Pareto Academy
Log inStart free
Science & Technology

Optical fibre communication

How glass fibres carry light by total internal reflection, who pioneered them and how India uses them in BharatNet; a common general science and current affairs topic.

Pareto Academy · updated 26 October 2026

At a glance

An optical fibre is a hair-thin strand of very pure glass (or plastic) that carries information as pulses of light. Light stays inside the fibre because of total internal reflection at the boundary between the inner core and the outer cladding. Fibres carry far more data, over longer distances and with less interference, than copper wires, and they form the backbone of the internet and of India's rural broadband network, BharatNet.

Key facts

  • Principle: total internal reflection (TIR)
  • Structure: core (higher refractive index) surrounded by cladding (lower refractive index), with a protective outer coating
  • Conditions for TIR: light must travel from a denser to a rarer medium, and the angle of incidence must exceed the critical angle
  • Critical angle: sin C = n2 / n1 (n1 = denser medium, n2 = rarer medium)
  • "Father of Fibre Optics": Narinder Singh Kapany (born 31 October 1926, Moga, Punjab; died 4 December 2020)
  • Kapany coined the term "fibre optics": in a 1960 article in Scientific American
  • Kapany's Padma Vibhushan: 2021 (posthumous)
  • Nobel link: Charles K. Kao won the 2009 Nobel Prize in Physics for work on light transmission in fibres for optical communication
  • Other uses: endoscopy in medicine, sensors, decorative lighting
  • BharatNet: began in 2011 as the National Optical Fibre Network (NOFN) to connect all gram panchayats

How it works

Total internal reflection. When light in glass strikes the glass–cladding boundary at an angle larger than the critical angle, none of it escapes; it is reflected back into the core. Repeated reflections guide the light along the fibre even when it bends.

Types of fibre.

Type Core Use
Single-mode Very thin; one light path Long-distance, high-speed links (telecom backbones, undersea cables)
Multi-mode Thicker; many light paths Short distances (inside buildings, data centres)

Advantages over copper. Much higher bandwidth, lower signal loss over distance, immunity to electromagnetic interference, lighter cables and harder to tap.

Other examples of TIR. The sparkle of a diamond (very small critical angle, about 24°), mirages in deserts and the shining appearance of an air bubble in water.

BharatNet. Approved in 2011 as NOFN and renamed BharatNet in 2015, it is implemented by Bharat Broadband Network Ltd (BBNL), now merged with BSNL. In August 2023 the Cabinet approved the Amended BharatNet Programme at ₹1,39,579 crore to connect about 2.64 lakh gram panchayats in a ring topology, with BSNL as project management agency. It is funded mainly through the Digital Bharat Nidhi, which replaced the Universal Service Obligation Fund.

Recent developments

  • 25 Oct 2026: In Mann Ki Baat (episode 139), the Prime Minister marked the coming birth centenary of Narinder Singh Kapany (31 October 2026).

Exam traps

  • Optical fibres work by total internal reflection, not by refraction or ordinary reflection from a mirror coating.
  • The core must have a higher refractive index than the cladding.
  • Kapany is the "Father of Fibre Optics"; Charles Kao won the Nobel (2009) for fibre communication. Kapany did not win a Nobel.
  • BharatNet was earlier called NOFN; it is not the same as the National Knowledge Network (NKN), which links research and education institutions.

Quick check

  • Q: On which principle does an optical fibre work? A: Total internal reflection.
  • Q: Who is known as the Father of Fibre Optics? A: Narinder Singh Kapany.
  • Q: What was BharatNet originally called? A: National Optical Fibre Network (NOFN).

Further reading

Sources

In the news

Every time this topic has appeared in our current affairs, newest first:

  1. 26 October 2026Centenary of Narinder Singh Kapany, the "Father of Fibre Optics"