Lee, 2003 - Review of the present status of optical fiber sensors

ors

certain, highStrain,g sensores andal fiberpecially,sensorshas beenufferuously

n. Var-various

en com-tudied,essful.ference

Optical Fiber Technology 9 (2003) 57–79

www.elsevier.com/locate/yofte

Invited paper

Review of the present status of optical fiber sens

Byoungho Lee

School of Electrical Engineering, Seoul National University, Kwanak-Gu Shinlim-Dong,Seoul 151-744, South Korea

Received 28 August 2002

Abstract

The current status of optical fiber sensors is reviewed. The optical fiber sensors haveadvantages that include immunity to electromagnetic interference, lightweight, small sizesensitivity, large bandwidth, and ease in implementing multiplexed or distributed sensors.temperature and pressure are the most widely studied measurands and the fiber gratinrepresents the most widely studied technology for optical fiber sensors. Fiber-optic gyroscopfiber-optic current sensors are good examples of rather mature and commercialized opticsensor technologies. In this paper, among the various fiber-optic sensor technologies, estechnologies such as fiber grating sensors, fiber-optic gyroscopes, and fiber-optic currentare discussed with emphasis on the principles and current status. Today, some successfound in the commercialization of optical fiber sensors. However, in various fields they still sfrom competition with other mature sensor technologies. However, new ideas are being contindeveloped and tested not only for the traditional measurands but also for new applications. 2003 Elsevier Science (USA). All rights reserved.

Keywords: Optical fiber sensor; Fiber grating; Fiber-optic gyroscope; Optical fiber current sensor

1. Introduction

Almost thirty years have passed since the study of optical fiber sensors begaious ideas have been proposed and various techniques have been developed formeasurands and applications. To date, some types of optical fiber sensors have bemercialized, but it is also true that, among the various techniques that have been sonly a limited number of techniques and applications have been commercially succOptical fiber sensors have advantages such as immunity to electromagnetic inter

E-mail address: [email protected].

1068-5200/03/$ – see front matter 2003 Elsevier Science (USA). All rights reserved.doi:10.1016/S1068-5200(02)00527-8

58 B. Lee / Optical Fiber Technology 9 (2003) 57–79

ds, suchd in thed among

lightmpeteto usersensorsested inhavingal fibertectinging sys-e casesshould

erablenearing

s suches inf thehows(OFS-

erenceeld of

Fig. 1. Distribution of OFS-15 papers according to measurands. Papers not directly related to measuranas those that discuss fiber grating sensor interrogators, multiplexing, light sources, etc., are not includestatistics. If one paper deals with more than one measurand, the counted paper number is equally dividethe measurands. Special session papers on fiber-optic gyroscopes are included in the statistics.

(EMI), lightweight, small size, high sensitivity, large bandwidth, and ease in signaltransmission. However, in many fields of application, optical fiber sensors should cowith other rather mature technologies such as electronic measurements. To appealalready accustomed to other mature technologies, the superiority of optical fiber sover other techniques needs to be clearly demonstrated. Typical users are not interspecific techniques involved in measurement. They simply desire sensor systemsgood performances with reasonable price except for very special uses. Hence, opticsensor systems should be available in the form of complete systems including deand signal-processing electronics. In some cases such as electric protection relaytems, the sensor systems are simply subsystems of rather larger systems. In somsuch as optical gyroscopes and optical current sensors, the optical fiber sensorscompete with other optical bulk sensors as well. Even with these difficulties, considefforts have been made to study of optical fiber sensors, and some of them are nowmaturity.

There have been excellent review books and articles on optical fiber sensoras Refs. [1–5]. It is impossible to review all of the fiber-optic sensor technologia journal article with a limited length. In this paper, the current status of some oactively studied or well-developed optical fiber sensors will be reviewed. Figure 1 sthe distribution of papers presented at the 15th Optical Fiber Sensors Conference15: IEEE catalog number 02EX533) according to measurands of interest. The confwas held in Portland, Oregon, USA in May 2002, and is a major conference in the fi

B. Lee / Optical Fiber Technology 9 (2003) 57–79 59

echnol-ber-optic

searchre strainshows

grating

ptical-optic, other

studyn wasr gainunica-ome of

Bragggatingcore

ratingent po-

Fig. 2. Distribution of OFS-15 papers according to technologies. If one paper deals with more than one togy, the counted paper number is equally divided among the technologies. Special session papers on figyroscopes (FOGs) are included in the statistics.

optical fiber sensors. Hence the statistics of OFS-15 provide information on recent retrends in the area of optical fiber sensors. The most highly discussed measurands aand temperature, the same as in the conference of five years ago [6]. Figure 2the technologies involved in the optical fiber sensors presented at OFS-15. Fibersensors are clearly the most widely studied topic.

In Section 2 fiber grating sensor technology, which is the most popular topic in ofiber sensors, is reviewed. In Sections 3 and 4 two rather mature topics—fibergyroscopes (FOGs) and fiber-optic current sensors—are reviewed. In Section 5sensors are briefly discussed, which is followed by some concluding remarks.

2. Fiber grating sensors

Although the formation of fiber gratings had been reported in 1978 [7], intensiveon fiber gratings began after a controllable and effective method for their fabricatiodevised in 1989 [8]. Fiber gratings have been applied to add/drop filters, amplifieflattening filters, dispersion compensators, fiber lasers and so on for optical commtions [4]. Extensive studies have also been performed on fiber grating sensors and swhich have now reached commercialization stages.

Figure 3 shows types of fiber gratings. Under phase matching conditions, a fibergrating (FBG) couples the forward propagating core mode to the backward propacore mode. A long-period fiber grating (LPG) can couple the forward propagatingmode to one or a few of the forward propagating cladding modes. A chirped fiber ghas a wider reflection spectrum and each wavelength component is reflected at differ


ating,

tiltedgatingreflectf grat-hangeds.is

Fig. 3. Types of fiber gratings. (a) Fiber Bragg grating, (b) long-period fiber grating, (c) chirped fiber gr(d) tilted fiber grating, (e) sampled fiber grating.

sitions, which results in a delay time difference for different reflected wavelengths. Afiber grating can couple the forward propagating core mode to the backward propacore mode and a backward propagating cladding mode. A sampled fiber grating canseveral wavelength components with equal wavelength spacing. All these types oings have been utilized in various types of fiber grating sensors and wavelength cinterrogators. Among them, however, FBGs are the most widely used as sensor hea

In FBGs the Bragg wavelengthλB, or the wavelength of the light that is reflected,given by

λB = 2neffΛ, (1)


gratinger forriation,ut oneal re-

.-m-e

houldnd instic ofcodedwave-this

imeow-s suchhysical

effectseter or

pic andach islatedgratingFBGs

whichametererature

to ex-. Thece, thesurandse theys have

ited inlicatedf themes andriment. When

whereneff is the effective refractive index of the fiber core andΛ is the grating period. InEq. (1) it can be seen that the Bragg wavelength is changed with a change in theperiod or the effective refractive index. The former is the case for strain and the latttemperature variation. The grating period can also be changed with temperature vabut around room temperature the effect of temperature on refractive index is aboorder of magnitude larger than that of thermal expansion (or contraction). The typicsponse of the Bragg wavelength shift to strain is∼0.64 pm/µε (µε = microstrain) near theBragg wavelength of 830 nm,∼1 pm/µε near 1300 nm, and∼1.2 pm/µε near 1550 nm [9]The unit of strain isε, which is read as “strain”. It is a relative concept, that is, if a 1long fiber is elongated by 1 µm, the strain is 1 µm/1 m= 1 µε. The typical temperaturresponse is∼6.8 pm/◦C near 830 nm,∼10 pm/◦C near 1300 nm, and∼13 pm/◦C near1550 nm [9] although the values depend on FBG types [10]. (These FBG types snot be confused with fiber grating types of Fig. 3. Detailed information can be fouRef. [4].) This wavelength-encoded measurand information is a unique characteriFBGs. In addition to the common advantages of fiber sensors, this wavelength-encharacteristic provides robustness to noise or power fluctuation and also enableslength division multiplexing (WDM). Hence multi-point sensors can be realized usingtechnique. Sometimes WDM is combined with spatial division multiplexing (SDM), tdivision multiplexing (TDM) and code division multiple access (CDMA) techniques. Hever, it must be admitted that multi-point FBG sensors are not fully-distributed sensoras backscattering sensors or optical time-domain reflectometers (OTDRs) because pparameters can be measured only at the FBG positions.

As discussed above, FBGs respond to both strain and temperature. Hence theirneed to be separated from each other, in order to measure each physical paramto measure both simultaneously. Considerable effort has been focused on this tovarious solutions have been proposed. A straight forward and very practical approto use a reference grating [11]. Another FBG (the reference grating), which is isofrom one parameter, e.g., strain, is placed near the sensor FBG. The referencecan be on the same fiber as the sensor FBG [12]. Another method is to use twowith much different Bragg wavelengths (in general, two light sources are needed),show different responses to the same measurands [13]. FBGs written on different-difibers have also been proposed, which give different strain responses, while the tempresponses are the same [14,15].

Demodulators or interrogators are required for FBG sensors. Their roles aretract measurand information from the light signals coming from the sensor headsmeasurand is typically encoded in the form of a Bragg wavelength change, and heninterrogators are typically expected to read the wavelength shift and provide meadata. Optical spectrum analyzers are not suitable for real sensor systems becauare expensive and their wavelength scanning speed is too slow. Various techniquebeen developed for the interrogators [16]. Some are quite simple but are more limmeasurement resolution, dynamic range or multiplexing, and some are more compand provide better resolution but are more expensive or need stabilization. Not all oare appropriate for commercialized systems. Table 1 summarizes interrogator typTable 2 summarizes their performances [17–62]. Many of these are laboratory experesults. Civic structures such as bridges require the measurement of dynamic strain


es

–21]

3]3]]

7]

range)

by theecausespan.ted by

Table 1Fiber grating sensor interrogator types

Types Technologies Referenc

Passive detection schemes Linearly wavelength-dependent device [17CCD spectrometer [22–25]Power detection [26–29]Identical chirped-grating pair [30]

Active detection schemes Fabry–Perot filter [31–3Unbalanced Mach–Zehnder interferometer [34–4Fiber Fourier transform spectrometer [44,45Acousto-optic tunable filter [46–48]Matched FBG pair [49–52]Michelson interferometer [53]LPG pair interferometer [54]

Other schemes Wavelength-tunable source [55–5Mode-locked fiber laser with wavelength-time conversion [58]Optical CDMA correlator [59,60]Frequency modulation [61]Intra-grating sensing [62]

Table 2Strain measurement resolution of some fiber grating sensor systems/interrogators

Static/quasi-static resolution Dynamic resolution References (measurement

±20 µε [58] (> 3500 µε)∼12 µε [44]4.12 µε [49]

∼ ±3.5 µε 1.5 µε/√

Hz [18] (∼16,000 µε)3.5 µε 6 nε/

√Hz [40] (2 kHz)

∼ ±3 µε 0.5 µε/√

Hz [20] (>1050 µε)3 µε [50]

±2 µε [32] (±1300 µε)1.9 µε [55]

±0.25 µε 5 nε/√

Hz [25]40 nε 7 pε/

√Hz [54]

±8.04 µε [56] (±1000 µε)42 nε/

√Hz [57]

10 nε/√

Hz [43]10 nε/

√Hz [51] (> ±100 µε)

2 nε/√

Hz [35] (>10 Hz)1.5 nε/

√Hz [42] (10–2000 Hz)

∼7 fε/√

Hz [36]

the dynamic signal is measured, the minimum detectable strain is determinedbackground noise-level. The magnitude of noise changes with the frequency span bthe noise power in the detector and amplifying circuit depends on the frequencyGenerally, the amount of noise magnitude in other bandwidths can be approxima


oupler)–Perot: optical

. Thus,

le of]. The

s quiten fact,

(a)

(b)

Fig. 4. Some typical interrogators for FBG sensors. (a) Linearly wavelength-dependent device (cmethod [20]. (b) CCD spectrometer method [24]. (c) Fabry–Perot filter method [32] (FFP: fiber Fabryfilter). (d) Unbalanced Mach–Zehnder interferometer (pseudo-heterodyne detection) method [37] (OPDpath length difference, PZT: piezoelectric transducer, BPF: band pass filter).

scaling the power spectral density of the noise by the square root of the bandwidththe normalized minimum detectable dynamic strain is displayed in units ofε/

√Hz.

Figure 4 shows some typical types of interrogators. Figure 4a is an exampinterrogators that use linearly wavelength-dependent devices (couplers or filters) [20Bragg wavelength shift is monitored by the detected power change. This structure isimple and has been commercialized, but it is not suitable for multiplexed sensors. I


f FBGation isloss)

CCDanglecturesuch

(c)

(d)

Fig. 4. (Continued.)

this type of power-detection method does not fully use one of the key advantages osensors—measurand information is coded as wavelength change and the informnot affected by fluctuations in light power. In Fig. 4a to remove the light power (orfluctuation effect, a power-ratio detection technique is used. Figure 4b shows thespectrometer interrogator [24], which takes advantage of the fact that the diffractionis dependent on the wavelength of the light incident on a diffraction grating. The strushown in Fig. 4b adopts both WDM and SDM. Compared with other interrogators


metertained

two-le ofratory

WDMr theirof theand theWDMrogatorription

hndereter

uation.d withffect) is

mines,railwayucturalBG

have

yearssed on

tion ofg in

travelw that

ingle-or.aisederating

as those adopting scanning filters and TDM, the advantage of the CCD spectrointerrogator is its light-effectiveness, that is, a high signal-to-noise ratio can be obeven with low input optical power. A one-dimensional CCD can be used instead of thedimensional CCD if TDM is used instead of SDM [25]. Figure 4c shows an exampthe scanning fiber Fabry–Perot filter interrogator system. U.S. Naval Research Labotested this for a 64-FBG sensor system [32]. The basic principle is to locate theBragg wavelengths within the free spectral range of the Fabry–Perot filter and monitochanges by spectrally-scanning the filter. In real systems, generally, the ditheringfilter spectrum is adopted for a fine measurement in the case of a single FBG sensorzero-crossing of the time derivative of the received power is monitored in the case ofFBG sensors. Figure 4d shows an unbalanced Mach–Zehnder interferometer intersystem adopting a pseudo-heterodyne detection technique [37]. A detailed descof the principle of operation can be found in Ref. [16]. The unbalanced Mach–Zeinterferometer provides very high-resolution interrogation. However, this interferomis quite sensitive to its environment such as temperature change or even air fluctHence, a reference grating for the interrogator system (this should not be confusethe reference grating for the sensor head to distinguish the temperature and strain erequired as shown in Fig. 4d and the interrogator should be well-stabilized.

FBG sensors have been tested in various fields such as bridges, dams,composite laminates, airplanes, generators, ship waterjets, geotechnical fields, andsystems [25,43,63–66]. Some FBG sensors have been commercialized for strmonitoring [67] and oil/gas reservoir monitoring [68]. For example, CiDRA’s Fpressure/temperature sensor was reported to show good functionality at 150◦C, 5000 psifor over two years with output drift within 0.015% full scale/year [68]. Such sensorsbeen deployed in oil/gas wells—for example, in a 15,000-feet downhole [68].

3. Fiber-optic gyroscopes

It is generally recognized that the first demonstration of the FOG was achieved 27ago [69], though there had been a few previous studies. The basic concept is bathe Sagnac interferometer and is quite simple. It is a good example of an applicaspecial relativity. For a rotating optical fiber coil, as shown in Fig. 5, two lights travelinopposite directions in the coil experience different lengths, which results in differenttimes and a phase difference in the two optical waves. Simple analyses [70,71] shothe phase differenceφ is given by

φ = 8πN

λcA · �, (2)

whereN is the number of coil turns,λ the wavelength in vacuum,c the speed of light invacuum,A the area vector of the fiber coil (Its magnitude is the area enclosed by the sturn coil and direction is normal to it.), and� the rotating rate (angular frequency) vect

Like the output of typical interferometers, the output response of the FOG is a rcosine function with respect to the phase difference. In the response curve, if the oppoint is at maxima (or minima) such as the point corresponding toφ = 0, the sensitivity


CW)oint tofigure.

o thesponseat the

an beration.l, suchpositech asrrival[71].

al anduch anicallyws a

of aourcese isre root

tion ofin thet and

Fig. 5. Principle of the fiber-optic gyroscope. In this figure, the fiber coil is rotating in the clockwise (direction. Hence, for the CW and counter-clockwise (CCW) rotating lights to meet at the same exit pinterfere with each other, they should have entered the coil at different times at different points in theDifferent entering times mean different entering points because the fiber coil is rotating.

is low and the rotational direction of the fiber coil cannot be distinguished due tsymmetric response. Hence, the operating point is shifted to a position where the reslope is not zero. This is accomplished by the use of a phase modulator placedend of the fiber coil. There are two types of basic configurations in which a FOG cconstructed; one is an open-loop configuration and the other is a closed-loop configuAs shown in Fig. 6a, a dynamic phase modulation is done at one end of the fiber coithat two lights that start at the coupler at the same time and rotate the fiber coil in opdirections experience different optical path lengths within the phase modulator (sua fiber wound around a piezoelectric transducer (PZT) tube) due to their different atimes at the modulator [72]. This open-loop structure has a limited dynamic rangeIn the closed-loop configuration a feedback signal is applied to null the output signmaintain the operation of the system in the linear range [73,74]. Figure 6b shows sexample using an integrated optics chip (IOC) to modulate the phase. The IOC is typa lithium niobate modulator, which has a larger bandwidth than the PZT and alloproper modulation for the feedback control.

When a FOG is at rest, the output signal is a random function that is the sumwhite noise and a slowly varying function. The photon shot noise is an important sof white noise and limits the fundamental accuracy of the FOG. The white noiexpressed in terms of the standard deviation of the equivalent rotation rate per squaof bandwidth of detection (like the case of the dynamic strain measurement resolufiber grating sensors), in other words, the equivalent noise power spectral densityunit of deg/h/

√Hz. The white noise causes noise in measured rotation rate outpu

results in an angle random walk (ARW) in the unit of deg/√

h. The slowly varying noisecan be induced by several sources and results in long-term drift or bias instability.


lation).

atureseen inng lasernks toarket

e mostntage

suchlaser

play a

(a)

(b)

Fig. 6. Basic configurations of FOG. (a) Open-loop type (SLD: superluminescent diode. PM: phase modu(b) An example of a closed-loop type (IOC: integrated optics chip modulator).

The performance of a FOG has been continuously improved and is now quite mand capable of meeting the most accurate gyroscope requirements. As can beFig. 7, the FOG has competing technologies such as mechanical gyroscopes and rigyroscopes. The cost of the FOG has been constantly falling in recent years thaeconomies of scale and the dramatic explosion in the optical fiber communications m(component prices are decreasing) [75]. Currently, FOGs are considered to be thcost-efficient solution for various inertial navigation applications. One important advaof the FOG is its ruggedness. It contains no moving parts unlike other competitorsas mechanical gyroscopes and ring laser gyroscopes (dithering is involved in ringgyroscopes). Due to these unique advantages, it seems likely that the FOG willsignificant role in both military and commercial markets.


m tech--laser

ctures

raturefn soldstems,stems,ruction,

yingze anyystems.ers or

s thatuper-

tion ofdo not

ndentny new

Fig. 7. Comparison of gyroscope technologies and applications (MEMS: micro-electro-mechanical systenology, DTG: dynamically tuned gyroscope (mechanical type), FOG: fiber-optic gyroscope, RLG: ringgyroscope, AHRS: attitude heading reference systems).

Some recent reports indicate that Honeywell Space Systems currently manufahigh-precision FOGs with a flicker noise below 0.0001 deg/h and an ARW of∼80µdeg/

√h [76] and Ixsea manufactures high-level performance FOGs with a tempe

bias stability better than 0.01 deg/h (0.003 deg/h at ambient) for a noise level o0.001 deg/

√h [75]. FOGs have been developed by many companies and have bee

or applied in various fields such as commercial aircraft attitude heading reference symilitary helicopters, missile guidance systems, marine, and submarine navigation sypipe-mapping (gas, power, and communication cables), compasses for tunnel constrockets, and automotive navigation systems [71,75–81].

4. Fiber-optic current sensors

With the growth in the capacity of electric power systems, the role of protection relasystems is becoming more important. Such a system can immediately recognisudden failures, such as a surge, and separate the failure parts from the power sThese relaying systems require current sensors, referred to as current transformcurrent transducers (CTs). Most CTs currently in use are electromagnetic devicesuffer from magnetic saturation effects and residual field effects. Moreover, with the sincrease in voltages (several hundred kV) in power distribution systems, the insulathe CTs becomes more difficult and expensive. Hence, optical current sensors thatsuffer from electromagnetic interference are good substitutes for conventional CTs.

In addition to protection relaying systems, the deregulation and growth of indepepower producers and regional transmission companies have created a need for ma


rationresult

[82].

tationion ofs are

ystal-xamples

ld peret

or it byoughr CTsclosedhigher

coil.ircularrrent-, afterzationgle in

thate linearutputly bydone

ucedr, thelinearctorsause

ngenceirefrin-factorg flint

high voltage revenue-metering points [82]. In the transfer of power from a genecompany to a regional transmission company, a 0.5% uncertainty in metering mayin an uncertainty of millions of dollars per year at a high power metering locationHence the potential use of optical CTs that provide high accuracy is promising.

The concept of the optical CTs is quite old [83,84] and based on the Faraday roeffect, which states that the polarization of light waves is rotated with the propagatthe light along (or opposite to) a magnetic field inside some material. Optical fiber CTnot the only optical CTs. Bulk-optic CTs such as flint glass closed-loop type and crbased (Faraday cell) CTs have also been extensively studied and tested. Some eof characteristics of bulk devices are as follows—{material, Verdet constant [deg/Oe cm]at wavelength [µm], temperature coefficient}: {Flint (Pb) glass, 0.84× 10−3 at 0.85 or1.1 × 10−3 at 0.63,< ±0.5% (−25–100◦C)}, {BGO, 0.31× 10−2 at 0.85,< ±1.5%(−25–85◦C)}, {FR-5 glass, 0.21× 10−2 at 0.85,< ±15% (−25–85◦C)}, {YIG, 0.27at 1.30,< ±7.0% (−25–85◦C)}, {RIG, 7.0 at 0.83,< ±0.5% (−20–80◦C)}. Here theVerdet constant indicates the rotation angle of the polarization per unit magnetic fieunit propagation length and 1 Oe= 79.6 A/m. Compared with the bulk devices, the Verdconstant of optical fibers is quite small, 1.2× 10−4 deg/Oe cm (at 850 nm) to 2.13× 10−4

deg/Oe cm (at 633 nm), but the optical path length can be increased to compensate fwinding the fiber around a current conducting element a large number of turns. Alththe bulk-optic CTs provide better mechanical stability and smaller sizes, optical fibeprovide ease in forming a closed-loop (to make the sensor respond only to the encurrent), adjustability of the sensitivity and dynamic range, less insertion loss, and asignal-to-noise ratio.

In optical fiber CTs, linearly polarized optical waves are input to the optical fiberThe linear polarization can be expressed mathematically as a superposition of two cpolarizations (right-hand and left-hand). The magnetic field induced around a cucarrying element induces a circular birefringence inside the optical fiber coil. Hencepassing through the coil, a relative phase difference between two circular polaricomponents is generated, which results in the rotation of the linear polarization anproportion to the enclosed current and the number of fiber turns.

Although the concept is quite simple, in actual implementation, several difficultieslimit the resolution of the sensor systems are encountered. Optical fibers have sombirefringence due to the imperfection of the core shape, which may distort the osignals of optical fiber CTs. This linear birefringence can be reduced considerabannealing [85]. But, it has a difficulty in practice because the annealing is generallyafter the winding process of the fiber coil. An inevitable linear birefringence, indby bending of optical fiber around the current-carrying element, exists. Moreoveeffects of vibration, mechanical stress or strain and temperature variation on thebirefringence are also critical. In some applications, high-current-carrying conduvibrate. The vibration in such a direction to rotate the fiber coil is more critical becthe fiber coil acts as a FOG in that case [86].

Several techniques have been proposed to cope with these problems. If a birefribias corresponding to 258-degree phase difference is applied, the effect of linear bgence variation can be minimized [87]. However, the sensitivity is reduced by aof 0.217. Tokyo Electric Power Company has been developing current sensors usin


tg

cessful

rcularhighm atical

mayy to

onallytion,oil isangle

elled.current-tionalotatortwo

or andfter theence)optical

Fig. 8. Reflection-type fiber-optic current sensor.

glass fibers that show a low photoelastic coefficient (4.5×10−10 cm2/kg) and a high Verdeconstant (∼0.065 min/Oe cm) [88], but they suffer from higher loss, difficulty in splicinwith other fibers and higher cost. A recent report indicates that the system was sucin hammering and thermal shock tests for a differential current relaying system [86].

The use of twisted optical fiber has also been proposed, in which a high cibirefringence is induced, thus reducing the effect of linear birefringence [89]. Abirefringent spun fiber was also proposed for this application, which is pulled frorotating silica preform during the fiber draw process [90]. In most of the today’s opfiber CTs these types of methods of increasing circular birefringence are in use.

In practice, the linear birefringence and intentionally induced circular birefringencevary with time due to vibration and temperature variation. A simple and efficient wareduce this effect is to use a reflection type structure as shown in Fig. 8. The intentiinduced circular birefringence is reciprocal with the reversal of light propagation direcwhile the Faraday rotation is nonreciprocal. Hence if a light traveling along the fiber creflected by a mirror and then travels back along the fiber coil, the Faraday rotationis doubled, while the effect of the intentionally induced circular birefringence is cancThe structure has another advantage, in that it can be easily mounted around thecarrying element because one end of the fiber coil is open. However, if a convenmirror is used, the effect of linear birefringence is also doubled. However, a Faraday rmirror can be utilized to minimize the linear birefringence effect, in which case theorthogonal linear polarization components are switched at the Faraday rotator mirrexperience the same amount of phase delay (despite the linear birefringence) around trip [90,91]. Toshiba reported that, for its reflection type optical CT, the influof mechanical shock from circuit breaker vibration of 8g (g = gravitational accelerationwas less than the rms value of the electronic noise [92]. Sagnac interferometer type


r FOG

e beenhown

re

s [95].ith an

withinncearchnsation0.2%

en com-the lightction,sensor8].nosticfiber.ue forbut

uch asimeter

nks,g. One

Fig. 9. An example [94] of a high-performance fiber-optic current sensor using technology developed fo(IOC: integrated optics chip modulator, PC: polarization controller).

fiber CTs are also insensitive to reciprocal effects [93]. Several techniques that havdevised for FOGs can be applied in these optical fiber CTs. With the structure sin Fig. 9, EPFL has achieved±0.2% accuracy over the±500 kA range for a temperaturange between 0 and 50◦C [94]. The Sagnac structure using a 3×3 fiber optic coupler wasalso tested. This structure enables the interferometer to be optimally biased at all timeSome other recent reports indicate that Siemens has tested an optical fiber CT wannealed fiber coil for a generator with a measurement accuracy error below 0.25%the temperature range of 40–90◦C [96] and NxtPhase showed a linearity performabetter than±0.2% from 0.5 to 120% of the rated current [82]. ABB Corporate Resehas developed a robust fiber-optic current sensor with inherent temperature compeof the Faraday rotation effect [97]. Insensitivity of the sensor to temperature withinwas demonstrated between−35 and 85◦C.

5. Others

Some other types of optical fiber sensors based on very simple concepts have bemercialized. Some examples include the displacement or pressure sensor based oncoupling of two fibers, the liquid-level sensor based on frustrated total internal reflethe pressure sensor using a wiggled (periodically bent) fiber, and the temperaturebased on the detection of radiation from a heated sensor head (blackbody cavity) [9

One of the most well-developed and commercialized in-line fiber sensors or diagtools is OTDR, which is based on the monitoring of the backscattering along theThe concept is also quite old [99] and the OTDR has become a standard techniqtesting optical fiber links [100]. It typically provides sub-meter spatial resolutionimproved techniques can provide mm-order resolution. More complicated methods soptical frequency domain reflectometry have been studied to achieve mm or sub-mill(∼10 µm) spatial resolution [101].

While OTDRs are generally aimed at monitoring optical fiber communication liactive research has also been done on distributed sensors for civil structure monitorin


tures ofousticmountre andpatial

lution

beenc low-]. The

orderre, which

usingross-1% of;

[107].].. Theflective

carbonmidityemente of asensors [111].y roleG can

m theddingan be

he in-00 mm

s soonensors.tory ofes such

example is a distributed temperature sensor for monitoring concrete setting temperaa large dam [102]. The principle is based on the stimulated Brillouin scattering. An acwave couples two counter-propagating beams, which are frequency-shifted by an athat is dependent on temperature or strain. A commercialized distributed temperatustrain monitoring system shows the measurement range of up to 20 km with a sresolution of 0.8 m over 1 km (2–5 m at 10 km and 5–15 m at 20 km), a strain resoof 20 µε (measurement range of up to 25 mε) and a temperature resolution of 1◦C [103].

Optical fiber acoustic sensors or optical fiber hydrophone systems have alsointensively studied and tested for marine or submarine applications [104]. Fiber-opticoherence interferometry has also been commercialized for civil applications [105dynamic range of the commercialized deformation sensor using the method is of theof a few tens of mε for elongation (∼5 mε for shortening) [103]. A fiber optic pressusensor using the fiber Fabry–Perot interferometer method was also commercializedshows a dynamic range of 0–3000 psi with±1.0% (of full range) accuracy and±0.5%(of full range) linearity [106]. There are other examples of commercialized sensorsFabry–Perot interferometers (or thin film Fizeau interferometers) and white-light ccorrelators: a force and load transducer (load capacity: 4500 kg, resolution: 0.0full scale); strain gauges (range:±500 to ±5000 µε, resolution: 0.01% of full scale)a temperature transducer (range:−40 to 350◦C, accuracy:±0.5 to±1 ◦C or 0.5–1% of fullscale); a displacement transducer (linear stroke: 20 mm, resolution of up to 2 µm)Cryogenic temperature sensing is also an attractive field for fiber-optic sensors [108

Fiber-optic chemical sensors or biosensors have been continuously studiedprinciples are based on the monitoring of absorbance, reflectance, luminescence, reindex change, or light scattering and aimed at the measurement of oxygen, pH,dioxide, ammonia, detergents, biochemical oxygen demand, pesticides, and hu[5,109]. In many cases optical fibers are simply used to guide light to the measurpoint in the specimen. In some cases optical fibers are monitoring the responsmaterial deposited on the end of the fiber [110]. In some other cases well-developedtechnologies such as FBG temperature sensors have been used for biological testA good example of optical fiber chemical sensors in which the fiber itself plays a kein the measurement is the use of LPGs [112,113]. As discussed in Section 2, an LPcouple the core mode to a cladding mode. If the coating or jacket is removed frooptical fiber, the evanescent field of the cladding mode that exists outside the claexperiences the refractive index change of the outside material. The sensitivity cadjusted by fiber etching [114]. An example of a commercialized fiber biosensor is tvivo blood pressure sensor that uses the white light interferometry (pressure range: 5Hg to 1060 mm Hg, precision:±1 mm Hg or±1% of reading) [107].

6. Concluding remarks

In this paper the current status of optical fiber sensors has been briefly reviewed. Aas optical fibers were developed, it was concluded that they could also be used for sHence, the history of research in optical fiber sensors is almost as old as the hisoptical fiber communication research. Optical fiber sensors have unique advantag


bilitye noty have

edictsefore

willnomicrt theat the

et ofby

wever,, which2006–arketaturemotivemicro-ctronicywellSensorring thers [118].trends

opticalfor civilsinceh asexitederisticn civil

FOGs,opticalcost-

ltage

itionalns suchny field-eeringumbertation

as high sensitivity, immunity to EMI, small size, lightweight, robustness, and the ato provide multiplexed or distributed sensing. Although the optical fiber sensors havexperienced the dramatic commercial success of optical fiber communications, thebeen continuously and enthusiastically studied.

At present, the economic situation is not good. One of the gloomy forecasts prthat the worldwide optical transport market will decline through the year of 2004 bresuming modest growth in 2005 (by Dell’Oro Group) [115]. It says the 2004 salesbe only 35% of the peak in 2000. Some other analyst groups predict more rapid ecorecovery. Strategies Unlimited predicts that the optical component market will starecovery from 2003. Communications Industry Researchers (CIR) also predicts thlong haul market will start its recovery from 2003. It also predicts that the markintegrated optics for multiplexing, switching, and computing will grow to $400 millions2006 [116]. These forecasts are on the market related to optical communications. Hothe competitiveness of optical fiber sensors relies on the component cost reductionis greatly dependent on the optical communication market. The sensor forecast of2011 published in April of 2002 by the Freedonia Group predicts that U.S. mfor sensors will grow at a healthy pace, fueled by economic recovery in more mapplications such as process control, industrial machinery, and conventional autosensors. It also predicts that the fastest growth will occur in emerging areas such aselectro-mechanical systems and telematics, and that nearly all types of opto-elesensors including fiber optic sensors will exhibit healthy gains [116]. Recently HoneAutomation and Control Solutions has signed an agreement to acquired InvensysSystems [117], and General Electric has employed an aggressive strategy for entesensor’s arena such as temperature, humidity, pressure, gas, and oxygen sensoAlthough the sensors involved here are not confined to optical fiber sensors, theseare encouraging to the researchers in the field of optical fiber sensors.

Fiber grating sensors have been the most widely studied topic among variousfiber sensor technologies. Some fiber grating sensors have been commercializedhealth monitoring and oil industries. FBGs have been shipping for WDM devices1997 [119]. But for WDM filter applications, FBGs have strong competitors sucarrayed-waveguide gratings and thin-film filters. Several FBG vendors have recentlythe market [119]. However, for sensor applications, FBGs provide a unique charactof multi-point EMI-resistant measurement, and they have started to be deployed iand oil industry fields.

There are other rather mature optical fiber sensor technologies such as OTDRs,and optical fiber current sensors. The OTDR has become a standard technique incommunication line fault monitoring. Today, FOGs are considered as the mostefficient solution for various inertial navigation applications. Optical current and vosensors became to be installed in real power industry [120].

New ideas are continuously being proposed and tested for not only various tradmeasurands such as strain, temperature, and pressure but also for new applicatioas biosensors. Papers on optical fiber sensors have already begun to appear in maapplication journals such as civil engineering journals, sensor journals, power enginjournals, chemical engineering journals, and bioengineering journals. In 2002, the nof papers on optical fiber sensors published in the journals listed in Scientific Ci


rnals.el fromnsorsrature,al andill be

nsorsother

emicalto find

nsors

logy,

tems,

s and

. 372

ggittishers,

ation

erse

Eds.),

ratured strain

urface-

two fiber

effects

Index (SCI) is about 110. Many of the papers are published in the field-application jouHence, the research in the optical fiber sensors is more active than optics people fethe journals of their main interest. The U.S. patent applications on optical fiber seduring recent two years records several hundreds in number, among which tempestrain, displacement, refractive index, damage detection, current, vibration, biologicchemical sensors are frequent topics [121]. Biosensors for medical applications wan important application field of optical fiber sensors. Now, the optical fiber sereached the stage at which optics people should collaborate with specialists infields such as civil engineering, mechanical engineering, material engineering, chengineering, and bioengineering to develop sensor systems useful in real fields andnew applications.

With the continuing effort and enthusiasm, the application fields of optical fiber sewill be extended and more commercial successes will almost certainly be found.

Acknowledgment

The author thanks Dr. Minho Song for valuable comments on this paper.

References

[1] F.T.S. Yu, S. Yin (Eds.), Fiber Optic Sensors, Dekker, New York, 2002.[2] K.T.V. Grattan, B.T. Meggitt (Eds.), Optical Fiber Sensor Technology, Vol. 2—Devices and Techno

Chapman & Hall, London, 1998.[3] K.T.V. Grattan, B.T. Meggitt (Eds.), Optical Fiber Sensor Technology, Vol. 3—Applications and Sys

Kluwer Academic Publishers, Boston, 1999.[4] A. Othonos, K. Kalli, Fiber Bragg Gratings—Fundamentals and Applications in Telecommunication

Sensing, Artech House, Boston, 1999.[5] M.D. Marazuela, M.C. Moreno-Bondi, Fiber-optic biosensors—an overview, Anal. Bioanal. Chem

(2002) 664–682.[6] Z.Y. Zhang, K.T.V. Grattan, Commercial activity in optical fiber sensors, in: K.T.V. Grattan, B.T. Me

(Eds.), Optical Fiber Sensor Technology, Vol. 3—Applications and Systems, Kluwer Academic PublBoston, 1999, Chap. 10, pp. 257–306.

[7] K.O. Hill, Y. Fujii, D.C. Johnson, B.S. Kawasaki, Photosensitivity in optical fiber waveguides: applicto reflection filter fabrication, Appl. Phys. Lett. 32 (1978) 647–649.

[8] G. Meltz, W.W. Morey, W.H. Glenn, Formation of Bragg gratings in optical fibers by a transvholographic method, Opt. Lett. 14 (1989) 823–825.

[9] Y.-J. Rao, Fiber Bragg grating sensors: principles and applications, in: K.T.V. Grattan, B.T. Meggitt (Optical Fiber Sensor Technology, Vol. 2, Chapman & Hall, London, 1998, pp. 355–389.

[10] X. Shu, Y. Liu, D. Zhao, B. Gwandu, F. Floreani, L. Zhang, I. Bennion, Dependence of tempeand strain coefficients on fiber grating type and its application to simultaneous temperature anmeasurement, Opt. Lett. 27 (9) (2002) 701–703.

[11] M.G. Xu, J.L. Archambault, L. Reekie, J.P. Dakin, Thermally-compensated bending gauge using smounted fiber gratings, Int. J. Optoelectron. 9 (1994) 281–283.

[12] M. Song, S.B. Lee, S.S. Choi, B. Lee, Simultaneous measurement of temperature and strain usingBragg gratings embedded in a glass tube, Opt. Fiber Technol. 3 (1997) 194–196.

[13] M.G. Xu, J.L. Archambault, L. Reekie, J.P. Dakin, Discrimination between strain and temperatureusing dual-wavelength fiber grating sensors, Electron. Lett. 30 (13) (1994) 1085–1087.


surement

nt with

gs, in:

Bragg

fibre

) BraggC ’97)

length

ighly

bele,

rating

patial

ectricference

straintional. 530–

artially

etricn, 1996,

plica-

nique

fiber

em forerence

ors forf the 13th3746,

fero-

sitive

ion and

[14] S.W. James, M.L. Dockney, R.P. Tatam, Simultaneous independent temperature and strain meausing in-fibre Bragg grating sensors, Electron. Lett. 32 (12) (1996) 1133–1134.

[15] M. Song, B. Lee, S.B. Lee, S.S. Choi, Interferometric temperature-insensitive strain measuremedifferent diameter fiber Bragg gratings, Opt. Lett. 22 (11) (1997) 790–792.

[16] B. Lee, Y. Jeong, Interrogation techniques for fiber grating sensors and the theory of fiber gratinF.T.S. Yu, S. Yin (Eds.), Fiber Optic Sensors, Dekker, New York, 2002, Chap. 7, pp. 295–381.

[17] S.M. Melle, K. Liu, R.M. Measures, A passive wavelength demodulation system for guided-wavegrating sensors, IEEE Photon. Technol. Lett. 4 (5) (1992) 516–518.

[18] A.B. Lobo Ribeiro, L.A. Ferreira, M. Tsvetkov, J.L. Santos, All-fibre interrogation technique forBragg sensors using a biconical fibre filter, Electron. Lett. 32 (4) (1996) 382–383.

[19] M. Song, S.B. Lee, S.S. Choi, B. Lee, Fiber laser strain sensor using an LPG (long period gratingwavelength demodulation filter, in: The 2nd Optoelectronics and Communications Conference (OECTechnical Digest, Seoul, Korea, 1997, pp. 676–677.

[20] M.A. Davis, A.D. Kersey, All-fibre Bragg grating strain-sensor demodulation technique using a wavedivision coupler, Electron. Lett. 30 (1) (1994) 75–77.

[21] Q. Zhang, D.A. Brown, H. Kung, J.E. Townsend, M. Chen, L.J. Reinhart, T.F. Morse, Use of hovercoupled couplers to detect shifts in Bragg wavelength, Electron. Lett. 31 (6) (1995) 480–482.

[22] A.D. Kersey, M.A. Davis, H.J. Patrick, M. LeBlanc, K.P. Koo, C.G. Askins, M.A. Putnam, E.J. FrieFiber grating sensors, J. Lightwave Technol. 15 (8) (1997) 1442–1463.

[23] C.G. Askins, M.A. Putnam, G.M. Williams, E.J. Friebele, Stepped-wavelength optical fiber Bragg garrays fabricated in line on a draw tower, Opt. Lett. 19 (1994) 147–149.

[24] Y. Hu, S. Chen, L. Zhang, I. Bennion, Multiplexing Bragg gratings combined wavelength and sdivision techniques with digital resolution enhancement, Electron. Lett. 33 (23) (1997) 1973–1975.

[25] R. Willsch, W. Ecke, H. Bartelt, Optical fiber grating sensor networks and their application in elpower facilities, aerospace and geotechnical engineering, in: The 15th Optical Fiber Sensors ConTechnical Digest, Portland, OR, 2002, pp. 49–54.

[26] S.C. Kang, H. Yoon, S.B. Lee, S.S. Choi, B. Lee, Real-time measurement for static and dynamicusing a fiber Bragg grating and the ASE profile of EDFA, in: Proceedings of the 13th InternaConference on Optical Fiber Sensors (OFS-13), Kyongju, Korea, in: Proc. SPIE, Vol. 3746, 1999, pp533.

[27] S. Kim, J. Kwon, S. Kim, B. Lee, Temperature-independent strain sensor using a chirped grating pembedded in a glass tube, IEEE Photon. Technol. Lett. 12 (6) (2000) 678–680.

[28] A.D. Kersey, M.A. Davis, T. Tsai, Fiber optic Bragg grating strain sensor with direct reflectominterrogation, in: Proceedings of the Optical Fiber Sensors Conference (OFS-11), Sapporo, Japapp. 634–637.

[29] V. Grubsky, J. Feinberg, Long-period fiber gratings with variable coupling for real-time sensing aptions, Opt. Lett. 25 (4) (2000) 203–205.

[30] R.W. Fallon, L. Zhang, A. Gloag, I. Bennion, Identical broadband chirped grating interrogation techfor temperature and strain sensing, Electron. Lett. 33 (1997) 705–706.

[31] A.D. Kersey, T.A. Berkoff, W.W. Morey, Multiplexed fiber Bragg grating strain-sensor system with aFabry–Perot wavelength filter, Opt. Lett. 18 (1993) 1370–1372.

[32] S.T. Vohra, M.D. Todd, G.A. Johnson, C.C. Chang, B.A. Danver, Fiber Bragg grating sensor systcivil structure monitoring: applications and field tests, in: Proceedings of the 13th International Confon Optical Fiber Sensors (OFS-13), Kyongju, Korea, in: Proc. SPIE, Vol. 3746, 1999, pp. 32–37.

[33] P.J. Henderson, D.J. Webb, D.A. Jackson, L. Zhang, I. Bennion, Highly-multiplexed grating-senstemperature-referenced quasi-static measurements of strain in concrete bridges, in: Proceedings oInternational Conference on Optical Fiber Sensors (OFS-13), Kyongju, Korea, in: Proc. SPIE, Vol.1999, pp. 320–323.

[34] A.D. Kersey, T.A. Berkoff, W.W. Morey, High-resolution fibre-grating based strain sensor with intermetric wavelength-shift detection, Electron. Lett. 28 (3) (1992) 236–238.

[35] R.S. Weis, A.D. Kersey, T.A. Berkoff, A four-element fiber grating sensor array with phase-sendetection, IEEE Photon. Technol. Lett. 6 (12) (1994) 1469–1472.

[36] K.P. Koo, A.D. Kersey, Bragg grating based laser sensors systems with interferometric interrogatwavelength division multiplexing, J. Lightwave Technol. 13 (1995) 1243–1249.


oton.

s using

in-rate

ling of

f fibern Lasers

ivision

a shipl Fiber

n of–1295.

nsors

ingle

ating

ion of

fiber-

kson,1–54.tron.

sensor1461–

n for

ensorensors

gation,

r using

swept

arrayCom-

rray,

nsors

[37] A.D. Kersey, T.A. Berkoff, Fiber-optic Bragg grating differential-temperature sensor, IEEE PhTechnol. Lett. 4 (10) (1992) 1183–2285.

[38] A. Dandridge, A.B. Tveten, T.G. Giallorenzi, Homodyne demodulation scheme for fiber optic sensorphase generated carrier, IEEE J. Quant. Electron. 18 (1982) 1647–1653.

[39] Y.L. Lo, J.S. Sirkis, C.C. Chang, Passive signal processing of in-line fiber etalon sensors for high straloading, J. Lightwave Technol. 15 (1997) 1578–1585.

[40] M. Song, S. Yin, P.B. Ruffin, Fiber Bragg grating strain sensor demodulation with quadrature sampa Mach–Zehnder interferometer, Appl. Opt. 39 (7) (2000) 1106–1111.

[41] S.C. Kang, S.B. Lee, S.S. Choi, B. Lee, A novel demodulation technique for the wavelength shift oBragg grating sensors using the I/Q signal processing scheme, in: Proceedings of the Conference oand Electro-Optics—Pacific Rim (CLEO/Pacific Rim ’99), Seoul, Korea, 1999, pp. 135–136.

[42] T.A. Berkoff, A.D. Kersey, Fiber Bragg grating array sensor system using a bandpass wavelength dmultiplexer and interferometric detection, IEEE Photon. Technol. Lett. 8 (11) (1996) 1522–1524.

[43] G.A. Johnson, S.T. Vohra, B.A. Danver, K. Pran, G.B. Havsgard, G. Wang, Vibration monitoring ofwaterjet with fiber Bragg gratings, in: Proceedings of the 13th International Conference on OpticaSensors (OFS-13), Kyongju, Korea, in: Proc. SPIE, Vol. 3746, 1999, pp. 616–619.

[44] M.A. Davis, A.D. Kersey, Application of a fiber Fourier transform spectrometer to the detectiowavelength-encoded signals from Bragg grating sensors, J. Lightwave Technol. 13 (7) (1995) 1289

[45] K.B. Rochford, S.D. Dyer, Demultiplexing of interferometrically interrogated fiber Bragg grating seusing Hilbert transform processing, J. Lightwave Technol. 17 (5) (1999) 831–836.

[46] M. Volanthen, H. Geiger, M.G. Xu, J.P. Dakin, Simultaneous monitoring fibre gratings with a sacousto-optic tunable filter, Electron. Lett. 32 (1996) 1228–1229.

[47] H. Geiger, M.G. Xu, N.C. Eaton, J.P. Dakin, Electronic tracking system for multiplexed fibre grsensors, Electron. Lett. 32 (1995) 1006–1007.

[48] J.P. Dakin, M. Volanthen, Distributed and multiplexed fibre grating sensors, including discussproblem areas, IEICE Trans. Electron. E83-C (3) (2000) 391–399.

[49] D.A. Jackson, A.B. Lobo Ribeiro, L. Reeckie, J.L. Archambault, Simple multiplexing scheme for aoptic grating sensor network, Opt. Lett. 18 (1993) 1192–1194.

[50] G.P. Brady, S. Hope, A.B. Lobo Ribeiro, D.J. Webb, L. Reekie, J.L. Archambault, D.A. JacDemultiplexing of fibre Bragg grating temperature and strain sensors, Opt. Commun. 111 (1994) 5

[51] M.A. Davis, A.D. Kersey, Matched-filter interrogation technique for fibre Bragg grating arrays, ElecLett. 31 (1995) 822–823.

[52] S.C. Kang, S.Y. Kim, S.B. Lee, S.W. Kwon, S.S. Choi, B. Lee, Temperature-independent strainsystem using a tilted fiber Bragg grating demodulator, IEEE Photon. Technol. Lett. 10 (10) (1998)1463.

[53] Y.J. Rao, D.A. Jackson, L. Zhang, I. Bennion, Dual-cavity interferometric wavelength-shift detectioin-fiber Bragg grating sensors, Opt. Lett. 21 (19) (1996) 1556–1558.

[54] J. Jung, Y.W. Lee, B. Lee, High-resolution interrogation technique for fiber Bragg grating strain susing long period grating pair and EDF, in: The 14th International Conference on Optical Fiber S(OFS-14), Venice, Italy, 2000.

[55] G.A. Ball, W.W. Morey, P.K. Cheo, Fiber laser source/analyzer for Bragg grating sensor array interroJ. Lightwave Technol. 12 (1994) 700–703.

[56] T. Coroy, R.M. Measures, Active wavelength demodulation of a Bragg grains fibre optic strain sensoa quantum well electroabsorption filtering detector, Electron. Lett. 32 (1996) 1811–1812.

[57] S.H. Yun, D.J. Richardson, B.Y. Kim, Interrogation of fiber grating sensor arrays with a wavelength-fiber laser, Opt. Lett. 23 (11) (1998) 843–845.

[58] M.A. Putnam, M.L. Dennis, J.U. Kang, T.-E. Tsai, I.N. Duling, I.E.J. Friebele, Sensor gratingdemodulation using a passively mode-locked fiber laser, in: Technical Digest of the Optical Fibermunication Conference, Dallas, TX, 1997, Paper WJ4, pp. 156–157.

[59] A.D. Kersey, A. Dandridge, M.A. Davis, Low-crosstalk code-division multiplexed interferometric aElectron. Lett. 28 (1992) 351–352.

[60] K.P. Koo, A.B. Tveten, S.T. Vohra, Dense wavelength division multiplexing of fibre Bragg grating seusing CDMA, Electron. Lett. 35 (1999) 165–167.


ng an

rement.nsors,

smart

auvin,ference

atingsDigest,

ensors

ctionference

ol. 2,

York,

cope,

07.Lett. 9

otonet-. 1–4.tive, in:

ptical

Optical

ertialchnical

fiberhnical

itachi5–38.currentPortland,

twave

ectionerence

[61] P.K.C. Chan, W. Jin, J.M. Gong, M.S. Demokan, Multiplexing of fiber Bragg grating sensors usiFMCW technique, IEEE Photon. Technol. Lett. 11 (11) (1999) 1470–1472.

[62] M. LeBlanc, S.Y. Huang, M. Ohn, R.M. Measures, A. Guemes, A. Othonos, Distributed strain measubased on a fiber Bragg grating and its reflection spectrum analysis, Opt. Lett. 21 (1996) 1405–1407

[63] Y.J. Rao, S. Huang, Applications of fiber optic sensors, in: F.T.S. Yu, S. Yin (Eds.), Fiber Optic SeDekker, New York, 2002, Chap. 10, pp. 449–490.

[64] K.-T. Lau, L.-M. Zhou, P.-C. Tse, L.-B. Yuan, Applications of composites, optical fiber sensors andcomposites for concrete rehabilitation: an overview, Appl. Compos. Mater. 9 (2002) 221–247.

[65] L. Maurin, J. Boussoir, S. Rougeault, M. Bugaud, P. Ferdinand, A.G. Landrot, Y.-H. Grunevald, T. ChFBG-based smart composite bogies for railway applications, in: The 15th Optical Fiber Sensors ConTechnical Digest, Portland, OR, 2002, pp. 91–94.

[66] P.M. Nellen, A. Frank, A. Kenel, High strain and high strain gradients measured with fiber Bragg grin structural engineering applications, in: The 15th Optical Fiber Sensors Conference TechnicalPortland, OR, 2002, pp. 111–114.

[67] E. Udd, How to start a small high tech business in Troutdale, Oregon?, in: The 15th Optical Fiber SConference Technical Digest, Portland, OR, 2002, pp. 23–26.

[68] D.L. Gysling, F.X. Bostick III, Changing paradimes in oil and gas reservoir monitoring—the introduand commercialization of in-well optical sensing systems, in: The 15th Optical Fiber Sensors ConTechnical Digest, Portland, OR, 2002, pp. 43–46.

[69] V. Vali, R.W. Shorthill, Fiber ring interferometer, Appl. Opt. 15 (1976) 1099–1100.[70] J. Blake, Fiber optic gyroscopes, in: K.T.V. Grattan, B.T. Meggitt (Eds.), Optical Fiber Technology, V

Chapman and Hall, New York, 1998, pp. 303–328.[71] P.B. Ruffin, Fiber gyroscope sensors, in: F.T.S. Yu, S. Yin (Eds.), Fiber Optic Sensors, Dekker, New

2002, pp. 383–415.[72] R.P. Moeller, W.K. Burns, N.J. Frigo, Open-loop output and scale factor stability in a fiber-optic gyros

J. Lightwave Technol. 7 (2) (1989) 262–269.[73] J.L. Davis, S. Ezekiel, Closed-loop, low-noise fiber-optic rotation sensor, Opt. Lett. 6 (1981) 505–5[74] B.Y. Kim, H.J. Shaw, Gated phase-modulation feedback approach to fiber-optic gyroscopes, Opt.

(1984) 263–265.[75] T. Gaiffe, From R&D brassboards to navigation grade FOG-based INS: the experience of Ph

ics/Ixsea, in: The 15th Optical Fiber Sensors Conference Technical Digest, Portland, OR, 2002, pp[76] S.J. Sanders, L.K. Strandjord, D. Mead, Fiber optic gyro technology trends—a Honeywell perspec

The 15th Optical Fiber Sensors Conference Technical Digest, Portland, OR, 2002, pp. 5–8.[77] G.A. Pavlath, Fiber optic gyro based inertial navigation systems at Northrop Grumman, in: The 15th O

Fiber Sensors Conference Technical Digest, Portland, OR, 2002, p. 9.[78] R. Usui, A. Ohno, Recent progress of fiber optic gyroscopes and applications at JAE, in: The 15th

Fiber Sensors Conference Technical Digest, Portland, OR, 2002, pp. 11–14.[79] J. Nasu, K. Saito, A. Kurokawa, F. Hayashi, I. Nakatani, Application of fiber gyros at MPC—in

naigation and guidance system for M–V rocket, in: The 15th Optical Fiber Sensors Conference TeDigest, Portland, OR, 2002, pp. 15–18.

[80] R.B. Dyott, S.M. Bennett, D. Allen, J. Brunner, Development and commercialization of open loopgyros at KVH Industries (formerly at Andrew), in: The 15th Optical Fiber Sensors Conference TecDigest, Portland, OR, 2002, pp. 19–22.

[81] T. Kumagai, W. Ohnuki, S. Yamamoto, A. Hongo, I. Sone, Optical fiber sensor applications at HCable, in: The 15th Optical Fiber Sensors Conference Technical Digest, Portland, OR, 2002, pp. 3

[82] G.A. Sanders, J.N. Blake, A.H. Rose, F. Rahmatian, C. Herdman, Commercialization of fiber-opticand voltage sensors at NxtPhase, in: The 15th Optical Fiber Sensors Conference Technical Digest,OR, 2002, pp. 31–34.

[83] U.S. Patent #3,324,393 (1967).[84] U.S. Patent #3,605,013 (1971).[85] A.H. Rose, Z.B. Ren, G.W. Day, Twisting and annealing optical fiber for current sensors, J. Ligh

Technol. 14 (11) (1996) 2492–2498.[86] K. Kurosawa, Y. Tashiro, K. Ohkawara, Differential current relaying system with optical phase det

using flint glass fiber type optical current transformers, in: The 15th Optical Fiber Sensors ConfTechnical Digest, Portland, OR, 2002, pp. 549–552.


twave

4 (11)

bers,

Opt.

hgear

. Power

a fibreR, 2002,

rrent

MVA, 2002,

urrent

, New

aracter-

easure-

c Test

usingl Fiber

nsors,

e 15th

ensors

entalonfer-

l Fiber

fiber

erlays,.

[87] A.J. Rogers, Optical-fibre current measurement, Int. J. Optoelectron. 3 (1988) 391–407.[88] K. Kurosawa, S. Yoshida, K. Sakamoto, Polarization properties of the flint glass fiber, J. Ligh

Technol. 13 (7) (1995) 1378–1384.[89] S.C. Rashleigh, R. Ulrich, Magneto-optic current sensing with birefringent fibers, Appl. Phys. Lett. 3

(1979) 768–770.[90] R.I. Laming, D.N. Payne, Electric current sensors employing spun highly birefringent optical fi

J. Lightwave Technol. 7 (12) (1989) 2084–2094.[91] N.C. Pistoni, M. Martinelli, Polarization noise suppression in retracing optical fiber circuits,

Lett. 16 (10) (1991) 711–713.[92] M. Takahashi, H. Noda, K. Terai, S. Ikuta, Y. Mizutani, Optical current sensor for gas insulated switc

using silica optical fiber, IEEE Trans. Power Delivery 12 (4) (1997) 1422–1428.[93] J. Blake, P. Tantaswadi, R.T. de Carvalho, In-line Sagnac interferometer current sensor, IEEE Trans

Delivery 11 (1) (1996) 116–121.[94] F. Briffod, D. Alasia, L. Thevenaz, G. Cuenoud, Ph. Robert, Extreme current measurements using

optics current sensor, in: The 15th Optical Fiber Sensors Conference Technical Digest, Portland, OPostdeadline paper PD3.

[95] K. Bohnert, H. Brandle, G. Frosio, Field test of interferometric optical fiber high voltage and cusensors, in: Proc. OFS-10, 1994.

[96] M. Willsch, T. Bosselmann, Optical current sensor application in the harsh environment of a 120power generator, in: The 15th Optical Fiber Sensors Conference Technical Digest, Portland, ORpp. 407–410.

[97] K. Bohnert, P. Gabus, J. Nehring, H. Brändle, Temperature and vibration insensitive fiber-optic csensor, J. Lightwave Technol. 20 (2) (2002) 267–276.

[98] E. Udd, Overview of fiber optic sensors, in: F.T.S. Yu, S. Yin (Eds.), Fiber Optic Sensors, DekkerYork, 2002, Chap. 1, pp. 1–39.

[99] M.K. Barnoski, S.M. Jensen, Fiber waveguides: a novel technique for investigating attenuation chistics, Appl. Opt. 15 (1976) 2112–2115.

[100] J. Beller, OTDRs and backscatter measurements, in: D. Derickson (Ed.), Fiber Optic Test and Mment, Prentice Hall, Upper Saddle River, NJ, 1998, Chap. 11, pp. 434–474.

[101] W.V. Sorin, Optical reflectometry for component characterization, in: D. Derickson (Ed.), Fiber Optiand Measurement, Prentice Hall, Upper Saddle River, NJ, 1998, Chap. 10, pp. 383–433.

[102] L. Thevenaz, M. Facchini, A. Fellay, P. Robert, D. Inaudi, B. Dardel, Monitoring of large structuresdistributed Brillouin fiber sensing, in: Proceedings of the 13th International Conference on OpticaSensors (OFS-13), Kyongju, Korea, in: Proc. SPIE, Vol. 3746, 1999, pp. 345–348.

[103] http://www.smartec.ch.[104] G.D. Peng, P.L. Chu, Optical fiber hydrophone systems, in: F.T.S. Yu, S. Yin (Eds.), Fiber Optic Se

Dekker, New York, 2002, Chap. 9, pp. 417–447.[105] D. Inaudi, N. Casanova, SMARTEC: bringing fiber optic sensors into concrete applications, in: Th

Optical Fiber Sensors Conference Technical Digest, Portland, OR, 2002, pp. 27–30.[106] http://www.fiberdynamics.com/index.html.[107] http://www.fiso.com.[108] Y.W. Lee, B. Lee, High resolution cryogenic optical fiber sensor system using erbium-doped fiber, S

Actuators A Phys. 96 (1) (2002) 25–27.[109] G. Orellana, M.C. Moreno-Bondi, From molecular engineering of luminescent indicators to environm

analytical chemistry in the field with fiber-optic (bio)sensors, in: The 15th Optical Fiber Sensors Cence Technical Digest, Portland, OR, 2002, pp. 115–118.

[110] F.J. Arregui, D. Galbarra, I.R. Matias, K.L. Cooper, R.O. Claus, ZrO2 thin films deposited by theelectrostatic self-assembly method on optical fibers for ammonia detection, in: The 15th OpticaSensors Conference Technical Digest, Portland, OR, 2002, pp. 265–268.

[111] D.J. Webb, M.W. Hathaway, D.A. Jackson, S. Jones, L. Zhang, I. Bennion, First in-vivo trials of aBragg grating based temperature profiling system, J. Biomed. Opt. 5 (1) (2000) 45–50.

[112] S.W. James, N.D. Rees, R.P. Tatam, G.J. Ashwell, Optical fiber long period gratings with thin film ovin: The 15th Optical Fiber Sensors Conference Technical Digest, Portland, OR, 2002, pp. 119–122


er, in:

rating

fm).

/home.

://lw.

[113] T. Allsop, D.J. Webb, I. Bennion, A high sensitivity long period grating Mach–Zehnder refractometThe 15th Optical Fiber Sensors Conference Technical Digest, Portland, OR, 2002, pp. 123–126.

[114] S. Kim, Y. Jeong, S. Kim, J. Kwon, N. Park, B. Lee, Control of the characteristics of a long-period gby cladding etching, Appl. Opt. 39 (13) (2000) 2038–2042.

[115] Optical equipment market to decline through 2004, Aug. 1, 2002 (http://wdm.pennnet.com/home.c[116] http://www.giikorea.co.kr.[117] Honeywell to acquire sensor systems business from Invensys, Aug. 19, 2002 (http://lfw.pennnet.com

cfm).[118] Frost, Sullivan, Sensor market watch: To buy or to sell? That is the question, Sep. 25, 2002.[119] M. Fuller, Product diversification is key to success in FBG market, Lightwave, May 2002 (http

pennwellnet.com/home.cfm).[120] http://www.nxtphase.com/index.asp.[121] http://www.uspto.gov/patft.

Lee, 2003 - Review of the present status of optical fiber sensors

Documents

Transcript of Lee, 2003 - Review of the present status of optical fiber sensors