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26 May 2005
A look at some of the innovations in optics unveiled at CLEO/QELS 2005.
IMAGING
• A Caltech team has fabricated a microfluidic circuit that contains a compact optical imager-on-a-chip. In the future, the chip could potentially perform tasks such as screening for white blood cells or cancer cells. The fluid sample flows over a gold film containing an array of submicron-sized holes that function as light receivers. The sample is illuminated from above, and a CCD sensor below the gold film images the cells as they pass over the holes. Using state-of-the art nanofabrication technology, the scientists feel that it should be possible to create an imager with sub 100 nm resolution. (Paper - CFF4)
PULSE SHAPING
• Scientists in the US have created a programmable on-chip ultrashort-pulse shaper by combining a micro-machined actuator array with a chirped fibre Bragg grating (CFBG). The University of Michigan device works by using micro-machined silicon actuators to locally apply a pressure of up to hundreds of micro-Newtons to the CFBG. The tiny pressure-actuators mechanically strain the fibre at a number of predetermined positions along its length, altering its refractive index and shifting the local Bragg-wavelength. In initial proof of principle experiments, it was able to increase the duration of pulses generated by a chirped-pulse amplification set-up from 1.5 to 4 ps (FWHM). The team says that the technique can generate arbitrary pulse shapes in a time window from 10 ps to 1 ns. (Paper - CFK6)
LASERS
• Researchers based at University of California at Santa Barbara, US, have made a semiconductor laser with an ultra-low lasing threshold by embedding InAs/GaAs quantum dots (QDs) into photonic crystal microcavities. The optically pumped structure has a lasing threshold of around 160 nW and offers single mode lasing between 910 and 975 nm, making it an attractive option for cavity-quantum electrodynamics experiments and single QD lasing. The team optically excites its QD laser by piezo scanning 780 nm continuous wave emission from a laser diode over the surface. (Paper - QWA1)
LEDs
• Taesung Kim and colleagues at the University of Illinois, US, have used a photonic crystal (PC) technique to boost the external wall-plug efficiency of a GaN LED by 30%. The researchers found that their PC enhanced device showed almost identical spectral properties to a conventional LED emitting at 450 nm. "The only difference between the conventional and PC LED was the presence of the holes of the PC pattern inside of the inner ring contact," say the authors in their paper. A maximum output power of about 200 µW was obtained for a drive current of 80 mA. (Paper - CMR3)
OPTICAL POSITIONING
• The task of sizing, positioning and separating nanoparticles could soon become much easier thanks to the work of scientists in Japan. A team from Japan Science and Technology Agency and Tokyo University has managed to align gold nanoparticles on the edge of a Si wedge by controlling particle-substrate and particle-particle interactions with an optical near field. Illuminating through the Si substrate with 690 nm light for 60 seconds transported particles towards its top edge where the optical near field energy is enhanced. The researchers explain that their set-up could form the basis of a nano-dot coupler for guiding electromagnetic energy. (Paper - CThL1)
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