at The Hong Kong Polytechnic University are refining the design
of a vital component capable of bringing Internet up to superfast
way of taking Internet and other mulit-point networks forward to
meet tomorrows demands is to make it all-optical, says Prof
Alex P K Wai, Principal Investigator of the PolyU project.
A key component that limits the speed of data
being transmitted in todays Internet is the router, he added.
Routers are like interchanges on a highway
and direct emails and other data to their assigned destinations.
Wai setting up a trial all-optical network
they operate in the electrical domain, they lead to bottlenecks because
data flowing through Internets optic fibre backbone networks
needs to be converted from optical to electrical signals before it
can be processed by the routers.
processing, the data is converted back to an optical signal so it
can re-join the optical highway. Electronics are fast, but not
as fast as light, said Prof Wai. If we adopt an all-optical
network, we will avoid the bottlenecks and therefore achieve much
Wais research has resulted in the making of an optical switch,
the one vital component missing from advancing todays optical-electro-optical
networks to all-optical.
and his team took a readily available, inexpensive Fabry-Perot laser
diode and used some of its physical properties in a way that no one
has used before to provide an optical switch. Details of how this
is achieved is the subject of a patent application.
is transmitted in packets, explained Prof Wai, just like
letters in the postal system. Each packet has a header which
contains the destination address. The remainder of the packet is the
payload, or the data being transmitted (see illustration below).
the header that needs to be converted from an optical to an electrical
signal so it can be read and processed by the electrical router.
Wais research has demonstrated switching of packets at transmission
rates of 10 billion bits per second (10 Gb/s) without converting
any part of the packets into electrical signals.
is an important step forward towards the construction of an all-optical
packet-switched network, said Prof Wai. He expects to have
a trial version of the worlds first all-optical packet switched
network working by year end.
the meantime, he is working on a couple of problems.
stability of the device; finding a way to prevent its laser beam frequency
from drifting. In the experimental stage, this occurs
after about 15 to 20 minutes and switching ceases.
problem is the polarisation of light entering the diode. This
affects the performance of the diode which means the diode cannot
read the signal it contains.
difficulty with switching optically is that optical memory is still
under development, said Prof Wai. Memory is needed to store
the decision of the header processor and tell the payload where
is easy in the electrical domain, Prof Wai added. But
until now there has been no electrical equivalent of optical memory.
of the diodes natural properties, the subject of the patent
application, provides the answer.
difficulty is to make light of different wavelengths affect one
another, necessary for the switching process.
low cost of Fabry-Perot diodes will be an advantage if an all-optical
approach is eventually adopted. The diodes cost about HK$800 each.
However, changing to all-optical networks will mean that all existing
electrical routers will need to be replaced.
Wai believes all-optical networks are essential for modern day practices
such as telemedicine where, for example, a surgical operation may
be taking place in one location but its supervision is based elsewhere.
involved needs to be sharing the same information and detail, and
you need high image quality. Just having a lot of bandwidth is not
enough, said Prof Wai.
Prof Alex P
K Wai : email@example.com