Patent US6597458B2 successfully refreshed from Google Patents.
US6597458B2
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Method and system for stabilizing and demodulating an interferometer at quadrature
Assignee: Texas Christian University
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Filing: 2001-02-02
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Granted: 2003-07-22
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Expires: 2021-02-02
Abstract
Abstract A method and system for stabilizing and demodulating an interferometer at quadrature are described. In response to receipt of a signal indicative of optical power of the interferometer, an interferometer control system determines an optical path length correction required to stabilize the interferometer at quadrature utilizing signal amplitudes appearing at multiple harmonics of the signal. In a particularly preferred embodiment, the signal amplitudes are calculated utilizing the Goertzel algorithm, a computationally efficient discrete Fourier transform. The interferometer control system then outputs an error signal indicative of the optical path length correction. In a preferred embodiment, the error signal forms the DC component of a composite stabilization signal, whose AC component is the reference modulation signal utilized to excite a transducer to modulate the optical path length of the interferometer. With the interferometer stabilized at quadrature, the interferometer control system determines a first signal amplitude of a particular harmonic without target oscillation and a second signal amplitude of the same harmonic with target oscillation. Based upon the relative magnitudes of the first and second signal amplitudes, the interferometer control system determines a solution set for the displacement amplitude of the interferometer target. Any ambiguity in the displacement amplitude can then be eliminated utilizing additional information gained from the signal amplitude present at a harmonic of a target oscillation frequency.
Inventors
- 👤 Tristan J. Tayag
- 👤 Christopher A. Belk
Bibliographic Details
Application Number
—
Jurisdiction
US
Data Source
google_patents
Last Synchronized
2026-11-09 11:32
CPC Classifications
G; G01; G01B; G01B9/00; G01B9/02; G01B9/02083; G01B9/02084; G01B9/02055; G01B9/02062; G01B9/02067
Claims Analysis
Total Claims: 33
Claim 1
Independent Claim
63 words
A method of stabilizing an interferometer at quadrature, said method comprising: digitizing an input to obtain a digital signal indicative of optical power; from the digital signal, determining an optical path length correction required to stabilize the interferometer at quadrature utilizing signal amplitudes appearing at multiple harmonics of the digital signal; and outputting an error signal indicative of the optical path length correction.
Claim 2
Independent Claim
63 words
A method of stabilizing an interferometer at quadrature, said method comprising: digitizing an input to obtain a digital signal indicative of optical power; from the digital signal, determining an optical path length correction required to stabilize the interferometer at quadrature utilizing signal amplitudes appearing at multiple harmonics of the digital signal; and outputting an error signal indicative of the optical path length correction.
Claim 3
Dependent Claim
27 words
The method of claim 1 , wherein the determining step comprises computing the signal amplitudes appearing at multiple harmonics of the digital signal utilizing a Goertzel algorithm.
Claim 4
Dependent Claim
32 words
The method of claim 2 , wherein the computing step comprises computing the signal amplitudes appearing at the second and third harmonics of a reference modulation signal component of the digital signal.
Claim 5
Dependent Claim
31 words
The method of claim 3 , and further comprising: if the interferometer is at quadrature, storing the magnitude of the signal amplitude appearing at the third harmonic of the digital signal.
Claim 6
Dependent Claim
40 words
The method of claim 1 , and further comprising: computing a magnitude of the error signal; and if the magnitude of the error signal magnitude is out of range, resetting the magnitude of the error signal to an initial value.
Claim 7
Dependent Claim
31 words
The method of claim 1 , said generating step comprising generating a stabilization signal having said error signal as a DC component and a reference modulation signal as the AC component.
Claim 8
Dependent Claim
26 words
The method of claim 1 , and further comprising: at quadrature, demodulating the digital signal to determine a displacement amplitude of a target of the interferometer.
Claim 9
Dependent Claim
54 words
The method of claim 7 , said demodulating step further comprising: determining first and second signal amplitudes of a particular harmonic in the digital signal with and without target oscillation; and determining a displacement amplitude of the target based upon the relative magnitudes of the first and second signal amplitudes of the particular harmonic.
Claim 10
Dependent Claim
28 words
The method of claim 8 , and further comprising eliminating ambiguity in the displacement amplitude by determining a signal amplitude at a harmonic of a target oscillation frequency.
Claim 11
Dependent Claim
59 words
An interferometer control system, comprising: means for digitizing an input to obtain a digital signal indicative of optical power; means for determining an optical path length correction required to stabilize the interferometer at quadrature utilizing signal amplitudes appearing at multiple harmonics of the digital signal; and means for outputting an error signal indicative of the optical path length correction.
Claim 12
Dependent Claim
59 words
An interferometer control system, comprising: means for digitizing an input to obtain a digital signal indicative of optical power; means for determining an optical path length correction required to stabilize the interferometer at quadrature utilizing signal amplitudes appearing at multiple harmonics of the digital signal; and means for outputting an error signal indicative of the optical path length correction.
Claim 13
Dependent Claim
32 words
The interferometer control system of claim 10 , wherein the means for determining comprises means for computing the signal amplitudes appearing at multiple harmonics of the digital signal utilizing a Goertzel algorithm.
Claim 14
Dependent Claim
37 words
The interferometer control system of claim 11 , wherein the means for computing comprises means for computing the signal amplitudes appearing at the second and third harmonics of a reference modulation signal component of the digital signal.
Claim 15
Dependent Claim
35 words
The interferometer control system of claim 12 , and further comprising: means for, if the interferometer is at quadrature, storing the magnitude of the signal amplitude appearing at the third harmonic of the digital signal.
Claim 16
Dependent Claim
46 words
The interferometer control system of claim 10 , and further comprising: means for computing a magnitude of the error signal; and means for resetting the magnitude of the error signal to an initial value if the magnitude of the error signal magnitude is out of range.
Claim 17
Dependent Claim
36 words
The interferometer control system of claim 10 , said means for generating comprising means for generating a stabilization signal having said error signal as a DC component and a reference modulation signal as the AC component.
Claim 18
Dependent Claim
34 words
The interferometer control system of claim 10 , and further comprising: means for demodulating the digital signal when the interferometer is at quadrature to determine a displacement amplitude of a target of the interferometer.
Claim 19
Dependent Claim
61 words
The interferometer control system of claim 16 , said means for demodulating further comprising: means for determining first and second signal amplitudes of a particular harmonic in the digital signal with and without target oscillation; and means for determining a displacement amplitude of the target based upon the relative magnitudes of the first and second signal amplitudes of the particular harmonic.
Claim 20
Dependent Claim
32 words
The interferometer control system of claim 17 , and further comprising means for eliminating ambiguity in the displacement amplitude by determining a signal amplitude, at a harmonic of a target oscillation frequency.
Claim 21
Dependent Claim
27 words
An interferometer system, comprising: an interferometer; and an interferometer control system in accordance with claim 10 , wherein said interferometer control system is coupled to said interferometer.
Claim 22
Dependent Claim
73 words
An interferometer control system, comprising: a digital processor; memory, coupled to the processor, that stores stabilization code executable by the processor, wherein the stabilization code causes the processor to determines an optical path length correction required to stabilize an interferometer at quadrature utilizing signal amplitudes appearing at multiple harmonics of a digital signal indicative of an optical power of the interferometer, and output an error signal indicative of the optical path length correction.
Claim 23
Dependent Claim
73 words
An interferometer control system, comprising: a digital processor; memory, coupled to the processor, that stores stabilization code executable by the processor, wherein the stabilization code causes the processor to determines an optical path length correction required to stabilize an interferometer at quadrature utilizing signal amplitudes appearing at multiple harmonics of a digital signal indicative of an optical power of the interferometer, and output an error signal indicative of the optical path length correction.
Claim 24
Dependent Claim
32 words
The interferometer control system of claim 20 , wherein the stabilization code causes the processor to compute the signal amplitudes appearing at multiple harmonics of the digital signal utilizing a Goertzel algorithm.
Claim 25
Dependent Claim
37 words
The interferometer control system of claim 21 , wherein the stabilization code causes the processor to compute the signal amplitudes appearing at the second and third harmonics of a reference modulation signal component of the digital signal.
Claim 26
Dependent Claim
32 words
The interferometer control system of claim 22 , wherein the stabilization code causes the processor to store the magnitude of the third harmonic of the signal if the interferometer is at quadrature.
Claim 27
Dependent Claim
42 words
The interferometer control system of claim 20 , wherein the stabilization code causes the processor to compute a magnitude of the error signal and reset the magnitude of the error signal to an initial value if the magnitude as out of range.
Claim 28
Dependent Claim
37 words
The interferometer control system of claim 20 , wherein the stabilization code causes the processor to output a stabilization signal having said error signal as a DC component and a reference modulation signal as the AC component.
Claim 29
Dependent Claim
48 words
The interferometer control system of claim 20 , wherein the memory further comprises demodulation code executable by the processor, wherein the demodulation code causes the processor to demodulate the digital signal when the interferometer is at quadrature to determine a displacement amplitude of a target of the interferometer.
Claim 30
Dependent Claim
59 words
The interferometer control system of claim 26 , wherein said demodulation code causes the processor to determine first and second signal amplitudes of a particular harmonic in the digital signal with and without target oscillation and, based upon the relative magnitudes of the first and second signal amplitudes of the particular harmonic, determine a displacement amplitude of the target.
Claim 31
Dependent Claim
31 words
The interferometer control system of claim 27 , wherein said demodulation code eliminates ambiguity in the displacement amplitude by determining a signal amplitude at a harmonic of a target oscillation frequency.
Claim 32
Dependent Claim
22 words
The interferometer control system of claim 20 , and further comprising an analog-to-digital converter coupled to a signal input of said processor.
Claim 33
Dependent Claim
27 words
An interferometer system, comprising: an interferometer; and an interferometer control system in accordance with claim 20 , wherein said interferometer control system is coupled to said interferometer.
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