Columbia-SUNY Team Slices Magnetic Crystal; Applications Seen For Miniaturized Optical Devices

        They have taken the first important step toward creating amicrochip that combines electronics and its optical equivalent, photonics.The technology could simplify fiber optic communications and lead to thedevelopment of such miniaturized optical devices as tiny lasers andimplantable medical sensors.

        The Columbia scientists, working with colleagues from the StateUniversity of New York at Albany, have bonded an ultra-thin sheet ofmagnetic garnet, a photonic material that transmits light in only onedirection, to a semiconductor, a component of microelectric circuitry.

        "Ultimately, manufacturers will be able to combine optical andelectronic capacity on the same silicon crystals, which are superiorelectronics platforms," said Richard M. Osgood, Higgins Professor ofElectrical Engineering and professor of applied physics and co-author ofthe research.

        A crucial step was slicing an ultra-thin sheet - 9 microns, ormillionths of a meter, thick - from the magnetic garnet crystal, thesubject of a scientific paper published in the Nov. 3 issue of AppliedPhysics Letters.  Columbia has applied for a patent on the new technology.

        Professor Osgood and the co-inventor of the new technology, MiguelLevy, senior research scientist at Columbia, have already begun to receiverequests for single-crystal magnetic garnet films from other laboratoriesaround the world, for such diverse research applications as microwaveelectronics and optical isolators.  Columbia is the only institution thatcan produce the thin films.

        The work took place at Columbia's Microelectronics SciencesLaboratory and at the Columbia Radiation Laboratory, both in the FuFoundation School of Engineering and Applied Science.  The research groupincluded two materials scientists at the State University of New York atAlbany, Hassaram Bahkru and Atul Kumar, who assisted in processing thegarnet used in the experiments at SUNY Albany's ion accelerator.

        "I'm excited that this technology can be used to build a whole newrange of miniaturized systems, from medical sensors to ultra-small,powerful laser systems," Professor Osgood said.

        Miniaturized optical processors for fiber optic telecommunicationsare also possible.  Currently, optic messages travel by laser light to anisolator that prevents destabilization of the laser by outsideinterference, then to a modulator that imprints a signal, then to amultiplexer that combines signals of different wavelengths, each of whichcan carry a different message.  A similar system is required at thereceiving end to decode the light message into sound or picture.

        "Right now, these are all very bulky devices," Dr. Levy said.  "Ifyou could put all these optic circuits on a chip, it would be cheaper, moreefficient and sturdier, and there has been a lot of research geared towardsintegrating these components.  Our work is an important step in thisdirection."

        Such integration between photonics and electronics had not beenpossible because garnet and other magnetic crystals cannot be grown on asemiconductor substrate.  Magnetic isolators cannot be made efficiently onany material other than magnetic garnets.  Thus the need to place garnetcrystals on semiconductors, providing a bridge to an already maturetechnology, the researchers said.

        The Columbia research team fired high-energy beams of helium ionsat a planar region that is just below the surface of the crystallinematerial, yttrium iron garnet (YIG), to loosen it from its substrate,gadolinium gallium garnet.  They then applied chemicals to the region tocut the bonds entirely, slicing off an ultra-thin sheet of magneticmaterial from a single crystal.  The sample was then lifted off and bondedto a high-quality semiconductor.

        The goal of this effort is to make devices that allow light to goin only one direction on a fiber optic microchip, Professor Osgood said.Light guides etched into the magnetic crystal, when exposed to a magneticfield, allow the light to travel in one direction only, making the lightguide an effective routing device in an optic fiber network.

        The work is the result of a collaboration between Columbia and theUniversity of Minnesota to create integrated photonic devices for use infiber optic communications systems.  The collaboration is funded by thefederal Advanced Research Projects Agency.