Foundations of fibre optics: In fibre-optic communications, thin glass (or plastic) fibres are used for efficient transmission of light over distance.

Introduction:
The statement addresses the basic idea behind fibre-optic communication: using very pure, thin strands of glass or plastic to guide light signals with low attenuation and high bandwidth. Recognizing why fibres are efficient light guides is essential background for optical systems.

Given Data / Assumptions:

• Fibre consists of a core with refractive index n1 and a cladding with slightly lower index n2.
• Guidance is by total internal reflection when light attempts to exit the higher-index core.
• Typical telecom wavelengths are near 850 nm, 1310 nm, and 1550 nm, where fibre loss is very small.

Concept / Approach:

Efficient transmission arises from two factors: very low material absorption/scattering in the selected wavelength windows, and waveguide confinement by total internal reflection. The numerical aperture determines the acceptance cone, while dispersion engineering (single-mode or graded-index) preserves pulse integrity for high data rates over long distances.

Step-by-Step Solution:

Verification / Alternative check:

Network deployments worldwide (long-haul, metro, FTTH) rely on fibre backbones, confirming practical efficiency and scalability compared with copper for high-capacity links.

Why Other Options Are Wrong:

• False: contradicts the operational reality of global fibre networks.
• Only if the core is metallic: a metallic core would absorb light; optical fibres are dielectric.
• True only for infrared: fibres can guide both visible and infrared; telecom bands are chosen for loss/dispersion reasons.
• Hollow fibres only: hollow-core fibres exist but are specialized; standard fibres are solid glass.

Common Pitfalls:

Confusing guidance with lack of any loss; fibres are efficient, not perfectly lossless. Also, bandwidth is limited by dispersion and nonlinearity, not just by loss.

Final Answer:

True