Abstract

Digitally enhanced interferometry (DI) can be used to distinguish between interferometric signals and simultaneously monitor in-line object displacements with subnanometer sensitivity. In contrast to conventional interferometry—where these signals interfere with each other and degrade performance—we experimentally show that by using DI, each of these signals can be isolated and measured at the same time. We present what we believe to be the first demonstration of DI’s signal multiplexing capabilities, showing simultaneous length sensing of three sections of an optical fiber. The cross talk between length measurements was less than 2.6×103 with a displacement noise floor of 200pm/Hz, which corresponds to a strain sensitivity of less than 80 picostrain (pϵ) in each sensor. We also enhance our system’s displacement sensitivity at low frequencies by combining information from multiple lengths to suppress errors due to laser frequency noise.

© 2011 Optical Society of America

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References

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    [CrossRef]
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    [CrossRef] [PubMed]
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    [CrossRef] [PubMed]
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    [CrossRef]
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    [CrossRef]

2009 (1)

2007 (2)

1999 (1)

J. W. Armstrong, F. B. Estabrook, and M. Tinto, Astrophys. J. 527, 814 (1999).
[CrossRef]

1993 (1)

N. Bobroff, Meas. Sci. Technol. 4, 907 (1993).
[CrossRef]

1981 (1)

A. Dandridge and A. B. Tveten, Appl. Phys. Lett. 39, 530(1981).
[CrossRef]

Armstrong, J. W.

J. W. Armstrong, F. B. Estabrook, and M. Tinto, Astrophys. J. 527, 814 (1999).
[CrossRef]

Bobroff, N.

N. Bobroff, Meas. Sci. Technol. 4, 907 (1993).
[CrossRef]

Chua, S.

Dandridge, A.

A. Dandridge and A. B. Tveten, Appl. Phys. Lett. 39, 530(1981).
[CrossRef]

de Vine, G.

Dubovitsky, S.

Estabrook, F. B.

J. W. Armstrong, F. B. Estabrook, and M. Tinto, Astrophys. J. 527, 814 (1999).
[CrossRef]

Lam, T. T.-Y.

Lay, O. P.

McClelland, D. E.

Rabeling, D. S.

Shaddock, D. A.

Slagmolen, B. J. J.

Tinto, M.

J. W. Armstrong, F. B. Estabrook, and M. Tinto, Astrophys. J. 527, 814 (1999).
[CrossRef]

Tveten, A. B.

A. Dandridge and A. B. Tveten, Appl. Phys. Lett. 39, 530(1981).
[CrossRef]

Ware, B.

Wuchenich, D. M.

Appl. Phys. Lett. (1)

A. Dandridge and A. B. Tveten, Appl. Phys. Lett. 39, 530(1981).
[CrossRef]

Astrophys. J. (1)

J. W. Armstrong, F. B. Estabrook, and M. Tinto, Astrophys. J. 527, 814 (1999).
[CrossRef]

Meas. Sci. Technol. (1)

N. Bobroff, Meas. Sci. Technol. 4, 907 (1993).
[CrossRef]

Opt. Express (1)

Opt. Lett. (2)

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Figures (5)

Fig. 1
Fig. 1

Digital interferometry setup for monitoring length changes of L 1 , L 2 , and L 3 by tracking reflections from R 1 , R 2 , R 3 , and R 4 . Signal generators are used to inject test signals for performance characterization.

Fig. 2
Fig. 2

Simultaneous displacement measurements of fiber lengths when stretched with different waveforms. Modulating L 1 with a 1 Hz square wave, L 2 with a 3 Hz triangle wave, and L 3 with a 5 Hz sine wave. DI clearly recovers the individual displacement signals.

Fig. 3
Fig. 3

Time domain data showing low cross talk between signals when modulating L 2 with a 5 Hz sine wave.

Fig. 4
Fig. 4

RPSDs of δ L 1 , δ L 2 , and δ L 3 when modulating L 2 with a 5 Hz sine wave. The cross talk between length measurements is determined by the ratio of the amplitudes of the 5 Hz peak in each spectrum.

Fig. 5
Fig. 5

RPSDs of δ L 2 and δ L 2 L 2 L 1 δ L 1 . Frequency noise can be suppressed by correlating two displacement measurements with an appropriate scaling factor.

Equations (3)

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δ L 1 = λ 4 π n ( ϕ R 2 ϕ R 1 ) ,
ϕ ˜ R i = 1 f chip ( k = 1 N P k P i 1 ) [ rad / Hz ] ,
δ L i δ L i + δ ν ν L i ,

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