New optical filtering technique to result in fatter pipes
2/15/2007 9:41:51 AM, by Chris Lee
In last month's Nature,
Photonics reported a nice combination of an old optical
telecommunications trick with new photonic technologies. in doing so
the researchers who performed the work have opened the door to using
these new devices in standard telecommunications networks.
Optical communications achieves very high data rates through a
combination of fast modulation of a single channel (around 10Gbps) and
running multiple channels down the same fiber. Each channel is a
slightly different wavelength (color), so the maximum bandwidth depends
on how closely these channels can be spaced. The minimum channel
spacing is set by the ability to separate light of different
wavelengths.
New photonic devices, such as the microtoroid pictured at left, are
very good at separating and combining very closely spaced channels. For
any particular device, however, the performance depends on the
polarization of the light, which is the spatial orientation of the
electric and magnetic fields. This is undesirable because normal fiber
optic cable randomizes the polarization of light.
Researchers took advantage of a property of polarization, that light
of any polarization is really a combination of two light beams of
different brightness and polarized at right angles to each other. The
researchers split the incoming, randomly polarized, light into two
beams with well-defined orthogonal polarizations. These two beams were
then transported to two slightly different microrings, each optimized
to act as an add-drop filter for that particular polarization. The new
signal, with one channel removed and a different channel added, is then
recombined into the original randomly polarized light, which can then
be directed back into a fiber optic cable.
This trick is currently used in fiber-based optical isolators and
circulators. However, the combination of this trick with microrings is
very cool and will eventually lead to narrower channel spacings and
hence fatter pipes. It is not, however, the huge breakthrough that some
technology journalists seem to think it is.
http://arstechnica.com/news.ars/post/20070215-8853.html
Wish somebody found it helpful.BTW haven't seen such a discussion lacking forum in a while.
