Xerox in Optical Switch Advance
Scientists at the Palo Alto Research Center (PARC) of Xerox Corp. (NYSE:XRX)
appear to have made a significant advance in the development of the arrays of
tiny tilting mirrors used in all-optical switches. They've come up with a new way of
making micro-electro-mechanical systems (MEMS) which promises to be more
manufacturable, more scaleable, and lower loss than existing technologies.
PARC is pretty late to the party. The MEMS scene is already crowded with at
least a dozen other vendors aiming to make MEMS-based optical switches (see
Optical Switching Fabric: MEMS). Some of them, like Cspeed Corp., have been
working for three or four years and still haven't got products to market. But,
according to Eric Peeters, who directs the Electronic Materials Laboratory at
PARC, the Xerox technology is so revolutionary that it will allow them to leap-frog
the competition.
"[Our MEMS chips] are a lot simpler to build, so we can crank out a batch in a
week, as opposed to the month it takes in the rest of the industry," Peeters
says. This will allow PARC to speed up the development cycle, he adds. In fact,
Peeters claims that it only took six months to develop a process for making
1156-by-1156 mirror arrays with 100 percent yield.
Those figures are likely to get systems vendors very excited. Making the innards
of large-scale optical switches is quite challenging, and achieving this without
having to scrap any dud devices is almost unheard of.
So, how do they do it? The answer lies in the material used to make the mirrors.
Unlike the rest of the industry, which uses silicon, PARC's mirrors are made from
thin-film metals.
Metal is much easier to work with than silicon. It can be deposited by a simple
process called sputtering. The metal films are pre-stressed, so that when the
surface is patterned, the mirrors pop up on their own to relieve that stress (rather
than being lifted up from the substrate by intricate micromachining). What's more,
there's no need to machine hinges. The mirrors are bent instead of tilted, simply
by applying a voltage.
"Anyone can build stress into a metal film -- usually it's there whether you want it
or not -- but we've got good at doing it reproducibly," says Peeters.
However, the really big deal is not just the manufacturing, but the fact that the
mirrors can be scanned through a much wider range of angles than usual. PARC
is claiming twice the tilt angle of traditional MEMS. This is due to the fact that the
structures can be raised much higher above the surface of the substrate.
This helps solve a key problem for optical switches -- that losses increase with
switch size. That's because the light beam spreads as it travels. Steering the
beam over a wider range of angles allows the beam to travel a shorter distance
inside the switch, which reduces the spreading.
"We have already demonstrated scan angles that are considerably larger than all
competitors that we know about", says Peeters. "Our modeling shows that we
should be able to achieve angles that are so large that we could actually scale
the size of the fabric to 10,000 ports. It's not clear to us that anyone wants this
yet, but it's good to know we have the power under the hood."
Perhaps Peeters hasn't heard of Integrated Micromachines Inc. (IMMI), a startup
that is also claiming it can tilt its mirrors through twice what the competition can
do -- 50 degrees as opposed to a mere 22 degrees in developments by Calient
Networks Inc. (see Calient Claims Breakthroughs On Optical Switches , Switch
Startup Raises MEMS Questions and Dark Horse Joins Optical Switch Race ).
IMMI says it uses electromagnetic forces to turn its mirrors, delivering 1000 times
more turning force than electrostatic (applied voltage) techniques.
Using Peeters' reasoning, it would appear that IMMI also has the potential to
scale to monster switch sizes. But PARC would still have the edge, it claims, for
three big reasons. One, as already noted, is the ease of manufacturing.
Two, the electrical power consumption is low. Other approaches typically require
huge amounts of electrical power, particularly for big switch sizes and large tilt
angles -- it could be as much as 1000 watts. This is like having the switch sit in
an oven, which can cause lifetime and reliability problems. In contrast, PARC's
MEMS run off low power and low voltage. "The power is actually low enough so
you could run the switch off a compact backup battery for quite a while," claims
Peeters.
And three, the mirrors can be tilted more accurately, thanks to a proprietary
feedback control mechanism, which was developed at PARC as part of a
separate ten-year project. Peeter's reckons lots of other MEMS vendors are still
struggling with the problem of aiming their mirrors accurately.
What happens next has not been decided. According to Peeters, one route is to
partner with a company that has competency in making low port-count switches.
PARC has the expertise in making the switching fabric, but needs to find the
skills in fiber alignment and subsystem design, so that it can build the box
around the switch core.
Another possibility is that Xerox will spin out a startup or form a joint venture, in
the same way that it spun out SDL Inc. (Nasdaq: SDLI - message board) twelve
years ago. But whatever happens, it's going to happen fast, as PARC tries to
catch up and overtake the other players in the MEMS switch space.
-- Pauline Rigby, senior editor, Light Reading lightreading.com
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