This paper presents an overview of fiber optic sensor technology.

1. FIBER OPTIC SENSORS

2. 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 interferometric
fiber sensor and the fiber optic gyroscope.

3. 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.

4. Fiber optic sensor
• The fiber optic sensor is illustrated diagrammatically in
Fig.1
Fig.1
A fiber optic sensor is a sensor that uses optical fiber as the
sensing element.

5. 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 sensor
A very simple extrinsic sensor based on light transmission is
shown in Fig.2

6. 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.

7. 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.

8. Two important types of fiber sensors
• a)Mach-Zehnder interferometric sensor-
• A simple construction of Mach-Zehnder
interferometer is given in the fig.4

9. • Mach-Zehnder interferometer is the most
sensitive arrangements for a optic sensor,used
when extreme sensitivity is required.A
collimated 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,the
output from the second mirror enter the two
detectors where they are sense and detected.

10. b) Fiber optic gyroscope-
• A simple fiber optic gyroscope configuration is
given in the Fig.5
Fig.5

11. • 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.

12. 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.

13. REFERENCES
•Fiber optic sensor
http://en.wikipedia.org/wiki/Fiber_optic_sensor
•Mach-Zehnder interferometric sensor
http://en.wikipedia.org/wiki/MachZehnder
_interferometer
•Fiber optic gyroscope
http://en.wikipedia.org/wiki/Fibre_optic_gyroscope