Analysis of the swelling silicone coating on the optical sensor head has been calculated based on the time and length-different due to exposure. In initial state, cladding refractive index (n2) is higher than core refractive index (n1). This situation cause the light that propagate in fiber optic leak to atmosphere. In the exposed state, cladding refractive index will decrease and results in light propagating based on total internal reflection. This situation has been described and calculated from the beginning until the maximum value.

1. Secondary Theoretical Analysis of Swelling
Characteristic of Silicone Coating for Plastic
Optical Fiber Sensor
( SPECTECH Research Group - Internal Seminar
11 November 2011, FKAB Meeting Room)
Harry Ramza, Mohd Hazwan Harun,
Ramza,
Khairul Anuar Ishak, Mohammad Syuhaimi Ab-Rahman
Ishak, Ab-
Spectrum Technology Research Group
Department Electrical, Electronic and System Engineering
Universiti Kebangsaan Malaysia
Bangi,
Bangi, Selangor Darul Ehsan
MALAYSIA
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2. Content
1. Basic FOS.
FOS.
2. Typical Fiber Optical Sensor Mechanism
3. Configuration of Fiber Optical Sensor.
Sensor.
4. Types of Fiber Optical Sensor.
Sensor.
5. Analysis.
Physical Design Analysis.
6. Equations
7. Fiber Probe Properties
8. Analytical Result
9. Conclusion.
Conclusion.
2

3. Basic FOS
FIBER OPTIC SENSOR :
• A sensor that measures a physical quantity based on
its modulation on the intensity, spectrum, phase, or
polarization of light traveling through an optical
fiber.
Advantages :
1. Compact size. 4. Multiplexing
2. Multi functional. 5. Resistant to harsh
3. Remote Accesible. environment.
6. Immunity to electro-
magnetic interference
3

4. Typical Fiber Optical Sensor Mechanism
Transmission Measurement
Photo-detector
Light source Focus Sensing
lens element
Reflection Measurement
Coupler
Light source Focus
lens
Photo-detector
4

5. Configuration of Fiber Optical Sensor
Point sensor: detect Opto-
electronics
measurand variation Sensing
element
only in the vicinity of the Output, M(t)
sensor
Multiplexed sensor: Opto-
Multiple localized sensors are electronics
placed at intervals along the Output, M(t, Z ) i
fiber length.
Distributed sensor: Opto-
electronics
Sensing is distributed along
the length of the fiber Output, M(t,z)
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6. Types of Fiber Optical Sensor
1. Intrinsic:
the effect of the measurand on the
light being transmitted take place in
the fiber
2. Extrinsic:
the fiber carries the light from the
source and to the detector, but the
modulation occurs outside the fiber
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7. Types of Fiber Optical Sensor
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8. Types of Fiber Optical Sensor
Intensity-based: measure physic
Intensity-
measurand based on the intensity of the
light detected through the fiber, e.g. fiber
break, OTDR
Interferometric (phase modulation):
– Fabry-perot Interferometer.
Fabry-
Grating based (wavelength modulation)
– Fiber Bragg Grating (FBG).
– Long Period Fiber Grating (LPFG)
8

9. Intensity-based Optical Fiber Sensor
Intensity-
Advantages:
• Simple signal processing
• Inexpensive measurement instrument
Disadvantages:
• Susceptible to power fluctuation of the light
source
• Susceptible to fiber bending losses
• Variation in modal power distribution in
Multi-mode fiber (MMF).
9

10. Intensity-based Optical Fiber Sensor
Intensity-
Reference: “Split-spectrum intensity-based optical
Reference: “Split- intensity-
fiber sensors for measurement of
microdisplacement, strain, and pressure”, by Anbo
Wang et al.
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11. Physical Design Analysis
Model of refractive index
changes in swelling
silicone rubber coating
11

12. Physical Design Analysis
Extrinsic Fabry-Perot
Fabry-
Interferometer (EFPI)
12

13. Equations
Intensity normalized recipient a Fabry-Perot cavity in
Fabry-
reflection of light
1  cos 
Ir 
1  R  2 R cos 
2
where R is power reflectivity of interface on core and cladding
index
I r  1  cos 
Error In Determining Phase Difference:
Difference:
4 nclad L
 

13

14. Equations
The maximum error is influenced by phase difference at
2(m+1
2(m+1/2), where m is an integer. While minimum
integer.
error occurs in the range of /2 at q-point .
Fabry-perot
Fabry-
Interferometer
and two beam
approximation
14

15. Equations
Light reflection R and transmission T:
reflection
R1 and R2 can be obtained from the calculation of
equation:
15

16. Fiber Probe Properties
Model of refractive index changes
in swelling silicone rubber layer
the equation for ammonia concentration on x-position from the
x-
surface
16

17. Fiber Probe Properties
the initial state of and
the equation for ammonia concentration on x-position
x-
from the surface is given
17

18. Fiber Probe Properties
1.E+07
1.E+06
1.E+05
1.E+04
Absorption Coeffcient (/cm)
1.E+03
1.E+02
1.E+01
1.E+00
1.E-01
1.E-02
1.E-03
1.E-04
1.E-05
1.E-06
1.E-07
1.E-08
200 300 400 500 600 700 800 900 1000 1100 1200 1300 1400
Wavelength (nm)
Absorption Coefficient of Silicone
18

19. Analytical Result
Reflectivity of
light beam on
refractive index
differences
Silicone
19

20. Analytical Result
REFPI and EFPI
normalization
intensity of
receiver result
with differences
silicone
refractive index
20

21. Analytical Result
A B
The function of vapor concentration (a) Ammonia vapor concentration based on
variation of cladding thickness; (b) Ammonia vapor concentration based on
exposure time
21

22. Analytical Result
Ammonia
vapor
concentration
based on long
exposure time
22

23. Conclusion
The results shows that deadband of ammonia vapor
ead
detection is 0 s/mm2 until 3.3 s/mm2 where the responsivity
determined by using
and the response time could reach 10 seconds. In sensor
seconds
structure, the fiber was straightened and consumes low air
pressure in test container to enhance measurement
response rate. The test container has to be free from
rate.
contamination of vessel reaction to tested steam. Small
steam.
differences level will occur in long-duration response.
long- response.
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24. Thanks for your attention,,,,,
Wassalam…..
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