Flexible chips

Start-up Optical Crosslinks, Inc. claims it has the ideal material for optical integration.

It's a polymer. But unlike other polymers, which are coated onto silicon wafers, Optical Crosslinks' material is manufactured as a flexible sheet. This gives it quite a few advantages, says director of sales and marketing Lynore Abbott.

A key benefit of the material is "almost no residual stress." That means it doesn't suffer from birefringence (preferred optical directions) and it can accommodate tight bend radii, down to just 3 millimeters. (Stress allows light to leak out of fiber bends, for example, because it lowers the refractive index on the outside of the bend.)

Wafer-coating polymers are usually a type called polyimides. In these materials, the molecules are tightly held together, so the polymer isn't very flexible, Abbott explains. Optical Crosslinks uses a polyacrylate, in which the bonds between molecules are much longer and looser. "People didn't look at polyacrylate originally, because it has a very large temperature dependence," Abbott says. "What we found is, though it expands and contracts, the waveguide properties magically stay the same."

What’s the big deal? Making chips more flexible and bendable means that they can be installed in a variety of applications. This makes the integration of certain parts and functions much easier to accomplish. More tightly integrated components reduce costs and compress functionality into smaller areas. Ultimately, this means service providers will be able to use smaller, more advanced equipment at lower cost. Hopefully, they will be able to pass along the benefits to end users.

The flexible polymer discovery was made by Bruce Booth while at Dupont. He spun off the company in 1998, licensed the technology from Dupont, and has never looked back. The start-up was originally called Polymer Photonics but changed its name to better reflect its market position.

It has seed funding from telecom executives Chad Paul and John Englesson, as well as Essex Investment Mgt. Co. LLC and a number of individuals.

Like most companies targeting optical integration, Optical Crosslinks is starting with something simple. It's already selling what it calls a "pitch transition device" to manufacturers of vertical cavity surface emitting lasers (VCSEL). This is a bunch of tapered waveguides that pipe light from a VCSEL array to a fiber ribbon.

"One of my customers is using a 4x12 VCSEL array," Abbott says. "The closer he can pack those VCSELs [on the wafer], the more money he can make. But he still needs to be compatible with the 250-micron pitch in the fiber ribbon." She figures this to be a huge-volume application.

Right now, the product is undergoing Telcordia 1209 and 1221 reliability testing. Optical Crosslinks claims it's closing in on some large OEM contracts and design wins for this product but won't name names. "To our customers, we're the secret advantage," Abbott says.

Future products have not been determined. "There are a million places to apply it," Abbott says. Gratings, couplers and switches can all be made easily in Optical Crosslinks' polymer, she says. On the start-up's Web site, there's a white paper featuring pictures of a bubble switch, rather like the one from Agilent Technologies but made from polymer, along with claims that the polymer processing technology will result in higher-performance switches.

However, it could be a whille before products designed to operate with dense wavelength division multiplexing around 1550 nanometers become a reality. Abbott says one reason the firm is targeting VCSEL manufacturers in the first instance is because "it will buy us some time so we can work at dropping optical losses" at telecom wavelengths. According to the start-up's datasheets, losses are 0.1 decibel per centimeter at 850 nanometers (where the VCSEL arrays operate), but rise to 0.3 decibel per centimeter at 1300 nanometers and 0.7 decibel per centimeter at 1550 nanometers.

It's worth pointing out that other start-ups have had a lot of trouble reducing losses in optical polymers. Lightwave Microsystems Corp. is one. "We could build a one-off, low-loss [polymer] device, but you need to be able to do it more than once," says Drew Lanza, founder of Lightwave Micro and now a partner at Morgenthaler Ventures. He says that Lightwave Micro hasn't given up on polymers altogether but now views them as a much longer-term goal.

This story, "Flexible chips " was originally published by Network World.

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