Fiber-optic current sensor with polarimetric detection scheme
First Claim
1. A method for measuring a current comprising the steps ofsending left and right circularly polarized light waves at least once along a sensing fiber extending around said current,passing said right and left circularly polarized light waves through an optical retarder for generating two orthogonally linearly polarized returning light waves,sending a first part of said returning light waves to a first detector, a second part of said returning light waves to a second detector, characterized by the step ofsending a third part of said returning light waves to a third detector, wherein said first part of said returning light is passed through a first circular analyzer before impinging on said first detector, wherein said second part of said returning light waves is passed through a second circular analyzer before impinging on said second detector and having a polarization opposite to said first circular analyzer, and wherein said third part of said returning light waves is passed through a linear analyzer before impinging on said third detector,wherein said first detector generates a signal I+ and said second detector generates a signal I−
- and said third detector generates a signal IL, and knowledge of the three signals I+, I−
, IL allows to obtain the current even if the values for fringe visibility V and arriving optical power I0 are not known in advance.
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Accused Products
Abstract
The current in a conductor is measured by exploiting the Faraday effect in a sensing fiber. The light returning from the sensing fiber is split into at least two parts, at least one of which is analyzed by a first circular analyzer for generating a first signal. A second part may e.g. be analyzed by a second circular analyzer, and a third part may be analyzed by a linear analyzer. By combining the signals obtained in this way, the current induced phase delay in the returning light can be measured efficiently and accurately.
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Citations
17 Claims
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1. A method for measuring a current comprising the steps of
sending left and right circularly polarized light waves at least once along a sensing fiber extending around said current, passing said right and left circularly polarized light waves through an optical retarder for generating two orthogonally linearly polarized returning light waves, sending a first part of said returning light waves to a first detector, a second part of said returning light waves to a second detector, characterized by the step of sending a third part of said returning light waves to a third detector, wherein said first part of said returning light is passed through a first circular analyzer before impinging on said first detector, wherein said second part of said returning light waves is passed through a second circular analyzer before impinging on said second detector and having a polarization opposite to said first circular analyzer, and wherein said third part of said returning light waves is passed through a linear analyzer before impinging on said third detector, wherein said first detector generates a signal I+ and said second detector generates a signal I− - and said third detector generates a signal IL, and knowledge of the three signals I+, I−
, IL allows to obtain the current even if the values for fringe visibility V and arriving optical power I0 are not known in advance. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15)
- and said third detector generates a signal IL, and knowledge of the three signals I+, I−
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16. A method for measuring a current comprising the steps of
sending left and right circularly polarized light waves at least once along a sensing fiber extending around said current, passing said right and left circularly polarized light waves through an optical retarder for generating two orthogonally linearly polarized returning light waves, sending a first part of said returning light waves to a first detector, characterized by the step of passing said first part of said returning light through a first circular analyzer before impinging on said first detector, passing a further part of said returning light waves through a linear analyzer before impinging on a further detector, wherein said first detector generates a signal I+ or I− - and said further detector generates a signal IL,
and knowledge of the two signals I+ or I−
and IL allows to eliminate an arriving optical power I0 and to calculate the phase shift Δ
φ
assuming that a fringe visibility V is known or has been measured in different manner. - View Dependent Claims (17)
- and said further detector generates a signal IL,
Specification