation, with a period that is half of the period of the phase mask. This UV-induced surface structure was found only on the side of the fibre facing towards the incident UV-irradiation and did not appear on the rear surface. The AFM probe scanned a 10×10 μm2 surface area at seven sites along the 6.0 mm length of fibre that was exposed to the UV-irradiation. The amplitude of the spatial corrugation pattern observed on the AFM image was quantified for each site. It was found that the amplitude in a range of 0.7–3.2 nm was a function of UV-laser intensity distribution and the type of fibre. Hydrogen loaded optical fibres exhibited a corrugation with an amplitude twice as large as that observed in the Ge–B doped fibres that were not hydrogen-loaded. This correlates with the increase in photosensitivity produced by the hydrogen loading. A similar UV-induced spatial corrugation was also observed on standard telecom fibres, but without inducing the refractive index change in the fibre core. The observation of surface topology provides an insight into the structural changes induced during FBG fabrication. UV-induced densification and laser ablation could account for the formation of the surface troughs.  相似文献   

11.
Germanosilicate thin films have been elaborated by the sol–gel process and the dip-coating technique. Pulsed or continuous wave UV laser (244 nm) was used to write permanent gratings in these films. In the case of exposure to cw laser, the grating diffraction efficiencies were measured using a focused beam from a He–Ne laser at 633 nm and photo-induced changes in refractive index as high as 4×10−3 have been obtained. The thermal behaviour of these gratings has been investigated showing a good stability up to 400°C. Exposure to pulsed fringe pattern led to a glass photo-expansion modulated by a strong corrugation which can be due mainly to photo-ablation at the places of the bright fringes. The waveguide surface at the grating places was investigated through Atomic Force Microscopy (AFM) and microscopic profilometry techniques. Preliminary results on the kinetics of the grating growths are also reported.  相似文献   

12.
A tunable narrow band filter based on a Bragg grating with surface plasmon polaritons is developed and investigated numerically by using the finite-difference time-domain method. A defect state with narrow transmission peak (about 15?nm) is shown to appear in the bandgap by introduction of a defect into the Bragg grating, which can thus be used as filtering device. We also show that double-channel filtering can be realized by introducing two defects into the Bragg grating. The resonant wavelengths in the bandgap are related to the position of defects and the refractive index of the insulator. Our results may provide useful information in the design of tunable narrow band filters in nano-circuits.  相似文献   

13.
    
The assessment of particles in terms of their size and shape, as well as concentration (number of particles per unit volume) is of crucial importance in a wide range of applications, both industrial and medical.Ellipsometry is an optical technique using polarised light which can be used for such purpose. However,in its simple form ellipsometry is a time-consuming measurement technique. We have investigated the possibility of constructing a multi-channel ellipsometer to overcome this disadvantage and in this paper we report on the use of this instrument for the assessment of a range of particles of known size and concentration.  相似文献   

14.
    
Simultaneous measurement of multi-parameters is demonstrated quantitatively using two fibre Bragg gratings inscribed on a high birefringence photonic crystal fibre (PCF) and common PCF, respectively. The birefringence coefficient and the Bragg wavelengths corresponding to the fast-axis mode and slow-axis can be magnetic-controlled by filling magnetic fluid (MF) into several cladding air-holes. Based on the dependence of the MF refractive index on temperature and magnetic field, the sensitivity of the spectral response of the device to longitudinal strain, magnetic field and temperature are characterized, and the results of its application as a multi-parameter sensor are also presented.  相似文献   

15.
蒋泽  刘丽莉 《光电工程》2006,33(1):54-58
基于取样光纤布拉格光栅(SFBG)的光Interleaver能将一路光信号解复用为两路奇偶波长信号,具有插入损耗低、各信道反射率均匀和低色散等优点,特别适用于未来全光DWDM中波长复用/解复用、插入/分离。为此介绍了取样光栅Interleaver的基本设计理论,给出了设计实例,对取样光栅Interleaver等光器件的实用化有一定的参考意义。  相似文献   

16.
散斑干涉条纹图的总变分去噪方法   总被引:2,自引:0,他引:2  
去除散斑条纹图中的噪声是电子散斑干涉测量技术的关键问题.提出将总变分图像去噪方法应用于电子散斑干涉条纹图滤波过程中,并对保真系数进行了改进.用总变分模型定义图像的能量函数,利用变分法求得满足能量函数的最优解,将图像去噪过程转化为求解偏微分方程的过程.分别对计算机模拟的条纹图和实验获得的条纹图进行了测试,定性和定量分析的结果表明该技术能够在显著滤波的同时保持条纹的对比度.  相似文献   

17.
基于倾斜光纤光栅的传感解调技术   总被引:2,自引:0,他引:2  
该文设计了一种基于倾斜光纤光栅(tilted fiber Bragg grating,TFBG)的不受温度影响的光纤布拉格光栅(fiber Brag ggrating,FBG)应变解调系统.将倾斜光纤光栅用作边沿痣波器,当周围环境温度变化时,利用倾斜光纤光栅纤芯模与包层模的温度特性与普通光纤布拉格光栅相同这一特点,无需另加温度补偿,就可以实现FBG应变传感的动态解调,消除温度噪声对应变信号的影响.由实验可知,当温度在25℃到39℃范围变化时,解调系统的性能基本不发生改变,解调范围达到6nm.  相似文献   

18.
非相干组束中反射体布拉格光栅的衍射潜力(英文)   总被引:1,自引:0,他引:1  
基于耦合波理论,提出了一种推导反射体布拉格光栅衍射效率方程的新方法.在被推导的衍射效率方程基础上,获得了平面单色和高斯光束反射体布拉格光栅衍射的详细理论模型,分析了平面单色、发散单色和多色光束的衍射效率.结果表明:平面单色波的角和谱选择性随光栅厚度和空间频率而变化,角选择性的范围从低于0.01mrad到超过100mrad,谱选择性的范围从低于0.1nm到超过100nm;当光束的角发散或谱宽等于光栅的角选择或谱选择性时,光栅能提供超过88%的衍射效率;当光束的角发散或谱宽远小于光栅的角选择或谱选择性时,光栅衍射效率下降不明显,不到平面单色波的1%.  相似文献   

19.
20.
介绍了光纤光栅研制及其应用研究的情况。研究包括:光纤光栅的基本特性,光纤光栅外腔半导体单频和锁模激光器、光纤光栅稳频光纤环形激光器和主动锁模光纤激光器、基于光纤光栅的波长转换器和基于啾啁光纤光栅的可调谐激光器等。  相似文献   

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