Startup in Laser Control Breakthrough
When radios evolved from AM (amplitude modulated) to FM (frequency modulated), the quality of radio transmissions leaped upwards. Startup FiberSpace Inc. figures its technology could have a similar impact on optical networks. Today's optical networks are amplitude modulated, that is, the amplitude of the signal carries the information. Optical networks don't use frequency modulation because the frequency of the lasers can't be controlled accurately enough at present.
FiberSpace has developed a technique that can improve the accuracy of a laser's frequency (or wavelength) by a factor of a thousand, it claims. It does this by taking any off-the-shelf laser, and adding a proprietary opto-electronic circuit. The circuit measures the laser's wavelength and uses an optical feedback loop (rather than an electrical one) to keep it stable.
The most obvious benefit of a frequency-stable laser is that it can help signals go farther on an optical fiber without optical regeneration, says Leonardo Berezovsky, FiberSpace's founder and CEO. That's because chromatic dispersion – an effect that causes different wavelengths to travel at different speeds in the fiber – is less of a problem when the wavelength is more accurately defined. Berezovsky doesn't know how much farther signals would go, but thinks it would be a significant improvement. "Part of our near-term work is to quantify this," he says.
Frequency-stable lasers could also help squeeze DWDM (dense wavelength-division multiplexing) channels closer together by reducing interference between neighboring channels.
The above improvements can be made without changing the basic nature of the optical signal, i.e., it is still AM. But ultimately, Berezovsky believes that frequency modulation will play a more important role.
"In metro applications there may be thousands of different channels, and the challenge is to deliver the right wavelength to the right customer," says Bob Welch, FiberSpace's VP for marketing. One way is to use optical crossconnects or switches. Another would be to let the receivers pick out which wavelength they're receiving. "For this you need a 'heterodyne receiver', like the one in the radio on your kitchen table," Welch explains. A heterodyne receiver would contain a frequency-accurate laser, which it tunes to the incoming signal.
FiberSpace received first round funding of $12.5 million from J.P. Morgan & Co. (Nasdaq: JPM) and one of its affiliates and Morgenthaler Ventures (see Laser Startup Has $12M First Round).
It all sounds impressive, but the startup is very early stage. It hopes to be in a beta testing phase by the end of 2001. Don't touch that dial.
-- Pauline Rigby, senior editor, Light Reading http://www.lightreading.com