Giant Fiber Lasers For Secure Communication

Physicists at Tel Aviv University and the California Institute of Technology propose spanning the distance between two people (call them Alice and Bob for convenience) who want to exchange a sensitive piece of information with an erbium-doped fiber. Erbium makes the fiber act like a laser, and the amount of power in the fiber laser depends on mirrors at their respective ends of the fiber laser.

To exchange information, imagine that Alice and Bob each have two types of mirrors on hand and that they agree to let one type of mirror represent the number 0 and the other type represent the number 1. To send a single bit of information, each of them place one of their mirrors at their end of the fiber. Because Alice knows which mirror she chooses, when she measures the power in the fiber laser she can determine which mirror Bob has chosen. Similarly, Bob can use the same reasoning to tell which mirror Alice has chosen.

An eavesdropper who is not allowed to see the mirrors but measures the power in the laser might be able to determine that one person chose mirror 0 and the other chose mirror 1, but she could not tell which person chose which mirror. As a result, she would not have enough information to determine what numbers Alice and Bob are exchanging.

A sensitive enough measurement of the light in the fiber could theoretically reveal the information that Alice and Bob are transmitting, but the authors show that including filters in the system and injecting random noise into the fiber would allow them to arbitrarily increase the technical challenges a would-be snooper faces in trying to eavesdrop. Unlike quantum communication, which is potentially absolutely secure, the fiber laser system could be designed to be just secure enough to ensure that communications are secret while keeping material costs down and long distance transmission speeds up.

Nobel In Physics: Creators Of Optical Fiber Communication And CCD Image Sensor

The Master of Light

This year’s Nobel Prize in Physics is awarded for two scientific achievements that have helped to shape the foundations of today’s networked societies. They have created many practical innovations for everyday life and provided new tools for scientific exploration.

In 1966, Charles K. Kao made a discovery that led to a breakthrough in fiber optics. He carefully calculated how to transmit light over long distances via optical glass fibers. With a fiber of purest glass it would be possible to transmit light signals over 100 kilometers, compared to only 20 meters for the fibers available in the 1960s. Kao’s enthusiasm inspired other researchers to share his vision of the future potential of fiber optics. The first ultrapure fiber was successfully fabricated just four years later, in 1970.

Today optical fibers make up the circulatory system that nourishes our communication society. These low-loss glass fibers facilitate global broadband communication such as the Internet. Light flows in thin threads of glass, and it carries almost all of the telephony and data traffic in each and every direction. Text, music, images and video can be transferred around the globe in a split second.

If we were to unravel all of the glass fibers that wind around the globe, we would get a single thread over one billion kilometers long – which is enough to encircle the globe more than 25 000 times – and is increasing by thousands of kilometers every hour.

A large share of the traffic is made up of digital images, which constitute the second part of the award. In 1969 Willard S. Boyle and George E. Smith invented the first successful imaging technology using a digital sensor, a CCD (Charge-Coupled Device). The CCD technology makes use of the photoelectric effect, as theorized by Albert Einstein and for which he was awarded the 1921 year’s Nobel Prize. By this effect, light is transformed into electric signals. The challenge when designing an image sensor was to gather and read out the signals in a large number of image points, pixels, in a short time.

The CCD is the digital camera’s electronic eye. It revolutionized photography, as light could now be captured electronically instead of on film. The digital form facilitates the processing and distribution of these images. CCD technology is also used in many medical applications, e.g. imaging the inside of the human body, both for diagnostics and for microsurgery.

Digital photography has become an irreplaceable tool in many fields of research. The CCD has provided new possibilities to visualize the previously unseen. It has given us crystal clear images of distant places in our universe as well as the depths of the oceans.