Startup Gets Flexible

A flexible sheet of polymer could be a new wonder material for integrated optics

February 28, 2001

3 Min Read
Startup Gets Flexible

Startup Optical Crosslinks Inc. claims it's got the ideal material for optical integration.

It's a polymer. But unlike other polymers, which are coated onto silicon wafers, Optical Crosslinks' stuff 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 of a type called polyimides. Inside these materials, the molecules are tightly held together so the polymer isn't very flexible, explains Abbot. 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," says Abbott. "What we found is, though it expands and contracts, the waveguide properties magically stay the same."

This discovery was made by Dr. Bruce Booth while at Dupont. He spun out the company in 1998, licensed the technology from Dupont, and has never looked back. The startup 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, Essex Investment Mgt. Co. LLC and a number of private 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 (VCSELs -- see Laser Blazers). 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," says Abbott. "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," Abbot says.

Future products have not been determined. "There are a million places to apply it," says Abbott. Gratings, couplers, and switches can all be made easily in Optical Crosslinks' polymer, she says. On the startup's Website, there's a white paper featuring pictures of a bubble switch, rather like the one from Agilent Technologies Inc. (NYSE: A) but made from polymer, along with claims that the polymer processing technology will result in a higher performance switch (see Agilent Unveils Optical Switching Breakthrough).

However, it could be a while before products designed to operate with DWDM (dense wavelength-division multiplexing) at around 1550 nanometers become a reality. Abbot 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 startup's datasheets, losses are 0.1 dB per cm at 850nm (where the VCSEL arrays operate), but rise to 0.3 dB per cm at 1300nm and 0.7 dB per cm at 1550nm.

It's worth pointing out that other startups 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.

-- Pauline Rigby, senior editor, Light Reading

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