MIT puts optics on a chip
An interdisciplinary team at MIT has found a new way to integrate photonic circuitry on a silicon chip. Their 'optics on a chip' may revolutionize computing with the addition of the power and speed of light waves to traditional electronics. "The new technology will also enable supercomputers on a chip with unique high-speed capabilities for signal processing, spectroscopy and remote testing, among other fields." And because such chips can be mass-manufactured for the first time, the researchers think that their optical components could be integrated on silicon chips within five years.
This research has been partially conducted by Erich P. Ippen, professor of electrical engineering and physics, Franz X. Kaertner, professor of electrical engineering and computer science, and Henry I. Smith, professor of electrical engineering. The team used the NanoStructures Laboratory and the Scanning-Electron-Beam Lithography Facility.
Here is a short description of the problem of the integration of light waves with traditional silicon chips.
Microphotonics technology aims to "mold" the flow of light. By using two different materials that refract light differently, such as silicon and its oxides, photons can be trapped within a miniscule hall of mirrors, giving them unique properties. The stumbling block has been that microphotonics devices are sensitive to the polarization of light.
Below is an illustration showing the integrated polarization diversity solution found by the MIT team. "Polarization-transparent microphotonic circuits are constructed from polarization-sensitive components. Arrows depict the orientation of the electric field. An arbitrary input polarization state is split into its orthogonal components and one of these components is rotated to achieve a single on-chip polarization state. Two identical copies of arbitrarily polarization-sensitive photonic structures are used for the two arms of the architecture. At the output, the two arms are recombined after one of the polarization components is rotated to prevent interference between the two signals." (Credit for image and caption: MIT, via Nature Photonics)
And here is a more general description of the MIT's solution.
The MIT researchers' innovative solution involves splitting the light emanating from an optic fiber into two arms-one with horizontally polarized beams and one with vertical beams-in an integrated, on-chip fashion.
Setting these two at right angles to one another, the researchers rotated the polarization of one of the arms, also in an integrated way. The beams from the two arms, now oriented the same way, then pass through identical sets of polarization-sensitive photonic structures and out the other side of the chip, where the two split beams are rejoined.
And what can we expect from this integration?
The advantage in integrating optics with silicon technology is that silicon fabrication technology "is already highly developed and promises precise and reproducible processing of densely integrated circuits," Kaertner said. "The prospect of integrating the photonic circuitry directly on silicon electronic chips is ultimately also an important driver."
As mentioned above, the new devices could be in demand within five years, added Ippen.
This research work has been published by Nature Photonics under the name "Polarization-transparent microphotonic devices in the strong confinement limit" (Volume 1, Issue 1, Pages 57-60, January 2007). Here are two links to the abstract and to the full paper (PDF format, 4 pages, 331 KB). The above illustration has been extracted from this paper.
Sources: Massachusetts Institute of Technology news release, via EurekAlert!, February 5, 2007; and various other websites
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