Page 8 - Science Focus (Issue 018)

But it was easier said than done. At that time, that it would not be useful to remove the impurities
there were many practical obstacles of using light for because it is the intrinsic properties of glass which
signal transmission. The main problem was the high make it unsuitable for being the material for light
attenuation rate. As light passes through a medium, its transmission. Fortunately, Prof. Kao did not give up.
intensity is reduced, and hence cannot be transmitted He traveled the globe to promote his idea, and
effectively. Even when the “most transparent” glass at successfully attracted many research groups to enter
that time was used as the medium, the attenuation the field. In addition, Prof. Kao approached many glass
coefficient would have reached 200 decibels per manufacturers and persuaded them to develop the
kilometer (dB/km) [1] – that means, for every kilometer glass that fits the requirements mentioned in the paper.
the light propagates, the intensity would reduce Finally in 1970, Corning successfully manufactured
by 10 times. This makes optical communication the glass with an attenuation coefficient of 17 dB/km,
20
impossible. which allowed Prof. Kao’s hypothesis to be confirmed.
(Corning even reduced the attenuation coefficient to
One of the seminal papers that made Prof. 0.4 dB/km two years later!) After that, the technology
Kao famous was entitled Dielectric-fibre surface matured rapidly. Now, the attenuation coefficient of a
waveguides for optical frequencies, which was co- modern optical fiber can be less than 0.1 dB/km [3], and
authored by Prof. Kao’s colleague, George Hockham. every fiber can transmit a few tens of TB (10 bytes)
12
They postulated that if the attenuation coefficient of of data per second. This enables us to easily obtain a
glass could be reduced to 20 dB/km, long-distance large amount of information.
communication would become possible [2]. Simply
put, if we can make glass that is “clean” enough, The advancement of modern technology enables
light should be able to propagate within it for a long us to communicate instantly and conveniently. This
distance without attenuating too much. Prof. Kao and changed our daily life and shortened the distance
his colleague attributed the high attenuation rate among people – the birth of the Internet, followed by
to the impurities within the glass – iron ions (Fe and the invention of social media and instant messaging
2+
Fe ions). Therefore, if they could purify the glass, they apps. Prof. Kao refused to patent his invention on
3+
should be able to overcome this problem. optical fiber, which in part accelerated its broad
and rapid adoption around the world. If modern
However, the paper in 1966 did not catch the communication technology is a sprawling fire, then
attention of most others. Some groups even thought Prof. Kao must be the initial, indispensable sparks.

sir charles k. kao –

igniting the fire of modern

technology

৷ᎂ { ତ˾߅Ҧٙዴࡡʘ˦