FIBER OPTIC SENSORS

ABSTRACT

• This paper presents an overview of fiber optic sensor technology ,basic classifications of optic sensors, namely the extrinsic sensors and the intrinsic sensors and their operation principles, also discussed the basic functions of optical fiber sensors . Fiber optic sensing presents unique features that have no match in conventional sensing techniques.This paper also discusses the two important fiber optic sensors , namely the Mach - Zehnder interferometricfiber sensor and the fiber optic gyroscope.

INTRODUCTION

• The field of measurement and instrumentation,and particular sensor development,is one of that,that has expanded rapidly in recent years.The need of high quality sensors to be integrated into measurement and control system is clear.In parallel with rapid advance in the development of sensors based on microelectronics,those based on optical techniques have expanded significantly over last few years.

Fiber optic sensor

• The fiber optic sensor is illustrated diagrammatically in Fig.1

Fig.1A fiber optic sensor is a sensor that uses optical fiber as the sensing element.

The basic components are simple.Light is taken to modulation region using a fiber and modulated there by physical or chemical phenomena,and modulated light is transmitted back to a receiver,detected and demodulated.

1.1(a) Extrinsic fiber optic sensorA very simple extrinsic sensor based on light transmission is

shown in Fig.2

1.1(b) Intrinsic fiber optic sensor

A simple intrinsic fiber optic sensor is shown in Fig.3.

• Extrinsic fiber sensors are the ones where the light signal modulation occurs outside the optical fiber and are delivered by optical fiber,the light transmission depends on the alignment of of fiber cores i.e.,input fiber core and the output fiber core,the light is detected by a light detector.Any deviation of fiber pair from perfect alignment is immediately sensed by the detector.

Fig .3

In intrinsic sensors the physical parameter changes

some characteristic of the propagating light beam that

is sensed,here the optical fiber itself works as

tranducer,only a simple source and a detector is used.

Two important types of fiber sensors

• a)Mach-Zehnder interferometric sensor-

• A simple construction of Mach-Zehnderinterferometer is given in the fig.4

• Mach-Zehnder interferometer is the most sensitive arrangements for a optic sensor,usedwhen extreme sensitivity is required.Acollimated beam is passed through a fiber optic coupler,which splits the beam in two equal amplitudes, the two beams are then passed to second mirror through two arms,theoutput from the second mirror enter the two detectors where they are sense and detected.

b) Fiber optic gyroscope-

• A simple fiber optic gyroscope configuration is given in the Fig.5

Fig.5

• The principle of operation of fiber optic gyroscope is based on sagnac effect.It senses the orientation,performing the function of a mechanical gyroscope.

• Due to sagnac effect,the beam travelling against the rotation experiences a slightly shorter path delay than the other beam,the time taken by the beams are different,this difference in phase shift results in change of intensity which is measured through interferometer.

CONCLUSIONS

• A brief overview of fiber optic sensors and its types are given this paper,also discussed the major two types of optic sensors viz., the Mach-Zehnder interferometric sensor and the fiber optic gyroscope.

REFERENCES

•Fiber optic sensor

http://en.wikipedia.org/wiki/Fiber_optic_sensor

•Mach-Zehnder interferometric sensorhttp://en.wikipedia.org/wiki/MachZehnder

_interferometer

•Fiber optic gyroscopehttp://en.wikipedia.org/wiki/Fibre_optic_gyroscope