CN111537010A - 基于otdr的f-p干涉型传感头多点测量方法及装置 - Google Patents
基于otdr的f-p干涉型传感头多点测量方法及装置 Download PDFInfo
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Abstract
本发明涉及基于OTDR的F‑P干涉型传感头多点测量方法及装置,包括OTDR、长距离单模光纤延迟线、滤波器、FP传感头;利用耦合器制作出一个N×N路的链式结构,再每一条光路上设有不同的延迟线,当某一待测量发生改变时,FP传感头的干涉光谱将发生漂移,经过滤波器后波长漂移转换成强度的变化,由OTDR接收。由于OTDR检测的特定位置是由所处光路的2倍决定,而每一条光路的延迟线长短不同,所以每条光路返回的信号光在时域上具有一定的间隔。通过观测OTDR在时域上不同点的光强度变化,对N2个FP传感头的外界待测量进行实时测量,从而实现了F‑P传感头的复用与多点测量。本发明提出一种成本低、灵敏度高、基于OTDR的F‑P干涉型传感头多点测量方法及装置。
Description
技术领域
本发明属于光纤传感技术领域,特别涉及基于OTDR(光时域反射仪)的 F-P干涉型传感头多点测量方法及装置。
背景技术
人类已进入信息时代,传感器技术是信息技术的重要基础,是获取信息的主要技术途径。光纤传感器经过这些年的发展,已在科研和工业应用方面占重要的一席之地,其最主要的原因在于光纤和金属导线之间的根本区别。以光作为传感和波导媒介的最大优势是传输容量大、灵敏度高,抗电磁干扰,成本低,以及作为光波载体的光纤(光波导)所具有的化学惰性、柔软性,便于复用、便于成网。在智能材料、智能结构和大型结构监测、高电压、强磁场、核辐射以及生物医学等方面,光纤传感器是最具竞争力的测量手段。并且它能够在人达不到的地方(如高温区),或者对人有害的地区(如核辐射区),起到人的耳目的作用。而且还能超越人的生理界限,接收人的感官所感受不到的外界信息。光纤传感器虽然有很多优点,但仍存在交叉敏感等问题限制了实际中的应用。
光纤传感器的原理是利用光波导技术及半导体集成光电子技术将各种不同的光波导与光纤集成一体。当待测量发生变化时,光纤性质发生改变,导致光纤中传输光的光学特性发生变化(如光的强度、波长、频率、相位、偏振态等)。通过检测并分析输出光的光学特性的变化与对应待测变量的关系,即可测得待测变量。
光纤传感器技术发展的主要方向是:(1)多用途。即一种光纤传感器不仅只针对一种物理量,要能够对多种物理量进行同时测量。(2)提高分布式传感器的空间分辨率、灵敏度,降低其成本,设计复杂的传感器网络工程。注意分布式传感器的参数,即压力、温度,特别是化学参数(碳氢化合物、一些污染物、湿度、PH值等)对光纤的影响。(3)新型传感材料、传感技术等的开发。(4) 在恶劣条件下(高温、高压、化学腐蚀)低成本传感器(支架、连接、安装)的开发和应用。(5)光纤连接器及与其它微技术结合的微光学技术。
目前常见的光纤传感器包括光纤光栅(FBG)传感器和干涉型光纤传感器等。光纤布拉格光栅传感器(FBS)是一种使用频率最高,范围最广的光纤传感器,这种传感器能根据环境温度以及/或者应变的变化来改变其反射的光波的波长。通过全息干涉法或者相位掩膜法来将一小段光敏感的光纤暴露在一个光强周期分布的光波下面。这样光纤的光折射率就会根据其被照射的光波强度而永久改变。这种方法造成的光折射率的周期性变化就叫做光纤布拉格光栅。是目前技术较为成熟的一种传感器,广泛应用于准分布式测量,但其灵敏度与干涉型光纤传感器相比一般较低。
干涉型光纤传感器如M-Z(马赫-增德尔)干涉仪型和F-P(法布里-珀罗)干涉仪型等,具有灵敏度高,结构简单,成本低,易操作等优点。其中,F-P 干涉型传感器是通过在光纤内制作两个反射面,从而在两个反射面内形成一个 F-P腔。当光束沿光纤入射时,光束被两端面反射后沿原路返回并形成干涉光。当外界待测量变化作用于F-P腔时,就会导致F-P腔的光程差发生变化,因而输出的反射光的光谱发生漂移。通过检测反射光光谱的漂移量,就可以得到待测变化量。但F-P传感头的反射光谱通常为类正旋,具有波峰和波谷,光谱成分较复杂,导致F-P干涉型传感头不易实现多点测量,无法满足多点同时测量的实际应用场合的需求。
针对F-P干涉型传感头不易实现多点测量,无法满足多点同时测量的实际应用场合的需求等问题,本发明提出了一种基于OTDR的F-P干涉型传感头多点测量装置。本发明具有灵敏度高、可同时多点测量、制作成本低、适用于远距离测量等优点。
发明内容
针对F-P干涉型传感头不易实现多点测量的问题,本发明提出了一种灵敏度高、可同时多点测量、适用于远距离测量的基于OTDR的F-P干涉型传感头多点测量方法及装置。
本发明为解决技术问题所采取的方法包括如下步骤:
步骤一:选择一台OTDR,一个滤波器,若干个耦合器,若干根长度不同的单模光纤延迟线,若干个F-P传感头;所述的滤波器其中心波长和带宽与 OTDR光源的某一主峰一致,所述的F-P传感头的中心波长需与滤波器一致,自由光谱范围(FSR)需比滤波器的带宽大。
步骤二:OTDR的光输出端通过单模光纤与滤波器相连滤波出一个窄带光脉冲,再经单模光纤与耦合器连接后将光路等分成N条,每条光路上又各自通过单模光纤与耦合器连接再将光路分成N条支路,一共N2条测量光路。每一条光路都连接长度不同的单模光纤延迟线,单模光纤延迟线的长度依次递增,最后再每条延迟线各连接一个F-P传感头。
步骤三:信号光通过单模光纤传输到F-P传感头时,分别在F-P腔的两端面反射后沿原路返回并相遇而产生干涉。
其中,反射光强度I表示为:
I1和I2分别是F-P腔的两端面反射光的反射强度,L是F-P腔的长度,n 是F-P腔内部的折射率,λ是光的波长。
λd是与光的最大强度相对应的波长,即为干涉峰。m是任意整数;
FSR是两个相邻反射波峰或波谷之间的距离,与单个光谱周期的带宽有关,其中FSR公式为:
F-P传感头的灵敏度S可以表示为:
Δλ表示波长漂移量,k为待测量,Δk为待测量的变化。
步骤四:当第m路的延迟线连接的F-P传感头其反射光的中心波长与滤波器的一致时,光谱的重合部分为最大值,即反射光强为最大值;当F-P传感头的反射光谱发生漂移,滤波器与F-P传感头的反射光谱的重合部分减少,此时,反射光强将会减小;当F-P传感头的反射光谱与滤波器的光谱图完全不重合时,反射光强为最小值;滤波后的光强度变化体现了外界待测量的变化,由OTDR 接收后,通过监测特定位置上的光强度变化得到第m路的外界待测量的变化,实现传感头的测量。
滤波器的滤波函数为:
λ0为滤波器的中心波长,a为滤波器比例系数,ω为滤波器高斯函数的半宽。
F-P传感头随待测量变化的反射光谱I如(1)式,即:
OTDR接收到的第m条光路的反射光强Sm可表示为:
由(8)式可以看出,由OTDR接收到的光强与F-P腔折射率n以及腔长L 有关,从而与外界待测量有关。OTDR通过监测第m条光路的反射光强的变化,就可以得到对应待测量的变化。
当所有光路耦合成一路,由OTDR接收。由于OTDR检测的特定位置是由所处光路的2倍决定,而每一条光路的延迟线长短不同,所以每条光路返回的信号光在时域上具有一定的间隔,间隔由延迟线的长短差异决定。通过观测 OTDR在时域上不同点的光强度变化,对N2个FP传感头处的外界待测量进行实时测量,从而进行F-P传感头的复用与多点测量。
为了实现F-P干涉型传感头的多点测量,本发明还提供了基于OTDR的 F-P传感头多点测量装置应用于上述的方法中:
包括了一台OTDR,一个滤波器,若干个耦合器,若干根长度不同的单模光纤延迟线,若干个F-P传感头。OTDR的光输出端通过单模传输光纤与滤波器的光输入端相连,滤波器的输出端滤波出一个窄带光脉冲,经单模光纤与耦合器信号输入端连接,再将光路等分成N条由N个信号输出端输出,每条信号输出端又各自通过单模光纤与另一个耦合器的信号输入端相连,再次将光路分成N 路由N个信号输出端输出,一共形成N2条测量光路。每一条测量光路都连接长度不一样的单模光纤延迟线,延迟线的长度依次递增,最后每条延迟线各连接一个F-P传感头。所述的滤波器其中心波长和带宽与OTDR光源的某一主峰一致。所述的F-P传感头的中心波长需与滤波器一致,自由光谱范围(FSR)需比滤波器的带宽大。
本发明的有益效果为:
1、本发明利用耦合器制作出一个N×N路的链式结构,再每一条测量光路上设有不同的延迟线,可直接将每条测量光路的反射光的反射光谱在时间轴上区分开来。
2、本发明采用OTDR作为光信号的产生接收装置,不仅可以测得反射光强的变化,还可以计算出信号发出与接收的时间。由于每一条光路的延迟线长短不同,使得每一路的反射光谱在时间轴上具有一定的间隔。通过观测OTDR 在时域上不同点的光强度变化,实现F-P传感头的复用与多点测量。
附图说明
图1为基于OTDR的F-P干涉型多点测量传感器装置示意图。
图2为基于OTDR的F-P干涉型多点测量传感器测试原理图。
图3为基于OTDR的F-P干涉型多点测量传感器测试结果示意图。
具体实施方式
下面结合附图对本发明作进一步描述。
如图1所示,OTDR的F-P干涉型传感头多点测量传感器装置示意图,包括OTDR 1、滤波器2、耦合器3、延迟线4、F-P传感头5。OTDR 1的光输出端通过单模传输光纤与滤波器2的光输入端相连,滤波出一个窄带光脉冲。窄带光的脉冲带宽与OTDR光源的某一主峰一致,与F-P传感头的干涉主峰相对。再经单模光纤与耦合器3连接后将光路等分成N路,每条支路上的光又各自通过单模光纤与耦合器连接再将光路分成N路,这样一共形成了N2条测量光路。每一条测量光路都连接长度不同的单模光纤延迟线4,延迟线的长度依次递增,最后再每条延迟线各连接一个F-P传感头5。
如图2-1所示,F-P传感头的中心波长与滤波器的中心波长完全重合,此时F-P传感头和滤波器的重合部分为最大值,即反射光强为最大值。当外界待测量变化时,F-P传感头的反射光谱发生漂移。如图2-2所示,F-P传感头和滤波器的重合部分减小,反射光强逐渐减小。所以可以通过测得反射光强的变化实现对外界待测量的检测。
如图3所示,N条光路的反射光强在OTDR上显示。不同时间点上,对应的F-P传感头的反射光强随外界的待测量变化而变化。通过观测OTDR在时域上不同点的光强度变化,实现了F-P传感头的复用与多点测量。
本发明的工作方式为:OTDR 1发出的信号光,从单模传输光纤输入到滤波器2中,滤波出一个窄带光脉冲。窄带光脉冲再经单模光纤与耦合器3连接后将一束信号光等分成N路,每条支路再通过单模传输光纤与耦合器相连各自再分成N个支路。一共N2条光路再各自通过长度依次递增的延迟线4与N2个 F-P传感头5的单模光纤端相连。N2束光在经F-P传感头反射后耦合成一路,由OTDR接收。当第m路的外界待测量改变时,对应的F-P传感头的干涉光谱将会发生漂移。OTDR通过监测第m条光路的反射光强的变化,就可以得到对应待测量的变化。同理,当所有光路耦合成一路,由OTDR接收。由于OTDR 检测的特定位置是由所处光路的2倍决定,所以每条光路返回的信号光在时域上具有一定的间隔,间隔由延迟线的长短差异决定。通过观测OTDR在时域上不同点的光强度变化,对N2个FP传感头的外界待测量进行实时测量,从而实现了F-P传感头的复用与多点测量。
该装置能够实现基于OTDR的F-P干涉型传感头的复用与多点测量的关键技术有:
1、F-P传感头反射光的中心波长与滤波器透射光谱的中心波长一致,实现波长漂移到光强度变化的转变。
2、延迟线作用与每条光路的时间间隔需远大于OTDR的精度(≥10倍),使得***能够很好的分辨每条支路的光信号。
本发明的一个具体实施例中,OTDR发出的激光波长范围为 1530-1557nm,脉冲宽度为5ns。滤波器带宽为0.5nm,其中心波长与所连接的 OTDR 1550nm处的主峰相对,滤波出一个窄带光脉冲,再经1×4耦合器后将光路等分成4路,每条支路上的光又各自经1×4耦合器后分成4路,一共形成了16条光路。每一条光路都连接长度不同的单模光纤延迟线,延迟线的长度分别为100米、200米、300米……1600米。最后再每条延迟线各连接一个F-P传感头,F-P传感头的中心波长为1550nm,自由光谱范围为12.5nm。实验结果表明,在25℃到75℃温度范围内,基于OTDR的F-P干涉型多点测量温度传感器的灵敏度可以达到1.210dB/℃。
本领域的技术人员应理解,上述描述及附图中所示的本发明的实施例只作为举例而并不限制本发明。
本发明的目的已经完整并有效地实现。本发明的功能及结构原理已在实施例中展示和说明,在没有背离所述原理下,本发明的实施方式可以有任何变形或修改,这些变化和改进都落入要求保护的本发明的保护范围。
Claims (2)
1.基于OTDR的F-P干涉型传感头多点测量方法,其特征在于如下步骤:
步骤一:选择一台OTDR(光时域反射仪),一个滤波器,若干个耦合器,若干根长度不同的单模光纤延迟线,若干个F-P传感头;所述的滤波器其中心波长和带宽与OTDR光源的某一主峰一致,所述的F-P传感头的中心波长需与滤波器一致,自由光谱范围(FSR)需比滤波器的带宽大;
步骤二:OTDR的光输出端通过单模光纤与滤波器相连滤波出一个窄带光脉冲,再经单模光纤与耦合器连接后将光路等分成N条,每条光路上又各自通过单模光纤与耦合器连接再将光路分成N条支路,一共N2条测量光路;每一条光路都连接长度不同的单模光纤延迟线,单模光纤延迟线的长度依次递增,最后再每条延迟线各连接一个F-P传感头;
步骤三:信号光通过单模光纤传输到F-P传感头时,分别在F-P腔的两端面反射后沿原路返回并相遇而产生干涉;
其中,反射光强度I表示为:
I1和I2分别是F-P腔的两端面反射光的光强度,L是F-P腔长度,n是F-P腔内部折射率,λ是光的波长;
λd是与光的最大强度相对应的波长,即为干涉峰,m是任意整数;
自由光谱范围(FSR)是两个相邻反射波峰或波谷之间的距离,与单个光谱周期的带宽有关,其中FSR公式为:
F-P传感头的灵敏度S可以表示为:
Δλ表示波长漂移量,k为待测量,Δk为待测量的变化;
步骤四:当第m路的延迟线连接的F-P传感头其反射光的中心波长与滤波器的一致时,光谱的重合部分为最大值,即反射光强为最大值;当F-P传感头的反射光谱发生漂移,滤波器与F-P传感头的反射光谱的重合部分减少,此时,反射光强将会减小;当F-P传感头的反射光谱与滤波器的光谱图完全不重合时,反射光强为最小值;滤波后的光强度变化体现了外界待测量的变化,由OTDR接收后,通过监测特定位置上的光强度变化得到第m路的外界待测量的变化,实现传感头的测量;
滤波器的滤波函数为:
λ0为滤波器的中心波长,a为滤波器比例系数,ω为滤波器高斯函数的半宽;
F-P传感头随待测量变化的反射光谱I如(1)式,即:
OTDR接收到的第m个光路的反射光强Sm可表示为:
由(8)式可以看出,由OTDR接收到的光强与F-P腔折射率n以及腔长L有关,从而与外界待测量有关;
当所有光路耦合成一路,由OTDR接收,由于OTDR检测的特定位置是由所处光路的2倍决定,而每一条光路的延迟线长短不同,所以每条光路返回的信号光在时域上具有一定的间隔,间隔由延迟线的长短差异决定;通过观测OTDR在时域上不同点的光强度变化,对N2个FP传感头处的外界待测量进行实时测量,从而进行F-P传感头的复用与多点测量。
2.基于OTDR的F-P传感头多点测量装置,该装置应用于权利要求1的多点测量方法,其特征在于,包括了OTDR、滤波器、耦合器、长距离单模光纤延迟线,F-P传感头;所述OTDR的光输出端通过单模传输光纤与滤波器的光输入端相连,滤波器的光输出端通过单模传输光纤与耦合器相连等分成N条光路,每条光路再通过单模传输光纤与耦合器相连各自再分成N个支路,一共N2条测量光路,每条测量光路的末端连接有长度不均等的单模光纤延迟线,每条长距离单模光纤延迟线与F-P传感头的单模光纤端相连;所述的滤波器的中心波长和带宽与OTDR光源的某一主峰一致,所述F-P传感头中心波长需与滤波器一致,自由光谱范围(FSR)比滤波器的带宽大。
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