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  • Speed-reading Optical Data
Feb 2009
WASHINGTON, Feb. 4, 2009 – Optical data speed is now catching up to the latest technology.

Currently, millions of phone calls and cable television shows per second are dispatched through fibers in the form of digital zeros and ones formed by chopping laser pulses into bits.

This slicing and dicing is generally done with an electro-optic modulator, a device for allowing an electric signal to switch a laser beam on and off at high speeds (the equivalent of putting your hand in front of a flashlight). Reading that fast data stream with a compact and reliable receiver is another matter. A new error-free speed-reading record using a compact ultrafast component – 640 Gb/s (Gbps, or billion bits per second) – has been established by a collaboration of scientists from Denmark and Australia, who report their results in the journal Optics Express, the Optical Society of America’s (OSA) open-access journal.

New technology and new ways of doing business require new approaches to old procedures. Conventional readers of optical data depend on photodetectors, electronic devices that can operate up to approximately 40 Gb/s. This in itself represents a great feat of rapid reading, but it’s not good enough for the higher-rate data streams being designed now. The data receiving rate has to keep up.

Sometimes to speed up data transmission several signals are multiplexed: Each, with its own stream of coded data, is sent down an optical fiber at the same time. In other words, 10 parallel streams of data could each be sent at a rate of 10 Gb/s and then added up to an effective stream of 100 Gb/s. At the receiving end, the parallel signals have to be read out in a complementary demultiplexing process. Reliable and fast multiplexing and demultiplexing represent a major bottleneck in linking up the electronic and photonic worlds.

In 1998, researchers in Japan created a data stream as high as 640 Gb/s and read it back, but the readout apparatus relied on long lengths of special optical fiber. This particular approach is somewhat unstable. The new demultiplexing device demonstrated at Technical University of Denmark, by contrast, can handle the high data rate and can do so in a stable manner. Furthermore, instead of fibers 50 m long, they accomplish their demultiplexing of the data stream with a waveguide only 5 cm long, an innovation developed at the Centre for Ultrahigh Bandwidth Devices for Optical Systems, or CUDOS, in Australia. Another benefit of the new device with the compact size is the potential for integration with other components to create more advanced ultrafast functional chips. The dynamics involved in the CUDOS device even could allow for still higher data rates approaching terabits per second (Tb/s, or trillion bits per second).

One author of the new report, Danish scientist Leif K. Oxenløwe, says that the record speeds of demultiplexing represented by his tiny glass microchip are a boon to circuit designers and open the door to faster network speeds. In the near future, the Danish and Australian researchers hope to achieve 1 Tb/s Ethernet capability.

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electro-optic modulator
A device that uses an applied electrical field to alter the polarization properties of light.
The combination of two or more signals for transmission along a single wire, path or carrier. In most optical communication systems this is referred to as wavelength division multiplexing, in which the combination of different signals for transmission are imbedded in multiple wavelengths over a single optical channel. The optical channel is a fiber optic cable or any other standard optical waveguide.
The technology of generating and harnessing light and other forms of radiant energy whose quantum unit is the photon. The science includes light emission, transmission, deflection, amplification and detection by optical components and instruments, lasers and other light sources, fiber optics, electro-optical instrumentation, related hardware and electronics, and sophisticated systems. The range of applications of photonics extends from energy generation to detection to communications and...
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