Radiant energy – Photocells; circuits and apparatus – Optical or pre-photocell system
Patent
1996-07-12
1998-03-17
Allen, Stephone B.
Radiant energy
Photocells; circuits and apparatus
Optical or pre-photocell system
324 96, 385 12, G02F 101
Patent
active
057290059
ABSTRACT:
A fiber optic subassembly for a Faraday-effect current sensor has an optical sensing fiber supported by a tubular holder in a square or rectangular configuration, with the three of the four corners thereof designed with bends which have a net zero bend-induced birefringence. The bends are formed by providing two loops which have effective angles of about 90.degree., the two loops lying in orthogonal planes, such that the fast axis of birefringence in the first loop is parallel to the slow axis of birefringence in the second loop, and the slow axis of birefringence in the first loop is parallel to the fast axis of birefringence in the second loop. In this manner, retardance accumulated in the first loop is offset by retardance accumulated in the second loop. If the loops are substantially identical, the offsetting of the retardance is effectively complete such that the bend exhibits negligible bend-induced birefringence.
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Article entitled "Recent Progress In Optical Current Sensing Techniques" by Ning et al., 1995 American Institute of Physics, Rev. Sci. Instrum. 66(5), Woodbury NY. May 1995, pp. 3097-3111.
Geometrical separation between the birefringence components in Faraday-rotation fiber-optic current sensors, by A. Ben-Kish, et al., pp. 687-689, May 1, 1991, vol. 16, No. 9, Optics Letters.
Temperature insensitive fiber coil sensor for altimeters, by Y. Amai, et al., pp. 975-978, Mar. 1, 1990, vol. 29, No. 7, Applied Optics.
Dawson Jay W.
Johnson Leonard A.
MacDougall Trevor W.
Allen Stephone B.
Chernivec Gerald F.
Minnesota Mining and Manufacturing Company
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