Page 6 - Science Focus (Issue 018)

On September 23, 2018, an 84-year-old invention of telegraph, radio and telephone in the
gentleman passed away in Sha Tin, Hong Kong. At that 19th century. Trans-continental communication has
time, you might have mourned his passing, like many become much more convenient, but there were still
others who deeply respected him. Although he is a limitations. It remained challenging to transmit a huge
household name in Hong Kong, do you actually know amount of information through a long distance at
his contribution to our daily life? His research is crucial an affordable price. The scientists in the 20th century
to the modern communication technology so that it placed their hopes on a promising material, glass.
could reach its current height and made our life much
more convenient. This gentleman is the winner of the Fiber optics is a thin fiber which is usually made of
Nobel Prize in Physics 2009, the "Father of Fiber Optics," glass or plastic to conduct light signal. The physical
Prof. Sir Charles K. Kao. principle behind is simple. Light has different refractive
indices when passing through different media. It is
Fiber optics (optical fiber), is a common term. refracted to different extents depending on the angle
But what does it really mean? Why was it such a of incidence (n sin θ = n sin θ ). When light passes
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1
2
1
breakthrough at the time of its development? Let’s from a medium with a higher refractive index to one
start from the very beginning, and consider the history with a lower refractive index, and if the incident angle
of long-distance communication.
is greater than a certain degree (i.e. the critical angle),
If we traveled back in time to a thousand years the light will fully reflect back to the original medium.
ago, it would be very difficult for us to contact our This phenomenon is called "total internal reflection
friends and family who were thousands of miles away. (Figure 1)." Fiber optics harnesses this phenomenon
A famous Chinese poet, Du Fu (712–770), once said – the core of the fiber is made by a medium with a
"a letter from home is worth ten-thousand pieces of higher refractive index and the cladding is composed
gold," which reflects the difficulty for ancient soldiers of another material with a lower refractive index. By
to receive news from their families during a war. By selecting an appropriate angle of incidence, the light
the time a family letter arrived at the battlefield, the that enters the fiber can be confined to the core and
recipient might have already been a casualty of war. “bounces” towards the end of the fiber. Light signal
Thankfully, progress has been made. First, with the can therefore be guided and transmitted.

By Nicole Wu 胡欣蕾