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From "World Oil Magazine" Vol 226, No 9, Sept 2005 by PERRY A. FISCHER, EDITOR Subsea meets space. Researchers studying how to measure and detect extremely faint gravitational wave signals from outer space hit upon a novel idea that led to a breakthrough in fiber optic acoustic sensing. The research team, from the Centre for Gravitational Physics at Australian National University, worked with Dr. Ian Littler from the University of Sydney to develop the ground-breaking technique. The technology is 100 times more sensitive than current acoustic techniques and the fiber optic sensors are deployable up to 100 km away from a central recording station without significant degradation of signal quality. Our industry could benefit tremendously. The ANU-led team bettered the world record in fiber strain sensitivity by more than a factor of 100, and achieved it at the end of a 5-km long optical fiber. Patents have been applied for. The sensor is reported to detect acoustic waves "with almost unimaginable sensitivity." It is described as being able to detect changes on the order of a human hair (100 micrometers) at an Earth-Moon distance, a sensitivity level known as sub-picostrain." The acoustic sensor is a variation on the well-known Faby-Perot interferometer, where laser light is sent through the fiber and reflected at the end. If the end sensor has moved even minutely, it will show as a change in the interference pattern created by the sent light and the reflected light. This is already commercially available, but the difference here is that there are reflectors at both ends of the fiber. Light bounces back and forth many times before exiting the system, effectively magnifying the sensitivity threshold. This is a technique that is used in gravitational wave detection, to measure an extremely tiny warp in space-time due to massive astrophysical objects such as black holes and supernova. The breakthrough is not just in the signal mechanics, but also in the ability to extract the laser interference signal due to minute changes from a sensor located at a great distance away, and with no loss in fidelity. A Sydney-based Australian marine geotechnical services company, called Benthic Geotech, was the first to approach the team about jointly working toward full commercialization of the fiber sensors. The obvious application would be a radical sensitivity increase in passive seismic monitoring, perhaps even hearing fluid flow itself rather than just the cracks and creaks from rock movement. On the potential problem side, if crowded areas and permanent seismic systems already suffer from noise pollution, this could prove to be too sensitive a receiver for those areas. |