Optical sensors: new solutions for advanced applicationsacademic.sun.ac.za/physics/websites/alc_workshop_2011/... · 2011-11-17 · FM: frequency modulated discriminator board is

4th African Laser Centre Student Workshop4 African Laser Centre Student Workshop

Optical sensors: new solutions for advanced applications pp

Andrea Galtarossa [email protected] of Information EngineeringUniversity of Padova, Italy

Outline

Fiber-Optic Sensor (FOS) System and Communication System: are they so different?

Why to use Fiber Optic Sensors?

FOS applications

FOS Working principle

FOS ClassificationFOS Classificationo With respect to sensing regiono With respect to modulation mechanismp

FOS in Padova: Acoustic Emissions detection

2Andrea Galtarossa, “Optical sensors; new solutions for advanced applications”, November 11th, 2011

Magnetic Fields

Introduction: Optic Communication and Sensor Systems

Source ModulatorFiber OpticCHANNEL

Demodulator Receiver

Optic Communication System

CHANNEL

UNKNOWN Signal Recovered“NOISE” Signal

by“perturbation”

suppressionUnknown

NOISE

suppressionExternal

perturbation Sensor outputby analysis of

KNOWN Signal

y ythe perturbed

signal“Measurand”

Source ModulatorFiber OpticSENSOR

Demodulator Receiver

3

Fiber Optic Sensor System

Andrea Galtarossa, “Optical sensors; new solutions for advanced applications”, November 11th 2011

Why to use FOSs?

High SensitivityHigh SensitivityLarge BandwidthLong term operabilityLong term operabilityRemote operabilityCompatible with multiplexed and distributedCompatible with multiplexed and distributedmeasurementsHarsh environment proof (EMI highHarsh environment proof (EMI, hightemperature and pressure, chemicalcorrosion )corrosion…)Light weight and small size

4Andrea Galtarossa, “Optical sensors; new solutions for advanced applications”, November 11th 2011

FOS Applications

Current applications

Mechanical measurements: force, pressure strain/stresspressure, strain/stress, displacement, temperature, acceleration, vibration, acoustics NASA's Ikhana, ,

Electrical and magnetic

NASA's Ikhana

Measurements

Chemical and biological sensingChemical and biological sensing


FOS Working principle

MEASUREMENTZONE

OPTICAL SOURCE/TRANSMITTER

OPTICAL RECEIVERFOS

Feed fiber R t i fib

ZONE

Feed fiber Returning fiber

spectrum


FOS classification with respect to sensing region

Intrinsic fiber optic sensor has a sensing region within th fib d li ht t f th fibthe fiber and light never goes out of the fiber.

Light inOptical fiber Modulated

Light Outg

Parameterf

Light Out

In extrinsic sensors, light has to leave the fiber and h th i i t id d th b k

of interest

reach the sensing region outside and then comes back to the fiber.

«Light modulator/External transducer»ModulatedLight OutLight in

7

Parameterof interest


Intrisic FOS: an example

Fiber Optic MicrobendPressure Sensor


Extrinsic FOS: an example

Fiber Optic polarization-basedp pPressure Sensor


FOS classification with respect to modulation mechanism

Intensity modulated

Phase modulated( )φω += tEeE cos||ˆ

Wavelength modulated

Polarization modulated


Intensity based FOS

Based on the measurement of the power at the output fiber VersatileSimple design and easy signal interpretationUsually suffers from intensity fluctuations and low sensitivity


Intensity based FOS

Reflection type• Source: broadband• Fiber: multimode is better• P proportional to L• Pout proportional to L• Mainly used as distance or

pressure sensorspressure sensors

Transmission type• Similar to a movable

reflectorreflector• Used as strain or distance

sensors

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sensors


Some examples

Variable reflectance shaft

RotaryEncoder

Input/output fibersDistance

Input light

Detectors

Collection fibersLiquid

13

Liquid LevelPosition


Some examples


Phase modulated FOS

th h f li ht icompare the phase of light in a sensing fiber to a reference fiber in a d i ll d i t f tdevice called interferometer

light is not required to exit the fiber atlight is not required to exit the fiber at the sensor (no optical loss)

l i d imore complex in design

better sensitivity and resolutiony


Phase modulated FOS: Multi-Beam Interferometers

Referencearm

MichelsonMichelsonInterferometer

Perturbation

Referencearm

Mach-ZehnderI t f t

Perturbation

Interferometer

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Perturbation


Some Examples

StrainPressure

a) Sounda) Soundb) Magnetic Fieldc) Electric Field


FOS in Padova: distributed birefriingence

Andrea Galtarossa, “Fiber Optic Sensors: a review", Novembre 2011 18

FOS in Padova: Acoustic Emission Sensor

FIBER OPTIC SENSOR FOR DETECTION OF PRECURSORY ACOUSTIC SIGNALS IN ROCKFALL EVENTSACOUSTIC SIGNALS IN ROCKFALL EVENTS



FIBER OPTIC SENSOR FOR DETECTION OF PRECURSORY ACOUSTIC SIGNALS IN ROCKFALL EVENTSACOUSTIC SIGNALS IN ROCKFALL EVENTS

Requirements and factsAE sensors for hazard assessment of rockfall are required to be:q

very sensitive and fast;with large bandwidth (approx [20-100] kHz);

tibl ith di t ib t d fi ticompatible with distributed configuration;lightning-proof.

The nowadays methodology of AE sensing for hazard assessment of rockfall, based on the use of accelerometers and piezoelectric sensors, lacks some of these requirements.

For this field of application, Fiber Optic Sensor (FOS) technology, based on interferometric approach, can easily overcome the limits of traditional

t l i t f b l t f b t l di t

20

sensors not only in terms of absolute performance, but also regarding cost-effectiveness.



The fiber optic AE sensor under development, is basically a Mach-Zehnder interferometric FOS:

AOM: up-shifts the frequency of the beating around 40 MHz, far from the low-frequency region, dominated by amplitude fluctuations.External perturbation on the fiber coil originates an instantaneous modulation of the optical phase at the output of the sensing arm.FM: frequency modulated discriminator board is used to detect the

21

FM: frequency modulated discriminator board is used to detect the instantaneous frequency shift due to the perturbation.



FOS A FOS B

FOS C

Courtesy of Davide Iannuzzi, Vrije UniversiteitAmsterdam

22

FOS CAmsterdam



Setup

PiezoSource



Tests conducted at the Geophysics Dept. of the University of Padova

24

p y p y



BEFORE

PZTFOS

AFTER


FOS in Padova: Magnetic field measurement

Distributiveness is an unique properties of fiber opticsensors (FOS).

Magnetic field FOSs are studied and exploited sinceseveral decades; yet, distributed magnetic-field FOSsare not available.

Faraday rotation is a polarization effect that can beand is exploited to build magnetic field FOSs.

Polarization sensitive reflectometry (PSR) based onRayleigh scattering is an effective tool for thedistributed characterization of polarization propertiesof fibersof fibers.

PSR can be used to make a Faraday-baseddi t ib t d ti fi ld FOS

26

distributed magnetic field FOS.



THE IDEABackscattered SOP carries information about fiber polarizationinformation about fiber polarization properties (including Faraday rotation).

THE PROBLEMSFaraday rotation in germano-silica We need rather highy gfiber is quite feeble (Verdet constant @1550nm: 0.6 rad/m/T).

We need rather high magnetic fields

W d itAll polarization effects (Faraday, We need quite an accurate theoretical model

All polarization effects (Faraday, temperature, strain, pressure, …) are mixed up by round-trip propagation.

THE GOOD NEWSAmong polarization effects, Faraday rotation is unique in being

27

g p , y q gnonreciprocal.



1Measure the round-trip SOP ;( )Bs z

2Calculate the round-trip birefringence ( )B zβ

3 Calculate the backward Mueller matrix byi t ti th diff ti l ti

4 Calculate the birefringence vector as:

integrating the differential equation:

Calculate the birefringence vector as:

Reciprocal birefringence

Nonreciprocal birefringence(Faraday rotation)

28

( y )



Faraday rotation:

V: Verdet constant

ψ

V: Verdet constantB(z): magnetic induction

For more details: L. Palmieri and A. Galtarossa, “Distributed polarization-sensitive fl t t i i l i l d ti l fib ” J Li ht T h l l 29

29

reflectometry in nonreciprocal single-mode optical fibers”, J. Lightw. Technol., vol. 29, pp. 3178−3184, Nov. 2011.



Effective spatial resolution: 0.5 ÷ 10 cmRelative SOP uncertainty: 1 ÷ 2 %

Distance range: 30 m (potentially up to 500 m)Measured DOP: > 97%Measurement time: 10 ÷ 15 min (90% of which for raw data analysis and transfer)

30

analysis and transfer)





Magnetic resonance imaging scanner

magnetic induction: 1.5 T

32

L. Palmieri, A. Galtarossa, “Fiber optic sensor for distributed measurement of magneto-static fields”, IEEE Sensors 2011



OC

AL

GEN

CE

REC

IPR

OB

IREF

RIN

GB

PRO

CA

LG

ENC

EO

NR

ECIP

IREF

RIN

G

33

NO B





118 points where 2 fibers intersect along different directions118 points where 2 fibers intersect along different directions

9 points where 3 fibers intersect along different directions



Sensitivity ≈ 100 mTestimated from “zero” magnetic induction measurementsestimated from zero magnetic induction measurements

Accuracy ≈ 7%estimated from the “3 fiber” intersectionsestimated from the 3-fiber intersections

Resolution along the fiber ≈ 3 cmd t b t 1 6 l d 2 5 l

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corresponds to about 1.6 cm along x and 2.5 cm along y



Acknowledgements

“Polarization effects in nextgeneration high capacity optical fibergeneration high capacity optical fibersystems”,Bilateral project Italy - South Africa,p j y ,DEI-NMMU (2011-2013)

Thank you for your attention


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Optical sensors: new solutions for advanced applicationsacademic.sun.ac.za/physics/websites/alc_workshop_2011/... · 2011-11-17 · FM: frequency modulated discriminator board is