Issue No 8: May 2004
New round of funding approved
Nine projects awarded $27.5m
Q&A: Peer-review policy kept under constant review
‘Simple’ solution to reducing data flow bottlenecks
New use for common laser diode provides key for all-optical network
Design ideas bring smart antenna down to size and with less radiation
Algorithm leads to boost in performance
Filter contributes to success of two-way global positioning system
Mobile phone circuits to get even smaller

Researchers at The Hong Kong Polytechnic University are refining the design of a vital component capable of bringing Internet up to superfast speeds.
One way of taking Internet and other mulit-point networks forward to meet tomorrow’s demands is to make it all-optical, says Prof Alex P K Wai, Principal Investigator of the PolyU project.
Prof Wai setting up a trial all-optical network
A key component that limits the speed of data being transmitted in today’s Internet is the router, he added. Routers are like interchanges on a highway and direct emails and other data to their assigned destinations.
As they operate in the electrical domain, they lead to bottlenecks because data flowing through Internet’s optic fibre backbone networks needs to be converted from optical to electrical signals before it can be processed by the routers.
After 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 higher speeds.”
Prof Wai’s research has resulted in the making of an optical switch, the one vital component missing from advancing today’s optical-electro-optical networks to all-optical.
He 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.
“Data 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).

It’s 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.
Prof Wai’s 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.
“This 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 world’s first all-optical packet switched network working by year end.
In the meantime, he is working on a couple of problems.
One is 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.

Another 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.”
“The 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 to go.
“Memory is easy in the electrical domain,” Prof Wai added. “But until now there has been no electrical equivalent of optical memory.”
Use of the diode’s natural properties, the subject of the patent application, provides the answer.
Another difficulty is to make light of different wavelengths affect one another, necessary for the switching process.
Comparative 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.
Prof 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.
“Everyone 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.

Principal Investigator
Prof Alex P K Wai :