It is shown that a recently proposed phase-retrieval technique for Bragg gratings [Opt. Lett. 22, 93 (1997); J. Lightwave Technol. 15, 1314 (1997)] is not well suited for gratings with imperfections. The reconstructed group delay is in many cases not a more accurate estimate than the simulated group delay of the perfect, designed grating, independently of how small the errors in the grating structure are. The error in the group delay may be especially large near the zeros in the reflection spectrum.
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