機(jī)械外文翻譯文獻(xiàn)翻譯使用了光纖光柵技術(shù)的光學(xué)水位傳感器

1、 使用了光纖光柵技術(shù)的光學(xué)水位傳感器基于光纖光柵( fbg )技術(shù)我們開(kāi)發(fā)了一種光學(xué)高精度水位傳感器。該傳感器可用于測(cè)量河流,湖泊和污水處理系統(tǒng)的水位。傳感頭由一個(gè)膜片,一個(gè)特制的彈簧管和兩個(gè)光纖光柵組成, 一個(gè)用于張力測(cè)量另外一個(gè)用于溫度補(bǔ)償。光纖光柵貼在彈簧管上，由于水位的上升，來(lái)自光纖光柵的發(fā)射光，使中心波長(zhǎng)改變。通過(guò)波長(zhǎng)檢測(cè)設(shè)備檢測(cè)中心波長(zhǎng)，波長(zhǎng)檢測(cè)設(shè)備由一個(gè)調(diào)諧f-p濾波器組成。我們實(shí)現(xiàn)了傳感器精度為0.1%即為1cm，水位測(cè)量范圍為10m。幾個(gè)傳感頭可以通過(guò)一個(gè)光纖串聯(lián)在一起。用一塊波長(zhǎng)訊問(wèn)設(shè)備可以同時(shí)測(cè)量不同的水位。1簡(jiǎn)介：河川管理員具有非常重要的責(zé)任,是維護(hù)其河設(shè)施和監(jiān)測(cè)流域狀

2、況。由于河川設(shè)施是沿著河流域分散的，管理員要定期檢查這些設(shè)施。這一工作是非?；ㄙM(fèi)員工的時(shí)間和體力的。此外, 很難對(duì)這些設(shè)施進(jìn)行抽查,以確定其結(jié)構(gòu)完整性,在發(fā)生自然災(zāi)害 ,如洪水沖刷,地震干擾。從這個(gè)角度出發(fā)，日本政府沿著其河川流域建立了光纖網(wǎng)絡(luò)。利用這種光纖網(wǎng)絡(luò)近日有效地研制光纖傳感器和傳感系統(tǒng), 而適用于流域防洪設(shè)施的安全管理。光纖傳感器及其系統(tǒng),有以下的優(yōu)點(diǎn)：1. 低傳輸損耗使光纖遙感超過(guò)幾十公里。2. 實(shí)時(shí)監(jiān)控是通過(guò)傳感頭連接在一起，測(cè)量設(shè)備直接使用光纖。3. 傳感頭為全光通信無(wú)源器件,不需要進(jìn)行電力供應(yīng)，傳感器頭已裝入。4. 由于是不受電磁干擾的一個(gè)光學(xué)傳感器, 它不遭受觸電有害影響的

3、,如發(fā)生了雷擊。水位傳感是一個(gè)河川最關(guān)鍵的問(wèn)題,無(wú)論是河流管理者和附近居住的立足點(diǎn)都是一個(gè)流域設(shè)施的維修以及預(yù)防自然災(zāi)害。 我們已開(kāi)發(fā)出光學(xué)水位傳感器利用光纖光柵(fbg),擁有的優(yōu)勢(shì)比上述更多。在本文中,我們?cè)敿?xì)闡述了光纖光柵作為應(yīng)變傳感器, 水位傳感應(yīng)用的業(yè)績(jī),獲得了實(shí)用領(lǐng)域。2光纖光柵技術(shù)及傳感應(yīng)用 ：2.1 光纖光柵的原理fbg是一個(gè)沿著給定長(zhǎng)度光纖的折射率的調(diào)制解調(diào)器。圖1所示光柵的結(jié)構(gòu)示意圖，由于耦合關(guān)系向前和向后傳播方式, 特定波長(zhǎng)的光前其折射率取決于調(diào)制周期，反映在光柵位置上。入射光反射時(shí)它的波長(zhǎng)等于布拉格光柵波長(zhǎng) ,定義為下式：= 2（1）是有芯模有效折射率 ，是光柵周期。其

4、他波長(zhǎng)的光傳送通過(guò)fbg及下一個(gè)光纖光柵的照射 。因此，他是一個(gè)可以實(shí)現(xiàn)多點(diǎn)傳感在一個(gè)串聯(lián)的光纖光柵上。各自有不同的反射波長(zhǎng)。光譜的反射光來(lái)自光柵，可實(shí)現(xiàn)對(duì)應(yīng)力和溫度的分別測(cè)量，布拉格波長(zhǎng)的變化量和應(yīng)變和溫度的關(guān)系。.（2）其中是有效的光彈性系數(shù)，是應(yīng)變，是熱光系數(shù) ，是溫度的變化量。使用普通的單模光纖通信 ，他的有效光彈性系數(shù)是0.22 ,靈敏度在應(yīng)用軸向應(yīng)變和溫度補(bǔ)償1.2分/微應(yīng)變和10分/ 分別在1.55微米波長(zhǎng)范圍內(nèi)。2.2 光纖光柵的制作圖2顯示了光纖光柵的制作工藝， 我們使用了聚酰亞胺涂層光纖的光纖光柵作為應(yīng)變傳感器 ，在邊界上覆蓋涂層不讓其滑動(dòng)，使外部應(yīng)變正確地轉(zhuǎn)移到光柵上。用

5、來(lái)制造光纖光柵的光纖用經(jīng)過(guò)紫外線的照射處理。提前寫(xiě)光柵，聚酰亞胺涂層光纖受到一摻氫處理，為了獲得足夠的光致折射率變化量，摻氫過(guò)程是在紫外線照射之前完成。聚酰亞胺涂層,部分外用一種化學(xué)溶劑溶蝕。krf準(zhǔn)分子激光器的輸出波長(zhǎng)為248nm，隨著縱向掃描通過(guò)相位掩膜法fbg刻在光纖核心區(qū)域。底片感應(yīng)折射率調(diào)制沿著光纖，即趾剖面可以控制的可編程掃描速度的激光束。我們采用高斯切趾法,以抑制分辨損失的反射光譜 。之后寫(xiě)光柵，加聚酰亞胺涂層是為了保護(hù)剝離部分。最后,光纖與光纖光柵受到高溫( 300)熱處理30分鐘，為確保長(zhǎng)期穩(wěn)定。3光學(xué)水位傳感器用光纖光柵3.1 結(jié)構(gòu)光學(xué)水位傳感器 圖5和圖6分別顯示了光學(xué)水

6、位傳感器結(jié)構(gòu)示意圖和原理圖，傳感器是一個(gè)壓力轉(zhuǎn)換元件。傳感頭由一個(gè)膜片,一個(gè)特制的彈簧管和兩個(gè)光纖光柵組成, 一個(gè)光柵是用于張力測(cè)量，另一個(gè)光柵用于溫度補(bǔ)償。這一水位傳感器用于測(cè)量水壓和水位的比例，水壓傳送到內(nèi)部有硅油的彈簧管。這是彈簧管將油壓轉(zhuǎn)換為彈簧管尖的張力，然后利用玻璃管的高彈性將油壓轉(zhuǎn)換為管部頂端的張力并且擴(kuò)張到 fbg，即在頂端和底部串成一串。因此,光纖光柵是拉伸比例隨水位上升。 光纖光柵是有輕微的預(yù)拉伸初期,為使測(cè)量水位直線下降,最低水平 布拉格波長(zhǎng)隨溫度的變化而變化，也和石英玻璃的遮光系數(shù)有關(guān)。補(bǔ)償?shù)臏囟纫蕾囆? 另一種是光柵串聯(lián)與光柵傳感頭拉伸測(cè)量。傳感器在安裝溫度補(bǔ)償?shù)墓饫w

7、光柵是在不受任何壓力（如水壓力）的基礎(chǔ)上的。內(nèi)在波長(zhǎng)漂移比例的水位變化的計(jì)算: 這里是貼在彈簧管上的光纖光山的波長(zhǎng)，其中包含溫度的動(dòng)蕩，是測(cè)量過(guò)溫度補(bǔ)償了的光纖光柵的波長(zhǎng)，k是光纖光柵的溫度系數(shù)，將這個(gè)值置1來(lái)校準(zhǔn)光纖光柵設(shè)備。氣壓傳感器的平衡情況與外部大氣壓力的空氣感應(yīng)水管, 內(nèi)部含有光纖的電纜有關(guān)。3.2光學(xué)水位傳感器的測(cè)量結(jié)果 圖7顯示來(lái)自光纖光柵傳感器測(cè)量系統(tǒng)反射光的探測(cè)波長(zhǎng)。寬帶光來(lái)自ase光源發(fā)射的光經(jīng)過(guò)fbg反射后經(jīng)由三個(gè)循環(huán)點(diǎn)返回的光。通過(guò)另一個(gè)循環(huán)點(diǎn)走向f-p濾波器作為光譜儀器。其他波長(zhǎng)的光通過(guò)光纖光柵,并傳遞到下一個(gè)光纖光柵, 不同波長(zhǎng)的光反射也不同。因此，通過(guò)將光纖光柵串

8、聯(lián)，一個(gè)光纖傳感器就可以實(shí)現(xiàn)多點(diǎn)測(cè)量水位，這主要是由光纖光柵反射不同波長(zhǎng)。 光纖使用幾個(gè)光學(xué)開(kāi)關(guān)開(kāi)關(guān)，該系統(tǒng)可連接多傳感器獲得的測(cè)量結(jié)果采用單一波長(zhǎng)訪問(wèn)設(shè)備。終端用戶的f-p可調(diào)諧濾波器是700個(gè),是傳輸帶寬的一半,最高接近0.1 nm, 而用波長(zhǎng)范圍是1530至1570 nm左右。調(diào)諧濾波器正在驅(qū)動(dòng)壓電換能器, 50赫茲三角波電壓掃描距離已廣泛應(yīng)用于f-p濾波器標(biāo)準(zhǔn)。為改善波長(zhǎng)準(zhǔn)確性,我們采用了溫控光柵作為參考, 這表明有固定波長(zhǎng)低于1時(shí)波動(dòng) ，而這些數(shù)據(jù)是平均值的10倍以上,以減少隨機(jī)噪聲。結(jié)果如圖8所示。當(dāng)平均超過(guò)10倍,波長(zhǎng)波動(dòng)可以抑制小于5pm。我們?cè)O(shè)計(jì)的最大應(yīng)變適用于在10米的水壓

9、，fbg拉伸測(cè)量0.3%左右。它相當(dāng)于一個(gè)3.6 nm的中心波長(zhǎng)的光纖光柵。為了核實(shí)準(zhǔn)確的水位測(cè)量,我們測(cè)量了波長(zhǎng)漂移的10倍。運(yùn)用偽水壓力傳感器膜片空氣穩(wěn)壓器，圖9顯示應(yīng)用壓力表測(cè)量壓力和應(yīng)用光纖光柵傳感器測(cè)量波長(zhǎng)的對(duì)應(yīng)關(guān)系。結(jié)果表明, 水壓力有良好的線性關(guān)系，且每個(gè)測(cè)量點(diǎn)的誤差小于3 pm/cmh2o，我們衡量在0 , 20和40,這些特定的溫度范圍內(nèi)這種傳感器的特性。結(jié)果如圖10所示，縱坐標(biāo)表示水位測(cè)量的誤差計(jì)算所得的線性擬合線，測(cè)量結(jié)果依賴于壓力和波長(zhǎng)兩者的變化。在每個(gè)溫度條件下,其誤差為每點(diǎn)不到1cm。我們證實(shí)了這種傳感器的重復(fù)性和耐久性，適用于測(cè)量水位在0到3米反復(fù)變化。圖11的結(jié)

10、果顯示，即使在100倍的壓力下，測(cè)量結(jié)果也接近真實(shí)值，測(cè)量誤差在1cm以內(nèi)。我們觀察了傳感器因溫度波動(dòng)或金屬疲勞要素導(dǎo)致結(jié)果的漂移和蠕變。3.3光學(xué)水位傳感器在河川中的實(shí)用性能 從1999年8月至2001年3月我們?cè)趉akehashi河流和kanazawa工作辦公室內(nèi)進(jìn)行了傳感器系統(tǒng)的實(shí)地測(cè)試。通過(guò)這次實(shí)地測(cè)試我們證實(shí)了傳感器和測(cè)量設(shè)備的穩(wěn)定性。他們操作超過(guò)一年半河流水位測(cè)量精度達(dá)到1cm,無(wú)致命的系統(tǒng)誤差。接下來(lái),我們安裝了這一系統(tǒng)配有三個(gè)傳感器,在uono和aburuma河, shinanogawa工作辦公室, hokuriku區(qū)域發(fā)展于2001年11月。系統(tǒng)圖及水位測(cè)量的結(jié)果顯示,分別如

11、圖12和圖13所示： 測(cè)量的同時(shí)，利用傳統(tǒng)的電熱水位儀表進(jìn)行測(cè)量，二者安裝在同一個(gè)測(cè)量點(diǎn)。兩種類型的傳感器水位測(cè)量數(shù)據(jù)大致是相符的，二者的不同的是光學(xué)水位傳感器的測(cè)量誤差小于1cm。通過(guò)實(shí)地測(cè)量我們證實(shí)了光學(xué)水位傳感器在液位測(cè)量上的優(yōu)勢(shì)，而且它可以遠(yuǎn)程和實(shí)時(shí)監(jiān)控，在傳感點(diǎn)上不需要電源供電。結(jié)論 們開(kāi)發(fā)的這種全光學(xué)的水位傳感器，其測(cè)量精度具有0.1%，水位測(cè)量范圍為10m。目前已經(jīng)在很多位置建立這種傳感器系統(tǒng)，如河川流域、湖泊和污水處理系統(tǒng),在那里持續(xù)工作,用來(lái)測(cè)量其實(shí)際水位。 傳感器技術(shù) 到目前為止，我們考慮到電磁輻射的自然特性，其來(lái)源和作用是物體和材料之間的接觸。據(jù)指出，感覺(jué)到的大部分的輻射

12、或放射目標(biāo)，通過(guò)空氣直到它由傳感器監(jiān)測(cè)。傳感器的組成和它的運(yùn)行是重要的學(xué)科范圍。它涉及的太多了以至于不能用一種方法講解。雖然如此，一些基本的概要在這能得到闡述。傳感器技術(shù)全面整體回顧。由日本的遙感協(xié)會(huì)開(kāi)發(fā)，而且在互聯(lián)網(wǎng)上找到這個(gè)鏡象站點(diǎn)。一些傳感器的有用的連接和它的應(yīng)用在這個(gè)叫做的nasa的地方包括了。我們指出許多讀者現(xiàn)在使用復(fù)雜的傳感器，這些傳感器使用的是下述的技術(shù)：數(shù)碼相機(jī)；更多是在這頁(yè)底部的常用的傳感器。很多遙感器都被設(shè)計(jì)來(lái)測(cè)量光子。傳感器運(yùn)行的潛在的基本原則主要集中在一個(gè)重要的元件上即探測(cè)器。這就是光電效應(yīng)的概念(是愛(ài)因斯坦首先詳細(xì)地解釋了，并且贏得了他的諾貝爾獎(jiǎng)。他的發(fā)現(xiàn)是，在光子物

13、理學(xué)發(fā)展上的關(guān)鍵性的一步。這點(diǎn)簡(jiǎn)單得說(shuō), 當(dāng)一些適當(dāng)?shù)墓饷舨牧弦粔K服從光子射線時(shí)將有負(fù)電子的放射。電子可能在板材中流動(dòng), 被收集,然后算作是信號(hào)。一個(gè)關(guān)鍵點(diǎn)是：產(chǎn)生的電流的幅度(單位時(shí)間內(nèi)產(chǎn)生光電的數(shù)量)與光強(qiáng)度成一定比例。因此，電流的變化可以用來(lái)測(cè)量光子的變化(數(shù)量；強(qiáng)度)，光子在指定的間隔時(shí)間觸擊扳子。被發(fā)布的光電子的動(dòng)能隨沖擊輻射的頻率(或波長(zhǎng))而變化 。但是, 不同的材料接受光電效應(yīng)釋放的電子有不同的波長(zhǎng)間隔時(shí)間；每個(gè)都有一個(gè)現(xiàn)象開(kāi)始的門限波長(zhǎng)并且有它停止的一個(gè)更長(zhǎng)的波長(zhǎng)。現(xiàn)在，有了建立在多數(shù)遙感器的操作的基礎(chǔ)上的原則，讓我們總結(jié)傳感器類型(典型)幾種主要想法在這兩張圖上：一是幾組傳感

14、器的一種功能處理, 被作為三角圖, 壁角成員由主要參量的測(cè)量來(lái)確定；光譜；空間；強(qiáng)度。從這張宏偉的名單,我們 將集中討論光學(xué)機(jī)械電子。輻射計(jì)和掃描器，在別處把照相機(jī)影片系統(tǒng)和主動(dòng)雷達(dá)留為考慮,主題是在講解和熱量系統(tǒng)的描述對(duì)一個(gè)最小值(見(jiàn)第9部分的進(jìn)一步處理)。上面的小組包括我們主要考慮及早在這個(gè)部分的地球物理的傳感器。傳感器 (能量導(dǎo)致輻射被接受來(lái)自一個(gè)外部來(lái)源，即太陽(yáng)) 和積極得(能量引起了從傳感器系統(tǒng)內(nèi)部, 放光向外, 并且分?jǐn)?shù)返回被測(cè)量)。傳感器可能是非想象的(測(cè)量輻射被接受從所有點(diǎn)在感覺(jué)的目標(biāo),報(bào)告結(jié)果作為電子信號(hào)強(qiáng)度或某一其它定量屬性, 譬如發(fā)光)或想象；因?yàn)樵谀繕?biāo)輻射與具體點(diǎn)有關(guān),

15、，最終結(jié)果是影象圖片或光柵顯示如同平行線地平線 在電視屏幕。輻射計(jì)是一個(gè)一般用為定量地測(cè)量em 輻射在em 光譜的在某一間隔時(shí)間的一種儀器。當(dāng)輻射是從狹窄的光譜帶且包括可看見(jiàn)光，光度計(jì)可能被替代。如果傳感器包括一個(gè)組分，譬如棱鏡或衍射濾柵,可能打破輻射延伸在光譜分離波長(zhǎng)和驅(qū)散(或分離)它們的部份在不同的角度對(duì)探測(cè)器,這稱分光儀。一種類型的分光儀 (被用在實(shí)驗(yàn)室為化工分析)通過(guò)多種波長(zhǎng)輻射到一個(gè)裂縫再生產(chǎn)裂縫依照被排行在各種各樣的間距在影片板材的一個(gè)分散的媒介。很多空氣/空間傳感器都是光譜聲音儀。能瞬間地測(cè)量輻射立即來(lái)自整個(gè)場(chǎng)面的傳感器叫做構(gòu)筑的系統(tǒng)，眼睛，照相機(jī)和電視光導(dǎo)攝象管屬于這個(gè)小組。被

16、構(gòu)筑場(chǎng)面的大小由定義視野的開(kāi)口和光學(xué)系統(tǒng),或fov確定。如果場(chǎng)面是點(diǎn)由點(diǎn)感覺(jué)的 (等效與小范圍在內(nèi))在有限計(jì)時(shí)連續(xù)線之內(nèi)，這個(gè)測(cè)量方式組成掃描系統(tǒng)。多數(shù)非照相機(jī)傳感器掃描操作從移動(dòng)的平臺(tái)圖象場(chǎng)面開(kāi)始。行動(dòng)的進(jìn)一步下來(lái)分支, 想象傳感器的光學(xué)設(shè)定為可能是圖象飛機(jī)或光學(xué)飛機(jī)聚焦(取決于光子光芒) 依照被顯示聚合的地方, 在這個(gè)例證中能看出來(lái)。在這個(gè)分類的其它屬性是傳感器經(jīng)營(yíng)在非掃描或掃描方式的地方。這是可能有幾個(gè)意思相當(dāng)棘手的對(duì)期限掃描暗示行動(dòng)橫跨場(chǎng)面的，在間隔時(shí)間并且非掃描提到傳感器被修理在現(xiàn)場(chǎng)或目標(biāo)利益照原樣感覺(jué)在非常片刻內(nèi)。影片照相機(jī)被剛性地拿著是非掃描的設(shè)備, 當(dāng)快門被打開(kāi)奪取光幾乎是瞬間

17、的描設(shè), 然后關(guān)閉。但當(dāng)照相機(jī)并且/或者目標(biāo)可能是靜態(tài)的(不移動(dòng))但是傳感器清掃橫跨感覺(jué)的場(chǎng)面, 可能掃描因?yàn)閭鞲衅鞅辉O(shè)計(jì)使它的探測(cè)器系統(tǒng)地行動(dòng)既使他們推進(jìn)橫跨目標(biāo)。這是您也許栓了入您的計(jì)算機(jī)的掃描器的情況。這里它的平板車平臺(tái)(圖片被安置) 的框和玻璃表面被留在原地；掃描可能被執(zhí)行通過(guò)投入了圖片或紙文件在一轉(zhuǎn)動(dòng)的鼓上(兩個(gè)方向:圓圈和在鼓軸方向的轉(zhuǎn)移) ,在掃描照明上是一條固定的射線?；蛘?另外兩個(gè)相關(guān)的例子：攝像機(jī)包含光擊中那光子的敏感表面而產(chǎn)生電子被去除在連續(xù)的光導(dǎo)攝象管(線每英尺是電視性能)能有措施被固定或可能旋轉(zhuǎn)對(duì)打掃在場(chǎng)面(自身空間掃描操作)的英寸并且可能及時(shí)掃描當(dāng)它繼續(xù)監(jiān)測(cè)場(chǎng)面的時(shí)

18、候。一個(gè)數(shù)字相機(jī)包括有包含被釋放他們的光子導(dǎo)致的電子在連續(xù)的轉(zhuǎn)變成變化的電壓信號(hào)的x-y 一些探測(cè)器。放電的發(fā)生是由系統(tǒng)地掃描探測(cè)器引起的。相機(jī)本身能被固定或移動(dòng)。所有這要義(在某種程度上明顯) 是, 期限掃描可能向整個(gè)傳感器的運(yùn)動(dòng)被申請(qǐng)和, 在它的更加共同的意思,對(duì)一個(gè)或更多組分在檢測(cè)系統(tǒng)或移動(dòng)輕的匯聚, 場(chǎng)面觀察用具或光或輻射探測(cè)器逐個(gè)讀導(dǎo)致信號(hào)的過(guò)程。多數(shù)掃描器兩個(gè)寬廣的類別由期限光學(xué)機(jī)械和光學(xué)電子定義, 由區(qū)別參加掃描場(chǎng)面和后者由有感覺(jué)的輻射移動(dòng)直接地通過(guò)光學(xué)線性或列陣探測(cè)器。另一個(gè)屬性遙感傳感器,而不是表現(xiàn)在分類 涉及到模式中的那些遵循一些向前發(fā)展的軌道(簡(jiǎn)稱為軌道或航道) 搜集他們

19、的資料。這樣做,據(jù)說(shuō)能監(jiān)測(cè)道路通過(guò)在區(qū)域道路的對(duì)面；這就是帶寬。遙感探測(cè)器陣列通常小于整個(gè)場(chǎng)面的帶寬,這比整個(gè)場(chǎng)面帶寬通常狹窄的光被通過(guò)外徑，包含天文望遠(yuǎn)鏡全視場(chǎng)角 (普通望遠(yuǎn)鏡)。翻譯原文：optical water-level sensors using fiber bragg gratingtechnologyabstract: we developed an optical high-precision water-level sensors based on fiber bragg grating (fbg) technology. the sensors can be applie

20、d to measure the waterlevels of rivers, lakes, and sewage systems. the sensor head consists of a diaphragm, a customized bourdon tube and two fbgs, one for tensile measurement and the other for temperature compensation. the fbg attached to the bourdon tube is strained as the water level increases an

21、d causes a shift of the center wavelength of the reflected light from the fbg. the center wavelength is in turn detected by the wavelength interrogation equipment composed of a tunable fabry-perot filter. we achieved the sensor accuracy of +/ 0.1% f.s., i.e., +/ 1 cm for the full water-level measure

22、ment range of 10 m. several sensor heads can be connected in series through one optical fiber, and the water level at different places can be measured simultaneously by using one piece of wavelength interrogation equipment.(1)introductionriver administrators have theveryimportant responsibilities to

23、 maintain their river facilities and monitor river basin conditions. since river facilities are widely dispersed along a river basin, it is a great expense of time andlabor for the staff of river administrators to go around periodically to check these facilities. moreover, it is difficult to perform

24、 spot checks on these facilities to ascertain their structural integrity in the event of natural disasters such as floods, washouts, and seismic disturbances. from this point of view, projects to build up the optical fiber networks around river basins have been advanced by the japanese government. t

25、o utilize such an optical fiber network effectively, optical fiber sensors and sensing systems have been researched and developed recently, which are applicable to the safety management of river basins and their flood control facilities.optical fiber sensors and their systems have the following adva

26、ntages:1) the low transmission loss of optical fiber enables remote sensing over tens of kilometers.2) real-time monitoring is achieved by connecting sensor heads directly to the measuring equipment using optical fiber.3) the sensor head consists of all-optical passive components and there is no nee

27、d for an electric power supply where the sensor heads are installed.4) due to immunity from electromagnatic interference of an optical sensor, it does not suffer from the deleterious effects of electrical shock, such as the occurrence of lightning strikes. the water level sensing of a river is a mos

28、t critical matter for both the river administrators and the residents living around a river basin from the standpoint of the facility maintenance and the prevention of natural disasters.we have developed optical water-level sensors using fiber bragg gratings (fbgs) that possess the advantages descri

29、bed above and a few more. in this paper, we describe details of the fbg as a strain sensor, water level sensing applications and the performance results obtained in a practical field.(2)fiber bragg grating technology for sensing application2.1 principle of fbgthe fbg is a permanent periodic modulati

30、on of the refractive index along a given length of optical fiber. figure 1 shows the schematic structure of the fbg. due to the coupling between the forward and backward propagating modes, the specific wavelength light depending on the modulation period of the refractive index is reflected at the lo

31、cation of the fbg. the incoming light is reflected when its wavelength is equal to the bragg wavelength b of the grating, defined as(3)b= 2 neff, (1)where neff is the effective core refractive index and is the period of the refractive index modulation. the other wavelength lights are transmitted thr

32、ough the fbg and irradiate the next fbgs. thus, it is possible to achieve multi- point sensing at one optical fiber by connecting fbgs in series,each of which has a different reflected wavelength from the others.fig. 1 schematic structure of fbg. the specific wavelength light,depending on the modula

33、tion period of the refractive index, isreflected from the fbg. the other wavelength lights are transmittedthrough the fbg and irradiate the next fbgs.the spectrum of the reflected light from the fbg is shifted according to the applied strain and temperature. the bragg wavelength change bin response

34、to strain and temperature is given by= (1 p) t, (2)where p is the effective photo-elastic coefficient, is the applied strain, is the thermo-optic coefficient, and t is the change in temperature. using ordinary single mode fiber for telecommunication, the effective photo-elastic coefficient pis0.22,

35、(3), (4)so the sensitivity to an applied axial strain and the temperature dependence are 1.2 pm/micro-strain and 10 pm/, respectively in 1.55 m wavelength range.2.2 fabrication of fbgfigure 2 shows the process for fabricating an fbg. we use a polyimide-coated optical fiber for the fbgs as the strain

36、 sensor, which causes no slippage on the border of the coating layer, so that externally applied strain can be precisely transferred to the fbg. the fbg is fabricated by the uvirradiation of the fiber. in advance of writing the bragg grating, the polyimide-coated optical fiber is subjected to a hydr

37、ogen loading treatment to enhance the effect of photo-induced refractive index change. the polyimide layer is then partially etched away by using a chemical solvent. as shown in fig. 3, the bragg grating is inscribed in the core region of the optical fiber by irradiating a krf excimer laser emitting

38、 at 248 nm through a phase mask, with the scanning in the longitudinal direction. photo-induced refractive index modulation along the fiber, i.e., apodization profile can be controlled by the programmable scanning speed of the laser beam. we adopted a gaussian-shape apodization to suppress side-lobe

39、 losses of the reflection spectrum. after inscribing the grating, the polyimide layer is re-coated to protect the stripped part. finally, the optical fiber with a fbg is subjected to a high-temperature(under 300) heat treatment for 30 min. to ensure long-term stability. figure 2 figure 3 figure 4 sh

40、ows the typical transmission and reflectionspectrum of an fbg. transmission rejection was about10db, that is, the reflection ratio was almost 90%. the fwhm(full width at half maximum) of the reflection was less than 0.2 nm (3)optical water-level sensor using fbg3.1 structure of optical water-level s

41、ensorfigures 5 and 6 show the schematic structure of the optical water-level sensor and the principle diagram of the pressure conversion element of the sensor, respectively. the sensor head consists of a diaphragm, a customized bourdon tube and two fbgs, where one fbg is used for tensile measurement

42、 and the other fbg is used for temperature compensation. this water level sensor is the type used for measuring water pressure in proportion to water level. the water pressure is transmitted to the inner silicone oil in the bourdon tube. then the bourdon tube converts the oil pressure to the tensile

43、 force at the tip of the tube within its elastic limit and stretches the fbg, which is strung between the tip and the base. thus, the fbg is strained in proportion to the water level increase. the fbg is set with slight pre-tension initially, to enable water level measurement linearly from the lowes

44、t level. the bragg wavelength varies with temperature due to the temperature dependence of the refractive coefficient of silica glass.to compensate the temperature dependency, another fbg is connected in series with the fbg for tensile measurement at the sensor head. the temperature compensation fbg

45、 is mounted in the sensor case free from any strain based on the water pressure. the intrinsic wavelength shift w.l.in proportion to the water level change is calculated bywl=(3)where tens.is the wavelength shift of the fbg attached to the bourdon tube, which includes the temperature turbulence,and

46、temp.is the wavelength shift as measured by the temperaturecompensation fbg. k is the coefficient of the temperature fbg, and we set this value to 1 according to adjust the position of fbg mounting.the air pressure in the sensor case is balanced with the outer atmospheric pressure through the air in

47、duction pipe that contains the optical fiber approach cable inside.3.2 measurement result for optical water-level sensorfigure 7 shows the schematic diagram of the measurement system for detecting the wavelength of the reflected light from the fbgs in each sensor. the broad-band light from an ase li

48、ght source is launched into the optical fiber via a 3-port circulator, and the reflected light from fbg comes backthrough another port of the circulator toward the fabry-perot tunable filter as a spectroscopic device.(3) (5)other wavelength lights pass through the fbg and transmit to the next fbgs,w

49、here a different wavelength light will be reflected. thus, it is possible to achieve the multi-point measurement of water level with one optical fiber when sensors are connected in series,which are comprised of fbgs reflecting different wavelengths from each other. switching the several optical fibe

50、rs by using an optical switch, the system can connect and obtain the measurement results of multiple sensors by using a single piece of wavelength interrogation equipment. the finesse of the fabry-perot tunable filter is 700, the transmission bandwidth at half maximum is almost 0.1 nm, and the used

51、wavelength range is 1530 to 1570 nm. the tunable filter is being driven by piezoelectric transducer, and 50 hz triangular wave voltage has been applied to it to scan the distance of the fabry-perot etalon. fig. 7schematic diagram of the measurement system for detecting the wavelengths of the reflect

52、ed light from fbgs in each sensorto improve the wavelength accuracy, we used a temperature-controlled fbg as a reference, which indicated a constant wavelength having less than +/1 pm fluctuation. and the data was averaged over 10 times to reduce the random noise. the result is shown in fig.8. when

53、the averaging exceeds 10 times, the wavelength fluctuation can be suppressed less than 5 pm.we designed the maximum strain applicable to the tensile measuring fbg to be about 0.3% at 10-m water pressure, which corresponded to a 3.6-nm center wavelength shift of the fbg. to verify the accuracy of the

54、 water level measurement,we measured the wavelength shift 10 times, applying pseudo- water pressure to the sensor diaphragm using the air pressurizer. figure 9 shows the correlation between the applied pressure measured by a pressure gauge and the wavelength measured by the sensor fbg. the result sh

55、owed that there was good linearity over the full range of the water pressure, and the error at each point was less than 3 pm/cmh2o. we measured this characteristic at 0, 20 and 40, which was the specified temperature range of this sensor. the results are shown in fig.10. the ordinate of this graph i

56、s the water level measurement error obtained from the linear fitting line that was calculated from the result of the dependency measurement between the pressure and the wavelength shift. there were good agreements at every temperature condition, and the error at each point was less than+/-1cm. we co

57、nfirmed the repeatability and the durability of the sensor by applying pressure from 0 to 3 mh2o repeatedly. the result is shown in fig. 11. even after 10,000 times pressurization, the measured water level indicated the true value at the error within +/1cm. no drift or creep conceivable caused by te

58、mperature fluctuation or metal fatigue of elements of the sensor was observed.3.3 practical performance of optical water-level sensor in riverwe performed a river field test of this sensor system at the kakehashi river, kanazawa work office, hokuriku regional development bureau from august 1999 to march 2001.through this field test, we confirmed the robustness of the sensor and the measuring equipment: they operated ove