帮忙翻译 １

最佳答案 - 由投票者2008-06-07 04:16:03选出

此文连结上一部分引言。
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This paper first introduces the background of fiber Bragg grating sensor technology and then follows by the high-speed
demultiplexing/interrogation system for FBG sensor arrays,
FBG sensor fabrication and package units. In this paper, the
installation and experimental setup in the Tsing Ma bridge are
also described, and the preliminary observation results on the
structural health monitoring of the Tsing Ma bridge using the
FBG sensor units are presented, analyzed and compared with
the conventional strain gauges employed in the WASHMS of
the Tsing Ma bridge. Some conclusions are made, and further
measurements and discussions in detail will be reported in
another subsequent paper [31 ].
这篇论文首先引出了布拉格光纤光栅的技术背景，然后介绍了FBG传感器阵列的分用/探询系统，和FBG传感器的制备及包装部分。本论文还介绍了传感器在青马大桥上的安装和实验步骤。提供了在使用FBG传感器的青马大桥上进行的结构健康监测而得到的初步观察结果，这些结果与传统的应变计(应变测量仪)所得到的结果进行分析和比较。本文最后提供了一部分结论，其他进一步的测量方法和细节讨论，将会在下一篇论文中作详细介绍。[31 ]

2. Background of fiber Bragg grating sensor technology
In the field of fiber-optic sensors (FOSs) 。
2. 布拉格光纤光栅传感器技术在光纤传感器(FOSs) 领域的背景介绍。
The FBG sensors are one of the most exciting developments in recent years. They have a unique property and many advantages over other FOSs
due to their quasi-point sensing and multiplexing capability.
The most important advantage of an FBG sensor is that the
measurand is encoded directly in terms of the wavelength,
which is an absolute parameter and does not suffer from
disturbances of the light paths [32].
FBG传感器技术是近年最激动人心的发展之一。由于它们的准点传感特性和复用能力，与其他光纤传感器(FOSs)作比较，具备一种独一无二的特性和许多优点。FBG传感器最重要的优势在于，量度信息根据波长编码，因为波长是个绝对值，FBG传感器就不会受到光路干扰的影响。[32]
Hence, the output signal is independent of the intensity of the source,
and losses in the connecting fibers and couplers.
Furthermore, each of the reflected signals will have a unique wavelength and can be easily monitored; an array of wavelength-multiplexed FBG sensors may thus be implemented for simultaneous
multiple measurements using a single fiber. A typical FBG is a periodic
perturbation of the refractive index in the fiber core as shown in
Fig. 1.

因此，输出信号与光源无关，与连接光纤和耦合器中的损耗无关。
而且每一个反射信号都有一个独一的波长，很容易被监测到。波长复用的FBG传感器阵列靠一根光纤就可以同时进行多种数据测量。一个典型的FBG在光纤纤芯中是一个周期性的折射率微扰。这显示在图1中。
2.1. FBG-based sensing principle
基于FBG的传感原理
A FBG is a periodic structure, which is written into a
segment of germanium-doped single-mode fiber in which a
periodic modulation of the core refractive index (RI) is formed
along the fiber length by exposure of the core to a spatial
pattern of UV light at 197 or 248 nm wavelengths.
When light within a fiber passes through a FBG, multiple Fresnel
reflections take place along the entire length of the grating due
to the variations in refractive index.
FBG在结构上是周期性的。它可以被导入掺锗石英心单模光纤中。当紫外线在197和248nm的波长时，把纤芯暴露在紫外线可以照到的空间上，延光纤长度就可以形成纤芯折射率的周期性调制 。当光纤中的光线通过FBG的时候，由于折射率的变化，沿整个光栅长度就会产生多种菲涅耳反射。


Constructive interference
between the forward wave and the contra-propagating light
wave occurs when the wavelength of the propagating light in
the fiber doubles the grating pitch, i.e. the Bragg (or phase
matching) condition is satisfied.
当光纤中传输波的波长使光栅栅距 加倍的时候，前向传输波和反向传播存在着一个结构上的相互干涉，比如，在满足光波相位匹配条件 下。
This leads to narrowband back-
reflection of light. The reflected wavelength is known as the
Bragg wavelength, XB, and is given by
公式 (1)
这就导致了窄波段的后向反射。反射后的波长被称为布拉格波长XB，可用用下面公式得到：
公式 (1)
where n is the effective refraction index of the fiber core and
A the period of the index modulation.
n是纤芯的有效折射率，A是解调指数的周期。

Both n and A depend
on temperature and strain, consequently the Bragg wavelength
is sensitive to both strain and temperature.
n 和 A都与温度和应变有关。结果就是，布拉格波长对温度和应变都灵敏。

A FBG is thus
an intrinsic fiber-optic sensor. Light that does not satisfy the
Bragg condition passes through the FBG with very low loss,
as shown in Fig. 1 [33].
The changes of index created in FBGs
are relatively permanent and FBGs are sensitive to a number
of physical parameters.
FBG本质上是光纤传感器。不满足布拉格条件的光在穿过FBG时，会有少量的损耗。这显示在图1中。[33]
布拉格光纤光栅中指数的变化相对来说是永久性的，布拉格光纤光栅对很多物理量敏感。
Thus, by monitoring the resultant
changes in reflected wavelength, FBG sensors can be used in
a variety of sensing applications to measure physical quantities,
for example, strain, temperature, pressure, ultrasound, high
magnetic field, force and vibration.
这样，通过监测反射波长的变化，FBG传感器可用于广泛的传感领域，来测量物理量的数据。比如：应变，温度，压力，超声，强磁场，力和振动。
Each of the reflected signals
will have a unique wavelength and can be easily monitored, thus
achieving multiplexing of the outputs of multiple sensors using
a single fiber. However, the FBG central wavelength will vary
with the change of these parameters experienced by the fiber. For an applied longitudinal strain change of A, the wavelength
shift, AJ~as, is given by
每一个反射信号都有一个独一的波长，很容易被监测到。使用同一根光纤的多个传感器的输出就可以实现复用。然而，FBG的中心波长将随光纤中变量的变化而变化。
对于应变纵向变化A来说，波长移位AJ由下面公式计算：
公式 (2)
where Ps is the photoelastic coefficient of the fiber, given by
Ps是光纤的光弹性系数，由下列公式给出。

公式 (3)

where Pll and Pl2 are the components of the fiber-optic
strain tensor and v the Poisson's ratio. For the silica fiber,
the wavelength-strain sensitivities of 800 nm and 1.55 Ixm FBG sensors have been measured as ~0.64 pm/µε and
0. 15 pm/µεrespectively [7,34].
For a temperature change of
A T, the corresponding wavelength shift, A3. B r, is given by
where α and ξ are the thermal expansion coefficient and
thermo-optic coefficient of the fiber material respectively.
Pll 和 Pl2是光纤应变张量的分量， v 是泊松比。对硅纤维来说，当波长应变灵敏度在800 nm 和 1.55 Ixm时，FBG传感器被测到的数据分别是~0.64 pm 和0. 15 pm[7,34].如果温度变化是A T，相应的波长移位A3. B r,可以用下面公式得到：
公式 (4)
α 和 ξ分别是光纤材料的热膨胀系数和热光系数
For the silica fiber, the wavelength-temperature sensitivities of
800 nm and 1.55 Dm FBG sensors have been measured with
values of ~6.8 pm/℃ and ,-~13 pm/℃ respectively [7,34].
对硅石英光纤而言，在波长-温度灵敏度是800 nm 和 1.55 Dm时，FBG传感器被测到的数据分别是 ~6.8 pm/℃ and ,-~13 pm/℃。[7,34]

The refractive index and the grating period, and subsequently,
the Bragg wavelength vary with changes in axial strain Ae and
temperature A T. The shift in the Bragg wavelength in response
to strain and temperature is given by
折射率和光栅周期，随后是布拉格波长随轴向应变Ae和温度A T的变化而变化。因为应变和温度变化而得到的布拉格波长移位可以用下面公式计算：
公式 (5)

2.2. FBG multiplexing technique
FBG的复用技术。
The primary advantage of FBG sensors is their capability
for multiplexing operation. In most practical applications, FBG
sensors need to be multiplexed in order to achieve quasi-
distributed measurements and potentially to compete with
conventional electrical or other types of optical sensors. A large
array of FBG sensors may be addressed by a single source
and detector using one or a combination of the four standard
techniques: time-division multiplexing (TDM), spatial-division<B
R></BR> multiplexing (SDM), frequency-division multiplexing (FDM)
and wavelength-division multiplexing (WDM). In principle, the
multiplexing techniques which are suitable for conventional
fiber-optic sensors can also be applied to FBG sensors [35].
FBG传感器最基本的优点是它们的复用能力。在许多实际应用的场合，FBG传感器需要能够被复用，从而达到准分布式测量的目的，这样就能和其他传统的电子传感器或其他光学传感器竞争。一个单独的探测源可以对一个大FBG传感器阵列进行编址，可以使用下面其中一种技术，或组合使用。这4种技术是：时分复用(TDM)，空分复用(SDM)，频分复用(FDM)，波分复用（WDM)。原则上，适合于传统光纤传感器的复用技术也可以运用到FBG传感器中。[35].