Photonics: Computing At Light Speed

[continued from Homepage]

...exciting area of photonics research.

Today, many scientists around the world are researching photonics to improve our communication speed. For example, scientist Alex Jen at the University of Washington in Seattle and his team have created new materials to quickly process communication information. These materials are specially designed to convert electronic signals (like those from telephones or computers) into optical signals and back again. When the technology is perfected, we may experience even larger bandwidth and higher speeds for Internet computing.

Can you think of any ways that you would use light to communicate with someone? Let's imagine a dark, stormy night. You are stuck in your room and want to send a signal to your neighbor across the street. With your flashlight beamed toward your neighbor's window, you quickly pulse the flashlight button on and off. You and your neighbor have a secret code; two flashes mean "hello" and three flashes mean "goodbye."

This "flashlight code" is similar to the digital code that engineers use in communication devices. On and off pulses of light represent the numbers 1 (on) and 0 (off), which is called a binary sequence. It may be hard to believe, but thousands of ones and zeros lined up together can represent the information carried in our emails and telephone voice conversations. The more ones and zeros we have, the more information we have. Recently, scientists have worked to design a device that switches light on and off over a billion times per second.

As in the flashlight game, engineers have created devices to send these pulses of light through a fiber optic cable. Fiber optic cables are all over the world, even crossing the bottom of our oceans. In the cable, light travels through a tiny pipe of solid glass called a fiber, which is no thicker than a strand of your own hair. One fiber optic cable can hold around 100 fibers, which can carry up to 50,000 phone conversations. Fiber optic technology was invented few decades ago, but new ideas to enhance these systems are constantly tested by students and scientists at photonic research centers such as the National Science Foundation center headquartered at the University of Washington.

Images:

Previous page: A researcher holds hundreds of thin fiber optic cables. Courtesy of Pacific Northwest National Laboratory

Above: Professor Alex Jen studies electro-optic devices.

The Path Of Telecommunications

Let's track your phone conversation from here to the other side of the world. We'll use the knowledge you've already learned about fiber optic cables, the different wavelengths of light, and digital signals. Then we'll learn about the new Northwest research to improve the speed, cost, and efficiency of this everyday process.

As you speak into the phone, the sound waves from your voice vibrate a small diaphragm in the receiver. A magnet in the phone turns these sound vibrations into electrical pulses. This electric signal runs down a copper wire to the telephone lines and eventually to a base station. Scientists are hoping to replace electric signals with optical signals, because an all-optical network would be much faster. This technology still needs more research to develop.

At the base station, the electronic signals on the copper wire are converted into digital signals on a fiber optic cable. Using laser light (or a light emitting diode), a device called an optical modulator adjusts the intensity of light as it shines through the device. This device makes those ones and zeros for the digital code.

The signal is now a wavelength of light, transmitted along a fiber optic cable under the ocean. Your voice is now a stream of digital code—thousands of ones and zeros per second that represent your voice and words. At times, the signal needs to be controlled, for example, amplified (made stronger) and repeated to travel over long distances.

When the signal reaches the other side of the world, it reaches a photodetector, a device that detects photons and converts them into electrical signals. These signals are sent along a copper wire to a phone. A receiver converts the electrical signals back into sound waves and the phone's speaker projects your voice on the other side of the world.

This scenario is just one of the ways that long-distance telecommunication can work. There are many new technologies that researchers at the University of Washington are exploring today. In the area of materials research, scientists are creating different types of materials that allow signals to move even faster. In the area of signal processing, researchers are trying to add more signals to a cable so that it takes less time to download information from the Internet or less cable to carry telephone conversations.

Image: Examples of laser emitting diodes. Courtesy of Agilent

Dividing the Light Much like your television can carry many different channels, telecommunications uses different wavelengths of light to carry different digital signals. Let's say that we put one signal on red light and a second signal on blue light. In telecommunications, engineers encode signals on infrared light that we cannot see, but the idea is the same. By placing a digital signal on a specific wavelength, one fiber optic cable can hold a lot of digital signals. This means that more information can travel through the fiber optic cable.