Magnetic field integrated fiber optic sensor with improved sensitivity
AssigneeThe Texas A&M University System
InventorJames N. Blake
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Abstract
A current sensor coil design for reducing or eliminating long undulations of magnetic sensitivity. Such reduction or elimination improves isolation of the current sensor such that proximate currents and accompanying effects do not affect the accuracy of the current sensor determination of a current being measured. Several designs, which may be incorporated separately or in combination, include modifying the specifications of the quarter waveplate, cutting the fiber of the sensor coil to a proper length, choosing a proper perimeter length of the sensor coil or head, and using a particular length of fiber adjusted to work in conjunction with a multi-wavelength or broadband light source.
Claims32
A magnetic field integrating optical sensor comprising:
- a sensor head having a varying sensitivity of period ξ around its perimeter of the form S o + ∑ n = 1 ∞ S n cos ( 2 n π z ′ P + Ψ n ) ;
- and wherein:
- So is a sensitivity constant of said sensor head;
- Sn is an imperfection constant of said sensor head for n≧1;
- z′ is a distance along the perimeter of said sensor head;
- P is a length of the perimeter equal to m · ξ N ,
- where m is an odd integer not equal to kN;
- k is any integer;
- and N is a number of sensing fiber turns contained in the sensor head;
- and
- ψn's are constants.
A magnetic field integrating optical sensor comprising:
- a fiber-optic sensing coil formed from a spun birefringent fiber having a periodic structure, the fiber-optic sensing coil having a varying sensitivity around its perimeter of the form S o + ∑ n = 1 ∞ S n cos ( 2 n π z ′ P + Ψ n ) ;
- wherein:
- So is a sensitivity constant of said sensor head;
- Sn is an imperfection constant of said sensor head for n≧1;
- z′ is a distance along the perimeter of said sensor head;
- P is a length of the perimeter;
- and
- the ψn's are constants;
- and
- wherein the spun birefringent fiber has a long spatial period, ξ, approximately equal to 4 · L B 2 L rev ,
- where LB is the intrinsic polarization beat length of the spun birefringent fiber in its unspun state, and Lrev is the length of each period in the periodic structure of the spun birefringent fiber.
A magnetic field integrating fiber optic sensor comprising:
- a sensor head having fiber that exhibits a periodic undulation in sensitivity;
- a light source that emits multiple wavelengths;
- and
- a total fiber length greater than the ratio of the undulation period to the fractional light source spectral bandwidth such that L TOTAL = ( ξ · λ Δ λ ) ;
- wherein LTOTAL is the total length of the fiber, λ is the mean source wavelength, and Δλ is the wavelength spread of the source.
A magnetic field integrating fiber optic sensor comprising:
- a sensor head having a fiber with a periodic structure;
- and
- a means for launching at least one light wave into the fiber having a polarization state that substantially replicates itself after each period of the periodic structure.
A magnetic field integrating fiber optic sensor comprising:
- a sensor head having a fiber that exhibits a periodic undulation in sensitivity;
- and
- wherein the fiber has a total length substantially equal to an odd integer times a quarter-period of the undulation.
A magnetic field integrating fiber optic sensor comprising:
- a sensor head having a fiber that exhibits a periodic undulation in sensitivity;
- and
- the fiber has a total length substantially equal to an odd integer times a half-period of the undulation.
A magnetic field integrating fiber optic sensor comprising:
- a sensor head having a fiber that exhibits a periodic undulation in sensitivity of period ξ;
- and wherein:
- a relationship is between the undulation period and a perimeter length P of said sensor head;
- P = m ξ N ;
- m is an odd integer not equal to kN;
- k is any integer;
- and
- N is a number of sensing fiber turns contained in the sensor head.
A magnetic field integrating optical sensor comprising:
- a fiber-optic sensing coil formed from a spun birefringent fiber having a periodic structure, the fiber-optic sensing coil having a varying sensitivity around its perimeter;
- wherein the spun birefringent fiber has a long spatial period, ξ, approximately equal to 4 · L B 2 L rev ,
- where LB is the intrinsic polarization beat length of the spun birefringent fiber in its unspun state, and Lrev is the length of each period in the periodic structure of the spun birefringent fiber;
- and
- wherein a ratio of Lrev to LB is between three and eight.
Dependencies are inferred from the claim text.