n - Fachhochschule Jena

Fachhochschule Jena 

Fachbereich ET/IT – Studiengang Mechatronik 

Vorlesung Sensorik 

Faseroptische Sensoren (FOS) 

Prof. Dr. Reinhardt Willsch und Dr. Wolfgang Ecke 

Institut für Photonische Technologien (IPHT) Jena, Germany 

Arbeitsgruppe Faseroptische Systeme (e-mail: willsch@ipht-jena.de) 

� Physikalisch-technische Wirkprinzipien, faseroptische Komponenten 

� Multimode-FOS – intensitäts- und spektral-moduliert 

� Monomode-FOS – Interferometrie, Polarimetrie 

� Verteilte Sensorsysteme – OTDR-Technik, Raman & Brillouin-Rückstreuung 

� Fasergitter-Sensoren – Sensornetzwerke, Multiplextechniken 

� Anwendungen – Prozesskontrolle, Energietechnik, Transporttechnik uva. 

� Ausblick – biochemische Anwendungen, Marktentwicklung 

FOS - 1

Komponenten faseroptischer Sensoren (I) 

Lichtquellen und -detektoren (optoelektronische Bauelemente): 

- LED und Laserdioden auf GaAlAs-Basis für den sichtbaren und nahen IR- 

Spektral-bereich (z.B. 780 nm-Laserdioden der CD-Technik) 

- Miniatur-Glühstrahler als breitbandige Quellen (z.B. Halogen-Lampen) 

- spezielle Lichtquellen wie Superlumineszenzdioden (für Fasergyroskope), 

durchstimmbare Laser, Laserdioden-gepumpte Faserlaser u.a. 

- Si-Photodioden und Dioden-Arrays, CCD-Zeilen u.a. Photodetektoren 

FOS - 2

Komponenten faseroptischer Sensoren (II) 

Lichtwellenleiter: 

- Multimodenfasern (Stufen- oder Gradientenindex) 

- Monomodefasern (normal oder hochdoppelbrechend mit 

polarisationserhaltenden Eigenschaften) 

- Fasern mit speziellen Dotierungen (z.B. Seltene Erden) oder Überzügen 

(Metalle, magnetostriktive oder piezoelektrische Materialien u.a.) 

- Fasern aus Spezialgläsern (IR-durchlässige Chalkogenid- oder 

Fluoridglasfasern, poröse Borosilikatglasfasern u.a.) oder optisch 

transparente Polymere 

- Fasern mit hoher numerischer Apertur, mit Mehrfachkern oder spezieller 

Kern- bzw. Mantelgeometrie, Faserbündel, u.a. 

FOS - 3

Komponenten faseroptischer Sensoren (III) 

Miniaturisierte optische Bauelemente und Verbindungstechnik: 

- passive BE wie Koppler/Strahlteiler, Polarisatoren, Filter/Multiplexer, Linsen 

u.a. 

- aktive BE wie Modulatoren für Intensität, Phase, Polarisation oder 

Frequenz u.a. 

=> Faseroptik, Integrierte Optik oder Mikrooptik sowie Kombination 

verschiedener Mikrotechnologien und Aufbau- und Verbindungstechniken -> 

Mikrosystemtechnik 

=> Mikromechanik (z.B. in Si geätzte V-Nuten zur Faserpositionierung oder 

Mikroresonatoren, -membranen u.a. als Sensorelemente) 

FOS - 4

Mikromechanische Silizium-Komponenten 

für die Fasersensorik 

Sensorelement mit 2 Spiegeln für 

faseroptische Transmissionssensoren 

(Lichtschranken, Absorption bzw. 

Streuung in Gasen oder Flüssigkeiten 

Sensorelement mit reflektierender 

Zunge für faseroptische Vibrationsbzw. 

Beschleunigungssensoren 

FOS - 5

Typen von Lichtleitfasern 

Querschnitt Brechzahl- Eingangs- Wellenausbreitung Ausgangs- 

Profil Impuls Impuls 

FOS - 6

Advantages of Optical Fiber Sensors 

� Immunity against / applicable in 

- Strong electromagnetic fields, high voltage 

- Explosive or chemically aggressive & corrosive media 

- Nuclear / ionizing radiation environment 

- High temperature 

� Highly sensitive, miniaturized, flexible and lightweight (nano-probes) 

� Low-loss and non-interfering signal transmission (remote sensing) 

� Multiplexing capability, compatible to optical communication 

(sensor networks) 

� Embedding in composite materials (smart structures) 

FOS - 7

Photo: 

CFRP with Embedded Fiber-optic 

Strain Sensors 

A vision is becoming reality: 

Smart Structures with integrated “nervous system” 

Laminated carbon fiber reinforced polymer (CFRP) composite material 

containing embedded sensing optical glass fiber (Bragg grating array) 

FOS - 8

Basic Fiber Sensor Configurations 

Single-point sensor Optical fiber 

Multi-point (quasi-distributed) sensor 

Distributed sensor 

Continuous sensing element 

Sensing element 

Multiple sensing points 

FOS - 9

Häufig verwendete Messeffekte 

Extrjnsische Multimoden-Fasersensoren: 

- Reflexion am Lichtleiterende (bewegliche Spiegel, reflektierende Membranen u.a.) 

- Transmission zwischen zwei Lichtleitfasern (bewegliche Masken, Streuung an Teilchen u.a). 

- Photolumineszenz (Temperaturabhängigkeit der spektralen Intensitätsverteilung & Abklingzeit) 

Intrinsische Multimoden-Fasersensoren: 

- Mikrobiegung; Makrobiegung 

- Streu-, Absorptions- und Fluoreszenzprozesse in speziell dotierten Fasern bzw. durch 

Materialdefekte (Kernstrahlung u.a.). 

Interferometrische Fasersensoren: 

- Längenänderungen: Thermische Dehnung, mechanische Spannung, Magneto- & Elektrostriktion 

- Brechzahländerungen: Thermooptischer Effekt, Photoelastischer Effekt, Magneto- & 

elektrooptische Effekte 

Polarimetrisehe Fasersensoren: 

Änderungen der Doppelbrechung: mechanisch induzierte Doppelbrechung (elastooptischer Effekt), 

Faradayeffekt (magnetooptischer Effekt), Pockelseffekt (elektrooptlscher Effekt), 

Weitere wichtige Messeffekte: 

- der relativistische Sagnac-Effekt 

- nichtlineare Streuprozesse (Raman- oder Brillouin-Streuung) 

FOS - 10

Optical Fiber Sensors: Measurands 

• distance, position, displacement, deformation, strain 

• temperature 

• pressure, force 

• refractive index, liquid level, flow velocity 

• rotation rate 

• vibration 

• magnetic, electric and acoustic fields 

• electric current, voltage 

• nuclear radiation 

• chemical parameters 

• biochemical reactions 

and other 

FOS - 11

Optical Fiber Sensors: 

Basic Principle & Scheme 

Measurand X modulates (encodes) a parameter P of light guided in the fiber: 

E x,y (z,t) = A cos (ωt - kz+δ) 

• Intensity / amplitude A 

• Wavelength /spectral distribution λ = c 2π / ω 

• Optical phase δ 

• Polarization E x / E y 

• Time dependence t (pulse delay, fluorescence decay, modulation frequency,...) 

light source 

power supply 

transmitting fiber receiving fiber 

P o 

sensitive 

element 

(transducer) 

Measurand X 

P(x) 

optoelectronic 

detector 

S(x) 

electronic 

signal processing 

FOS - 12


Basic Signal Encoding & Processing Concepts 

� Intensity-modulated sensors 

- low-cost and simple technical solutions 

- poor accuracy & stability (influence of light-source intensity, fiber losses, ..) 

→ reference channel ( 2 wavelengths, spectral photometry, ... ) 

- applications in automation & control (on-off sensors), medicine, and other 

� Phase-modulated interferometric sensors 

- high-sensitive but expensive and sophisticated technical solutions (e.g. fiber gyro) 

- cross-sensitivities ( temperature, ... ) 

- applications in precision measurement, military (fiber hydrophones), seismic sensing 

� Spectral-encoded sensors 

- potential for cost-efficient high-performance technical sensors (FBG sensor systems, biochemical 

sensing,.) using standard optoelectronic signal processing (mini-spectrometers) 

- long-term stability, reproducibility and reliability 

- interchangeability (calibration by absolutely defined wavelength scale) 

- applications in industrial process control, environmental and structural monitoring, bio-medicine 

FOS - 13

Optical Fiber Sensor Systems and their Application 

• Intensity-modulated optical fiber sensors 

FOS - 14

Principle of Reflective Displacement Sensor 

a) 1 fiber + fiber coupler b) 2 parallel fibers 

Source, I 0 

1 

0.8 

0.6 

0.4 

0.2 

0 

L 

2R f 

Detector, I(L) 

I(L) ~ I 0 ·[R f /(R f + L·NA) ]² 

NA=0,25 

NA=0,15 

0 2 4 6 8 10 

L/R f 

L 

Characteristics 

depend on 

- Numer. Aperture 

- fiber radius 

- fiber distance 

0 2,5 L/mm 5 

FOS - 15

Example of an Intensity Sensor: 

Diaphragm Pressure Sensor 

Pressure, displacement, etc. 

Curves A, B, C: 

A: step index B: graded index C: 2 fibres 

FOS - 16

Application: 

Medical In-vivo Brain Pressure Sensor 

Fa. Camino/USA 

FOS - 17

Fiber-Optic Medical In-vivo 

Brain Pressure Sensing 


FOS - 18


Heart Pressure Sensing 


FOS - 19

Principle of Micro-Bending Fiber-Optic Sensors 

Optical transmission losses (leaky modes) caused by periodic fiber bending 

Interference of core modes and cladding modes: 

Core modes (e.g., n eff = n c ) ⇒ Cladding modes (e.g., n eff = n cl ) 

Max. sensitivity (losses) at optimal bending period L opt : 

(L opt ) -1 = ( λ / n c ) -1 – ( λ / n cl ) -1 

L opt mechanical transducer 

Cladding, n cl 

Core, n c 

Example: 

n c = 1,460 

n cl = 1,459 

λ = 0,8 µm 

L opt = 0,8 mm 

FOS - 20

Technical Micro-Bending Fiber-Optic Sensors 

force, pressure 

strain 

metal wire coiled on optical glass 

fiber with optimal bending period 

→ distributed intrusion detectors 

(Felten&Guilleaume; Herga) 

"Optical Strand" strain sensor 

(OSMOS DEHA-COM) 

FOS - 21

Application of Micro-Bending Sensors: 

Structure Monitoring in Civil Engineering 

Network of 56 "Optical Strand" fiber-optic micro-bending strain sensors for 

structure health monitoring of soccer stadium "Stade de France" 

in St. Denis/Paris (OSMOS DEHA-COM GmbH Cologne) 

FOS - 22


• Thin-film Fabry-Perot based extrinsic fiber sensors 

FOS - 23

I 0 

I R 

d, n 

Extrinsic Spectrally-Encoded FOS 

Using Thin-Film Fabry-Perot Transducers 

I T 

Partially reflecting mirrors 

I R 

Λ min~ d, n 

Grating 

LED 

Free Spectral Range > LED spectral width ! 

λ 

Polychromator 

CCD line 

detector 

1 mm 

LWL 

Fabry-Perot probe 

n H 

n Low 

FOS - 24

Porous Transducer Layers on 

Fiber End-Face: Humidity Sensor 

Nano-porous thin-film transducer Reflection spectra 

H 2 O vapor 

Optical fiber 

∅≈200 µm 

Reflectivity 

Wavelength [nm] 

1,0 

0,5 

H 2 0 filled pores 

Dry pores 

0,0 

600 700 800 900 1000 


812 

802 

792 

-90 

Sensor characteristic 

-60 -30 0 30 

Dew point [°C] 

FOS - 25

Fiber-Optic Humidity Sensor: Applications 

• On-line measurement of residual humidity in gases (natural gas, purified 

gases) and in organic liquids 

• Measuring range 

Dew Point T DP = - 80 °C…+20 °C 

= partial pressure p(H 2O) = 10 -2 …10 3 Pa 

Natural gas drying station 

(German Verbundnetz Gas AG) 

Hygrometer (BARTEC GmbH) 

Sensor 

FOS - 26

T-sensitive Transducer Layers: 

Temperature Sensor 

• Measuring range: T = -196 °C .. +600 °C (laser micro-welded mounting) 

• Resolution: 0,2 % 

• Application: gas industry, explosive media, 

high-voltage, high-frequency & micro-wave facilities 

Typical sensor characteristic 


850 

840 

830 

820 

810 

800 

790 

-100 0 100 200 300 400 500 600 

Temperature [°C] 

Sensor sample 

1 cm 

FOS - 27

Silicon Micro-Membrane Cavity on 

Fiber End-Face: Pressure Sensor 

• Measuring ranges: p = 0…1,5 bar…15 bar…50 bar…150 bar 

• Resolution: 0,5% 

• Application: gas industry, engines, medical engineering, .. 

Typical sensor characteristics 

Membrane bending [nm] 

800 

600 

400 

200 

0..1.5 Bar 

Measuring range 

limited by width of 

LED spectrum 

0..15 Bar 

0..50 Bar 

0..150 Bar 

0 

0 10 20 30 40 50 60 

Pressure [Bar] 

Sensor sample 

Membrane array fabricated on Si wafer 

Etched silicon membrane 

Anodically bonded 

sensor element 

Glass substrate 

Capillary, 

fiber inside 

FOS - 28


• Spectrally encoded sensors 

FOS - 29


Blood Oxygen Sensing 

FOS - 30

Schema: Fa. Asea 

Photolumineszenz-Temperatursensor 

Wirkprinzip: 

Temperaturabhängigkeit 

der spektralen 

Intensitätsverteilung der 

Photolumineszenz eines 

GaAlAs-Kristalls 

Messprinzip: 

2-Wellenlängen- 

Verfahren 

(Streckenneutralität!) 

FOS - 31

Sensorelement Saphirfaser Kollimator Strahlteiler Filter PD Division 

Al 2 O 3 - Iridium- 

Schutz- Strahler- 

Schicht -Schicht 

Hochtemperatursensor mit 

schwarzem Strahler 

λ 2 

λ 1 

λ 1 

λ 2 

Strahler-Charakteristik: 

E λ δλ=C 1/λ 5 ·[exp(C 2/λT)-1] -1 δλ 

C1 = 1,17 W·m²/s 

C2 = 0,144 K·m 

Sensorauswertung: 

T ~ I(λ 1)/I(λ 2) 

FOS - 32

Transmissivity 

UV Fiber Evanescent Field 

Absorption Spectroscopy (EFAS) Sensors 

In-situ monitoring of organic pollution (BTEX, PAK) in water, soil or in 

atmosphere using sensitive (permeable) optical polymer fiber cladding 

1,0 

0,8 

0,6 

0,4 

0,2 

Xylene 

Toluene 

Benzene 

Petrol 

Naphta 

250 300 350 400 450 


Claddin 

Analyte g 

(air, 

water) 

BTEX (Benzene, Toluene, Ethylbenzene, Xylene) 

spectra in water 

BTEX detection limits in air 

Substance 

Detection limit 

(ml/m 3 ) 

Max. allowed 

concentration 

Benzene 3 1 

Toluene 10 50 

Xylene 10 100 

FOS - 33

UV-EFAS Fiber-Optic 

Hydrocarbon Pollution Sensor 

• Sensor fiber: ∅ 200 µm silica core / 20 µm thick PDMS cladding (length 1 m) 

• Light source: Xe flash lamp 

• Spectrometer: MMS (Carl Zeiss), UV MINOS (IPHT) 

Scheme 

Control unit 

Battery 

Sensor fiber 

Power supply 

Sensor probe 

Fiber cable 

UV-Spectrometer 

UV lamp 

Test instrumentation 

for soil monitoring 

FOS - 34

Fiber-Optic UV Absorption Sensing of BTEX Pollution in Water: 

Long-Time Field Test in Groundwater Remediation Facility 

Transmission 

1,0 

0,8 

0,6 

0,4 

0,2 

0,0 

Partner: 

DBI Gas- und 

Umwelttechnik 

GmbH Leipzig 

Benzene 

Toluene 

Xylene 

Gasoline 

Diesel oil 

250 300 350 400 450 


Fiber 

coil 

FOS - 35

Fiber-Optic Hydrocarbon Sensors: 

Application 

Calibration of UV spectral sensor using 

standard BTEX test liquid: 

50% Benzene, 30% Toluene, 

5% Ethylbenzene, 15% Xylene, 

diluted per 1 l water: 


Application (example): 

In-situ filter process control 

in a groundwater remediation 

facility (Lauchhammer, Sax.) 

FOS - 36

Spectral In-situ Nutrient Analysis in Inland 

and Sea Water 

Analytes ranges Analytical methods Measurement 

Nitrate UV spectrophotometer 0,5 – 150 µmol/l NO 3 - 

o-Phosphate FIA with fluorescence detection 0,05 –5 µmol/l PO 4 3 - 

Ammonium FIA with fluorescence detection 0,1 – 20 µmol/l NH 4 + 

Sea-test on board of the ferry „Duchess of Scandinavia“ : 

Measurement of Nitrate concentration profile in the North Sea 

Ferry route 

Harwich (GB)-Cuxhaven (D) 

NO 3 -N [µg/l] 

500 

400 

300 

200 

100 

0 

Harwich 

harbour 

Elbe 

estuary 

0 2 4 6 8 12 14 16 18 

Journey tim e [h] 

Measuring data: Institute for Costal Research, GKSS, 01.06/02.06.2006 

FOS - 37


• Single mode fiber sensors - interferometric sensors 

FOS - 38

Laser 

Principle of Michelson Interferometer 

Linearly 

polarised 

laser mode 

Beam 

combining 

∆φ = (4π/λ0)·(n∆L+L∆n) ·2 

Photo 

detector 

Reflector 

Beam 

splitting 

L 0 

Beam splitter Reflector 

When does interference 

take place? 

• Coherence, i.e., defined 

phase relations: Path 

difference ∆L < coherence 

length 

L c ~ λ 0 2 /δλ (δλ spectral width) 

• Equal states of polarisation 

(superposition of electric field 

vectors !) 

• Almost equal wavelengths 

(frequency difference occurs 

as intensity modulation 

frequency !) 

FOS - 39

• Michelson 

- 2-beam interference 

- reflection type 

• Mach-Zehnder 

- 2-beam interference 

- transmission type 

• Fabry-Perot 

- multiple-beam interference 

- resonator type 

• Sagnac 

- ring interferometer 

- counter-propagating beams 

- relativistic effect 

- rotation sensor (fiber gyro) 

Types of Fiber-Optic Interferometers 

Laser 

Detector 

Laser 

Coupler 

Detector Coupler 

Parameter X 

Transducer 

X=f (L,n) 

Laser Coupler Coupler 

Laser 

Detector 

Coupler 

Parameter X 

Transducer 

X=f (L,n) 

Mirror 

Parameter X 

Transducer 

X=f (L,n) 

Mirror 

Detector 

Detector 

Fibre coil 

Parameter: Rotation 

Mirror 

Mirror 

FOS - 40

Application of Fiber-Optic Interferometers 

• seismic sensors, strain-wave measurement 

• hydrophones and hydrophone arrays, microphones 

• Atomic Force Microscopes (AFM) 

• rotation sensors (gyroscopes) 

• magnetic field sensors 

• electric current sensors (polarization-mode interferometry) 

• fiber grating interferometric strain sensors (extensometers) 

• laser wavelength stabilization 

Examples: 

• high temperature sensor (Fabry-Perot interferometer) 

• seismometer for deep bore-holes (Michelson interferometer) 

• rotation sensor / gyroscope (Sagnac interferometer) 

FOS - 41

Deep Borehole Fiber-Optic Seismometer 

Technical parameters of 

interferometric sensor system: 

max. operational temperature 300 °C 

Fibre lead length >10 km 

Path length resolution < 10 pm/√Hz 

Frequency range 0.1 .. 30 Hz 

Measuring range ± 1mm 

Laser wavelength 1309 nm 

Dimensions ∅ 65 mm 

length 215 mm 

Technical parameters of 

seismic sensor: 

3 components in 54° geometry 

max. operational temperature 260°C 

Eigen resonance 2.5Hz 

Attenuation 0.5 

from DFB laser 

Polyimide coated 

single mode 

optical fibre 

Splice 

Collimator 

f = 6.3 mm 

Frame 

Damper 

Pivot 

54.7° 

Feder 

(Hochtempera 

aus de 

Seismische 

Seismic 

mass Masse 

High Hochtemperatur- 

temperature 

spring 

to photo detector 

Single mode fibre-optic 

coupler 50:50 

(IPHT high temperature 

version) 

Fibre end-face, 

8° angled 

90° prism 

Reflector 

sphere 

Reflektor ø 

Hebelarm 

Cantilever 

FOS - 42

Scheme of Fiber-Optic 3-Axes 

Seismic Sensor System 

Monochromatic interferometry using wavelength modulation: 

FOS - 43

Seismic Deep Borehole Sensor System - 

Photograph 

3 axes in 54° geometry 

FOS - 44

Seismic Sensing: Measurement Example 

Measurement of Iran earthquake May 10, 1997 (Mb = 7.1) 

seismic measuring station Moxa/Germany 

Seismic movement [µm/s] 

Time [08:04 GMT + sec] 

FOS - 45

Fiber-Optic Hydrophone 

(Michelson-Interferometer) 

Naval Research Laboratory, Washington DC, USA 

FOS - 46

Measurand: 

Extrinsic Fiber-Optic 

Fabry-Perot Interferometer 

Width of air gap, which changes with strain and/or temperature 

FOS - 47

Fiber-Optic Temperature Sensor 

(Fabry-Perot Interferometer) 

Basic 

scheme, example of temperature sensor for high temperatures ≥2000 °C: 

FOS - 48

Fiber-Optic Sagnac Interferometer 

Gyroscope (Principle) 

δϕ s = 8πAN Ω / (λc) 

A – Area of fibre coil 

N – Number of fibre windings 

Ω – Angular velocity 

c – Light velocity 

Example: 

N = 800, R =10 cm (L = 500 m) 

λ = 0,8 µm, Ω =1°/h 

δϕ s = 13 µrad 

FOS - 49

Block Scheme of Fiber-Optic Gyroscope 

FOS - 50

Bias stability < 1 °/h 

Noise < 10 °/h/√Hz 

Range ± 200 °/s 

Scale factor error 

< 400 ppm 

Parameters of Fiber-Optic Gyro 

Teldix MKF4 (1993) 

Dimensions 100x70x80 mm³ 

Operational temperature 

-30..70 °C 

FOS - 51

1975 

1985 

1995 

2005 

Time Scale of Development of 

Fiber-Optic Gyroscopes 

First publication 

Lab proto @ 0.01 º/hr 

First commercial applications 

(Boeing 777) 

Broader Applications: 

(Subsea, automotive, etc) 

Photo: KVH Industries 

FOS - 52

Polarimetrischer Stromsensor 

(Magnetooptischer Effekt) 

FOS - 53


• Distributed Raman & Brillouin / OTDR 

fiber sensor systems 

FOS - 54

Distributed Fiber-Optic Sensor Systems 

• Principle: Optical Time Domain Reflectometry (OTDR) 

• Useable optical scattering processes: 

– RAMAN scattering R(T)=I a /I s =(λ s /λ a ) 4 exp(-hν/kT) → temperature 

– BRILLOUIN scattering ν B =2 n v A /λ → temperature, strain 

Local resolution: ∆L=c ∆t/2n ∆L=1m →∆t=10ns 

c – vacuum light velocity, n=1.5 (silica refractive index) 

Scattering spectrum of Ge-doped silica 

fiber (schematically) 

Raman scattering 

(Antistokes) 

≈ 

∆λ R ≈40nm 

(≈13THz) 

≈ 

Rayleigh scattering 

Brillouin scattering 

≈ 

ν B ≈12GHz 

Raman scattering 

(Stokes) 

λ 

FOS - 55

Distributed Fiber-Optic 

RAMAN Temperature Sensor Systems 

Scheme: Applications: 

Power cables with integrated fiber: 

Temperature distribution (hot-spot detection) 

Technical parameters (typical values) 

• Measurement range: 4…10 km (up to 30 km) 

• Local resolution: 1 m (0.3 .. 5 m) 

• T-range: -100…+120 (600) °C, resolution ±0.3 .. 3 °C 

• Meas. time: about 10 s (for 4 km and ±1 °C) 

� Geotechnical & Environmental Monitoring 

(GESO GmbH Jena) 

• Leakage detection of pipelines, gas storages 

• Dams, boreholes, dumps, ... 

� Health Monitoring Civil Engineering / Energy 

(LIOS GmbH Cologne) 

• Fire detection in tunnels (Siemens Cerberus) 

• Offshore platforms, pipelines (NKT Denmark) 

• Electric power cables (Felten & Guilleaume) 

Leakage detection pipeline (GESO) 

FOS - 56


• Fiber Bragg Grating (FBG) multiplexed 

sensor networks 

FOS - 57

Fiber Bragg Grating (FBG) 

Sensor and Multiplexing Principle 

Fiber Bragg grating: periodic refractive index structure inscribed in fiber core 

by illumination with UV laser interference pattern 

FBG sensor systems: strain, temperature,…(Wavelength Division Multiplexing) 

Λ 1 

Grating period Λ≈0.3 µm 

Bragg wavelength λB = 2·Λ⋅neff Sensor 1 .. .. Sensor 2 .. 16 

Measurands: 

e.g., temperature T, strain ε, hydrogen c(H 2 ) 

Λ 2 

Broad-band 

input light SLD 

800..850nm 

Reflected light to 

polychromator 

λB1 λB2 FOS - 58

Talbot-Interferometer 

Beam splitter 

UV Excimer laser 

single-pulse shots 

FBG Fabrication: Draw Tower Technology 

Preform material doped 

for high photo-sensitivity 

Sensor specific coating 

(Ormocer, Polyimide ... ) 

6% tensile strength ⇒ long term reliability 

Spectrum 

of sensor 

array: 

Reflectivity [%] 

20 

10 

0 

810 830 850 


870 

FOS - 59

Light 

source 

Spectrometer 

Signal 

processing 

FBG Sensor System (Schematically) 

I(λ) 

R(λ) 

R 

T 

λ B 

λB1 λ λ B2 Bn 

ε 

Temperature sensor: Strain sensor: 

∆T=1 K → ∆λ ~ 10 pm 

Fiber grating array – wavelength multiplexing 

Bragg wavelength: 

= f (T,ε) 

λ B 

λ B 

λ 

ε=∆L/L=10 -6 → ∆λ ~ 1 pm 

FOS - 60

FBG Sensor System: Basic Configuration 

• Broadband light source 800...850nm (LED, SLD) 

• Polychromator: imaging diffractive grating (polymer replicated by embossing) & CCD detector 

• Advantages: high performance & low-cost potential, higher WDM capacity than @ 1550nm 

Source 

spectrum 

820 840 860 880 


Spectrum analyzer 

Polychromator 

Broadband light source 

Superluminescence diode SLD 

Fiber optic 

beam splitter 

CCD array 

Fiber Connector 

(switch) 

Reference 

wavelength 

Reflection spectrum 

of sensor network 

825 830 835 840 845 850 


FBG1 

FBG2 

FBG3 

FBG4 

FBG5 

Sensor array attached 

to measuring object 

FOS - 61

Ethernet 

PC 

FBG Sensor System (IPHT Jena) 

805..860 nm SLD broad-band 

light source 

Polychromator 

New compact fast FBG sensor system: 

• CCD processing with ADSP SHARC 

• SLD illumination control 

• 32 sensors, 1000 meas./s 

• All FBG sensors are sampled simultaneously 

• Gauss correlation, Kalman filter 

• Strain 1σ repeatability 0.1 µε 

9V/0.5A 

Fiber-optic connectors 

to sensor lines 

Sensor 1.. 

Sensor ..16 

200×130 

FOS - 62

Optical Fiber Grating Sensor Systems: 

Performance Parameters 

Polychromator & optoelectronics (SPU): 

• Spectral resolution 27pm / CCD pixel @ 800...850 nm wavelength range 

• FBG peak (centroid) position resolution ±0.3 pm (automatic peak search & fitting) 

• Long-term wavelength stability < 5 pm @ -20...+70 °C, DSP control 

• Measuring time typically 1ms for FBG array (15 sensors) 

Quasi-static strain measurement (1kHz bandwidth): 

• Measurement range (typically) –1000...+3000 µm/m, max. >1% 

• Resolution < 1 µm/m, repeatability (accuracy) 7 µm/m 

Dynamic strain / vibration measurement ( 1MHz bandwidth): 

• Measurement range ±1800 µm/m, max. 0.5% 

• Resolution 5 nano-strain / Hz 1/2 

Temperature measurement: 

• Measurement range –50...+250 °C 

• Resolution 0.1 K, accuracy 0.5 K 

FOS - 63


• Applications 

FOS - 64

Einsatzbeispiele faseroptischer Sensoren (I) 

Industrielle Prozesskontrolle und Fertigungstechnik 

- Faseroptische Lichtschranken, Positions- und Näherungssensoren In der Automatisierungstechnik 

Flexibilität, geringer Platzbedarf, störsichere Datenübertragung, passive Vernetzbarkeit 

- Füllstands-, Druck-, Durchfluss-, Trübungs-, Feuchte- und refraktometrische Sensoren in der chemischen 

Industrie u.a. Bereichen 

- Interferometrische Weg- bzw. Dehnungssensoren in der Präzisionsfertigung 

Luft- und Raumfahrttechnik 

- Faserkreisel für Navigations- und Lagestabilisierungssysteme (erfolgreiche Tests in Flugzeugen und 

Weltraumraketen) 

- Erprobung verschiedener faseroptischer Sensoren (z.B. Drucküberwachung in Triebwerken) in 

Lichtleiterkontrollsystemen für Flugzeuge, Hubschrauber u.a. ("Fly by Light"-Entwicklungsprogramme) 

Medizintechnik 

- Serienproduktion von faseroptischen Blutgas- sowie Hirn- bzw. Herzdrucksensoren in den USA seit 1990 

(Stückzahlen von mehr als 100.000/Jahr) 

Abbildung unten zeigt den Aufbau eines invasiven Katheters zur Simultan-Messung von pH, p0 2 und pC0 2 in 

Blutgefäßen auf der Basis von Fluoreszenz bzw. Absorptionsänderungen in geeignet sensitiven chemischen 

Indikatormaterialien, die auf der Lichtleiterstirnfläche aufgebracht und mit einer für die nachzuweisenden Stoffe 

durchlässigen Membran umgeben werden: 

FOS - 65

Energietechnik 

Einsatzbeispiele faseroptischer Sensoren (II) 

- Faseroptische Strom- und Spannungssensoren (Faraday-Effekt bzw. Pockels-Effekt) in 

Hochspannungsanlagen, Generatoren, Transformatoren, Schaltern 

- Verteilte faseroptische Temperatursensoren in Starkstromkabeln, Erdöl- und Erdgaspipelines, 

Großtrafos, Kernkraftwerken, Gebäuden u.a. 

- Erprobung faseroptischer Vibrations- und Temperatursensoren in Hochspannungs-Generatoren 

- Verteilte faseroptische Dehnungssensoren in Hochspannungskabeln 

Sicherheitstechnik 

- Überwachung von Großbauwerken wie Kraftwerksanlagen, Brücken, Tunnel, Staudämme u.a. 

mit verteilten faseroptischen Belastungs-, Vlbrations-oder Rissdetektoren 

- Entwicklung komplexer faseroptischer Überwachungssysteme auf Bohrinseln, in Bergwerken 

(z.B. Methangas-Detektion), Kernkraftwerken (z.B. ortsauflösende Kernstrahlungs-Dosimetrie), 

Chemieanlagen und anderen explosionsgefährdeten Bereichen 

- Einbettung von Lichtleitfasern als Sensoren in Verbundwerkstoffe für Flugzeug- und Schiffbau, 

Bauindustrie und andere Bereiche. 

Weitere Einsatzfelder 

- Umweltmesstechnik, Biotechnologie: Chemische und biochemische Fasersensoren, z.B. 

Fernmessung von Schadstoffkonzentrationen in der Luft und im Wasser. 

- Geophysik, Geotechnik: verteilte faseroptische Seismometer & Bohrlochsensoren. 

FOS - 66

FBG Sensor Systems: 

Applications in Structural Health Monitoring 

• Energy 

– Generators, gas turbines (Siemens) 

– Wind turbines (Jenoptik, Enercon) 

• Aviation 

– Airbus (DaimlerChrysler, EADS) 

– Glider (Akaflieg) 

– AirCrane CL-75 prototype (Kayser-Threde, Cargolifter) 

• Space 

– NASA X-38 prototype CRV for ISS (Kayser-Threde,NASA) 

– ESA hydrogen tank monitoring (Kayser-Threde, TU Munich) 

• Transportation 

– Train pantograph/contact line interface (Siemens, SNCF Paris, ..) 

– Contact line inspection gate (Siemens, Furrer+Frey Bern, BLS Bern, ..) 

– Monolithic rigid rail (BAM, Deutsche Bahn) 

• Geotechnical & Civil Engineering 

– Rock-bolts (Ruhrkohle AG, GESO) 

– Tie bars (GESO, GFZ Potsdam) 

FOS - 67

Application of Fiber Grating Sensor Systems 

Power Generators 

FBG sensor arrays for measurement of temperature and strain vibrations in 

electrical power generators (at critical points of stator winding) 

Strain vibrations 

start at short circuit 

impact 

4 FBG vibration 

sensor positions 

FBG 

temperature 

sensors 

Partner: Siemens AG 

FOS - 68


Aircrafts 

CFRP aircraft wing fatigue test: 1 year complete lifetime simulation 

20 FBG strain sensors over full test: strain results correspond to resistive strain gauges 

Strain [µm/m] 

-800 - FEM model 

-1000 - 

-1200 - 

RSG 

FBG 

-1400 - 

0 50 100 150 200 250 

Sensor position 

Surface mounted 

resistive strain gages 

(RSG) and FBG sensors 

Partner: 

RSGs with heavy weight 

electrical cables 

FOS - 69


Spacecrafts 

Strain & temperature sensor network: 4 arrays (sensor pads) with 12 sensors 

• Health monitoring NASA X-38 CRV prototype for ISS 

Partners: IPHT & Kayser-Threde, NASA 


849 

848 

847 

846 

845 

844 

SPU box 

(NASA 

standard) 

-0.36nm=-560µε 

elongated sensor 

compressed sensor 

temperature sensor 

1.27nm =2000µε 

838 

0 5 10 15 20 25 

Time [min] 

FBG sensor pad 

(2 orthogonal strain 

& 1 temp. sensor) 

test measurement 

FOS - 70


Wind Turbines 

Strain monitoring in a blade of wind turbine E112: 

capacity 4.5 MW, blade length 53 m 

6 FBG strain sensor pads inside of blade (push-pull positions): 

FBG-SPU 

WLAN 

FBG strain sensor pads 

length 400 mm 

Partners: Enercon 

Jenoptik 

FOS - 71


Railways 

Test measurements for power distribution 

management: 

Temperature sensor arrays at overhead contact lines 

(OCL) 

(Partners: Siemens & IPHT) 

Test measurements in novel concrete / 

bitumen slab rail track systems: 

Strain sensor arrays embedded in concrete 

(Partners: BAM & IPHT, W. Habel et al. SSM-2002) 

FOS - 72

Force [N] 

600 

400 

200 

0 


Smart Monitoring in Train Systems 

FBG sensors monitoring railway interface 

Pantograph / Overhead Contact Line (OCL) 

Defect at OCL 

10 ms 

Driving direction 

Vertical direction 

0,1 

125 Hz 

0,2 

Time [s] 

0,3 

Current Collector 

Embedded FBG sensors 

monitoring 

strain and temperature 

Impact force measurements using 

"Smart Current Collector" 

FOS - 73

Steel rock-bolt with inclined 

sensors for measurement of 

high strain: 

compressed 

(19°) 

neutral 

(28°) 


Civil Engineering & Tunnels 

stressed FBG 

(40°) 

Rock bolt test 

facility of 

Ruhrkohle AG 

..20% strain 

..500kN 

tensile force 

Partners: 

GESO Jena 

Ruhrkohle AG 

FOS - 74

Rock-bolt with fiberoptic 

strain sensors 

Amplitude [a.u.] 

0,3 

0,2 

0,1 

0,0 

-0,1 

-0,2 


Geotechnical Exploration & Mining 

-0,3 

0 20 40 60 80 100 

Time [ms] 

Strain wave measurement 

at test blasting in a mine 

(seismic tomography for 

geophysical exploration) 

Transversal "S" waves 

Amplitude [a.u.] 

0,8 

0,6 

0,4 

0,2 

Silver Mine 

„Old Elisabeth“ 

(Saxonia, 200m) 

Results: Time response Frequency response 

"P" wave 

0,0 

0 500 1000 1500 2000 2500 

Frequency (Hz) 

Longitudinal "P" wave 

Partners: 

IPHT Jena 

GFZ Potsdam 

GESO Jena 

FOS - 75

Gas turbines 

FBG Sensing at Extreme Temperatures 

Flow & temperature sensing 

up to 1800 K 

EU project HEATTOP 2006-2009 

(partners: Siemens,RollsRoyce,...) 

Stellarator ring 

Strain & displacement sensing in 

superconducting magnets at 4...10 K 

Nuclear fusion reactor project 

(partner: MPI Plasma Physics) 

FOS - 76

FBG Evanescent-Field Chemical Sensing: 

Refractometer 

Analyte 

Evanescent field 

Optional transducer layers 

Temp. reference FBG 

Sensor FBG 

Refractometric process control 

of petrol products: 

Λ 

coating 

Refractometer Bragg wavelength shift: 

Side-polished 

optical fiber 

embedded in 

silica block 

Bragg Wavelength [nm] 

839,0 

838,8 

838,6 

838,4 

838,2 

838,0 

837,8 

Analyte n A 

∆λ B = 2·∆n eff (n A )·Λ 

1,30 1,35 1,40 1,45 

n A H2 O 

Ethanol 

26%NaCl/H 2 O 

OZ91 

OZ98 

SPO 

LMO 

DAO 

FOS - 77

evanescent 

field 

T-reference (FBG) 

Bragg wavelength [nm] 

828,00 

827,96 

827,92 

FBG Chemical and Bio-Sensing 

Bragg wavelength shift: 

∆λB = 2·∆neff (nA )·Λ 

analyte n A 

(gas or fluid) 

transducer layer(s) 

(optional) 

silica block coating 

sensor FBG (grating period Λ ) 

H 2 gas detection (Pd-film 200nm) 

Hydrogen 

concentration 

in Argon gas 

0 % 

1 % 

1 % 

2 % 

0 40 80 120 

time [min] 

single mode fiber 

(side-polished) 

Sensitive thin-film overlays: 

2 % 

Process control of petrol products 


838,23 

838,22 

838,21 

S4 

838,20 

S1 

S2 

S3 

838,19 

1,40 1,41 1,42 1,43 1,44 1,45 

SPR biochemical sensing (Au 30nm) 


831,70 

831,60 

831,50 

831,40 

Partner: IREE Praha 

TE polarization 

TM polarization 

analyte refractive index n A 

TE 

TM 

1,40 1,42 1,44 1,46 

analyte refractive index nA FOS - 78


• Outlook: 

- Biochemical sensing based on nano-fibers and 

- Fiber sensor market development 

FOS - 79

Fiber-Optic Chemical and Bio-Sensor Concepts 

Based on Functionalized Micro/Nano-Structures 

Micro-structured optical fibers 

PCF 

preform 

�Photonic crystal fibers 

�Hollow core fibers 

Integration of wave guiding and capillary 

structures → long interaction length 

�Enhanced analytic sensitivity at small 

sample volumes (gases and liquids) 

�Efficient light - matter interactions 

(absorption, fluorescence, Raman/SERS) 

Optical fiber taper 

2.8 µm 

�Miniaturized instruments for the analysis of 

cells and other microstructures 

�Enhanced evanescent field interactions 

Nanowires 

FOS - 80

absorbance [dBm -1 ] 

Photonic Crystal Fiber (PCF) 

Chemical Sensing 

Increased Evanescent Field Absorption in PCF compared to Silica Fibers 

Standard silica fiber 

2,50 

2,00 

1,50 

1,00 

0,50 

0,00 

absorbance max at 592 nm 

550 570 590 610 630 650 670 690 

wavelength [nm] 

PCF 

Standard EFAS fiber 

Spectral absorbance of Eosin dye solution 

measured in evanescent field of fibers 

permeable polymer 

coating 

∅ core = 200 µm 

α solid fiber < 0,14 dBm -1 

Microstructured PCF 

∅ core = 23.8 µm 

d = 4- 6 µm 

Λ = 6 µm 

α PCF = 2,53 dBm -1 

Sensitivity : PCF as EFA-Sensor → 20 times higher than for 200 µm silica fiber 

FOS - 81

Optical Nanowire Sensing 

Potential of Nanowire Technology for Optical Chemo- and Biosensing 

1. Sensitivity Enhancement of extrinsic 

Optical Fiber Sensors 

• Increasing sensitive surface applying 

disordered nanowires (dense grown 

„matted“ structures) 

• Resonant effects applying oriented 

periodic nanowire structures on fiber 

end-face (e.g. photonic crystals) 

2. Realization of Fiber Nano-sensors with tip 

diameters 10...100 nm 

• Sensibilized single nanowire as optical 

waveguide (evanescent field sensing) 

• Optical coupling to conventional fibers 

Si nanowires 

FOS - 82

FBG Plasmon Biosensing Using 

Metallic Nanoparticles 

DNA receptors 

Sensor FBG, period Λ 

DNA marked 

Au Nano-beads, ∅ 30 nm 

∆λ B = 2·∆n eff(n A)·Λ 

Example: Fiber-optic evanescent field DNA detection 

→ Bragg wavelength shift ∆λ B due to localized surface plasmon 

resonance (SPR) of adsorbed DNA-marked Au nano-beads 

→ high sensitivity, multiplexing capability, intrinsic temperature control 

FOS - 83

Outlook 

Fiber Optics + sub-wavelength Nanostructures : 

→ micro-nano integration + coupling to macro-world 

→ photonic sensing in molecular dimensions with 

ultra-high sensitivity, spatial & temporal resolution 

Intracellular fiber-taper nano-biosensor 

(schematically) 

SiO 2 nanowire on human hair 

(L.Tong/E.Mazur, Zhejiang/Harvard Univ.) 

FOS - 84


Applications, Products and Market Growth 

• Industrial process control and automation 

• Aerospace and transportation 

• Biomedical and environmental monitoring 

• Electric power and chemical oil & gas off-shore industries 

• Civil and geo-technical engineering 

• Military and security applications 

� Products: 

Position & displacement, gyroscopes, blood gas & pressure, 

distributed temperature, strain & vibration, current & voltage, 

organic pollution (BTEX), humidity, flow & level etc. 

� Market: 

800 million US$ in 2008 (civil sector) / 2.5 million sensors, 

growth rate 15% p.a. (up to 25% for strain and chemical sensors) 

FOS - 85

Chemical 

14% 

Source: 

Frost&Sullivan 

World Fiber Optic Sensor Market 

Distribution by Product Type / Measurand (2000) 

Pressure 

9% 

Gyroscope 

14% 

Flow 

7% 

Level 

1% 

Position/Displacement 

33% 

Temperature 

22% 

FOS - 86

Fiber Optic Sensor Market Development 

2002 - 2008 

Source: David A. Krohn, LightWaveVenture 

SPIE Vol. 5589 pp. 34-43 (2004) 

Distributed and 

Multiplexed 

Sensor Systems 

Single Sensors 

FOS - 87

Application Fields & Market Share Forecast 

of Distributed Fiber Optic Sensors 

Sources: Light Wave Venture LLC, USA OIDA 

cited in: Huff D.B., Lebby M.S., "Fiber Optic Sensing Technology: 

Emerging Markets and Trends", Proc. of SPIE, Vol. 6619, p. 661902-1 (2007) 

FOS - 88

n - Fachhochschule Jena

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