Total Internal Reflection (TIR) occurs when light travels from a denser medium to a rarer medium and the angle of incidence exceeds the critical angle, causing the light to be completely reflected back into the denser medium.
State the conditions for total internal reflection to take place in optical fiber.
For total internal reflection to occur in an optical fiber:
(i) The refractive index of the core must be greater than that of the cladding.
(ii) The angle of incidence at the core–cladding interface must be greater than the critical angle
\( \left( \theta_c = \sin^{-1}\left(\frac{\mu_2}{\mu_1}\right) \right) \).
Define the terms: (i) Numerical aperture (ii) Angle of acceptance.
Numerical Aperture (NA) is a measure of the light-gathering ability of an optical fiber and is given by
\( \text{NA} = \sqrt{\mu_1^2 - \mu_2^2} \). Angle of Acceptance is the maximum angle at which light can enter the fiber and still undergo total internal reflection.
In what way are the ray paths different in step index and graded index fibers?
In step index fibers, light rays travel in straight-line segments and undergo sharp reflections at the core–cladding interface, resulting in a zigzag path.
In graded index fibers, light rays follow curved paths due to the gradual variation of refractive index, which reduces modal dispersion.
In graded index optical fiber, the refractive index of the core is
Answer: (a) non-uniform
In graded index fibers, the refractive index decreases gradually from the center of the core towards the cladding.
Differentiate between step index and graded index optical fiber.
Step index fiber has a uniform refractive index in the core with a sudden change at the cladding, leading to higher dispersion.
Graded index fiber has a gradually varying refractive index in the core, which reduces dispersion and increases bandwidth.
Why is the refractive index of the core slightly higher than that of the cladding?
The refractive index of the core is kept higher than that of the cladding to ensure total internal reflection, which confines light within the core during propagation.
If \( \mu_1 \) is the refractive index of the core, \( \mu_2 \) that of the cladding, and \( \mu_0 \) of the surrounding medium, when can numerical aperture exceed unity?
Answer: (b) \( \mu_0 > 1 \)
When the surrounding medium has a refractive index greater than unity, the effective numerical aperture can exceed 1.
Write any two major advantages of optical fiber communication.
Optical fiber communication offers high bandwidth for fast data transmission and immunity to electromagnetic interference, ensuring reliable signal quality.
The refractive indices of core (\( \mu_1 \)) and cladding (\( \mu_2 \)) of an optical fiber satisfy the relation
Answer: (a) \( \mu_1 > \mu_2 \)
This condition is necessary to achieve total internal reflection within the optical fiber.