Facts and Figures

Photonics "Did You Know"

A single glass fibre the thickness of a human hair can theoretically carry the equivalent of 300 million simultaneous telephone calls.

Optical fibre is drawn from a large glass preform (approximately 1 metre long and 20 cm in diameter. One preform produces up to 250 km of optical fibre.

If seawater was as transparent as modern optical fibres, we could easily see to the bottom of the Marianas Trench (the deepest point on earth, 10,924 meters below the surface of the Pacific Ocean).

Light channelled down an optical fibre undergoes approximately 6000 "reflections" per meter.

One single optical fibre (1/4 mm diameter) can carry as much information as 30,000 twisted-pair copper cables (1/2 m diameter).

The light used in most optical fibre communications systems is in the infrared part of the spectrum. The common wavelengths are 900nm, 1300nm and 1550nm.

It is anticipated that the worldwide demand for optical fibre this year will exceed 70 million km, about 200 times the distance to the moon.

The compound eye of the Robber fly has thousands of tiny lenses, each with a separate cylindrical light pipe (Rhabdom) which acts as a natural optical fibre to channel light to its receptor cells.

The speed of components used by telecoms networks doubles roughly every 18 months, and the cost per bit of data they transmit halves.

The use of the Internet doubles every 100 days. Time-Warner Telecom in the US has ordered a fibre optic network that will be fast enough to allow everyone in the US and Canada to simultaneously send a one page e-mail across the network - if they really want to.

The DWDM (dense wavelength division multiplexing - method for sending many messages along an optical fibre simultaneously) systems market has grown from US$1.7 billion in1997 to US$10 billion in 2000.

In 1876, Alexander Graham Bell invented the telephone. Only 4 years later he invented the photophone, a device that could transmit speech via a light beam.

Lasers were first invented in 1960, and in their early development were referred to as "a solution looking for a problem".

Although using ideas developed in universities, the first lasers were all invented by people working for industry (eg. Hughes Aircraft, Bell Laboratories).

The first laser, based on a ruby rod, was invented in 1960 by Theodore Maiman at Hughes Aircraft Company. His scientific paper describing the invention was rejected by the leading physics publication at the time (Physical Review Letters), and his subsequent press conference was treated with scepticism.

The familiar helium-neon laser was the first gas laser invented, at Bell Laboratories in 1961. Semiconductor diode lasers, now by far the most common lasers, were invented as early as 1962, but they were unreliable until technical advances in the early 80s dramatically improved their lifetimes.

In 1964, William Bennett invented the argon-ion laser at Yale University. In 2000 his failing eyesight was corrected with retinal surgery using an argon-ion laser.

About 500 million lasers are currently sold worldwide each year, of which 400 million are for data storage (CD and DVD players).

The most powerful ultraviolet laser in the world, (the 60-terawatt Omega, at the Laboratory for Laser Energetics at the University of Rochester, New York) is used to test fusion experiments (the same nuclear energy that powers the sun). In less than a billionth of a second, the laser sends the temperature in a tiny pellet from just a few degrees above absolute zero to nearly 30 million degrees Celsius -- twice as hot as the core of the sun. For this brief period of time the laser power is about 100 times the peak power of the entire U.S. power grid. An even more powerful laser is under construction at the Lawrence Livermore National Laboratory in California.

Laser light can cool a gas of atoms to incredibly low temperatures, only a millionth of a degree above absolute zero.

The smallest laser is an indium-gallium-arsenide semiconductor disk only 2 microns across, and only about 400 atoms thick.

Lasers can commonly have their frequency (ie. colour) selected with a precision of one part in a billion.

The definitions of time and length rely on photonics. The unit of time (second) is based on atomic clocks, which use lasers to probe the structure of caesium atoms. Length is determined by the speed of light (c), and the metre is defined as how far a light beam travels in 1/c seconds.

The speed of light in a vacuum is exactly 299 792 458 meters per second, a fundamental constant of the universe. The vacuum speed of light is always the same regardless of the velocity of the observer.

Light moves at the fastest speed possible in our universe. It can circle the earth eight times in one second! But light does not travel through all substances at the same speed. In normal material the speed is still a reasonable fraction of the vacuum speed, but in recent laboratory experiments, the speed of light was slowed to a halt momentarily, before re-emerging.

The distance from the earth to the moon (about 384,000 km) can be measured to an accuracy of a few mm by timing the round trip of a laser pulse. The light is reflected off mirrors left by Apollo astronauts. The return signal is so weak that only a few photons are detected in each pulse. These experiments are amongst the most accurate scientific experiments ever undertaken, and are used to test Einstein's theory of relativity.

The shortest laser pulse reported is less than 5 femtoseconds (i.e 5 millionths of a billionth of a second) long. In that time, light travels only 1.5 microns, or about 1/20th of the diameter of a human hair. To appreciate how long such a pulse is, consider that 1 fs is to one second as one minute is to the age of the earth. If a laser emitting 1000 such pulses every second was operated continuously for 10,000 years, it would have emitted light for less than 1.6 seconds in total.

The human eye can detect a light intensity as low as 5 photons in 100ms.

The vibrant colours on many butterflies are not due to pigments (ie. biochemistry) but optical diffraction (photonics) caused by the physical structure of the wing surface. An aquatic creature called a sea mouse produces iridescent colours using hairs with arrays of microscopic holes, creating what is known as a photonic band gap. Natural structures such as these are being studied for their application to photonic devices.