4 March 2015

2015 – International Year of Light

By Dr Manas Kumar Haldar

A resolution designating 2015 as the International Year of Light (IYL) was adopted at the 68th session of the United Nations General Assembly in Paris. The resolution was co-sponsored by 35 countries. Meetings and lectures are planned at national and international levels.

We all know, of course, how important light is. Apart from allowing us to see better, especially at night, it is also important in many other aspects, including in our spiritual life. In the old days, calendars were based on lunar sightings and the sun and stars were used for navigation. The object of IYL is not a reminder of these events but rather it is to create awareness of the general public on the importance of optical technologies in their lives. The first use of optical technology that comes to mind is the invention of lenses for correcting eye sights, but optical technology has moved far beyond that.

First, we must discard the view that light is only something that allows us to see objects in the dark. Light is actually what is known as an electromagnetic wave. Frequency represents the number of times per second that a wave vibrates. Visible light occupies a very small range of frequencies of these waves, most light is invisible. Consider, for example, X-rays which your doctor will use for diagnostics, such as bone fractures. X-rays are invisible light with frequencies much higher than frequencies of visible light. Frequencies much lower than those of X-rays but still greater than those of visible light are very useful as well, for example, the light waves that carry information in optical fibres. These waves, called near-infrared light, are not visible. They are produced by semiconductor lasers. Both optical fibres and lasers are fairly recent inventions. The use of lasers is not limited to fibre optic communications. Lasers have been designed for many types of light. They are everywhere. At supermarkets lasers read the price from a barcode. You surely must have used a laser jet printer. If you have made a presentation as a teacher or marketing person you must have used a laser pointer. Have you been to laser light shows? You might have heard too that LED lights will soon replace other types of lights. This is because light bulbs are very wasteful of electrical energy. LED lights require much less electrical power. Their use will help us to reduce burning fossil fuel for electricity generation. But perhaps most importantly, they will reduce your electricity bill.

About 30 years ago, computers with a memory of 1Mb were considered great. A common man could not afford to buy them. Now, one is not content with a 1Gb computer. Media with huge capacities use optical disks with lasers, and the capacity is still growing. What about optical computers? Some signal processing can be done by optical elements. Although optical logic gates have been developed, a digital optical computer is still in the distant horizon.

A very interesting experiment using light for communication in space started last year when NASA launched its OPALS experiment. Currently, deep space missions communicate at 200 to 400 kilobit per second (kb/s). OPALS will study the feasibility using light to communicate at 50 megabit per second (Mb/s). Ultimately, it is hoped that communication from Mars to Earth at one gigabyte per second (Gb/s) will be possible using light.

Radio waves may also be considered light as they are electromagnetic waves. Traditionally, they are not considered to be so because the techniques used at optical frequencies are not often suitable at radio frequency. However, there is a border between radio waves and “light”. This is the region with frequency in terahertz (1 followed by 12 zeros and higher). There is intense research in this area both for communication and imaging. Mankind is yet to make full use of the range of frequencies from terahertz to the visible.

In this article we started first with very high frequency light, X-rays, and went on to consider lower frequencies. Is there any use of light with frequency higher than that of X-rays? Yes, they are called gamma rays. They typically have frequencies around 10 exahertz. This may sound unfamiliar even to those of us who habitually use mega and giga. Exa is 1 followed by 18 zeros. You may have heard of the gamma knife used in neurosurgery. It actually consists of concentrated radiation of gamma rays. Another use of gamma rays is in killing decay-causing bacteria in food. Gamma ray irradiation can also delay the ripening of fruits.

So let us celebrate the International Year of light. In what way can you think of?

Dr Manas Kumar Haldar is Associate Professor with the Faculty of Engineering, Computing and Science at Swinburne University of Technology Sarawak Campus. He is contactable at mhaldar@swinburne.edu.my