Bapak Fiber Optik

First, it was Jagadish Chandra Bose at the turn of the century, who was the first to demonstrate wireless signaling in 1895. Later, he even created a radio wave receiver called the 'coherer' from iron and mercury. Though he showed no interest in patenting it, Bose demonstrated his inventions in Kolkata and London. 

Sir Neville Mott, who won the Nobel Prize for Physics in 1978, in fact commented that Bose had foreseen the 'n' and 'p' type semiconductors, and was 'sixty years ahead of his time.' However, the Nobel Prize in Physics for wireless communication was awarded to Guglielmo Marconi in 1909, 14 years after Bose had demonstrated the possibility. Then came Satyendranath Bose, who sent a paper on the statistics of quanta of light–photons to Albert Einstein. Einstein supported the paper and got it published in Zeitschrift der Physik in 1924, and that in turn gave birth to the now famous Bose-Einstein statistics and the term 'Bosons' for all those elementary particles that follow it.Even though three Nobel Prizes have been awarded for works based on Bose statistics, the originator of the idea was never awarded one. Moving on, G N Ramachandran deserved a Nobel for his work on bio-molecular structures in general and, more particularly, the triple helical structure of collagen. E C George Sudarshan produced pioneering contributions to Quantum Optics and coherence, but his work was ignored, and Roy Glauber was awarded the Physics Nobel in 2005 for the same work.

And so to this week: The press release issued by The Royal Swedish Academy of Sciences on the Nobel Prize for Physics for 2009 says 'one half' of the prize has been awarded to Charles K Kao 'for groundbreaking achievements concerning the transmission of light in fibers for optical communication.' What the Academy omitted to note was that Moga, Punjab-born Narinder Singh Kapany, widely considered the Father of Fibre Optics, and, in this capacity, featured in a 1999 Fortune magazine article on the 'Unsung Heroes of the 20th Century', had far the stronger claim. Charles Kao in a 1996 paper put forward the idea of using glass fibres for communication using light; he tirelessly evangelised it and fully deserves a share of the Prize. However, the fact remains that it was Kapany who first demonstrated successfully that light can be transmitted through bent glass fibres during his doctoral work at the Imperial College of Science in London in the early fifties, and published the findings in a paper in Nature in 1954. Since then, Kapany irelessly developed applications of fibre optics for endoscopy during the fifties and later coined the term Fibre Optics in an article in Scientific American in 1960. His body of work provided the basis for the developments of any and all applications in communications.

In a book published in 2003 by Rupa & Co titled Sand to Silicon: The Amazing Story of Digital Technology, I had written of the respective contributions of Kapany and Kao to the field of Fiber Optics. A relevant excerpt (pages: 154-159): Very few Indians know that an Indian, Narinder Singh Kapany, a pioneer in the field, coined the term (Fibre Optics) in 1960. We will come to his story later on, but before that let us look at what fibre optics is. It all started with queries like: Can we channel light through a curved path, even though we know that light travels in a straight line?' Why is that important? Well, suppose you want to examine an internal organ of the human body for diagnostic or surgical purposes. You would need a flexible pipe carrying light. Similarly, if you want to communicate by using light signals, you cannot send light through the air for long distances; you need a flexible cable carrying light over such distances.'The periscopes we made as class projects when we were in school, using cardboard tubes and pieces of mirror, are actually devices to bend light. Bending light at right angles as in a periscope was simple. Bending light along a smooth curve is not so easy. But it can be done, and that is what is done in optic fibre cables.''For centuries people have built canals or viaducts to direct water for irrigation or domestic use. These channels achieve maximum effect if the walls or embankments do not leak.' 'Similarly, if we have a pipe whose insides are coated with a reflecting material, then photons or waves can be directed along easily without getting absorbed by the wall material.'

'A light wave gets reflected millions of times inside such a pipe (the number depending on the length and diameter of the pipe and the narrowness of the light beam).'

'This creates the biggest problem for pipes carrying light. Even if we can get coatings with 99.99 per cent reflectivity, the tiny 'leakage' of 0.01 per cent on each reflection can result in a near-zero signal after 10,000 reflections.''Here a phenomenon called total internal reflection comes to the rescue. If we send a light beam from water into air, it behaves peculiarly as we increase the angle between the incident ray and the perpendicular.'

'We reach a point when any increase in the angle of incidence results in the light not leaving the water and, instead, getting reflected back entirely. This phenomenon is called total internal reflection.'

'Any surface, however finely polished, absorbs some light, and hence repeated reflections weaken a beam.'

'But total internal reflection is a hundred per cent, which means that if we make a piece of glass as non-absorbent as possible, and if we use total internal reflection, we can carry a beam of light over long distances inside a strand of glass.'

'This is the principle used in fibre optics.'

'The idea is not new. In the 1840s, Swiss physicist Daniel Collandon and French physicist Jacques Babinet showed that light could be guided along jets of water.'

'British physicist John Tyndall popularised the idea further through his public demonstrations in 1854, guiding light in a jet of water flowing from a tank.'

'Since then this method has been commonly used in water fountains. If we keep sources of light that change their colour periodically at the fountainhead, it appears as if differently coloured water is springing out of the fountain.'

'Later many scientists conceived of bent quartz rods carrying light, and even patented some of these inventions. But it took a long time for these ideas to be converted into commercially viable products. One of the main hurdles was the considerable absorption of light inside glass rods.'

'Narinder Singh Kapany recounted to the author, "When I was a high school student at Dehradun in the beautiful foothills of the Himalayas, it occurred to me that light need not travel in a straight line, that it could be bent. I carried the idea to college. Actually it was not an idea but the statement of a problem. When I worked in the ordnance factory in Dehradun after my graduation, I tried using right-angled prisms to bend light.'

'However, when I went to London to study at the Imperial College and started working on my thesis, my advisor, Dr Hopkins, suggested that I try glass cylinders instead of prisms. So I thought of a bundle of thin glass fibres, which could be bent easily. Initially my primary interest was to use them in medical instruments for looking inside the human body. The broad potential of optic fibres did not dawn on me till 1955. It was then that I coined the term fibre optics."'

'Kapany and others were trying to use a glass fibre as a light pipe or, technically speaking, a 'dielectric wave guide'. But drawing a fibre of optical quality, free from impurities, was not an easy job. Kapany went to the Pilkington Glass Company, which manufactured glass fibre for non-optical purposes. For the company, the optical quality of the glass was not important.'

'"I took some optical glass and requested them to draw fiber from that," says Kapany. "I also told them that I was going to use it to transmit light. They were perplexed, but humoured me."'

'A few months later Pilkington sent spools of fibre made of green glass, which is used to make beer bottles. "They had ignored the optical glass I had given them. I spent months making bundles of fibre from what they had supplied and trying to transmit light through them, but no light came out. That was because it was not optical glass. So I had to cut the bundle to short lengths and then use a bright carbon arc source."'

'Kapany was confronted with another problem. A naked glass fibre did not guide the light well. Due to surface defects, more light was leaking out than he had expected. To transmit a large image he would have needed a bundle of fibres containing several hundred strands; but contact between adjacent fibers led to loss of image resolution.'

'Several people then suggested the idea of cladding the fibre. Cladding, when made of glass of a lower refractive index than the core, reduced leakages and also prevented damage to the core. Finally, Kapany was successful; he and Hopkins published the results in 1954 in the British journal Nature.'

'Kapany then migrated to the US and worked further in fibre optics while teaching at Rochester and the Illinois Institute of Technology. In 1960, with the invention of lasers, a new chapter opened in applied physics. From 1955 to 1965 Kapany was the lead author of dozens of technical and popular papers on the subject. His writings spread the gospel of fibre optics, casting him as a pioneer in the field.'

'His popular article on fibre optics in Scientific American in 1960 finally established the new term (fibre optics); the article constitutes a reference point for the subject even today. In November 1999, Fortune magazine published profiles of seven people who have greatly influenced life in the twentieth century but are unsung heroes. Kapany was one of them.'

'If we go back into the history of modern communications involving electrical impulses, we find that Alexander Graham Bell patented an optical telephone system in 1880. He called this a 'photophone'. Bell converted speech into electrical impulses, which he converted into light flashes.'

'A photosensitive receiver converted the signals back into electrical impulses, which were then converted into speech. But the atmosphere does not transmit light as reliably as wires do; there is heavy atmospheric absorption, which can get worse with fog, rain and other impediments.'

'As there were no strong and directional light sources like lasers at that time, optical communications went into hibernation. Bell's earlier invention, the telephone, proved far more practical. If Bell yearned to send signals through the air, far ahead of his time, we cannot blame him; after all, it's such a pain digging and laying cables.'

'In the 1950s, as telephone networks spread, telecommunications engineers sought more transmission bandwidth. Light, as a carrying medium, promised the maximum bandwidth. Naturally, optic fibres attracted attention. But the loss of intensity of the signal was as high as a decibel per metre.'

'This was fine for looking inside the body, but communications operated over much longer distances and could not tolerate losses of more than ten to twenty decibels per kilometre. Now what do decibels have to do with it? Why is signal loss per kilometre measured in decibels?'

'The human ear is sensitive to sound on a logarithmic scale; that is why the decibel scale came into being in audio engineering, in the first place.'

'If a signal gets reduced to half its strength over one kilometre because of absorption, after two kilometres it will become a fourth of its original strength. That is why communication engineers use the decibel scale to describe signal attenuation in cables.'

'In the early 1969s signal loss in glass fiber was one decibel per metre, which meant that after traversing ten metres of the fiber the signal was reduced to a tenth of its original strength.'

'After twenty metres the signal was a mere hundredth its original strength. As you can imagine, after traversing a kilometre no perceptible signal was left.'

'A small team at the Standard Telecommunications Laboratories in the UK was not put off by this drawback. This group was headed by Antoni Karbowiak, and later by a young Shanghai-born engineer, Charles Kao.'

'Kao studied the problem carefully and worked out a proposal for long-distance communications through glass fibres. He presented a paper at a London meeting of the Institution of Electrical Engineers in 1966, pointing out that the optic fibre of those days had an information-carrying capacity of one GHz, or an equivalent of 200 TV channels, or more than 200,000 telephone channels.'

'Although the best available low-loss material then showed a loss of about 1,000 decibels/kilometre (dB/km), he claimed that materials with losses of just 10 to 20 dB/km would eventually be developed.'

'With Kao almost evangelistically promoting the prospects of fibre communications, and the British Post Office (the forerunner to British Telecom) showing interest in developing such a network, laboratories around the world tried to make low-loss fibre. It took four years to reach Kao's goal of 20dB/km.'

'At the Corning Glass Works (now Corning Inc), Robert Maurer, Donald Keck and Peter Schultz used fused silica to achieve the feat. The Corning breakthrough opened the door to fibre-optic communications. In the same year, Bell Labs and a team at the Ioffe Physical Institute in Leningrad (now St Petersburg) made the first semiconductor lasers, able to emit a continuous wave at room temperature.'

'Over the next several years, fibre losses dropped dramatically, aided by improved fabrication methods and by the shift to longer wavelengths where fibers have inherently lower attenuation.'

'Today's fibres are so transparent that if the Pacific Ocean, which is several kilometres deep, were to be made of this glass we could see the ocean bed!'

'Note one point here. The absorption of light in glass depends not only on the chemical composition of the glass but also on the wavelength of light that is transmitted through it. It has been found that there are three windows with very low attenuation: One is around 900 nanometres, the next at 1,300 nm and the last one at 1,550 nm.'

'Once engineers could develop lasers with those wavelengths, they were in business. This happened in the 1970s and 1980s, thanks to Herbert Kroemer's hetero-structures and many hard-working experimentalists.'

The excerpt ends here. While working on this book and particularly this chapter, I had thought that with the world now firmly ensconced in the era of communications, it wouldn't be long before Narinder Kapany's pioneering work in the field was recognised with the Nobel Prize.

Now, two years later, I find that the name of the pioneer of fibre optics has been added to a very long list of Indians who, though richly deserving of the ultimate accolade, the Nobel Prize, have been mysteriously passed over by the august members of the Royal Swedish Academy of Sciences. 

sumber: http://www.rediff.com/news/report/how-india-missed-another-nobel-prize/20091008.htm