National Seminar on Recent Advances in Multifunctional Metamaterials

17-18 December, 2022

Use of optical fibers for sensing purpose: A theoretical note
Susheel Kumar Singh1, Akash Srivastava2, L.K. Dwivedi3
Department of Physics and Electronics, KNIPSS Sultanpur, Uttar Pradesh, India

Introduction
Fiber optic sensors are modern demand of present research and need of society due to their small size, high sensitivity, cost effectiveness and accuracy. They are taking in use for strain, stress, temperature, displacement, biosamples
measurement in several structures. As no electrical power is needed to operate an optical fiber so at the remote location fiber optic sensor gives advantages to conventional electrical sensor in certain applications, like in too high temperature
a semiconductor sensor is not useful. Similarly, in biosamples analysis where change in refractive index is very low (~𝟏𝟎−𝟕 ) an optical fiber can sense using surface plasmon resonance (SPR) based technique. Likewise, by monitoring the
change in intensity and phase of light with respect to reference signal an optical fiber sensor is applicable in various sensing purpose. Basically, Optical fibers are one kind of medium for illumination purpose that’s why most commonly used as
light guiding medium in medical and other applications where bright light needs to be brought to bear on a target without a clear line-of-sight path, most common example is medical and industrial endoscope. Some other examples of fiber
optic sensor is in bridge monitoring and crack monitoring, like in a bridge or decks or roofs where crack openings beyond 0.15 to 0.2 mm is measure it cause of leakage of water result heavy chance of corrosion of steel or iron, a fiber optic
senor is a good alternative of visual inspection. A fiber Bragg grating based sensor is also useful to make an optical fiber based humidity sensor which is a key tool to observe the variation in the moisture level of concrete. In this paper author
have shown that optical fibers is not only useful for communication purpose but also an extraordinary tool for sensing application and give a review for use of optical fiber for different kind of sensing purposes.

Basic components Basic principal of Surface Plasmon Resonance Characteristics of a Biosensor

optical sensing • Sensitivity
• Precision
(a) • Cost effective
• Utility
• Simplicity
• Reliability
• Reproducibility
• Speed Accuracy
• Stability
• Ease of calibration
Fig. 1 Basic components of a fiber-optical sensor system
➢ optical source (laser, LED, laser diode, etc.) Phase Modulated optical sensor
➢ optical fiber, sensing or modulator element transducing
the measurand to an optical signal
(b) (a)
➢ optical detector processing electronics (oscilloscope,
optical spectrum analyser

(b)

(a)
(c)
Fig.4(a)A fiber-optic Mach–Zehnder interferometer, in which two
3 dB fiber couplers (b) A fiber-optic Michelson interferometer
based sensor

References
[1] Homola J., Piliarik M., Surface Plasmon Resonance Based
(b) Sensors vol. 4, Springer, 2006, pp. 46–47.
[2] Srivastava A. and Prajapati Y. K., “Effect of sulfosalt and
polymers on performance parameter of SPR biosensor,” Optical
and Quantum Electronics, vol. 52, no. 10, (2020)
Fig. 3 (a) fiber-optic SPR sensor probe setup for the detection of human blood groups (b) Sarid, D.: long range surface plasmon wave on thin metal films.
Fig. 2(a) components of optical fiber (b) Total Internal Reflection bonding of antigen- antibody on biorecognition layer(c) SPPs at metal/dielectric interface Phys. Rev. Lett. 47, 1927–1930 (1981)
excited by p-polarized laser beam at incident angles greater than the critical angle for [3] Agarwal, S., Prajapati, Y.K., Maurya, J.B.: ‘Effect of metallic
➢ An optical fiber is composed of core, cladding, and total reflection. adhesion layer thickness on surface roughness for sensing
coating or buffer application’, IEEE Photon. Technol. Lett., 2016, 28, (21), pp. 2415–
➢ Excitation of free electrons takes when excite with P polarized (or TM 2418
➢ The core is a cylindrical rod of dielectric material and is
polarized) incident light under total internal reflection (TIR) condition . [4] Srivastava A., Verma A., Das R., Prajapati Y.K. “A Theoretical
generally made of glass. Light propagates mainly along
➢ This phenomenon gives rise to evanescent wave which is the strongest at Approach to Improve the Performance of SPR Biosensor using
the core of the fiber . MXene and Black Phosphorus”, Optik - International Journal for
metal dielectric interface.
➢ The core is a cylindrical rod of dielectric material and is Light and Electron Optics Vol.203, pp.1-9,2020
➢ The resonance of free electrons (Plasmon) realized in terms of minimum
generally made of glass. Light propagates mainly along [5] H. Khamh, E. Sachet, K. Kelly, J.-P. Maria, and S. Franzen, “As
reflectance where SPR angle reaches to its lowest value of reflection good as gold and better: conducting metal oxide materials for mid-
the core of the fiber
intensity. infrared plasmonic applications,” Journal of Materials Chemistry C,
➢ The cladding executes such functions as decreasing loss
➢ The mathematical expression of surface Plasmon resonance generation is vol. 6(31), pp. 8326–8342, 2018.
of light from core into the surrounding air, decreasing
given in Eq.1. [6] Belay A* and Assefa G “Concentration, Wavelength and
scattering loss at the surface of the core, protecting the Temperature Dependent Refractive Index of Sugar Solutions and
fiber from absorbing the surface contaminants and 𝒌𝒐 𝒏𝒑𝒓𝒊𝒔𝒎 𝒔𝒊𝒏𝜽𝒔𝒑𝒓 = 𝑹𝒆{𝒌𝒐 𝜺𝒎 𝜺𝒔 /(𝜺𝒎 + 𝜺𝒔 ) } (1)
Methods of Determination Contents of Sugar in Soft Drink
adding mechanical strength ➢ Where 𝜺𝒎 𝒂𝒏𝒅 𝜺𝒔 the dielectric constants of the metal and the sensing Beverages using Laser Lights” J Laser Opt Photonics, vol. 5(2), 2018
➢ The light-guiding principle along the fiber is based on the are layer respectively, and 𝒌𝟎 = 𝟐𝝅ൗ𝝀𝟎is the wavenumber of the incident [7] Q. G. Gu and Q. L. Zhou, “Preparation of high strength and
“total internal reflection”. light in free space,𝒏𝒑𝒓𝒊𝒔𝒎 is refractive index of dielectric material (prism). optically transparent silicone rubber,” European Polymer Journal,
vol. 34, no. 11, pp. 1727–1733, 1998.