We demonstrate a large improvement in the efficiency of the method proposed by Krug et al. [Opt. Lett. 20, 1767 (1995)] to measure the amplitude of the refractive-index modulation along a fiber Bragg grating. The basic idea consists of using what to our knowledge is a new modulation scheme for the probe beam that not only allows the user to get a better discrimination of the probe light incoherently scattered by the fiber from that scattered by the grating but also facilitates alignment of the setup.

© 2001 Optical Society of America

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  1. G. Meltz, W. W. Morey, W. H. Glenn, “Formation of Bragg gratings in optical fibers by a transverse holographic method,” Opt. Lett. 14, 823–825 (1989).
    [CrossRef] [PubMed]
  2. D. K. W. Lam, B. K. Garside, “Characterization of single-mode optical fiber filters,” Appl. Opt. 20, 440–445 (1981).
    [CrossRef] [PubMed]
  3. F. Ouellette, “Dispersion cancellation using linearly chirped Bragg grating filters in optical waveguides,” Opt. Lett. 12, 847–849 (1987).
    [CrossRef] [PubMed]
  4. P. A. Krug, R. Solte, R. Ulrich, “Measurement of index modulation along an optical fiber Bragg grating,” Opt. Lett. 20, 1767–1769 (1995).
    [CrossRef] [PubMed]
  5. M. Janos, J. Canning, M. G. Sceats, “Incoherent scattering losses in optical fiber Bragg gratings,” Opt. Lett. 21, 1827–1829 (1996).
    [CrossRef] [PubMed]

1996 (1)

1995 (1)

1989 (1)

1987 (1)

1981 (1)

Canning, J.

Garside, B. K.

Glenn, W. H.

Janos, M.

Krug, P. A.

Lam, D. K. W.

Meltz, G.

Morey, W. W.

Ouellette, F.

Sceats, M. G.

Solte, R.

Ulrich, R.

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Figures (5)

Fig. 1
Fig. 1

Experimental setup.

Fig. 2
Fig. 2

(a) Signal from the PMT when the beam crosses the core. The probe power is equal to 5 mW. The refractive-index modulation amplitude is 7 × 10-4. (b) 270-Hz sawtooth sweep voltage driving the optical scanner.

Fig. 3
Fig. 3

Scattered optical power from a 10-mm-long apodized grating.

Fig. 4
Fig. 4

Photomultiplier signal from the light scattered by a pristine fiber (SMF 28), obtained (a) by use of a chopper for modulating the probe beam, (b) by means of the transverse core scanning method.

Fig. 5
Fig. 5

Scattered optical power from a low-strength Bragg grating (Δn mod = 5.8 × 10-5).

Equations (3)

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sin(θext)=n0 sin(θ0)=λ/2Λ.
S=S12+S221/2=S cos ϕ2+S sin ϕ21/2,  tang ϕ=S2/S1.