OSA News

Research Published in OSA Journal Addresses Key Problem in Planar Photonic Crystal Technology

Results Bring Exciting Photonic Crystal Technologies Closer to Reality

September 4, 2002 (Washington, D.C.) - The Optical Society of America (OSA) announced today that a recent paper, published by scientists at the California Institute of Technology in OSA's Optics Express, shows how to confine light with very low loss in so-called "photonic crystals," materials that promise to advance optics in the same way that silicon forever changed electronics. The study suggests that physicists are closer than ever before to achieving some coveted photonic-crystal technological breakthroughs, such as "sub-microwatt threshold lasers" and high-speed light-emitting diode sources for optical communication, efficient single-mode single-photon sources for quantum key distribution, and ultimately strong coupling between single photon and single electron states in a semiconductor microcavity for coherent quantum information processing and communication.

One of the most exciting developments in modern optics, photonic crystals aim to control electromagnetic waves in multiple dimensions. Just as electronic devices such as computer chips, silicon, and other semiconductor materials permit only electrons of certain energies to exist within them, so too do photonic crystals allow only certain colors or "wavelengths" to travel in them while blocking other colors. To achieve this ability, photonic crystals are built of materials like silicon that are arranged in specific, regularly repeating patterns, such as honeycomb arrays of air holes in a semiconductor. The geometric arrangements of material cause light waves of undesired colors to cancel out, while permitting only desired colors to exist in the crystal. By introducing defects-breaks in a photonic crystal's regularly repeating pattern-it is possible to trap light to extremely small volumes, nearing the theoretical limit. However, past research demonstrated that such designs (termed "defect cavities") could suffer massive "radiation losses," in which significant amounts of light would leak out, thus hampering the development of photonic crystal cavities into practical optical devices.

OSA members Kartik Srinivasan, M.S. and Oskar Painter, Ph.D. of the California Institute of Technology, conducted an investigation into this very problem, with the ultimate goal of understanding the cause of radiation losses. They also sought to develop general guidelines for bringing about highly efficient light storage within planar photonic crystal waveguides-flat circuits that could guide lightwaves in the optical equivalent of electronic circuits.

"Radiation losses have been an important issue for us," said Srinivasan. "They must be reduced before planar photonic crystal resonant cavities or waveguides can be considered as viable candidates for novel light sources, ultra-high density planar lightwave circuits, and experiments examining electron-photon interactions in quantum optics. The results of our study help bring us closer to this ultimate goal."

To optimize results and observe the losses more clearly, these researchers examined how they could design defects that would manage to prevent light from escaping the crystal. They described the complex light field inside a photonic crystal as a combination of individual light waves (optical modes) with different values of momentum, and then investigated the best possible defects for eliminating those light waves that radiate. This "Fourier analysis" approach enabled Srinivasan and Painter to produce designs in square photonic lattices with the highest predicted cavity quality (Q) factors to date (105). Q factors describe how much light can build up in the crystal; a higher Q factor means that the crystal can hold more light. The implications from this investigation suggest that their Fourier design methodology is a powerful tool for creating not only high-Q resonant cavities, but various other low-loss photonic crystal optical devices such as specialized optical waveguides.

"We are pleased with the progress we made in this investigation and will continue to explore ways to decrease radiation loss in such environments," said Srinivasan. "We are thrilled that OSA was able to publish these results so quickly and hope that they provide a basis for many future investigations and developments."

About Optics Express
Optics Express, the 8th-ranked journal in the field of optics, reports on new developments in all fields of optical science and technology every two weeks. Optics Express is available at no cost to readers online at www.OpticsExpress.org. The journal provides rapid publication of original, peer-reviewed papers. Optics Express incorporates the use of multimedia and color graphics into many of its articles.

About OSA
Founded in 1916, the Optical Society of America (OSA) was organized to increase and diffuse the knowledge of optics, pure and applied; to promote the common interests of investigators of optical problems, of designers, and of users of optical apparatus of all kinds; and to encourage cooperation among them. The purposes of the Society are scientific, technical, and educational. The mission of OSA is to promote the generation, application and archiving of knowledge in optics and photonics and to disseminate this knowledge worldwide.