Alcatel Backs the Bubble

It's announced an all-optical cross-connect based on Agilent's bubble jet technology

July 31, 2000

3 Min Read
Alcatel Backs the Bubble

Alcatel SA (NYSE: ALA) today announced plans for an all-optical cross-connect called Crosslight.

Alcatel says that the first release of the switch will scale up to 512-by-512 ports, each operating at speeds of 10 Gbit/s, and will go into beta trials in the first half of next year. In the long term – by 2004 – it’ll handle as many as 4,000-by-4000 ports, each operating at 40 Gbit/s.

The real significance of the announcement, however, is that this is the first switch to be based on bubble technology from Agilent Technologies (NYSE: A). All of the other developments of large scale all-optical cross-connects have so far been based on arrays of tiny tilting mirrors, based on MEMS (micro-electro-mechanical systems).

Alcatel’s backing of bubble technology is an interesting development, although it comes with a couple of caveats.

First, Alcatel is also working on MEMS developments and is likely to use this technology rather than bubbles for its larger switches. “It’s very hard to get to thousands of ports using the bubble technology,” says Jay Liebowitz, director for optical components with RHK Inc..

Second, all of these technologies are at a very early stage of development, and it's really too early to say which one, if any, will end up in widespread use.

So far, vendors have built relatively small scale prototypes - up to 256-by-256 ports – sometimes dressing them up to look larger at trade shows (see Xros's OFC Splash Was All Wet and Siemens Launches Optical Cross Connect “Solution”). They’re a long way from proving that MEMS, bubbles or anything else can meet incredibly high reliability requirements for this type of equipment. This was acknowledged by Julie E. Fouquet, the inventor of Agilent’s bubble technology, at Opticon 2000, Light Reading's first conference today. “When you get into these very large scale switches, a failure would make headline news,” she said. Agilent’s big claim to fame is that its bubbles act like mirrors without suffering the drawback of having tilting mechanisms that could jam or wear out over time.

With Agilent’s way of doing things, the basic building block is a 32-by-32 port switch on a chip. Inside the chip, there’s a matrix of microscopic channels filled with a special liquid, through which light travels. At each intersection point, a bubble jet pen can heat up the liquid so that it boils and creates a tiny bubble. This acts like a mirror, glancing light onto the intersecting path (see Agilent Unveils Optical Switching Breakthrough). These 32-by-32 port modules can be linked together to create large scale switches.

Agilent makes a big thing out of the fact that its bubble jet technology has been used for years in its printers. The manufacturing process is well proven, and it’s made millions of pens. The pens themselves routinely blow bubbles day in, day out, year in, year out, without any problems.

The downside of this argument is that bubbles in printers only have to last a split second before they’re allowed to collapse. In an all-optical switch, they might have to be maintained indefinitely. This implies that the pen would have to keep heating up the fluid, and raises a question mark over whether this would increase the temperature of the fluid in adjoining channels – and whether that might interfere with their light-carrying properties.

Alcatel’s adoption of Agilent’s technology for its switch implies that it’s satisfied itself that this isn’t a problem.

Agilent also makes a big thing of its building-block approach, saying that it enables service providers to buy a small switch and then add modules to increase capacity as and when they need it.

However, there’s a limit to how many modules can be linked together, partly because more and more connections are required and partly because losses increase. In other words, the light signals get weaker and weaker until they need to be regenerated electrically – at which point the switch isn’t all optical any more.

by Peter Heywood, international editor, and Marguerite Reardon, senior editor, Light Reading, (

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