光隔离器法抑制Michelson干涉型光纤水听器中的SBS

光纤水听器是利用光的干涉信号进行探测的,但随着入射光功率的增加,易发生受激布里渊散射（stimulated Brillouin scattering,SBS）效应,并因而产生噪声,限制入射光功率的增加,极大地影响探测信号。为了抑制SBS效应,提高光纤水听器性能,以Michelson型光纤水听器为例,从实验和理论上研究了SBS及其阈值特性。根据阈值公式分析了提高阈值的方法,着重讨论了光隔离器法对SBS的抑制。最后利用时域有限差分方法对光纤内的入射光、Stokes光和声波的时空分布进行了分析。只要给出初始条件及光纤参数即可得出光纤内各波的时空分布。通过开展抑制此效应的研究,不仅为可调谐相干光的产生提供一个新途径,而且可作为一种有效手段来研究各种光纤系统中的散射特性。     

对基于光纤光栅的两种水听器灵敏度的讨论

本文简单介绍了基于光纤光栅的光纤布喇格光栅(FBG)水听器以及分布反馈式(DFB)光纤激光水听器的基本工作原理与信号解调的基本方法。在此基础上提出了FBG水听器和DFB光纤激光水听器波长漂移率、压力灵敏度系数、相位灵敏度与相位灵敏度级以及电压灵敏度的定义以及物理涵义.并且对干涉型光纤水听器与DFB光纤激光水听器在相位灵敏度以及物理涵义上的区别进行了说明.     

Interlaboratory evaluation of hydrophone sensitivity calibration from 0.1 to 2 MHz via time delay spectrometry

Knowing the low-frequency response of hydrophones, down to 100 kHz at least, is important for accurate biomedical ultrasound measurements. However, current international standards do not extend below 500 kHz. Furthermore, commercial hydrophone sources typically do not supply sensitivity data below 1-2 MHz. Therefore, to help identify and validate practical calibration methods below 2 MHz, the authors have extended their previous individual efforts in an interlaboratory evaluation of sensitivity calibration using the swept-frequency technique, time delay spectrometry (TDS). Calibrations were performed for needle and membrane PVDF hydrophones using each laboratory's TDS system. Each site employed the same purpose-built broadband source transducers, comprising both plano-concave and biconcave 1-3 piezocomposite elements 4 cm in diameter, with maximum and minimum thicknesses of approximately 1.5 and 0.1 cm. Agreement between laboratories was within the estimated measurement precision of +/-0.6 dB. The results demonstrated that a TDS system employing such transducers constitutes a viable method for hydrophone calibrations in this frequency range.     

Miniaturized mandrel-based fiber optic hydrophone

Fiber optic hydrophones typically use a long sensor fiber wrapped around an air-filled mandrel to achieve high responsivity. Minimum mandrel diameter is determined by fiber reliability considerations. A miniature hydrophone, with diameter of about a third that of previous hydrophones, is reported. Such a hydrophone has applications for very thin towed arrays. Small diameter fiber with high strength Bragg gratings written through the coating are key enablers.     

Fiber-optic hydrophone using a cylindrical Helmholtz resonator as a mechanical anti-aliasing filter

Two Michelson interferometric fiber-optic hydrophones that use panda polarization-maintaining fibers and devices have been constructed and tested. The low-frequency acoustic sensitivities of both hydrophones are -159 dB re 1 rad/microPa. One of the hydrophones tested has a small cylindrical Helmholtz resonator that has a break point near 1200 Hz and a measured roll-off of approximately 50 dB/octave, and it is a hydrostatic-pressure-insensitive design. This hydrophone is a prototype device for a class of sensors that can be used to eliminate aliasing in future sonar systems. To our knowledge, this is the first time that such a fiber-optic hydrophone has been reported.     

医用超声测量用PVDF探针形高频微型水听器的研制

本文叙述了用于医学超声测量的两种ＰＶＤＦ探针形高频微型水听器的设计特点，结构和它们的性能测量结果，最后介绍在非线性声学研究中的应用实例。     

A multiple-frequency hydrophone calibration technique

A method is described for comparing the sensitivity of two hydrophones over the frequency range 1-15 MHz. This technique forms the basis for the dissemination of national ultrasonic standards in the U.K. over this frequency range. A reference hydrophone is placed in an ultrasonic field and then the device being calibrated is substituted and the two output voltages are compared. This substitution method utilizes a broadband ultrasonic field produced by nonlinear propagation. Thus it is possible to cover the whole frequency range with a single measurement on each hydrophone. The overall uncertainty in the intercomparison of two hydrophones increases from +/- 4.2% at 1 MHz to +/- 8.2% at 15 MHz (95% confidence level). The method has been compared with discrete-frequency substitution, time-delay spectrometry, and absolute calibrations using the National Physical Laboratory (NPL) Primary Standard Laser Interferometer. Various designs and sizes of hydrophones were compared, and agreement was within the combined random uncertainties for all the comparisons.     

Rigid piston approximation for computing the transfer function and angular response of a fiber-optic hydrophone

The transfer function of a fiber-optic hydrophone (FOH) is computed for various fiber core radii. The hydrophone is modeled as a rigid disk, with plane waves impinging at normal or oblique incidence. The total sound field is written as the sum of the incident field and the field diffracted from the hydrophone. The diffracted field is approximated by the field generated by a vibrating planar piston in an infinite rigid baffle. For normal incidence and a pointlike fiber core, an analytical solution is presented. For finite fiber core radii, and for oblique incidence, the transfer functions are computed numerically. The calculated transfer functions exhibit an oscillatory frequency dependency that is most pronounced for small fiber cores. The solution for a core radius of 2.5 microm can be very well approximated by the analytical solution for a pointlike core at frequencies of up to 30 MHz. The results for normal incidence can be directly employed to deconvolute ultrasonic pressure signals measured with an FOH. From the transfer functions for oblique incidence, the angular response of the hydrophone is calculated. The angular response obtained here differs significantly from the model commonly used for piezoelectric hydrophones. The effective hydrophone radius derived from the angular response shows a strong frequency dependency. For low frequencies, it is found to be larger than the outer fiber radius, whereas it generally lies between the outer radius and the fiber core radius for frequencies above 10 MHz.     

Sensitivity of ultrasonic hydrophone probes below 1 MHz

Frequency responses of different PVDF polymer hydrophone probes, including membrane and needle designs, were measured and are presented in terms of end-of-cable voltage sensitivity versus frequency over a wide, 4.5 octave bandwidth ranging from 0.25 to 2.5 MHz. The probes are seldom, if at all, characterized in this frequency range due to the difficulties associated with a lack of adequate and readily implementable calibration techniques. To this end, a technique, which uses a combination of swept frequency chirp and reciprocity, so that both the relative and absolute plots of sensitivity versus frequency can be obtained, was developed and tested. Salient features of the technique including the design of a 6 octave auxiliary acoustic source are described. The experimental data indicate that a majority of the PVDF membrane hydrophones exhibit a relatively uniform (to within +/- 2 dB) response. While, in general, this is not the case for commercially available needle hydrophone probes, it is evidenced that a careful attention to the PVDF probe design results in frequency characteristics fairly close to those achievable with a membrane design. The overall uncertainty of the calibration technique was estimated to be better than +/- 1.5 dB in the considered frequency range. The results of this work are important to implement procedures for adequate determination of the Mechanical Index (MI) of ultrasound imaging devices. MI is widely accepted as a predictor of potential bioeffects associated with cavitation phenomena. Current efforts are focused on extending the applicability of the technique to frequencies below 100 kHz.     

光纤水听器解调技术研究进展

光纤水听器是水声研究领域的关键技术,在实际应用中具有显著优势,广泛应用于AUV导航定位、资源勘探、海水警戒等场景.光纤水听器将声信号转化为光信号传播,在接收信号时就需要对光信号进行解调提取出声压信号.总结了几种常用的信号解调算法及关键技术,包括PGC解调法、3×3耦合器解调法和外差解调法;介绍了各种解调算法的基本原理和...     

High-accuracy optical time delay measurement in fiber link [Invited]

Optoelectronic components and subsystems such as optically controlled phased array antennas, distributed radar networks, interferometric optical fiber hydrophones, and high-speed optoelectronic chips demand highaccuracy optical time delay measurement with large measurement range and the capability for single-end and wavelength-dependent measurement. In this paper, the recent advances in the optical time delay measurement of a fiber link with high accuracy are reviewed. The general models of the typical time delay measurement technologies are established with the operational principle analyzed. The performance of these techniques is also discussed.     

新型光纤光栅水声传感器的研究

提出了一种新型的光纤布拉格光栅(FBG)水声传感探头结构以及光纤光栅传感信号的自解调方法。利用一对匹配光栅构成推挽结构,实现了传感-解调的合二为一,大大地减小了系统的复杂度;并通过筒状弹性体结构,解决了裸光纤光栅测量水声信号的灵敏度过小的问题,并具有温度补偿作用。仿真与初步实验结果表明,该水听器探头的测量动态范围超过100 dB,在100~200 dB re 1μPa的水声压范围内,测量灵敏度为0.36 nm/Mpa。     

光纤水听器的原理与应用

为适应水声学应用特别是水下反潜战的需要，在光纤技术不断发展的基础上，光纤水听器应运而生．光纤水听器是一种基于光纤、光电子技术上的新型水下声传感器，因其在军事、民用各领域应用广泛，目前光纤水听器在国内外发展迅速，已经到达实用状态．全光光纤水听器系统的湿端采用全光实现，信号传感与传输皆基于光纤技术．具有抗电磁干扰、重量轻和造价低等优点．文章简述了光纤水听器的发展历史、现状，论述了光纤水听器的原理及其应用前景．     

A polyvinylidene fluoride needle hydrophone for ultrasonic applications

A new type of piezoelectric polymer hydrophone for the frequency range above 1 MHz is described, which consists of a needle, coated with a thin layer of polyvinylidene fluoride. The sensitive area is a small polarized zone of the polymeric material around the needle point. Special properties, caused by the constructive design of this ‘needle hydrophone’, are its non-directivity in a wide angular range, and high spatial resolution of the ultrasonic sound field pattern. Construction and performance are compared with other types of piezoelectric polymer hydrophones. Some possible applications are discussed.     

F-P型光纤水听器温度特性研究

温度漂移对水听器系统输出的影响是其实用化进程中的关键技术障碍。这主要表现在温度变化引起水听器探头背衬材料的胀缩和光纤折射率的变化。首先从弹性力学轴对称问题的准静态理论出发分析了背衬材料的应力特性,并用光弹理论及热应力理论分析了温度改变对光纤相位常数的影响,得出了温度影响干涉式光纤水听器光学相位输出的数学表达式。给出了温度变化对水听器光学相位输出影响的实验测量结果,得出了光学相位随温度变化的线性关系图,与理论计算结果吻合。     

1-60 MHz measurements in focused acoustic fields using spatial averaging corrections

The purpose of this research was to develop, implement and verify a measurement technique enabling rapid and dependable characterization of ultrasound hydrophone probes beyond 20 MHz. The technique employs focused acoustic sources to optimize signal-to-noise ratio and spatial averaging correction model to account for the finite aperture of the hydrophone probes. To minimize calibration time, substitution technique was chosen and its applicability was tested up to 60 MHz. The overall uncertainty of the measurements was on the order of +/- 1 dB. The results are presented for both needle and membrane type PVDF hydrophones having effective diameters ranging from 130-1200 microns. The fundamental limitations of the technique were determined and it is shown that the spatial averaging error is governed by the cross-section of the beam in the focal plane and the ratio of the effective diameters of the reference and tested hydrophone probes. The technique developed is being extended to frequencies beyond 60 MHz.     

基于光频调节的干涉型光纤水听器相位补偿检测方法

提出了一种基于光源频率调节的干涉型光纤水听器主动相位补偿的信号检测方法。详细介绍了该方法的基本检测原理,对信号解调误差进行了理论分析与仿真。为了验证该方法的可行性,搭建了实验系统,并编写了实时的信号采集、处理程序,对某一干涉型光纤水听器的声压灵敏度进行了测试。在频带20 Hz-1.3 kHz上,平均声压灵敏度为-162.2 dB(0 dB=1 rad/μPa),波动小于±0.8 dB,与采用相位载波调制解调方法测量的结果基本吻合。实验结果证明该方法是有效的。由于传感部分不含有源器件,便于实现全光纤化,且解调算法简单、检测频带宽,该方法能被广泛应用到各种干涉型光纤传感器的信号检测当中。     

Comparison of optical detection system ,PVDF detection system, and PVDF needle hydrophone for optoacoustic tomography

Optoacoustic tomography (PAT) is a two-dimensional medical imaging method that has the advantage of optical contrast and resolution of ultrasonic waves. The detection systems with a high sensitivity can be used for detecting small tumors, located deeply in human tissues, such as the breast. In this study, the sensitivity of existing ultrasonic detection systems has been compared experimentally with that by using thermoelastic waves as a broadband ultrasonic source. For the comparison, an optical stress transducer(OST), a polyvinylidene difluoride (PVDF) sheet and a calibrated PVDF needle hydrophone were used.To ensure all of the detection systems interrogated by the same ultrasonic field, a small optical instrument that fixed the generating laser head was constructed. The sensitivity was evaluated by measuring signalto-noise ratios (SNRs) and noise equivalent pressures (NEPs). The PVDF system, with a 4-kPa NEP has a 22 dB better performance than the OST. The OST showed nearly the same sensitivity as the hydrophone for detecting ultrasound waves at a 1-cm distance in water. PVDF detection system provides a useful tool for imaging of soft tissues because of its high sensitivity and broad detection range.     

一种有源型光纤水听器原理与实验分析

分析了一种有源型光纤水听器的水声传感原理,在一段掺铒光纤中写入具有π相移的光纤光栅构成光纤激光器,水声压力作用在激光器上引起激光波长的移位,采用干涉法检测出波长移位引起的相位变化即得到声压的信息.水声探测实验表明,有源型光纤水听器的声压灵敏度为-166.5 dB(参考值1 rad/μPa).将不同工作波长的四元光纤水听器串接于一根光纤内组成水听器阵列,使用带通波分复用器将阵列发出的激光分离至各独立通道后检测出相应的声压信号,测得水听器之间的级串扰小于-60 dB,且单元水听器水声响应的动态范围不受影响.