FiO Hot Topics: Hot Optics

New types of research that explore new avenues in medical imaging, solar power, communications and vision were presented during "What's Hot in Optics Today?" during Frontiers in Optics 2009 (FiO) Sunday.

About 100 conference early birds attended the late afternoon hot topics session, presented by the division chairs of Optical Society of America's (OSA) technical groups, to learn what's hot in biomedical optics; solar technology; information, acquisition, processing and display; photonics and optoelectronics; and vision and color.

Chris B. Schaffer of Cornell University began the session with his talk, Seeing the Almost Invisible, Using Novel Nonlinear Optical Effects for Image Contrast in Biology and Medicine.

Cornell University's Chris Schaffer talks on novel nonlinear optical effects for image contrast in biology and medicine as part of the Hot Topics session at OSA's Frontiers in Optics conference. (Photonics Media photo by Melinda Rose)

A key emerging area in biology and medicine, where observations often have to be made in living systems, is developing tools and techniques for molecularly specific imaging, Schaffer explained, with the best being nonlinear optical methods, because they will allow deep tissue imaging. Schaffer discussed nonlinear optical methods such as two-photon excited fluorescence, harmonic generation and coherent anti-Stokes Raman scattering.

Optical scattering results in a loss of image contrast. An ideal way to form a 3-D image is to excite the molecule in a 3-D localized spot, because then scattering doesn't matter. This overcomes a problem with imaging thick samples, where scattering is a problem, he said.

Schaffer talked of "packing the light" into short, femtosecond-length laser pulses for imaging the brain to a depth of 100 µm, with no loss of image quality until a depth of about 1 mm.

Coherent anti-Stokes Raman scattering (CARS) has turned out to be a fantastic way to image lipids, he said. "Lipid is something difficult to fluorescently label, at least in vivo," Schaffer said.

In all the methods mentioned, he said, the nonlinear effects are measured by looking at large changes in color. But some nonlinear effects that don't result in color changes can also be used for imaging, such as modulation transfer. In that method, one beam of a two-beam interaction is modulated and one looks at the effect on the nonmodulated beam.

Schaffer cited a December 2008 study at Harvard in which stimulated Raman scattering was imaged by modulation transfer. In that method, the pump photons were converted into Stokes photons. The pump beam is left on all the time and the Stokes beam is turned off and on, then the tiny changes in intensity are measured.

"Intensity changes of 10^-7 to 10^-6 are readily detected," he said, and different kinds of lipids can be detected better than CARS.

Using nonlinear optical effects enables micrometer resolution deep into scattering biological tissue. Two-photon excited fluorescence has a 1 mm limit, while other nonlinear optical techniques have a limit on the hundreds of microns scale. "It's not a way to look at your heart from outside your body, but it can image cells," he said.

R. John Kostel of Photon Engineering LLC and the College of Optical Sciences at the University of Arizona presented information on solar trends. Currently solar provides less than .1 percent of the electricity in the US, but less than two percent of the land dedicated to grazing and farming in this country could provide all the electricity needed.

Hot embossing of antireflective coatings for solar cells looks promising for the future, because the optical quality it provides is excellent, he said.

David Brady of Duke University, chairman-elect of the OSA Information Acquisition, Processing and Display Div., discussed compressive measurement and holography. Images are often compressed after measurement, but a new technique, being reported this week at the Computational Optical Sensing and Imaging (COSI) topical meeting of the OSA Optics and Photonics Congress, involves compressing it during the measurement process. Superresolution detail provided by fluorescence imaging of optically controllable single-molecule emitters can be extended to three dimensions using a novel double-helix point spread function (PSF).

Brady said 2009 has seen major advances in digital holographic technologies, pointing to work by Zebra Imaging of Texas with defense applications and UK-based Light Blue Optics, a startup developing holographic projection displays for handheld devices. He also cited GE's announcement this year of an advancement in holographic storage with its 500-GB capacity standard DVD disk, the capacity of 100 regular DVDs.

Juerg Leuthold of Karlsruhe Institute of Technology (KIT) in Germany presented an overview of photonics communications advances for the Photonics and Electro-optics Div. He cited recent advances such as the first transmission of 32 Tb/s over 580 km of single-mode fiber (SMF)-28 ultralow loss fiber and the demonstration of 5.1 Tb/s single-channel 8-PSK and 16-QAM signals.

These achievements mean the limit talked about six or seven years ago, 100 Tb/s, is probably going to be surpassed, he said.

Another new trend is ODFM, he said, or orthogonal frequency-division multiplexing, and silicon photonics is advancing as well, with the ability to generate third harmonic generation on silicon demonstrated for the first time, as well as the all-CMOS silicon photonic transmitter.

In his presentation on the Secret Life of the Retina, Alex Wade of the University of California, San Francisco, described how a new class of photoreceptive cells in the retina that was previously unknown is causing excitement. The protein, melanopsin, was discovered in the retina of frogs and has the potential to treat seasonal effective disorder as well as restore some vision in the blind.

"This technology has advanced very quickly," Wade said, adding that tests in mice have shown that melanopsin is stable in the retina for at least 18 months.

Another hot topic he discussed is optogenetics, an emerging field that uses blue laser light to manipulate DNA.

Frontiers in Optics, collocated with Laser Science XXV, continues through Thursday at the Fairmont Hotel in San Jose. For more information, visit: www.frontiersinoptics.com

Melinda Rose
Senior Editor