Multiplexing of interferometric sensors using phase carrier techniques

This paper demonstrates the multiplexing of fiber-optic interferometric sensors using a CW phase generated carrier technique. The technique employs modulated diode laser sources at different carrier frequencies, nearly balanced interferometers (∼4-cm path difference), and phase generated carrier demultiplexing demodulation. This approach leads to a simple all-passive sensor array which has intrinsically low crosstalk. The system is analyzed in terms of shot noise performance and crosstalk. An experimental all optical implementation of a four sensor array was demonstrated; both the single sensor and multisensor arrays were limited by the laser phase noise to a sensitivity ofsim 18 murad/sqrt{Hz}. Crosstalk between individual channels was better than -60 dB and crosstalk between three sensors and the test sensor was better than -55 dB. In the absence of laser phase noise the demodulator/demultiplexer demonstratedsim 2-murad performance with both single sensor and four element array operation.     

光纤传感器的复用与数据融合

由于光纤传感器中存在交叉灵敏度,阐释传感器的测量及其相互关系是一个重要的课题。采用数据融合技术,对来自不同光纤传感器的信号进行综合处理,建立了分离光纤传感器中的时变耦合信号模型,即多光纤传感器的复用和数据融合的模型。在强度调制、时分调制、光栅调制和相位调制光纤传感器中,引入传感器、传感模型、复用和数据融合等四个层面的数据融合技术以分离时变耦合信号。     

Multiplexing of optical fiber sensors using a frequency-modulated source and gated output

A novel method is proposed and demonstrated for multiplexing fiber-optic interferometric sensors using the FMCW technique. The method uses a gas laser whose optical frequency is modulated sinusoidally by an external modulator. The use of gating and appropriate signal processing can achieve low crosstalk between sensors. Experiments on two and three sensor systems are reported. The minimum detectable signal measured is 1 mrad/sqrt{Hz}and the crosstalk factor achieved is -35 dB. The major causes of crosstalk are also analyzed.     

Demonstration of a 4-Sensor Folded Sangac Sensor Array with Active Phase Biasing Scheme

A 4-sensor folded Sagnac sensor array with an active phase biasing scheme is presented. The overlapping of the signal and noise pulse is avoided through a time division multiplexing scheme and the noise pulses is eliminated almost completely. The scheme can address 16 sensors when the repeat frequency of input pulse is at 68.3 kHz. The alternative phase bias technique is demonstrated, which can provide sensors with stable phase bias. The future benefit of this technique is that the 1/f noise in the circuit can be suppressed.     

Using Frequency-Shifted Interferometry for Multiplexing a Fiber Bragg Grating Array

We demonstrate a fiber Bragg grating (FBG) sensor multiplexing scheme based on frequency-shifted interferometry, in which a frequency-shifting element is placed asymmetrically in one arm of a folded Mach–Zehnder interferometer. The location and the reflection spectrum of each FBG sensor in an array can be resolved through Fourier transform. We experimentally investigated this multiplexing scheme in an FBG array constructed by ten low-reflectivity (${sim}$4%) sensors. A signal-to-noise ratio of 48 dB was achieved with crosstalk below ${-}$34 dB.      

传输序列干涉型光纤传感阵列

本文提出了一种新型干涉型光纤传感器复用系统。传感阵列部分采用光纤环路延迟线序列,并通过接收端的补偿干涉仪实现干涉效应和信号检测。具有结构简单、系统光功率利用率高、损耗低及高灵敏度、低串话等优点,适于大型传感器阵列应用。     

基于FBG震动传感器的边境安防系统研究

周界安防系统是重要区域和设施的第一道防线, 高性能的安防技术可以消除或减少外 部的威胁。基于窄带光纤光栅波长选择反射原理,设计了一种高灵敏度的光纤光栅震动传 感器并利用相位载波调制解调技术实现对传感器震动信号高精度实时解调。震动传感器通过 地埋的布设方式,利用光纤光栅震动传感器波分、空分、时分的复用技术,实现在较长的光 纤布设长度内对突发事件进行远程和实时监控。进行了野外试验,试验证明,通过合理算法 分析传感器时变信号的能量谱和峭度等参数该系统可准确的识别70 m 内人员走动和200 m内车辆行驶。该系统可广泛应用于边境线、机场 、核场所等重要区域的周界安防中。     

Crosstalk Analysis of a Fiber Laser Sensor Array System Based on Digital Phase-Generated Carrier Scheme

A detailed study on analyzing the crosstalk in a wavelength division multiplexed fiber laser sensor array system based on a digital phase generated carrier interferometric interrogation scheme is reported. The crosstalk effects induced by the limited optical channel isolation of a dense wavelength division demultiplexer (DWDM) are presented, and the necessary channel isolation to keep the crosstalk negligible to the output signal was calculated via Bessel function expansion and demonstrated by a two serial fiber laser sensors system. Finally, a three-element fiber laser sensor array system with a 50-dB channel-isolation DWDM was built up. Experimental results demonstrated that there was no measurable crosstalk between the output channels.     

Transmissive serial interferometric fiber sensor array

A transmissive serial array architecture for multiplexed interferometric fiber-optic sensors based on time division addressing is discussed. The configuration gives rise to intrinsic optical crosstalk between sensor elements of the system due to multiple cross-coupling of pulses between the series of sensor elements and the output fiber bus. This crosstalk is theoretically analyzed in detail, and compared to experimental results obtained with both three- and eight-sensor networks. Phase detection sensitivities as low as ~10 μrad/√Hz at a signal frequency of 1 kHz are reported     

Wireless MIMO Sensor Network with Power Constraint WLS/BLUE Estimators

Sensor networks are used in various applications. Sensors acquire samples of physical data and send them to a central node in different topologies to process the data and makes decisions. Multiple Input Multiple Output (MIMO) systems showed good utilization of channel characteristics. In MIMO Sensor Network, multiple signals are transmitted from the sensors and multiple antennas are used at the control node. This provides each receiver the whole combined signal and hence, array processing techniques helps in reducing the effects of noise. In this paper we devise the use of MIMO sensor network and array decision techniques to reduce the noise effect. The proposed Constrained Best Linear Unbiased Estimator (CBLUE) and Constrained Weighted Least Square (CWLS) estimators showed good performance BER when used with MIMO Sensor Network. Most importantly these estimates showed good perturbation results when the estimated channel matrix is not accurate. The condition for good performance was to have the number of receiving antennas at the central node to be equal to the number of transmitting sensors and no significant improve was seen if the number of antennas is greater than the number of transmitting sensors. If the number of sensors is greater than the number of receiving antennas, time or frequency multiplexing is possible to keep good performance for the devised system. Enhancing the BER results in longer battery life at sensor nodes.     

Multiplexing optical sensors using spatial light modulator

Most optical sensor multiplexing systems results in a decrease in signal to noise ratio for each additional sensor added to the network. A technique using a spatial light modulator (SLM) which overcomes this problem is described. The techniques has been tested in a system which addresses eight photoelastic strain sensors.<>     

Enhancement of multiplexing capability of low-coherence interferometric fiber sensor array by use of a loop topology

A novel technique for enhancing the multiplexing capability of low-coherence interferometric sensor array is proposed. The technique uses a fiber loop topology and allows for twice as many sensors as the conventional low-coherence reflectometry system to be multiplexed. Power budget and signal analyses for different sizes of sensor array are performed. A ten-sensor system was experimentally demonstrated and applied for quasi-distributed temperature measurement. An additional advantage of the technique is that it provides an extra degree of redundancy through the bidirectional interrogation of the sensor array and thus improves the system reliability.     

Sensor Multiplexing Based on a Finite-Impulse Response Lattice of Unbalanced Interferometers

A new approach for multiplexing interferometric fiber optic sensors is described and studied. The approach is based on a lattice of unbalanced Mach–Zehnder interferometers. This configuration is inherently low-loss and can be implemented and deployed in a simple manner. The signals from the cascaded sensors are extracted from the measured data via a layer peeling algorithm. A fifth-order polarimetric implementation of the proposed multiplexing technique has been constructed and characterized. The third sensor was buried in a sandbox while the rest of the sensors were spooled on a bobbin. The system successfully separated and monitored the pressure variations in the different sensors with minor crosstalk.      

On the Resiliency of MUSIC Direction Finding Against Antenna Sensor Coupling

Many classical direction of arrival (DOA) estimation algorithms suffer from sensitivity to sensor coupling. By applying a group of auxiliary sensors in a uniform linear array (ULA), we prove the resiliency of the MUSIC direction finding algorithm against array sensor coupling. We show that the performance of MUSIC algorithm under antenna array with unknown coupling can be very close to the case with known coupling. We can also estimate the mutual coupling coefficients before refining the DOA estimates by utilizing an extended sensor array. Moreover, our analysis on the effect of mutual coupling in direction finding illustrates the existence of some blind angles which should be avoided when the array is designed. Our simulation results corroborate our analysis.     

自适应双参考磁场梯度探测原理

本文使用4个单分量磁探头构成双参考磁场梯度探测装置.4个探头组成3个磁场梯度传感器,其中一个为信号传感器,另两个为噪声传感器.以信号传感器输出作为原始输入,噪声传感器输出作为参考输入,采用自适应噪声抵消技术,能有效消除因载体运动产生的涡流磁场及因磁探头方向相对地磁方向改变而引起的噪声输出.本文提出的双参考磁场梯度探测装置具有工艺性好,灵敏度高,虚警概率低的优点,可在实际磁探系统中使用.     

Large-scale multiplexing of interferometric fiber-optic sensorsusing TDM and DWDM

This paper describes multiplexing schemes for interferometric fiber sensors based on time-division multiplexed and dense wavelength-division multiplexing using optical add/drop multiplexers. The results of an experimental arrangement, which is based on one of the architectures, is also presented. Topics include a discussion of the noise sources in the system, dynamic range, and a characterization of the distributed feedback fiber laser source noise. We show the crosstalk levels in the experimental arrangement to be between -47 and -76 dB depending on the mechanism involved. The multiplexing schemes demonstrate the potential to address at least 192 interferometric sensors through two fibers based on a system with six wavelengths with a phase resolution less than 20 μrad/√Hz. For application to sonar arrays, our analysis has shown that hydrophones multiplexed in this type of architecture would achieve ambient acoustic noise-limited pressure resolution with an in-water dynamic range up to 135 dB at frequencies up to 10 kHz. In general, these architectures would find application in systems requiring very large numbers of sensors with a minimum of telemetry cabling required     

Low-crosstalk code-division multiplexed interferometric array

The results obtained using code-division multiplexing with an array of eight sensors are reported. It is demonstrated that crosstalk levels approximately -60 dB can be achieved using this approach using return-to-zero pulse coding.<>     

光纤F-P腔高灵敏加速度传感器理论模型研究

以提高光纤波长复用型加速度传感器的灵敏度为目标,分析光纤布拉格光栅(fiber Bragg grating, FBG)加速度传感器的增敏思路,阐明FBG加速度传感器灵敏度的增敏瓶颈和固有制约因素,提出波长复用型光纤法布里-珀罗(Fabry-Pérot, F-P)加速度传感器物理模型,理论研究其加速度传感原理,推导加速度传感器谐振频率和灵敏度的解析表达式,深入分析系统的结构体刚度、干涉级次、腔长对加速度传感器灵敏度和谐振频率的影响因素,并对比分析在不同系统刚度下FBG和F-P加速度传感器的灵敏度响应特性。由于灵敏度与谐振频率相互制约,进一步引入品质因子对比分析FBG和F-P加速度传感器的综合性能。在谐振频率为205 Hz时,传感器灵敏度高达198 nm/G,比基于FBG的传感器灵敏度理论上高出约2个数量级,并提出F-P型加速度传感器波长复用方案。理论分析表明F-P型加速度传感器与FBG型相比具有独特的优势,为光纤型加速度传感器的增敏和波长复用提供了新思路,并奠定理论基础。     

Efficient 2-D DOA estimation for coherent sources with a sparse acoustic vector-sensor array

This paper proposes a computationally efficient two-dimensional (2-D) direction-of-arrival (DOA) estimation algorithm based extended-aperture for acoustic coherent signals impinging on a sparse acoustic vector-sensor array. The coherency of incident signals is decorrelated through matrix averaging and the signal/noise subspaces are reconstructed through a linear operation of a matrix formed from the cross-correlations between some sensor data, where the effect of additive noise is eliminated. Consequently, DOAs can be estimated without performing eigen-decomposition (into signal/noise subspaces), and there is no need to evaluate all correlations of the array data. The derived estimates are automatically matched by translating eigenvalues into real-valued ones, furthermore, the proposed method can achieve the unambiguous direction estimates with enhanced accuracy by setting the vector sensors to space much farther apart than a half-wavelength, and it is also suitable for the case of spatially nonuniform noise, which may be more realistic scenario for the sparsely placed sensors. The performance of the proposed method is demonstrated through numerical examples.     

2D DOA and Frequency Estimation Method with One Vector-Sensor and Two Pressure Sensors Based on ESPRIT and Signal Power

We use one vector and two pressure sensors to form a sparse large aperture L-shape array for high performance two-dimensional (2D) direction of arrival (DOA) and frequency estimation. Because the number of sensors is small and there is only one vector sensor in the presented array, thus, the installation of sensors in the array is simpler and installation error is smaller, than the conventional array. Meanwhile, a high performance 2D DOA and frequency estimation method is presented. Firstly, utilizing single vector sensor and based on the ESPRIT, a group coarse 2D DOA and frequency parameters are obtained. Secondly, to restrain space noise or interference, a matrix filter is utilized to process the covariance matrix which comes from sensor array, so as to form a new covariance matrix which possesses high signal to noise ratio. Thirdly, utilizing the new covariance matrix and based on the ESPRIT again, accurate but ambiguity angles estimates are obtained. Fourthly, one signal power estimator and one optimization method are presented to solve the angle ambiguity and frequency ambiguity problems, respectively. The proposed method gains a high performance 2D DOA and frequency estimation results. Numerical simulations are performed to verify the feasibility of the proposed method.