Grooves Align Fiber and Crystal

Kevin Robinson

Researchers in upstate New York have developed a technique for attaching an optical fiber to a photonic crystal without using a tapered waveguide as an intermediary. The process incorporates stepped grooves in a silicon platform on which the photonic crystal is fabricated. By coupling the fiber output directly into the crystal, they have demonstrated insertion losses as low as 3.5 dB.

Yuri Suzuki and Lu Chen of Cornell University in Ithaca and Glenn E. Kohnke of Corning Inc. in Corning developed the prototype integrated platform, which is essentially a slab of silicon with four vertical walls running across its width.

"The one-dimensional crystal is made up of four walls, with the inner two walls spaced twice the distance as compared with the others," Suzuki said. "[It] blocks the transmission of light between 1400 and 1700 nm but allows the propagation of light at 1550 nm," a key telecommunications wavelength.

The researchers employed a combination of macroscopic and microscopic photolithography techniques to create the structure. They defined the layout of the photonic crystal using electron-beam lithography and two sequential masks of Cr/Au and SiO₂. They employed contact lithography to pattern the fiber alignment grooves, which they etched with the Bosch technique. Then they etched the photonic structure using high-density Cl plasma.

"The key in this integrated platform is that the stepped fiber grooves are fabricated so that they are accurately aligned with the photonic crystal structure," Suzuki said. "Then the fiber can be simply placed in the grooves and anchored with an adhesive."

The fiber positioning, she said, is accurate to within 100 nm. Another essential element to the system is constructing a crystal that is large enough for a dielectric constant to modulate the maximum divergent light from the fiber.

Suzuki plans to expand the work by developing two-dimensional photonic crystals integrated in a similar manner.