Chapter: Fibre Optics· Applied Physics

An optical fibre has a core of refractive index 1.48. It is to be clad so that total internal reflection takes place at the core–cladding interface for a ray with critical angle 80°. What is the refractive index of the cladding?

Q.5 An optical fibre has a core of refractive index 1.48. It is to be clad so that total internal reflection takes place at the core–cladding interface for a ray with critical angle 80°. What is the refractive index of the cladding?

Doubtly AI Asked 27 Oct 2026 AI-generated · not yet verified Practice test mu engineering Save WhatsApp Report

1 answer

Best answer

Answer: \(\mu_2=1.458\) (about 1.46).

At the core–cladding interface the critical angle \(\theta_c\) is given by \(\sin\theta_c=\dfrac{\mu_2}{\mu_1}\).

\[\mu_2=\mu_1\sin\theta_c=1.48\times\sin80^\circ=1.48\times0.9848=1.458\]

A cladding of refractive index 1.458 gives a critical angle of 80°; rays striking the interface at angles larger than 80° are totally internally reflected.

Doubtly AI · 27 Oct 2026 AI-verified · Oct 2026 Report

Was this answer helpful?

An optical fibre has a core of refractive index 1.48. It is to be clad so that total internal reflection takes place at the core–cladding interface for a ray with critical angle 80°. What is the refractive index of the cladding?

1 answer

Your answer