Optical fibre and the working principles

Optical fibre and the working principles:

Optical fibre is associated with the advanced technology which is used for data transmission that is transmitted by using the light pulses, which travels along the long fibre and is present inside optical fibre. The long fibre is made up of plastic or glass. These optical fibres can be used for either long distance or shorter distance transmission. The optical fibres which are used for shorter distance transmission are known as multi mode fibre while those who are used for long distance transmission are known as single mode fibre. Working principle of optical fibre is total internal reflection, and it consists of a cylindrical dielectric waveguide which is non conducting in nature. The light is transmitted along the axis by using the process of total internal reflection, and the fibre also consists of a core which surrounds by a cladding layer. Both of these components are made up of dielectric materials. (Paschotta, 2018)

Categories of optical fibre and their properties:

SM fibre is the single mode optical fibre which uses only one type of light in propagating the transmission. Single mode Optical Fibre is fine out to be highly beneficial for retaining the fidelity, which helps cover longer distance transmission efficiently. The properties of SM fibre includes that it consists of a small diametral core, and this allows the light to propagate in only one mode. Using this property helps in decreasing the multiple light reflections that are created by the light and other than this it also lowers attenuation and create an ability for the light signal to travel further while covering the long distance. The multi mode step index fibre is used for transferring of light for shorter distances. Different properties are associated with multi mode transmission, and the bandwidth size is lower one with the diameter of 50 to 200 micrometres. (Nagel et al., 2010).

Larger number of modes are associated with it, and it works with entirely different network infrastructure. Multi mode graded index fibre has a refractive index in it decreases with the increase in radial distance in concern to the optical axis of the fibre. The properties of graded index fibre includes that the refractive index decreases from the centre, and it tends to decrease to the core edge with the same value. (Gambling, 2000). This is in the refractive index leads to cause refraction rather than total internal reflection. So, the main property of graded index multimode fibre is that it shows refraction. Also, it has a higher bandwidth with a diameter of core of 50 micrometre. The light in this fibre travels in the form of sinusoidal oscillations or curves, and its performance is relatively better and is of higher cost. (Mirabeta et al., 2004).

Attenuation and dispersion principle in optical fibre:

            Attenuation in optical fibre is defined as the rate at which the intensity of the light decreases. This is the reason that glass is used to cover long distance transmission as glass fibre has relatively lower attenuation.  While on the other hand plastic fibre has the highest attenuation, and it is used to cover transmission for shorter range. Different causes are related to the appearance of attenuation, and the two factors that result in due to this phenomena is absorption and scattering of light. (Rajiv et al., 2009).  This is option phenomenon occurs due to the absorption of light, which results in conversion to the heat molecules present in the glass fibre. The absorber which are present in optical fibre are residual OH+ and dopants this primary absorbers help modify the refractive index of the glass. Different passive components that are involved in attenuation includes cables, cable splices, and the connectors. Attenuation is relatively higher in case of optical fibre as compared to other media. The efficiency of the optical fibre can be measured in the case if it has enough light to overcome the process of attenuation. The occurrence of attenuation in optical fibre leads to cause different losses in that optical fibre which are absorption losses, scattering losses, dispersion loss, radiation loss as well as coupling loss. Other than this, different mechanisms results in the outburst of attenuation mechanism. These mechanisms include spectral attenuation of a silica optical fibre and the attenuation of single mode step index fibre along with the multi mode graded index silica glass fibre. All these mechanisms occurs as a function of wavelength—attenuation results in the loss of the amount of light in comparison between the input and output. In contrast, the total attenuation is measured by the sum of all losses in the process of transmission. (Agarwal, 2010).

Dispersion is another phenomenon which occurs in optical fibre, and it is defined as the spread of light points while travelling down the optical fibre. (Mitschke, 2009). The results of dispersion are that it leads to limit the bad with as well as the information carrying capacity of the fibre. Lack of tolerance of dispersion can lead to cause issues in the light transmission. This is the reason that bit rates in optical fibre are lower in the to make all the pulses for farther apart. The distance in between the pulses lead to cause more excellent dispersion of light that can be tolerated.  There are four types of dispersion present in fibre optics which are model dispersion, material dispersion, waveguide dispersion, and polarization mode dispersion. Dispersion is not responsible for weakening the signal, but other than that it is responsible for blurring the signal. Model dispersion is caused due to different flight modes, and this occurs due to the reason that it has a larger core size. Material dispersion occurs due to the result of the finite line width and shows our dependence on the refractive index of the material which is used. Waveguide dispersion occurs due to the differences in the different wavelengths, and this difference is wavelength leads to different delays. The last one is the polarization mode in which that is pollution occurs in the case if waveguide is birefringent. (Mitschke, 2009).

This is all about the optical fibre principal different types of optical fibre and the attenuation and dispersion involved in the working principle of this fibre.

References:

Paschotta, D., 2018. Areas Of Competence Of RP Photonics: Fiber Optics. [online] Rp photonics.com. Available at: <https://www.rp photonics.com/topics_fibers.html> [Accessed 3 November 2020].

Agrawal, G. (2010). Fibre Optic Communication Systems (4 ed.). Wiley. DOI: 10.1002/9780470918524. ISBN 978 0 470 50511 3. [Accessed 3 November, 2020].

Gambling, W. A. (2000). The Rise and Rise of Optical Fibers . IEEE Journal on Selected Topics in Quantum Electronics. 6 (6): 1084–1093. Bibcode:2000IJSTQ...6.1084G. doi:10.1109/2944.902157. S2CID 23158230.

Mirabito, Michael M. A., and Morgenstern, Barbara L., (2004). The New Communications Technologies: Applications, Policy, and Impact, 5th Edition. Focal Press. (ISBN 0 240 80586 0).

Mitschke F., (2009). Fibre Optics: Physics and Technology, Springer. (ISBN 978 3 642 03702 3)

Nagel, S. R., MacChesney, J. B., Walker, K. L. (2010). An Overview of the Modified Chemical Vapor Deposition (MCVD) Process and Performance . IEEE Journal of Quantum Electronics. 30 (4): 305–322. doi:10.1109/TMTT.1982.1131071. S2CID 33979233.

Rajiv R., Kumar S., Galen S., (2009). Optical Networks: A Practical Perspective. Morgan Kaufmann. ISBN 978 0 08 092072 6.