OptoElectronic Instrumentation-Intrusion Sensor

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4/13/12

BORDER SECURITY USINGFIBER OPTICS INTRUSION

SENSOR

SUBMITTED BY –

MITESH GOLCHHA(08BEI044)

VINEET JESWANI08BEI080



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INTRODUCTION

A distributed FOS offers a low cost approach tomonitor the border for intruders.

It monitors long distances by analyzing the

RAYLEIGH Backscattered Signal.

A phase sensitive OTDR senses changes in theoptical phase of the back scattered light.

Intruder in the vicinity of the buried fiber producespressure and seismic waves which produces a

change in the optical path length and detected byOTDR. Monitorin can be extended to hundreds of



4/13/12FIG : Rayleigh backscattered signal with and withoutan intruder



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INTRUSION DETECTION

Light pulses from semiconductor laser areinjected into the fiber and backscatteredlight is detected by a photo detector.

Laser with a narrow line width is necessaryfor OTDR.

Disturbances along the fiber are detectedby comparing the consecutive pulses.

Distance is proportional to the time delay.



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Ø – OTDR SYSTEM

FIG : Block diagram for -OTDR based intrusionφ

detection system.

EDFA = erbium doped fiber amplifierBPF = band pass filter

PBS = polarization beam splitterPD = photo detector



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A highly coherent laser is used to introducepulses of light in the fiber.

The pulse period should be longer than time forthe optical pulse to propagate the length of thefiber and backscattered light to be completelydetected to avoid overlap of data.

Circulator is used for separation of the signals.

PBS is used for optimizing the probability of



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INTRUSION LOCALIZATION

It is possible by knowing the difference inconsecutive pulses.

FIG : Plot showing two consecutive pulses of the backreflected signal, and the difference between them.



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If the speed of the light in the fiber is known,

time differences in the consecutive pulsescan be converted to distance, using relation-

d=(v*t)/2

½ factor is necessary because the pulse must

travel the fiber twice , i.e., to that location,and the Rayleigh backscattered light back tothe detector.



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DATA ACQUISITION AND

PROCESSING

The FPGA is programmed through LabVIEW tohandle data acquisition and processing.

The FPGA constantly acquires data over twochannels at 1.5 MS/sec and processes it inreal-time.

The data is filtered to remove noise and iscompared against a preprogrammed intrusioncriterion.



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The FPGA is programmed to maintain a 10second buffer of data.

When an intrusion criterion is met, intrusion

signal is triggered.

After creating the file, the software resets itself

and waits for another intrusion.

Buffer and recording times are fully adjustable.



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INTRUSION ANALYSIS

The intrusion

file created bythe software asshown in fig.

Contain bothraw andfiltered data

over twochannels.

FIG: An intrusion file triggeredby a single human intruder on

foot.



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For a single intruder in (a), individualfootsteps are clearly identifiable.

For the automobile intruder in (b),there iscontinuous disturbance while it is in the rangeof the buried fiber.

The amplitude of the disturbance isproportional to the distance from the fiber asthe car drives by.



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CONCLUSION

The scalability of real-time signalprocessing is limited by the amount of memory available on the FPGA unit.

This system allows for detection alongthe length of buried optical fiber while

localizing intrusion to a specific point.

The exact location of the intrusion can bedetected without the knowledge of intruder.



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THANK YOU

OptoElectronic Instrumentation-Intrusion Sensor

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