Dispersion: New Version
The module, called Light Fixer, is the first dispersion compensator to make use of so-called etalon technology -- bouncing light back and forth between two mirrors. The same idea is already used in other components, such as lasers and wave lockers, but hasn't yet caught on for curing the smudging of light pulses that occurs when high data rates are carried over long distances.
This smudging happens because light pulses are made up of bunches of wavelengths that travel through fiber at slightly different speeds. As a result, the light pulses spread out when they travel long distances, eventually overlapping and becoming indistinguishable from one another (see Light Reading's Beginners Guide for the basics on Chromatic Dispersion and Polarization Mode Dispersion (PMD)).
Until now, two techniques have been used to tackle this problem.
The first is based on the use of special dispersion compensating fiber from vendors like Corning Inc. (NYSE: GLW). However, this solution is bulky, expensive, and can have high insertion loss, according to Ross Kocen, Accumux's VP of marketing. It's also fixed. The amount of dispersion compensation can't be adjusted, so this can't be used in networks that deploy optical switching.
The second solution uses Fiber Bragg Gratings (FBGs) from companies such as Alcatel Optronics (Nasdaq: ALAO; Paris: CGO.PA), Phaethon Communications, Sabeus Photonics Inc., Southampton Photonics Inc., TeraXion, and 3M Company, to name but a few. FBGs can be tuned to deliver different amounts of dispersion compensation, but there's another snag: They can't be used for multiple wavelengths. You need one FBG per wavelength, so this solution is expensive and cumbersome in networks using DWDM.
Accumux claims its etalon-based compensator has none of these drawbacks. It works by making some wavelengths of light bounce between its mirrors for longer than other wavelengths, in order to restore the original shape of the pulse. The upshot is compactness and the ability to compensate 80 channels at the same time, across the C and L bands.
As noted, Accumux claims to be the first to have an etalon-based dispersion compensator, but at least one other company -- JDS Uniphase Corp. (Nasdaq: JDSU; Toronto: JDU) -- is also working in the field, as visitors at the recent Optical Fiber Communication Conference and Exhibit (OFC) may have noticed.
At the OFC, Accumux was a little secretive about its Light Fixer, covering it with a cloth during most of the show. JDSU, on the other hand, made no bones about having a working prototype of a tunable etalon-based compensator on its booth. David Moss, from JDSU in Ottawa, also presented a research paper on the company’s developments in this field.
JDSU's presence in this market could be taken either as a validation of Accumux's technology, or as a huge threat. After all, how can a 20-person startup hope to compete with the 800-pound moose of the component industry?
What's more, JDS Uniphase's technology may be technologically more advanced. Accumux's device has limited tunability -- temperature is used to tune the dispersion of the device by up to 10 percent of its central value, according to Kocen. But the dispersion slope, which describes the varation in dispersion with wavelength, remains fixed. In contrast, the device described by JDS Uniphase in its research paper has tunability of over a much wider range of dispersion, and can offer different dispersion slopes (although the amount of slope is fixed during manufacturing).
JDSU is still in its development phase and hasn't said when its etalon-based products will hit the market. Mind you, Accumux isn't actually ready to ship either. It expects to field test the product in the summer, with volume shipments starting in 2003, according to Kocen.
Accumux was founded in January 2001. It has raised $7.3 million so far in its series A round, from Fortune Ventures, Smart Technology Ventures, Trimax, and Lite On IT Corp., which is enough to last until 2003. Nevertheless, it's seeking another $5 million before it closes the round, Kocen says.
— Pauline Rigby, Senior Editor, Light Reading