Adaptive filters for fiber optic sensors

1. A fiber optic current sensor comprising:

a light source;

a polarization beam splitter connected to said light source having a reciprocal port and a non-reciprocal port;

a Faraday rotator connected to said polarization beam splitter;

a first quarter-wave plate connected to said Faraday rotator;

a polarization maintaining fiber connected to said first quarter-wave plate;

a second quarter-wave plate connected to said polarization maintaining fiber;

a sensing fiber connected to said second quarter-wave plate;

a detector connected to said polarization beam splitter via said non-reciprocal port and having an output; and

an adaptive filter for filtering said output,

wherein said adaptive filter includes a comb filter,

further wherein said comb filter includes a register containing accumulators and a switch connected to said register.

2. The fiber optic current sensor of claim 1 , wherein said comb filter is a frequency tracking comb filter.

3. The fiber optic current sensor of claim 1 , wherein said adaptive filter uses a value to weight a comb filtered output to generate a weighted version of said comb filtered output and combines said weighted version of said comb filtered output with a weighted version of said detector output to generate a processed signal.

4. The fiber optic current sensor of claim 3 , wherein said value is generated by a comparator which compares said comb filtered output to said detector output.

5. The fiber optic current sensor of claim 1 , wherein said adaptive filter uses a value to weight a comb filtered output to generate a weighted version of said comb filtered output and combines said weighted version of said comb filtered output with a weighted version of said detector output to generate a processed signal.

6. The fiber optic current sensor of claim 5 , wherein said value is generated by a comparator which compares said comb filtered output to said detector output.

7. The fiber optic current sensor of claim 1 , wherein said adaptive filter is configured to receive a raw signal and output a comb filtered signal, and further comprises:

a comparator for comparing said raw signal to said comb filtered signal to determine a weighting value;

a first gain block for modifying said comb filtered signal based on said weighting value;

a second gain block for modifying said raw signal based on said weighting value; and

a combiner for creating a processed signal from outputs of said first and second gain blocks.

8. The fiber optic current sensor of claim 7 , further comprising:

a pre-filter for filtering said raw signal prior to said raw signal arriving at said comparator.

9. The fiber optic current sensor of claim 7 , wherein said comb filter is a frequency tracking comb filter and further comprising:

a summer for generating an output from summing said raw signal and a feedback signal;

a gain multiplier block for multiplying said output with a gain factor;

a switch controller which controls a pair of switches for switching values in and out of said register containing accumulators, wherein said pair of switches in conjunction with said register containing accumulators operate as a series of low pass filters;

a reset signal generator; and

a clock.

10. A fiber optic current sensor comprising:

a source which generates light;

a biasing element for biasing said light;

a polarization maintaining fiber connected to said biasing element;

a quarter-wave plate connected to said polarization maintaining fiber;

a sensing fiber connected to said quarter-wave plate;

a reflector connected to said sensing fiber;

a coupler connected to said light source and to a detector, wherein said detector receives light returning from said reflector and generates an output associated therewith; and

an adaptive filter for filtering said output,

wherein said adaptive filter includes a comb filter,

further wherein said comb filter includes a register containing accumulators and a switch connected to said register.

11. The fiber optic current sensor of claim 10 , wherein said biasing element is one of a Faraday rotator and a birefringence modulator.

12. The fiber optic current sensor of claim 10 , wherein said adaptive filter is a frequency tracking comb filter.

13. The fiber optic current sensor of claim 10 , wherein said adaptive filter uses a value to weight a comb filtered output to generate a weighted version of said comb filtered output and combines said weighted version of said comb filtered output with a weighted version of said detector output to generate a processed signal.

14. The fiber optic current sensor of claim 13 , wherein said value is generated by a comparator which compares said comb filtered output to said detector output.

15. The fiber optic current sensor of claim 10 , wherein said adaptive filter is configured to receive a raw signal and output a comb filtered signal, and further comprises:

a comparator for comparing said raw signal to said comb filtered signal to determine a weighting value;

a first gain block for modifying said comb filtered signal based on said weighting value;

a second gain block for modifying said raw signal based on said weighting value; and

a combiner for creating a processed signal from outputs of said first and second gain blocks.

16. The fiber optic current sensor of claim 15 , further comprising:

a pre-filter for filtering said raw signal prior to said raw signal arriving at said comparator.

17. The fiber optic current sensor of claim 15 , wherein said comb filter is a frequency tracking comb filter and further comprising:

a summer for generating an output from summing said raw signal and a feedback signal;

a gain multiplier block for multiplying said output with a gain factor;

a switch controller which controls a pair of switches for switching values in and out of said register containing accumulators, wherein said pair of switches in conjunction with said register containing accumulators operate as a series of low pass filters;

a reset signal generator; and

a clock.