simultaneous interrogation of refractive index at various

$: Simultaneous Interrogation of Refractive Index at Various$
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Simultaneous Interrogation of Refractive Index at Various

Temperatures employing a Passive Fiber Optic U-Shaped Sensor

Using a Tunable Light Source

S. Srinivasulu1 & Dr. S. Venkateswara Rao

2

1 Senior Research Fellow (SRF), Department of Physics, JNTUH – College of Engineering

Hyderabad, J N T University Hyderabad, Telangana State, India.

2 Professor of Physics, Department of Physics, JNTUH – College of Engineering Hyderabad, J N T

University Hyderabad, Telangana State, India.

ABSTRACT: Fiber optic sensors have become more popular over the conventional sensors like

mechanical sensors, chemical sensors, electrical sensors and bio-medical sensors etc, due to their

advantages with reference to sensitivity, size, weight, cost, safety and security, reliability, longevity

and flexibility in implementation and so on and so forth, for the last three and half decades since their

inception around 1970. An advanced sensor for detecting changes in chemical parameters comprises

a sensing U-shaped glass rod as core surrounded by a sensitive cladding, the absorption coefficient

which various due to the changes in chemical parameters, when applied as the cladding and a pair of

two transmissive optical fibers having a core surrounded by an insensitive cladding for connecting to

a remote light source and a detector. The changes in the output optical power with respect to the

changes in the concentration of the liquid cladding i.e. Toluene and tert-Butanol surrounding the U-

shaped glass rod used to determine the refractive index simultaneously at the operating wavelengths

of 630nm, 660nm, 820nm and 850nm, by employing a tunable light source at different temperatures.

Keywords: Different temperatures, Operating wavelengths of 630nm, 660nm, 820nm and 850nm,

Refractive index, tert-Butanol, Toluene, Transmissive optical fibers, U-shaped glass rod.

INTRODUCTION Depending upon the environmental parameters to be sensed, various detecting methods and the

corresponding designs have been employed in the traditional sensing technology to measure

mechanical parameters, chemical parameters, optical parameters, electrical parameters and bio-

medical parameters and so on and so forth. The fiber optic sensors which uses optical techniques are

proved to be superior over the conventional sensors which were introduced in early 1970’s and are

almost replacing the conventional sensors across the globe. With the advent of Lasers in 1960, the

first optical fiber was demonstrated by K. C. Kao and Hockham for communication purpose for long

distance applications. During 1970’s when the optical fiber technology for communication was

developing, it was realized that the light transmission properties of optical fibers were severely

affected by certain internal and certain external perturbations. On the observation of sensitivity of

optical fibers to these internal and external perturbations in transmitting the light, a new thought

began in the scientific community across the world. This has led to the development of the subject of

fiber optic sensors and systems [1].

Sensor can be define “a device which plays the role of converting a change in the magnitude of one

parameter into a change in the magnitude of another different parameter, which can be measured more

conveniently and more accurately [2]. Various advantages of optical fiber sensors which were

attracted intensive R & D effort across the world in the development of a new class of sensors based

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on optical fibers [3]. The initial developmental work of optical fiber sensors had concentrated mainly

on military applications such as undersea applications and gyroscopes for applications in ships,

aircrafts and missiles, fiber optic hydrophones for submarine and undersea applications. According to

conservative estimates, the sale of optical fiber sensors and the growth rates will reach 35% or more

during the coming decades [4].

In the general configuration of intensity modulated fiber optic sensors the measurand is used to

modulate the intensity of light transmitted through the sensors [5]. In fact intensity modulated fiber

optic sensors are most widely studied in the field of optical fiber sensors and are simple in design and

development due to the advantages of the construction and being compatible to multimode fiber optic

technology [6-8]. Various fiber optic sensors have been developed based on the parameters to be

measured, to measure several kinds of environmental parameters like transverse, longitudinal and

angular displacements, deep sea noise levels, pressure variations, surface structure, flow of pulp

suspension, vibrations, etc, reported in the literature [9-24].

The cross-talk fiber optic sensors were developed for the analog measurement of temperature and

refractive indices of liquids [25-27]. The configuration of Y-fiber coupler tip can also be exploited to

construct an optical fiber refractometer [28]. A macro-bend based intensity modulated sensor is

reported for the measurement of temperature [29-33]. A bare tapered multimode fiber has been used

as a refractometer in another configuration [34]. Takeo et al have reported a fiber optic refractometer

in which plastic clad silica (PCS) fiber has been bent into the form of a U-shape by removing plastic

cladding from a section of fiber [35].

EXPERIMENTAL DETAILS

The construction of experimental arrangement consist of a pair of PCS fibers of 200/230μm core and

cladding diameters respectively, a tunable light source of operating wavelengths at 630nm, 660nm,

820nm and 850nm, a light detector of detectability at various wavelengths, a thermometer of dynamic

range from 0oC to 100

oC, an electrical kettle to increase the temperature of the chemical solution and

a special arrangement of ice bath to decrease the temperature of chemical solution to 10oC.

The U-shaped glass rod acting as a core in the sensing zone has the same diameter as that of the core

of the transmissive fiber and the refractive indices of sensitive and insensitive cladding are less than

the refractive indices of cores of both transmissive optical fiber and sensing U-shaped glass rod. The

experiment is carried out in three parts.

PART-I: In the first part of the experimentation two chemicals i.e. 1. Toluene and 2. tert-Butanol

have been used with a view to have various range of concentrations (20ml+0ml, 18ml+2ml,

16ml+4ml, 14ml+6ml, 12ml+8ml, 10ml+10ml, 8ml+12ml, 6ml+14ml, 4ml+16ml,2ml+18ml,

0ml+20ml) of liquids ranging from 1.493nD to 1.382nD at room temperature. Both the liquids have

been taken in different proportions making the total volume 20ml using a two burette system and

employing Automatic Digital Refractometer of modal number RX-7000i (Atago make), the refractive

index of each mixture was determined at different temperature and each liquid is preserved in an air

tight glass bottle.

PART-II: The experimental arrangement of fiber optic U-shaped passive sensor to increase the

temperature of the chemical solution is shown in figure [1].

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Fig.-1: The experimental arrangement of fiber optic U-shaped passive sensor –

Setup to increase the temperature of the chemical solution.

In the second part of the experimentation the U-shaped glass rod is immersed in first mixture (20ml of

Toluene + 0ml of tert-Butanol) and the temperature of the mixture is raised to 60oC in steps of 5

oC

using an electric kettle heater and at each temperature the output power was noted at the operating

wavelength of 630nm. The experiment is repeated by employing the operating wavelengths of 660nm,

820nm and 850nm. Immersing the U-shaped glass rod into different mixtures and employing 630nm,

660nm, 820nm and 850nm source wavelengths, the experiment is repeated by noting down the output

power values at different temperatures.

PART-III: The experimental arrangement of fiber optic U-shaped passive sensor to reduce the

temperature of the chemical solution is shown in figure [2].

Fig.-2: The experimental arrangement of fiber optic U-shaped passive sensor –

Setup to reduce the temperature of the chemical solution.

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In the third part of experimentation the U-shaped glass rod is immersed into the first mixture (20ml of

Toluene + 0ml of tert-Butanol) in the glass beaker and the glass beaker in-turn is placed in the ice bath

for reduction of the temperature. The power is launched from the source operating at the wavelength

of 630nm and power reaching the detector is noted for temperatures ranging from 10oC to 30

oC in

steps of 5oC. The experiment is repeated by employing 660nm, 820nm and 850nm of source

wavelengths. Taking other chemical mixtures one by one the experiment is repeated and the output

powers corresponding to each wavelength at different temperatures were noted down against the

concentration.

Standard chemical properties of Toluene and tert-Butanol

Toluene (C7H8) tert-Butanol (C4H10O)

Structure

Molar Mass (g/mole) 92.141 74.123

Refractive index (n) 1.4967 at 20oC 1.3847 at 20

oC

Density (kg/m3) 0.8697 10

3 at 20

oC 0.7886 10

3 at 20

oC

Color Colorless Colorless

Boiling Point (oC) 110.6

oC 82.3

oC

RESULTS AND DISCUSSION

The light transmission does not suffer any loss during its transmission in the insensitive parts i.e. in

the pair of two PCS fibers, but it does suffers a substantial loss during its transmission along the

sensitive part i.e. along the U-shaped glass rod. The loss happens in the sensing zone is due to two

factors.

1. Due to U-shaped macro bending of the glass rod.

2. Due to the concentration of the liquid mixture.

Depending upon the thickness of the U-shaped glass rod and radius of curvature of U-shaped glass

rod, a fraction of light escapes into the liquid cladding as an evanescent wave. The loss of light

increases as radius of curvature of glass rod decrease and the loss increases as thickness of the rod

decreases. More is the refractive index of the liquid greater is the loss of the output power in the

detector. All the above results have been noted and tabulated for further use in the experimentation

[Tables 1-5].

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Table.1: Mole fraction and concentration of t-Butanol in Toluene + t-Butanol chemical mixture and

Refractive indices of mixtures at various temperatures.

S.

No.

Mole

fraction

of t-

Butanol

Refractive Index at various temperatures

10oC 15oC 20oC 25oC 30oC 35oC 40oC 45oC 50oC 55oC 60oC

1 0.0000 1.50915 1.50591 1.50171 1.49770 1.49325 1.48974 1.48582 1.48293 1.47795 1.47509 1.47102

2 0.0897 1.49411 1.49121 1.48884 1.48582 1.48215 1.47922 1.47588 1.47308 1.46901 1.46528 1.46211

3 0.1815 1.48305 1.48070 1.47721 1.47470 1.47102 1.46870 1.46528 1.46230 1.45905 1.45602 1.45323

4 0.2755 1.47413 1.47172 1.46821 1.46592 1.46211 1.45923 1.45602 1.45382 1.45070 1.44600 1.44282

5 0.3716 1.47413 1.45923 1.45602 1.45523 1.45008 1.44800 1.44402 1.44176 1.4387 1.43548 1.43209

6 0.4701 1.45008 1.44702 1.44441 1.44176 1.43808 1.43548 1.43221 1.42981 1.42603 1.42331 1.42002

7 0.5710 1.43915 1.43692 1.43327 1.43021 1.42712 1.42428 1.42183 1.41821 1.41600 1.41200 1.40798

8 0.6743 1.42603 1.42397 1.42082 1.41707 1.41404 1.41131 1.40821 1.40530 1.40258 1.39973 1.39602

9 0.7802 1.41529 1.41221 1.40930 1.40618 1.40311 1.40054 1.39752 1.39407 1.39112 1.38848 1.38575

10 0.8887 1.40311 1.40054 1.39770 1.39464 1.39112 1.38872 1.38516 1.38273 1.37902 1.3767 1.37376

11 1.0000 1.39407 1.39139 1.38848 1.38598 1.38205 1.37902 1.37561 1.37292 1.36971 1.3663 1.36312


Output power at various temperatures for the operating wavelength of the source 630nm

S.

No.

Mole

fraction of t-

Butanol

Concen-

tration

of t-

Butnaol

Output Power (dBm) at various temperatures


1 0.0000 0% -44.90 -44.53 -44.17 -43.73 -43.33 -42.97 -42.57 -42.27 -41.77 -41.47 -41.10

2 0.0897 10% -43.43 -43.13 -42.83 -42.57 -42.20 -41.80 -41.53 -41.33 -40.93 -40.53 -40.20

3 0.1815 20% -42.33 -42.03 -41.73 -41.43 -41.10 -40.87 -40.53 -40.23 -39.90 -39.57 -39.30

4 0.2755 30% -41.40 -41.13 -40.83 -40.57 -40.20 -39.93 -39.57 -39.33 -39.07 -38.57 -38.27

5 0.3716 40% -41.40 -39.93 -39.57 -39.50 -39.00 -38.80 -38.40 -38.13 -37.87 -37.53 -37.20

6 0.4701 50% -39.00 -38.70 -38.43 -38.13 -37.83 -37.53 -37.23 -36.97 -36.60 -36.33 -36.03

7 0.5710 60% -37.93 -37.73 -37.30 -37.07 -36.70 -36.40 -36.17 -35.83 -35.60 -35.20 -34.83

8 0.6743 70% -36.63 -36.37 -36.07 -35.70 -35.40 -35.13 -34.90 -34.60 -34.27 -33.97 -33.60

9 0.7802 80% -35.53 -35.23 -35.00 -34.63 -34.33 -34.00 -33.70 -33.43 -33.10 -32.83 -32.53

10 0.8887 90% -34.33 -34.00 -33.77 -33.47 -33.10 -32.87 -32.50 -32.27 -31.93 -31.67 -31.33

11 1.0000 100% -33.43 -33.13 -32.83 -32.57 -32.23 -31.93 -31.57 -31.23 -30.97 -30.60 -30.30



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S.

No.

Mole

fraction

of t-

Butanol

Concen-

tration of

t-Butnaol



1 0.0000 0% -45.23 -44.87 -44.47 -44.07 -43.63 -43.27 -42.87 -42.57 -42.03 -41.80 -41.40

2 0.0897 10% -43.73 -43.43 -43.17 -42.87 -42.53 -42.10 -41.87 -41.60 -41.20 -40.83 -40.50

3 0.1815 20% -42.60 -42.30 -42.00 -41.77 -41.40 -41.17 -40.83 -40.53 -40.20 -39.90 -39.63

4 0.2755 30% -41.73 -41.47 -41.13 -40.87 -40.50 -40.23 -39.90 -39.67 -39.37 -38.90 -38.57

5 0.3716 40% -41.73 -40.23 -39.90 -39.83 -39.30 -39.10 -38.70 -38.43 -38.17 -37.83 -37.50

6 0.4701 50% -39.30 -39.00 -38.73 -38.43 -38.10 -37.83 -37.53 -37.27 -36.93 -36.63 -36.30

7 0.5710 60% -38.23 -38.00 -37.63 -37.30 -37.00 -36.70 -36.47 -36.13 -35.93 -35.50 -35.13

8 0.6743 70% -36.93 -36.67 -36.37 -36.00 -35.70 -35.43 -35.23 -34.83 -34.57 -34.27 -33.90

9 0.7802 80% -35.83 -35.53 -35.30 -34.93 -34.63 -34.33 -34.03 -33.67 -33.40 -33.13 -32.87

10 0.8887 90% -34.63 -34.33 -34.07 -33.73 -33.40 -33.17 -32.80 -32.57 -32.20 -31.97 -31.67

11 1.0000 100% -33.67 -33.43 -33.13 -32.90 -32.50 -32.20 -31.87 -31.57 -31.27 -30.90 -30.60



S.

No.

Mole

fraction of

t-Butanol

Concen-

tration

of t-

Butnaol



1 0.0000 0% -46.87 -46.47 -46.17 -45.73 -45.30 -44.93 -44.57 -44.27 -43.77 -43.43 -43.07

2 0.0897 10% -45.53 -45.13 -44.80 -44.57 -44.20 -43.80 -43.50 -43.30 -42.93 -42.47 -42.20

3 0.1815 20% -44.47 -44.00 -43.73 -43.40 -43.07 -42.87 -42.47 -42.23 -41.87 -41.57 -41.30

4 0.2755 30% -43.37 -43.13 -42.80 -42.57 -42.20 -41.93 -41.57 -41.33 -41.07 -40.73 -40.23

5 0.3716 40% -43.37 -41.93 -41.57 -41.50 -41.00 -40.80 -40.37 -40.13 -39.87 -39.50 -39.20

6 0.4701 50% -41.00 -40.70 -40.43 -40.13 -39.80 -39.50 -39.23 -38.97 -38.60 -38.33 -37.90

7 0.5710 60% -39.97 -39.63 -39.30 -39.00 -38.70 -38.40 -38.17 -37.80 -37.60 -37.20 -36.80

8 0.6743 70% -38.73 -38.37 -38.00 -37.70 -37.37 -37.10 -36.87 -36.50 -36.27 -35.93 -35.60

9 0.7802 80% -37.50 -37.23 -37.00 -36.57 -36.33 -36.00 -35.70 -35.37 -35.10 -34.80 -34.53

10 0.8887 90% -36.33 -36.00 -35.73 -35.40 -35.10 -34.83 -34.50 -34.27 -33.90 -33.63 -33.30

11 1.0000 100% -35.37 -35.13 -34.80 -34.57 -34.20 -33.90 -33.53 -33.20 -32.97 -32.57 -32.30



S.

No.

Mole

fraction of

t-Butanol

Concen-

tration

of t-

Butnaol



1 0.0000 0% -47.20 -46.87 -46.43 -46.00 -45.63 -45.23 -44.87 -44.53 -44.03 -43.77 -43.43

2 0.0897 10% -45.73 -45.40 -45.17 -44.87 -44.50 -44.10 -43.83 -43.60 -43.17 -42.80 -42.47

3 0.1815 20% -44.60 -44.33 -44.00 -43.73 -43.43 -43.13 -42.80 -42.50 -42.20 -41.87 -41.60

4 0.2755 30% -43.70 -43.47 -43.10 -42.87 -42.47 -42.23 -41.87 -41.67 -41.27 -40.90 -40.57

5 0.3716 40% -43.70 -42.23 -41.87 -41.80 -41.30 -41.10 -40.70 -40.40 -40.13 -39.83 -39.50

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6 0.4701 50% -41.30 -41.00 -40.73 -40.40 -40.10 -39.83 -39.53 -39.27 -38.93 -38.60 -38.23

7 0.5710 60% -40.20 -39.93 -39.60 -39.30 -39.00 -38.70 -38.47 -38.13 -37.90 -37.50 -37.13

8 0.6743 70% -38.90 -38.67 -38.33 -38.00 -37.70 -37.43 -37.20 -36.83 -36.53 -36.27 -35.87

9 0.7802 80% -37.83 -37.53 -37.30 -36.93 -36.63 -36.30 -36.00 -35.67 -35.40 -35.10 -34.83

10 0.8887 90% -36.63 -36.30 -36.07 -35.70 -35.40 -35.17 -34.80 -34.50 -34.23 -33.97 -33.63

11 1.0000 100% -35.67 -35.43 -35.10 -34.87 -34.47 -34.23 -33.90 -33.57 -33.30 -32.90 -32.60

The mole fraction and concentration of t-Butanol have been determined in the mixture of Toluene + t-

Butanol and graphs are plotted between refractive index verses mole fraction and concentration at

different temperatures and also the dependence of all the three parameters on one another have been

shown graphically [fig. 3-5].

Fig.3: Relation between Mole fraction of

t-Butanol in Toluene + t-Butanol solution

and Refraction index.

Fig.4: Relation between Concentration of t-

Butanol in Toluene + t-Butanol solution and

Refraction index.

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Fig.5 Relation between Mole fraction of t-Butanol in Toluene + t-

Butanol solution, Refraction index and Temperature.

The variation of output power and mole fraction of t-Butanol in Toluene + t-butanol chemical mixture

at different temperature and at different operating wavelengths of source have been shown [fig. 6-9].

Fig.6: Relation between Mole fraction of t-Butanol in

Toluene + t-Butanol solution and Output power for

operating wavelength of the source 630nm.




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The behavior of output power with respect to temperature for different chemical mixtures and for

different wavelengths have been shown graphically in figure [fig. 10-13].

Fig.10: Relation between Temperature and Output

power of Toluene + t-Butanol solution for operating

wavelength of the source 630nm.

Fig.11 Relation between Temperature and Output



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power for of Toluene + t-Butanol solution operating


The depends of output power, refractive index, temperature at the wavelengths of 630nm, 660nm,

820nm and 850nm for different chemical mixtures represented by corresponding refractive indices on

one another have been shown in figures [fig. 14-17].

Fig.14: Relation between Refractive index, Output

Power and Temperature of Toluene + t-Butanol

solution for operating wavelength of the source

630nm.




660nm.

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820nm.




850nm.

CONCLUSION From the above interrogation, it is concluded that as the concentration of Toluene increases in the

binary mixture of Toluene + tert-Butanol, the refractive index of the guiding liquid also increases. It is

also observed that for all the wavelengths i.e. 620nm, 660nm, 820nm & 850nm, with increasing the

refractive index of guiding medium the output power decreases and hence power loss increases. The

graphs showing the variation of output power with the variation of the refractive index and

temperature of the guiding chemical solution can be used as calibration curves to measure the

refractive index of the unknown liquids or chemicals or bio-fluids, etc in the dynamic range of

1.363nD to 1.509nD at the temperatures from 10oC to 60

oC and operated at the wavelengths of 630nm,

633nm, 660nm, 820nm and 850nm. This method is useful in chemical, pharmaceutical, food and

beverage industries, where conventional methods fail to determine the refractive index of liquids at

higher temperatures.

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AUTHORS:

S. SRINIVASULU [M.Sc.(Physics), M.Sc.(Maths), B.Ed., BLISc., CSIR-UGC

NET, LMISCA] UGC–Senior Research Fellow (SRF), Department of Physics,

JNTUH-College of Engineering Hyderabad, Jawaharlal Nehru Technological

University Hyderabad, Telangana State, India. He has published 24 research

papers in reputed International Journals including UGC Recognized Journals and

UGC-CARE approved Scopus and Web of Science Journals. He has received

IARDO-Young Scientist Award for the year 2018, Researcher of the Year–2019,

Active Young Researcher Award and Outstanding Research Scholar Award.

412 | P a g e

Dr. S. VENKATESWARA RAO [M.Sc. (Solid State Physics), Ph.D. (Fiber

Optic Sensors), MISTE, MISCA] Professor and Chairman Board of Studies in

Physics at Jawaharlal Nehru Technological University Hyderabad, Kukatpally,

Hyderabad, Telangana State, India. He has 30 Years of teaching and research

experience in Physics. He has published many research papers in National and

International reputed Journals including UGC Recognized Journals and UGC-

CARE approved Scopus and Web of Science Journals. Prof. S. V. Rao

Received more than 10 International Awards for his Teaching and Research.

simultaneous interrogation of refractive index at various

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