Abstract

A correlation reflectometer operating in the frequency domain is described. It is shown that such an instrument is well adapted to detecting weak discrete reflections. The detection of end reflections in a 2.2-km length of fiber whose end is index matched is demonstrated. A round-trip range of over 70 dB is obtained with a 1-mW optical source power. The method shows promise for characterizing the reflective properties of optical fiber elements, such as tapers, microbends, and splices, and may be useful in fault location.

© 1981 Optical Society of America

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References

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  1. Y. Ueno, M. Shimizu, IEEE J. Quantum Electron. QE-11, 77D (1975).
  2. S. D. Personick, Bell Syst. Tech. J. 56, 355 (1977).
  3. P. Healey, P. Hensel, Electron. Lett. 16, 631 (1980).
    [Crossref]
  4. K. Okada, H. Hashimoto, T. Shibata, Y. Nagaki, Electron. Lett. 16, 629 (1980).
    [Crossref]
  5. W. H. Wells, Fiber Integrated Opt. 1, 243 (1978).
    [Crossref]
  6. J. Straus, I. S. Few, J. Conradi, Electron. Lett. 15, 306 (1979).
    [Crossref]
  7. J. Conradi, I. S. Few, Electron. Lett. 16, 414 (1980).
    [Crossref]
  8. B. S. Kawasaki, K. O. Hill, Appl. Opt. 16, 1794 (1977).
    [Crossref] [PubMed]

1980 (3)

P. Healey, P. Hensel, Electron. Lett. 16, 631 (1980).
[Crossref]

K. Okada, H. Hashimoto, T. Shibata, Y. Nagaki, Electron. Lett. 16, 629 (1980).
[Crossref]

J. Conradi, I. S. Few, Electron. Lett. 16, 414 (1980).
[Crossref]

1979 (1)

J. Straus, I. S. Few, J. Conradi, Electron. Lett. 15, 306 (1979).
[Crossref]

1978 (1)

W. H. Wells, Fiber Integrated Opt. 1, 243 (1978).
[Crossref]

1977 (2)

S. D. Personick, Bell Syst. Tech. J. 56, 355 (1977).

B. S. Kawasaki, K. O. Hill, Appl. Opt. 16, 1794 (1977).
[Crossref] [PubMed]

1975 (1)

Y. Ueno, M. Shimizu, IEEE J. Quantum Electron. QE-11, 77D (1975).

Conradi, J.

J. Conradi, I. S. Few, Electron. Lett. 16, 414 (1980).
[Crossref]

J. Straus, I. S. Few, J. Conradi, Electron. Lett. 15, 306 (1979).
[Crossref]

Few, I. S.

J. Conradi, I. S. Few, Electron. Lett. 16, 414 (1980).
[Crossref]

J. Straus, I. S. Few, J. Conradi, Electron. Lett. 15, 306 (1979).
[Crossref]

Hashimoto, H.

K. Okada, H. Hashimoto, T. Shibata, Y. Nagaki, Electron. Lett. 16, 629 (1980).
[Crossref]

Healey, P.

P. Healey, P. Hensel, Electron. Lett. 16, 631 (1980).
[Crossref]

Hensel, P.

P. Healey, P. Hensel, Electron. Lett. 16, 631 (1980).
[Crossref]

Hill, K. O.

Kawasaki, B. S.

Nagaki, Y.

K. Okada, H. Hashimoto, T. Shibata, Y. Nagaki, Electron. Lett. 16, 629 (1980).
[Crossref]

Okada, K.

K. Okada, H. Hashimoto, T. Shibata, Y. Nagaki, Electron. Lett. 16, 629 (1980).
[Crossref]

Personick, S. D.

S. D. Personick, Bell Syst. Tech. J. 56, 355 (1977).

Shibata, T.

K. Okada, H. Hashimoto, T. Shibata, Y. Nagaki, Electron. Lett. 16, 629 (1980).
[Crossref]

Shimizu, M.

Y. Ueno, M. Shimizu, IEEE J. Quantum Electron. QE-11, 77D (1975).

Straus, J.

J. Straus, I. S. Few, J. Conradi, Electron. Lett. 15, 306 (1979).
[Crossref]

Ueno, Y.

Y. Ueno, M. Shimizu, IEEE J. Quantum Electron. QE-11, 77D (1975).

Wells, W. H.

W. H. Wells, Fiber Integrated Opt. 1, 243 (1978).
[Crossref]

Appl. Opt. (1)

Bell Syst. Tech. J. (1)

S. D. Personick, Bell Syst. Tech. J. 56, 355 (1977).

Electron. Lett. (4)

P. Healey, P. Hensel, Electron. Lett. 16, 631 (1980).
[Crossref]

K. Okada, H. Hashimoto, T. Shibata, Y. Nagaki, Electron. Lett. 16, 629 (1980).
[Crossref]

J. Straus, I. S. Few, J. Conradi, Electron. Lett. 15, 306 (1979).
[Crossref]

J. Conradi, I. S. Few, Electron. Lett. 16, 414 (1980).
[Crossref]

Fiber Integrated Opt. (1)

W. H. Wells, Fiber Integrated Opt. 1, 243 (1978).
[Crossref]

IEEE J. Quantum Electron. (1)

Y. Ueno, M. Shimizu, IEEE J. Quantum Electron. QE-11, 77D (1975).

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Figures (6)

Fig. 1
Fig. 1

Experimental apparatus.

Fig. 2
Fig. 2

Frequency domain reflectometer signal from 2.2 km of graded-index fiber. Scan period 10 msec, scan width 89 MHz, other parameters as in text. Return from the cleaved fiber end occurs at 192 kHz

Fig. 3
Fig. 3

Linear plot of the power in the end reflection shown in Fig. 2 at receiver bandwidths of 100 and 10 Hz. Distance resolution is observed to be 3.5 m. Discrete nature of the spectrum is evident when the bandwidth is 10 Hz.

Fig. 4
Fig. 4

Spectrum of the end reflection of the 2.2-km fiber with reduced scan width (3 MHz). Resolution is 19 m. Noise levels observed in the absence of illumination are also shown. SNR is limited by mixer nonlinearity.

Fig. 5
Fig. 5

Reflection from the index-matched cleaved end of 2.2-km fiber compared with the reflection of the same end in air with the laser modulation reduced 70 dB. Noise levels shown were obtained by removing the laser modulation signal. Parameters as in Fig. 4.

Fig. 6
Fig. 6

Reflections from an end produced by breaking the fiber under torsion with and without index matching. Index matching has no observable effect. Level of the reflection is approximately the same as that of an index-matched cleaved end.

Equations (7)

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x = ( c Δ f i ) / ( 4 n f s f d ) ,
δ = ( c W d ) / ( 4 n f s f d ) .
W d = 2 f c ,
SNR f = [ P 0 A ( 1 A ) R 0 exp ( 2 α L ) ] 2 P r 2 · ( 1 2 L n f s c ) · ξ,
M = ξ ( 1 2 L n f s c ) · ( R 0 f R 0 c ) 2 · W t W d ,
R f = 1 2 f d f c f d f c + f d R 0 ( f ) d f ,
R 0 ( f ) = V 2 + S 2 · α ( NA ) 2 4 n 2 · 3 2 · exp ( 2 α δ ) , V = 2 α + exp ( 2 α δ ) [ B sin ( B δ ) 2 α cos ( B δ ) ] 4 α 2 + B 2 , S = B exp ( 2 α δ ) [ 2 α sin ( B δ ) + B cos ( B δ ) ] 4 α 2 + B 2 , B = 4 π f n c , α = backscatter coefficient ( Np / m ) .

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