Fibre optics and endoscopy

Overview

Total internal reflection, coherent and non-coherent bundles, and the advantages of endoscopy.

What you need to know

Answer each one before you reveal it.

Questions from this subtopic

Each one with the model answer underneath.

1. 1

   At what angle must light strike the core–cladding interface for total internal reflection to occur?

   Model answer

   Light must strike the interface at an angle greater than the critical angle.

2. 2

   What happens to light when total internal reflection occurs at the core–cladding boundary?

   Model answer

   All light is reflected back into the core; none is transmitted into the cladding.

3. 3

   State the formula for calculating the critical angle at the core–cladding interface of an optical fibre.

   Model answer

   sin θc = n_cladding / n_core, where θc is the critical angle, n_cladding is the refractive index of the cladding, and n_core is the refractive index of the core.

4. 4

   What two physical quantities determine the critical angle for total internal reflection in an optical fibre?

   Model answer

   The refractive indices of the core and the cladding.

5. 5

   In an optical fibre, how does the refractive index of the core compare to that of the cladding?

   Model answer

   The core has a higher refractive index than the cladding.

6. 6

   Describe the basic structure of an optical fibre.

   Model answer

   An optical fibre consists of a core surrounded by cladding, both made of glass or plastic with different refractive indices.

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