A step towards micro-optics
Many researchers and industrialists predict a great future for the combination of optics and electronics. However, the development of optoelectronic components faces many hurdles. Scientists took one of them by connecting a semiconductor to a wafer-thin magnetic crystal that allows light to pass in only one direction. Scientists are currently combining light and electricity in laboratories at Columbia University. They have taken the important first steps to create a microchip that combines electronics and their optical counterpart, photonics. This technology could facilitate communication over fiber optic cables and could be used to develop miniature optical instruments such assuch as tiny lasers and implantable medical sensors.
Columbia University scientists, in collaboration with their colleagues at the State University of New York, have bonded a 9-micrometer thin layer of magnetic garnet - a photonic material that transmits light in only one direction - to a semiconductor (Applied Physics Letters of 3 November).
The research team fired high-energy beams of helium ions just below the surface of a crystal of yttrium-iron garnet to dislodge it from its support material (gadolinum-gallium garnet). Then the researchers treated the area with chemicals to completely break the connections, slicing a wafer-thin layer of magnetic material from a single crystal. The sample was lifted off and connected to a high quality semiconductor.
The goal of this effort, explained Professor Osgood of Columbia University, is to produce components for optical microchips that only allow light to pass in one direction. Magnetic crystals fulfill this requirement in a magnetic field. Currently, optical messages travel via laser light to an isolator that prevents destabilization from outside influences, then to a modulator that mixes a signal, then to a multiplexer that combines signals of different wavelengths, each carrying a different message. A similar system is needed at the receiving end to decode the message contained in the light into sound or image.
Right now, these are all very cumbersome devices, said Dr. Levy, who helped develop the new technology. If you could put all this optical circuitry on one chip, it would be cheaper, more efficient, and safer. And there is already a lot of research going on towards the integration of these components. Our work is an important step in this direction.
Such integration between photonics and electronics was not previously possible because garnet and other magnetic crystals cannot grow on a semiconductor substrate. However, magnetic insulators can only be made from magnetic grenades. Hence the need, say the researchers, to attach garnet crystals to semiconductors to bridge the already mature semiconductor technology.
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