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21 Sep 2005
A look at some of innovations in optics this month including an efficient input/output coupler for use in silicon photonic circuits.
Communication
An efficient input/output coupler suitable for use in silicon photonic circuits has been developed by a team of researchers from the UK and Italy. The team claims that a coupling efficiency of 55% and an insertion loss of <= 0.05 dB are possible. (Optics Express 13 7374)
Fabricated on a silicon substrate, the so-called dual-grating assisted directional coupler features several layers that guide the light from an optical fiber into a thin silicon-on-insulator (SOI) waveguide.
"A fiber could be butt-coupled to a thick SiON waveguide and the light coupled to a Si3N4 waveguide using the first grating and to a thin SOI waveguide via the second grating," explain the authors. "The silicon nitride waveguide is crucial because it enables highly efficient coupling at both gratings."
Spectroscopy
A team from the Universität Düsseldorf in Germany has used cavity leak-out spectroscopy (CALOS) to detect carbonyl sulphide (OCS) in ambient air. Having achieved a detection limit of 7 parts per trillion (ppt), the team says that CALOS shows promise for other trace-gas monitoring applications at the ppt level where real-time data acquisition is essential. (Optics Letters 30 2314)
The measurements were made using a CO laser operating between 4.75 and 5.5 microns and emitting 50 to 300 mW single mode depending on the laser transition. "Our experiments demonstrate that CALOS is an excellent method for highly sensitive quantitative detection of OCS in the atmosphere," conclude the authors. "To our knowledge this is the first report of spectroscopic OCS monitoring in ambient air at the ppt level."
Visual inspection
Researchers at the US Department of Agriculture have unveiled a low-cost and convenient way to spot diseased chicken carcasses. The method involves adding two narrow-band filters to a pair of binoculars, which can then be used in a processing plant environment. (Applied Optics 44 5454)
By changing the filters, Fujian Ding and colleagues report that they can distinguish between healthy chickens and those suffering from the lung disease air-sac, improper bleeding, inflammatory processes, septicaemia-toxemia and tumors.
"Results show that for multi-target detection, the wave-band pair of (454 nm, 578 nm) is able to distinguish all six chicken conditions," say the authors. "For single-target detection of wholesome, air-sac, cadaver and tumor, the wave-band pairs of (449 nm, 571 nm), (441 nm, 576 nm), (458 nm, 576 nm) and (431 nm, 576 nm) respectively easily distinguish the target condition from the other five conditions."
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