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A spool of optical fibre glows green on a laboratory optical bench.
WonderFact

Fibre-optic cables carry data as pulses of light through strands of very pure glass about as thin as a human hair. Bundled into cables, these fibres run under streets and across ocean floors, carrying calls, videos and payments between continents.

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Light stays inside the fibre because of total internal reflection: when it meets the boundary with the surrounding layer of glass at a shallow angle, it bounces back in instead of escaping. In 1966 Charles Kao and George Hockham, working in England, argued that glass made pure enough could carry light over long distances; Kao later won the 2009 Nobel Prize in Physics. In 1970 the Corning glass company made the first fibre clear enough to be practical. The first transatlantic fibre-optic cable, TAT-8, began working in 1988. A single fibre carries far more data than a copper wire and loses less signal over distance. Today most of the data that crosses oceans travels through undersea cables rather than satellites, and repair ships stand ready for when fishing gear, anchors or earthquakes break them.

Türkçe oku
Fiber optik kablolar veriyi, insan saçı kadar ince ve çok saf camdan yapılmış liflerin içinde ışık darbeleri hâlinde taşır. Kablolarda bir araya getirilen bu lifler sokakların altından ve okyanus tabanlarından geçerek telefon görüşmelerini, videoları ve ödemeleri kıtadan kıtaya ulaştırır.

Işık, lifin içinde tam iç yansıma sayesinde kalır: Lifi saran dış cam katmanın sınırına yatık bir açıyla çarpınca dışarı kaçmaz, içeri geri yansır. 1966'da İngiltere'de çalışan Charles Kao ile George Hockham, yeterince saf camın ışığı uzun mesafelere taşıyabileceğini öne sürdü; Kao sonradan 2009 Nobel Fizik Ödülü'nü aldı. Kullanılabilecek kadar berrak ilk lifi 1970'te Corning adlı cam şirketi üretti. Atlantik'i aşan ilk fiber optik kablo TAT-8, 1988'de çalışmaya başladı. Tek bir lif, bakır bir telden çok daha fazla veri taşır ve uzun mesafelerde daha az sinyal kaybeder. Bugün okyanusları aşan verinin büyük bölümü uydular yerine deniz altındaki kablolardan geçer. Balıkçı ağları, gemi çapaları ya da depremler bu kabloları kopardığında onarmak için hazır bekleyen gemiler vardır.

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Image details

Erbium-doped telecom fibre illuminated with green laser light in a laboratory, 2012.

“Erbium-doped fiber with green light” — Ximeg, 2012, via Wikimedia Commons. CC BY-SA 3.0.

Image source · CC BY-SA 3.0

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Background reading: Optical fiber
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