Holey device traps light for lasers, filters.Structures known as photonic crystals block the transmission of light whose wavelength falls within a certain range. Researchers from the Massachusetts Institute of Technology Massachusetts Institute of Technology, at Cambridge; coeducational; chartered 1861, opened 1865 in Boston, moved 1916. It has long been recognized as an outstanding technological institute and its Sloan School of Management has notable programs in business, have now built a silicon device that integrates a photonic crystal with a light conduit, making a component that could lead to more efficient lasers and better optical filters. The new device consists of a thin strip of silicon--the conduit--deposited on silicon dioxide silicon dioxide: see silica. (SiO2) A hard, glassy mineral found in such materials as rock, quartz, sand and opal. In MOS chip fabrication, it is used to create the insulation layer between the metal gates of the top layer and the silicon elements below. , with a row of eight holes, each 0.2 micrometer micrometer (mīkrŏm`ətər, mī`krōmē'tər). 1 Instrument used for measuring extremely small distances. ([micro]m) in diameter, "punched all the way through," says MIT's Pierre R. Villeneuve. The holes form the photonic crystal, blocking out a 400-nanometer swath of wavelengths in the infrared part of the spectrum (SN: 3/28/92, p. 206). The holes are spaced at 0.22 [micro]m intervals, except for the fourth and fifth ones, which are farther apart. This irregularity A defect, failure, or mistake in a legal proceeding or lawsuit; a departure from a prescribed rule or regulation. An irregularity is not an unlawful act, however, in certain instances, it is sufficiently serious to render a lawsuit invalid. , essentially a defect in the crystal, captures one wavelength of light that would otherwise get blocked. The holes on either side of the larger gap act as mirrors, bouncing the light back and forth until it emerges from the silicon as a strong signal at 1.54 [micro]m. The device can thus emit light of a chosen frequency or act as a switch that picks out that frequency from a broader signal. Villeneuve and his colleagues report their findings in the Nov. 13 Nature. Adjusting the number, size, and spacing of the holes affects the wavelength and intensity of the emitted signal and the range of the blocked wavelength. Photonic crystals that block infrared and visible light are difficult to make because of the small feature size required. The MIT MIT - Massachusetts Institute of Technology group used a technique called X-ray lithography, which is not yet widespread in industry (SN: 11/8/97, p. 302). MIT's achievement represents "a step on the way to making very tiny [components] from other materials" that have better optical properties than silicon, says Eli Yablonovitch Eli Yablonovitch along with Sajeev John, was one of the two physicists who invented the field of photonic crystals in 1987. In addition to pioneering photonic crystals, he was the first to recognize that a strained quantum well laser has a significantly reduced threshold current of the University of California, Los Angeles UCLA comprises the College of Letters and Science (the primary undergraduate college), seven professional schools, and five professional Health Science schools. Since 2001, UCLA has enrolled over 33,000 total students, and that number is steadily rising. . Lasers and light-emitting diodes made with photonic crystals would operate with much lower currents than conventional devices, Villeneuve says. In telecommunications, such crystals could pick out individual signals from the many traveling down an optical fiber. |
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