Optical Fibre: Lecture Notes and Exercises for Engineering Physics, Summaries of Physics

Download Optical Fibre: Lecture Notes and Exercises for Engineering Physics and more Summaries Physics in PDF only on Docsity!

Jaipur Engineering College and Research Center

• Year & Sem. – B. Tech. I-Year, Semester - I
• Subject – Engineering Physics ( 1 FY 2 - 02 )
• Chapter - Optical Fibre
• Department - Applied Science

Vision and Mission

• Vision: ➢ To become a renowned centre of outcome based learning, and work towards academic, professional, cultural and social enrichment of the lives of individuals and communities.
• Mission: ➢ Focus on evaluation of learning outcomes and motivate students to inculcate research aptitude by project based learning. ➢ Identify, based on informed perception of Indian, regional and global needs, the areas of focus and provide platform to gain knowledge and solutions. ➢ Offer opportunities for interaction between academia and industry. ➢ Develop human potential to its fullest extent so that intellectually capable and imaginatively gifted leaders may emerge.

Lecture Plan of Coherence and Optical Fibre

S. No Topics

Lectures

required

Lect.

No.

Definition of Coherence, spatial &

temporal coherence, Coherence

length & Coherent time

Q - factor for light (spectral purity),

Visibility as measures of Coherence

Optical fibers as optical wave guide,

Types of fibres & working principle.

Numerical aperture of step index

fiber, maximum angle of acceptance

and it’s application.

Content

• Introduction
• Working Principle
• Structures of Fibre Cable
• Classification
• Numerical Aperture and Maximum angle of acceptance
• Applications
• Suggested reference books & links from NPTEL/IIT/RTU Platforms
• Important Questions.

Plan of Presentation

Working Principle: TIR

➢ When an ray of light travels from a denser to a rarer medium

such that the angle of incidence is greater than the critical angle,

the ray reflects back into the same medium this phenomena is

called total internal reflection (TIR).

➢ When light enters from one end of fibre, it undergoes successive

total internal reflection from side walls and travels down the

length of the fibre along a zig-zag path.

Structure of optical fibre

Single Fibre Cable

Multi Fibre Cable

Multi Fibre Cable

• Multi fibre cable consists of a number of fibres in a single jacket. Each fibre carries light independently.
• The cross sectional view of a typical telecommunication cable is shown in figure.
• It contains six insulated optical fibre stand consists of a core surrounded by a cladding which is coated with insulated jacket.
• The fibres are individually buffered and strengthened.
• Six insulated copper wires are distributed in the space between the fibres.
• They are used for electrical transmission.
• The assembly is then fitted with in a corrugated aluminium sheath.
• A polythene jacket is applied over the top for protection.

Single Mode Fibre(SMF)

• In single mode fibre only one mode can propagate through the fibre.
• It has small core diameter (5um) and high cladding diameter (70um).
• Difference between the refractive index of core and cladding is very small.
• There is neither dispersion nor degradation therefore it is suitable for long distance communication.
• The light is passed through the single mode fibre through laser diode.

Multi- Mode Fibre (MMF)

• It allows a large number of modes for light ray travelling through it.
• The diameter of core is 40 μm and of cladding is 70 μm.
• The relative refractive index difference is also large than single mode fiber.
• There is signal degradation due to multimode dispersion.
• It is not suitable for long distance communication due to large dispersion and attenuation of signal.

Step Index fiber

• Step index fiber is a fiber characterized by a uniform refractive index within the core and a sharp decrease in refractive index at the core-cladding interface so that the cladding is of a lower refractive index.
• In a step index fiber, the light rays propagate in zig-zag manner inside the core. The rays travel in the fiber as meridional rays and they cross the fiber axis for every reflection.
• Step index fiber is found in two types, that is mono mode fiber and multi mode fiber.
• Signal distortion is more in case of high-angle rays in multimode step index fiber.
• In single mode step index fiber, there is no distortion. The Step index fiber has a lower bandwidth.

Graded Index Fibre

• Graded index fiber is a type of optical fiber where the refractive index of the core is uniform at the center core and then it decreases towards core- cladding interface.
• The uniformity is present because the refractive index is higher at the axis of the core and continuously reduces with the radial movement away from the axis.
• However, the refractive index of the cladding is constant in the case of graded index fiber, hence the nature of the refractive index is somehow parabolic.
• The light rays in graded index fiber, propagate in the form of skew rays or helical rays. They will not cross the fiber axis. Also, it is important to note that inside the fiber, signal distortion is very low even though the rays travel with different speeds. The graded index fiber has a higher bandwidth.