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12 November 1984 Optical Fibre Magnetometer Using A Stabilised Semiconductor Laser Source
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Proceedings Volume 0514, 2nd Intl Conf on Optical Fiber Sensors: OFS'84; (1984)
Event: 2nd International Conference on Optical Fiber Sensors, 1984, Stuttgart, Germany
Fluctuations in the operating frequency of semiconductor lasers produce intensity noise in interferometric sensors with a path length difference. This noise has a 1/f frequency dependence and its magnitude increases in direct proportion to interferometer path length difference(1). An approximate value of the amplitude of these fluctuations, for the STL GaAlAs laser used to drive the magnetometer, is 105 Hz measured at a detection frequency of 1 kHz. To achieve a minimum detectable phase of 10-6 radians in a fibre interferometer with such a laser it is necessary to balance the interferometer arms to better than 1 mm. In order to reduce this noise source some authors(2) have reported locking the laser frequency to an external Fabry-Perot cavity by controlling the laser drive current. This is possible since the output frequency of a solid state laser is linearly dependent upon drive current. Compared with unstabilised lasers, improvements of 20 dB in laser output noise spectra have been reported using this technique. Similar results have been obtained in this work, but an all-fibre Fabry-Perot interferometer replaced the bulk optics device. This stabilised laser then acted as a source for a Mach-Zehnder sensing interferometer.
© (1984) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only.
R. H. Pratt, R. E. Jones, P. Extance, G. D. Pitt, and K. W. Foulds "Optical Fibre Magnetometer Using A Stabilised Semiconductor Laser Source", Proc. SPIE 0514, 2nd Intl Conf on Optical Fiber Sensors: OFS'84, (12 November 1984);

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