Fully distributed fiber-optic temperature sensing using acoustically-induced rocking grating

A highly sensitive fully distributed fiber-optic temperature sensing technique is proposed and demonstrated based on a transient and traveling rocking grating. The rocking grating is generated by pulsed acoustic torsional waves propagating along the fiber. The measured temperature sensitivity is 1000?ppm/°C and is experimentally demonstrated mainly due to the temperature dependence of the fiber birefringence. This traveling rocking grating based sensing technique may also serve other fully-distributed sensing applications by using specially designed fibers.     

嵌入至复合材料中的光纤温度传感器的研究

介绍了一种新型的光纤温度传感器,将它埋入复合材料试件中,可以测量出试件内部的温度变化。给出了理论推导,导出了条纹移动量与试件内部温度变化之间的关系。给出了实验装置和结果。     

All-fiber system for simultaneous interrogation of distributed strain and temperature sensing by spontaneous Brillouin scattering

We demonstrate a low-loss, long-range, single-ended distributed optical fiber sensor to measure both temperature and strain simultaneously and unambiguously. By using the Landau?Placzek ratio and cascaded Mach?Zehnder interferometric filters, we measure both the intensity and the frequency changes in the Brillouin backscattered signal. Strain and temperature measurements can then be independently resolved. A temperature resolution of 4 degrees C, a strain resolution of 290 muepsilon, and a spatial resolution of 10 m have been achieved for a sensing length of 15 km.     

光纤温度传感器实验的改进与分析

本文利用价格低廉的1310 nm商用光纤分束器、铝箔导热等对光纤温度传感器实验装置进行了改进,并测量了改进后传感器的温度系数,发现改进后的温度系数更加稳定,导热条件对温度系数的测量影响较大.最后对此实验的教学提出了建议.     

Large amplitude point-vibration measurement with optical-fiber moiré-based technique

We describe a technique that is used for the real-time measurement of the vibration of an object point. The technique can be used when the vibration is characterized by a large amplitude, i.e. several millimeters. The technique has additional advantages that it requires no special surface treatment and is insensitive to object in-plane displacements that are small. In this technique an object point is illuminated by a small diameter beam (at an angle) that is structured with straight parallel fringes. The illuminated object point is then imaged onto a Ronchi ruling. The total light transmitted through the Ronchi ruling is then used to recover the vibration of the object point, in real time, by using well-known servo techniques.     

Single-shot imaging of ground-state hydrogen atoms with a nonlinear laser spectroscopic technique

We report on a novel nonlinear laser spectroscopic technique for single-shot imaging of ground-state hydrogen atoms in harsh environments. H atoms from the ground state were first pumped to the 2s state via a two-photon excitation with a 243 nm laser beam, and the population of the 2s state was further probed through the 2s-4p transition with conventional polarization spectroscopy at 486 nm. A single Nd:YAG-pumped optical parametric oscillator laser system was enough to provide both laser beams. Single-shot visualization of native H atoms in an atmospheric pressure premixed H(2)/O(2) flame is demonstrated.     

Designing optical-fiber modulators by using magnetic fluids

To reduce interface loss between optical fibers and devices in telecommunication systems, the development of an optical-fiber-based device that can be fused directly with fibers is important. A novel optical modulator consisting of a bare fiber core surrounded by magnetic fluids instead of by a SiO2 cladding layer is proposed. Applying a magnetic field raises the refractive index of the magnetic fluid. Thus we can control the occurrence of total reflection at the interface between the fiber core and the magnetic fluid when light propagates along the fiber. As a result, the intensity of the outgoing light is modulated by variation in field strength. Details of the design, fabrication, and working properties of such a modulator are presented.     

Prospects for non-linear forward-scatter distributed optical-fibre sensing

Optical fibres offer special advantages for fully-distributed sensing. They comprise an essentially one-dimensional measurement medium which can be used to provide the spatial distribution of a variety of measurands within large structures. To date, most fully-distributed optical-fibre sensor systems have relied on backscatter, OTDR, techniques. This paper proposes an alternative, forward-scatter approach; it utilises non-linear interactions between counter-propagating beams in optical fibres. This latter approach offers possibilities for a significant improvement in performance for such sensors. Some possible systems based on this approach are described and preliminary experimental results are presented.     

Random‐access distributed fiber sensing

Optical sensing offers an attractive solution to the societal concern for prevention of natural and human‐generated threats and for efficient use of natural resources. The unprecedented properties of optical fibers make them ideal for implementing a ‘nervous system’ in structural health monitoring: they are small, low‐cost and electrically and chemically inert. In particular, the nonlinear interaction of stimulated Brillouin scattering allows for the distributed measurement of strain and temperature with tens of km range. In this work, a novel, radar‐inspired technique for random‐access Brillouin scattering‐based sensors is shown, making a significant step towards a real optical sensing nerve. The method selectively addresses each fiber segment as a distinct sensing element in a synaptic neuronal system. The measurement principle relies on phase‐coding of both the Brillouin pump and signal waves by a high‐rate, pseudo‐random bit sequence. Temperature measurements with 1 cm resolution are reported. The measurement range is scalable to several km.     

Frequency-domain approach to distributed fiber-optic Brillouin sensing

A novel approach to distributed fiber-optic Brillouin sensing is presented and numerically analyzed. An integral equation that directly relates the Brillouin gain to the Brillouin signal is derived in the frequency domain, and from this result a new technique for the quantitative reconstruction of temperature-strain profiles along an optical fiber is developed. We achieve the reconstruction by minimizing a cost function that represents the error between the measured and the model data. We effectively perform such a minimization by representing the unknown (temperature-strain) profile with a finite number of parameters. Numerical results confirm the effectiveness of the proposed approach and its stability against noise in the data.     

长距离分布式光纤传感技术研究进展

分布式光纤传感技术是光纤传感领域的重要组成部分,具有以下突出优势:无需在光纤上制作传感器,传感光纤集传感与传输于一体,可实现远距离、大范围的传感与组网;可连续感知光纤传输路径上每一点的温度、应变、振动等物理参量的空间分布和变化信息,单根光纤上能获得多达数万点的传感信息.由于在长距离连续传感方面具有不可替代的优势,分布式光纤传感技术在周界安防、石油电力、大型结构等领域的安全监控方面具有非常广阔的应用前景.本文主要介绍电子科技大学光纤传感与器件研究团队在长距离分布式光纤静(布里渊光时域分析仪)、动(相位敏感型光时域反射仪)态参量传感技术取得的研究进展,包括基础与应用研究两个方面.     

Mean temperature in a closed basin by remote sensing

Summary In this paper a procedure to determine the mean vertical temperature in a closed shallow basin will be presented. The procedure is based on the remotely observed surface temperature implemented by a calibration point at which usual meteorological measurements are performed. By the energy conservation equation applied at the calibration point the behaviour of the mean vertical temperature is obtained. Field measurement have been performed (June 1987) in a basin called Comacchio Valley (Italia). Experimental results are shown. This work has been in part supported by the Consiglio Nazionale delle Ricerche, Italy. The VAX 11/750 of the Centro Interdipartimentale di Calcolo Automatico ed Informatica Applica (CICAIA) of the University of Modena, Italy, has been used.     

Remote sensing of temperature by a TGS pyroelectric detector

Use of a TGS pyroelectric detector has been made for remote sensing of temperature. Radiant power is measured in terms of electrical quantities. The system is so designed that the ambient conditions do not effect the measurements.     

Potential of two-photon-excited fluorescence for distributed fiber sensing

The design and operating parameters of a new class of continuously distributed optical fiber sensor are described. By use of counterpropagating pulses, two-photon excitation of fluorescence from ions doped into the fiber enables any position to be monitored. By this means temperature and also strain may be sensed with high spatial and temporal resolution. As the doped fiber is transparent for single-photon absorption at the wavelength of the light pulses, attenuation does not set an upper limit to its length.     

Three-dimensional optical microscopy using axially distributed image sensing

We propose three-dimensional (3D) optical microscopy using axially distributed image sensing. In the proposed method, the micro-objects are optically magnified and their axially distributed images are recorded by moving the image sensor along a common optical axis. The 3D volumetric images are generated from the recorded axial image set using a computational reconstruction algorithm based on ray backprojection. Preliminary experimental results are presented. To the best of our knowledge, this is the first report on 3D optical microscopy using axially distributed sensing.     

Single-shot measurement of carrier-envelope phase changes by spectral interferometry

We demonstrated single-shot measurements of spectral interference between a white-light continuum generated in a hollow-fiber and its second harmonic. The interference has information on the carrier-envelope phase of an input pulse to the fiber and the time delay of the blue wing of the continuum. By analyzing the observed spectral interference, we estimated shot-by-shot changes of the carrier-envelope phase. This method is useful for determining the carrier-envelope phase changes of a low-repetition-rate, high-intensity laser.     

Single-shot measurement of temporal phase shifts by frequency-domain holography

Frequency-domain holography is used to measure ultrafast phase shifts induced either by the nonlinear susceptibility ?(3) of fused silica or by ionization fronts in air over a temporal region of 1 ps with 70-fs resolution in a single shot. The use of an imaging spectrometer adds one-dimensional spatial resolution to the single-shot temporal measurements.     

Efficient distributed moisture-ingress sensing using diamond-like carbon-nanocoated long-period gratings

We have demonstrated the possibility of efficient distributed water ingress sensing by making use of LPGs nanocoated with diamond-like carbon (DLC). Two long-period gratings (LPGs) with different coating thicknesses were tested. A portion of each LPG was soaked and the responses were measured by tracking both the center-wavelength shift and the LPG resonance minimum depth and by simulating a two-detector sensing arrangement in combination with a diffraction grating. The responses exhibit large linear sections and thus allow for a simple distributed sensing over the grating length.     

Three-dimensional free view reconstruction in axially distributed image sensing

In this Letter, we propose a three-dimensional(3D) free view reconstruction technique in axially distributed image sensing(ADS). In typical integral imaging, free view reconstructed images can be obtained by tilting all elemental images or tilting the reconstruction plane due to large lateral perspectives for 3D objects. In conventional ADS, the reconstructed images at only a front view can be generated since the sensor is moved along with its optical axis so that it has small lateral perspectives for 3D objects. However, the reconstructed 3D images at any viewing point may be obtained because the virtual viewing camera may capture these slightly different perspectives for 3D objects. Therefore, in this Letter, we employ the virtual viewing camera to visualize the 3D images at the arbitrary viewing point. To support our proposed method, we show the experimental results.