Fibre Optics
- What is the critical angle and when does total internal reflection of light take place? In one line The critical angle is the angle of incidence in the denser medium for which the refracted ray just grazes the boundary, and for... 1
- How does light propagate through an optical fibre by total internal reflection? In one line An optical fibre guides light because its core has a higher refractive index than its cladding, so light entering within the acc... 1
- What are the acceptance angle and acceptance cone of an optical fibre? In one line The acceptance angle is the maximum angle to the fibre axis at which light can enter the fibre and still be guided by total inte... 1
- What is the numerical aperture of an optical fibre and how is its formula derived? In one line Numerical aperture (NA) is the sine of the acceptance angle (times the index of the outside medium) and measures how much light... 1
- What is the difference between single-mode and multimode optical fibres? In one line A single-mode fibre has a very thin core that lets only one path (mode) of light travel, while a multimode fibre has a thicker c... 1
- How do step-index and graded-index optical fibres differ in structure and light travel? In one line In a step-index fibre the core has one uniform refractive index that drops suddenly at the cladding, while in a graded-index fib... 1
- What is attenuation in an optical fibre and how is the attenuation coefficient calculated? In one line Attenuation is the gradual loss of optical power as light travels along a fibre, and the attenuation coefficient gives this loss... 1
- What factors cause attenuation or signal loss in an optical fibre? In one line Attenuation in fibres is caused mainly by absorption, scattering and bending losses, plus losses at joints and connectors. Expla... 1
- What are the main blocks of a fibre optic communication system and what does each do? In one line A fibre optic communication system converts an electrical signal into light at the transmitter, sends it through an optical fibr... 1
- Why is optical fibre communication better than copper cable communication? In one line Optical fibres carry far more information over longer distances with lower loss and no electrical interference, while being ligh... 1
- The refractive indices of core and cladding materials of a step index fibre are 1.48 and 1.45 respectively. Calculate (1) Numerical Aperture, (2) acceptance angle, (3) the critical angle at the core cladding interface, (4) fractional refractive indic… Given: n₁=1.48 , n₂=1.45 , n₀=1 (air). (1) Numerical aperture: NA=√(n₁²-n₂²)=√(2.1904-2.1025)=√(0.0879)=0.2965 (2) Acceptance angle: θ_a=sin... 1
- Define the terms: Critical angle, Acceptance angle and Attenuation. Critical angle ( θ_c ): The angle of incidence in the denser medium (the core) at the core–cladding interface for which the angle of refract... 1
- Derive an expression for numerical aperture of a step index optical fibre. Give its physical significance. Set-up: A step-index fibre has a core of index n₁ and a cladding of index n₂ ( n₁>n₂ ). Light enters the core from a medium of index n₀ (air... 1
- An optical fiber of core refractive index of 1.50 is to be clad to ensure that TIR will take place for a light ray with critical angle 85°. What minimum refractive index is allowed for cladding? Given: n₁=1.50 , θ_c=85^° . Formula: sinθ_c=n₂/n₁⇒ n₂=n₁sinθ_c n₂=1.50×sin85^°=1.50×0.9962=1.494 Refractive index of cladding n₂≈1.494 This... 1
- Derive an expression for acceptance angle of a step index optical fiber. Set-up: A step-index fibre has a core of index n₁ and a cladding of index n₂ ( n₁>n₂ ). Light enters the core from a medium of index n₀ (air... 1
- Explain the following terms in optical fiber: a) Total internal reflection b) Critical angle c) Acceptance angle d) Attenuation e) Numerical aperture. a) Total internal reflection (TIR): When light travels from a denser medium (core, n₁ ) to a rarer one (cladding, n₂<n₁ ) at an angle of inc... 1
- An optical fiber has an acceptance angle of 30° and core refractive index of [value not printed in the source paper] calculate refractive index of cladding? Note: The core index is missing from the printed paper. As the paper allows, we assume n₁=1.5 (a typical glass core) and take the fibre to b... 1
- Derive an expression for numerical aperture of a step index optical fiber. Set-up: A step-index fibre has a core of index n₁ and a cladding of index n₂ ( n₁>n₂ ). Light enters the core from a medium of index n₀ (air... 1
- Compare Step Index fiber and Graded Index Fiber. PointStep-index fibreGraded-index fibre Index profileCore index n₁ is constant and drops abruptly (in a step) to n₂ at the claddingCore inde... 1