SUBJECT:OPTICAL FIBER COMMUNICATIONNAME:PALME MAWAGALI(STUDENT ID:- 13SF03102)SCHOOL:COMPUTER SCIENCE AND TECHNOLOGYTOPIC:OPTICAL FIBER SENSORS

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AGENDA

Introduction OFS Applications OFS Capabilities Advantages Disadvantages Fundamental components Classifications of OFS Challenges Conclusion

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Introduction

• Optical sensor is a transducer which converts any form of a signal to an optical signal in the measurable form.

• Optical fibers: strands of glass that transmit light over long distances (wire in electrical systems)

• Light: transmitted by continuous internal reflections in optical fibers (like electron in electrical systems).

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Optical fiber sensor system

Block Diagram of Optical Fiber Sensor System

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Optical TxOptical fibers

&Actuators

Optical Rx

Control systemData AcquisitionAnd health Assessment

What Does F.O.S. Look Like? (Cont’d)

Strain Gage

Embeddable Strain Gage

Pressure Transducer

Displacement Transducer

Temperature Transducer

What Does F.O.S. Look Like? (Cont’d)

Various Fiber Optic CensorsVarious Fiber Optic CensorsFiber Optic Shape TapeFiber Optic Shape Tape

OFS Applications Measurement of physical properties such as strain,

displacement, temperature, pressure, velocity, and acceleration in structures of any shape or size

Monitoring the physical health of structures in real time Damage detection Used in multifunctional structures, in which a combination

of smart materials, actuators and sensors work together to produce specific action

“Any environmental effect that can be conceived of can be converted to an optical signal to be interpreted,” Eric Udd, Fiber Optic Censors, John Wiley & Sons, Inc., 1991, p.3

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Fiber Optic Sensor Capabilities

• Rotation, acceleration

• Electric and magnetic fields

• Temperature and pressure

• Acoustics and vibration

• Strain, humidity, and viscosity

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Measured Parameters• Light intensity• displacement (position)• pressure• temperature• strain (rotation and displacement)• flow• magnetic and electrical fields• chemical compositions• velocity, acceleration and vibration• force and stress

Advantages of F.O.S

• Lightweight / nonobtrusive

• Passive / low power

• EMI resistant

• High sensitivity and bandwidth

• Environmental ruggedness

• Complementary to telecom / optoelectronics

• Flexible

• Non-flammable10

Disadvantage of fiber optic over copper wire cable

• Optical fiber is more expensive per meter than copper

• Optical fiber can not be join together as easily as copper cable. It requires training and expensive splicing and measurement equipment.

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Fundamental Components

• Optical fiber

• Light sources

• Beam conditioning optics

• Modulators

• Detectors

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Classification Of Fiber Optics Sensor Systems

The above classification of fiber optics sensor system can be explained in following manner:

A.Based on Sensor location

i. Intrinsic

ii. Extrinsic

B.Based on operating Principle.

i.Based on intensity

ii. Based on phase

iii. Based on frequency

iv. Based on polarization

C. According to application

i. Physical sensor

ii. Chemical sensor

iii. Bio-medical sensor13

Based on Sensor location

• INTRINSIC or ACTIVE SENSORS• Physical parameter to be sensed acts directly on

the fibre to produce changes in the transmission characteristics

• Eg. Pressure and liquid level sensors

• EXTRINSIC or PASSIVE SENSORS• Separate sensing element is used and the optical

fibre is a waveguide.• Eg. Displacement and laser Doppler velocimeter

sensors

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Extrinsic Fiber Optic Sensors

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Environmental signal

Input fiber Output fiber

Light modulator

Extrinsic Fiber Optic Sensors

• extrinsic sensors

– a coating or a device at the fiber tip performs the measurement.

Intrinsic Fiber Optic Sensors

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Environmental signal

Optical fiber

Intrinsic Fiber Optic Sensors

• intrinsic sensors

– fiber itself performs the measurement.

Fiber Optic Sensor

PrinciplesThe general structure of an optical fiber sensor system is shown in Figure aside. It consists of an optical source (Laser, LED, Laser diode etc.), optical fiber, sensing or modulator element (which transduces the measurand to an optical signal), an optical detector and processing electronics (oscilloscope, optical spectrum analyzer etc.).

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Classification of FOS

Based on application areas:

• physical sensors (measurement of temperature, strech, etc)

• chemical sensors (measurement of pH content, gas analysis, spectroscopic studies, etc.)

• biomedical sensors (measurement of blood flow , glucose content, etc.)

Optical Fiber Structure

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n (clad)

n (core)

Waveguide axis

Numerical aperture

There are three types of fiber optic cable commonly used

Single Mode

Step-index Multimode fiber

Plastic optic fiber

Fiber media

Optical fibers are the actual media that guides the light

How Does fiber optic transmit light

SNELL’S LAW:

n1 sin = n2 sin where n is refractive index

Optical Fiber

• Guidance is achieved through multiple reflections at the fiber walls.

• Core, transparent dielectric material, surrounded by another dielectric material with a lower refractive index called cladding. (n1 >n2)

• In practice, there is a third protective layer called jacket.

n1n2

1

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Ray Transmission through an Optical Fiber

Critical angle of reflection

(sin c= n2 /n1)

Fiber Optic SensorsBasic Components:

• source of light

• a length of sensing

(and transmission) fiber

• a photo-detector

•demodulator

• processing and display optics

• required electronics

The loss of fiber optic

• Material obsorption

• Material Scattering

• Waveguide scattering

• Fiber bending

• Fiber coupling loss

A Light Sources

LED (Light emitting diode) ILD (injection laser diode)

Detectors

•Detector is the receiving end of a fiber optic link. There are two kinds of Detectors1. PIN (Positive Intrinsic Negative)2. APD (Avalanche photo diodes)

PINAPD

Idea of Modulation

• When sending information by an optical fiber, the information must be encoded or transformed somehow into information that capable of being transmitted through a fiber. The signal needs to be modulated. There are two types of modulation Analog and digital.

Fiber Optic Strain SensorsA. Intensity Modulated Strain Gages

• Reflective sensors– One bundle is used to transmit the light to a reflecting target– Other collects the reflected light and transmits to a detector–Any movement of the target will effect the intensity of the reflected light.

–Plain reflective displacement sensors have a limited dynamic range of about 0.2 in.– Can be improved by a lens system to 5 in.– sensitive to the orientation and contamination of the reflective surface

Fiber Optic Strain Sensors

Fiber Optic Strain SensorsA. Intensity Modulated Strain Gages

• Micro-bend Sensors– If a fiber is bent, a portion of the trapped light is lost through the wall.

Fiber Optic Strain SensorsB. Phase Modulated Strain Gages

• Fabry-Perot Interferometers (FPI)– light source is conveyed via an optical fiber to two mirrors (reflectors).–When the displacement between the mirrors has changed due to strain, optical spectrum changes– absolute distance between the mirrors gives the strain.

Fiber Optic Strain Sensors

–Extremely sensitive

–provides point-sensing capability

–excellent mechanical properties

–output is easy to process

–difficult to make rugged enough for harsh

construction env. (embedding in concrete)

CONCLUSION

There are inherent advantages of fiber optic sensors which include their ability to be light in weight, very compact and small in size. Easy to launch light, low ISI, resistance to electromagnetic interference, high sensitivity, wide bandwidth and environmental ruggedness make them widely used in different fields. All these mentioned characteristics make best use of optical fiber as sensor and the networks which are made up of optical fiber are very advantageous in industry for long time investment areas of media access control, security and privacy.

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End!Thank you listen…

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