"3-D Etch A Sketch" Enables Extreme Polymer Optics

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Graduate student Keith Kamysiak aligns a polymer waveguide to a glass optical fiber using 3-D lithography.

Assistant Professor Bob McLeod has taken to calling his research equipment a "3-D Etch A Sketch," but it's definitely no child's toy.

The instrument built by his graduate students uses nanometer-accurate laser lithography to write or "etch" optical waveguides and waveguide arrays into a flexible, photo-sensitive polymer material, ultimately offering a less expensive alternative to the fiber optics now prevalent in the computer and telecommunications industries. If thousands of waveguides can be written in a three-dimensional polymer in just one step, it would greatly simplify fiber-optic telecommunications and medical manufacturing and lead to significantly lower costs, McLeod says.

McLeod's "Extreme Polymer Optics" group at CU-Boulder has earned research support from the National Science Foundation and is also partnering with a local data storage company, InPhase Technologies of Longmont, a spin-off of Lucent Bell Laboratories. InPhase developed the flexible polymer material for the next generation of holographic data storage devices, allowing the company to make 300 gigabyte compact discs by utilizing the entire volume of the medium for storage.

McLeod, who received his PhD in electrical engineering at CU-Boulder in 1995 and then worked in the data storage and telecommunications industries himself before joining the faculty, says the sensitivity, flexibility, and "self-processing" capabilities of the InPhase material make it a good match for his group's research.

An application of this technology funded by Intel will efficiently transport light from next-generation silicon processor chips, through the flexible polymer, to a glass optical fiber for off-chip communication. These "silicon photonics" chips route light on one-micron-wide silicon wires, requiring the instrument to have an accuracy of 50 nanometers—less than one-thousandth the diameter of a single strand of human hair.

"We need an insane level of precision because at widths of a few microns for each waveguide, it's very easy to miss the connection," McLeod says as graduate student Keith Kamysiak demonstrates an accurate alignment as indicated by the bright light exiting the end of the polymer waveguide.

"I believe this demonstrates the unexpected and unpredictable benefits of basic research." -Bob McLeod

The polymer starts as a liquid containing a light-sensitive dye. Kamysiak places optical fibers in the liquid InPhase polymer, which then cures to a rubbery solid—a process completed in a matter of minutes with little to no shrinking or warping, McLeod says. Microscopes built into the lithography instrument detect the locations of the fiber cores and report their 3-D position. Kamysiak then directs the computer-controlled instrument to write waveguides to these locations by drawing them with a moving 3-D focus. After all waveguides are inscribed, a second, large-area optical exposure removes all remaining dye, leaving an environmentally stable part that is no longer sensitive to light.

The researchers are working with Intel Corp., which wants to introduce high-speed optical communication into next-generation computer chips made from silicon, but needs a way to connect these to other chips or the Internet. "It's a problem of packaging, which is not trivial in the field of optics," McLeod says. He thinks his group can develop a coupling device that will accurately link the silicon chip's waveguides with optical fiber and seal it all in a polymer mass that is both durable and inexpensive.

Meanwhile, in a project being funded by a National Science Foundation Small Business Technology Transfer grant, Massachusetts-based Zenwa Inc. has an exclusive license with CU to use McLeod's patented polymer waveguide array technology to develop a family of disposable endoscope probes used by doctors for non-invasive surgery. The firm believes it can develop a product so inexpensive that it will ultimately replace the very costly endoscopic devices now based on glass fiber bundle technology while also offering higher resolution, which means a better view for the surgeon.

As part of this medical device research, McLeod says he is also working with Zenwa and the Smith-Kettlewell Eye Research Institute to develop new diagnostic procedures and treatments for individuals with vision impairments such as macular degeneration. The aim is to design an optical system to track an individual's eyes, image their retinas, and rearrange the images in such a way that would allow the person to see portions of the world otherwise blocked by macular degeneration.

Their goal is to perform all of this through the polymer waveguide array, keeping bulky components off the user's head.

"I believe this really demonstrates the unexpected and unpredictable benefits of basic research," says McLeod. "Here we are with a new material originally developed at Lucent for high-capacity data storage. It may end up as part of the next step in computer evolution, as an instrument for minimally invasive surgery, and possibly helping the legally blind to see. Figuring out what else might be possible is what gets us out of bed in the morning."


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