High-resolution characterisation methods for narrow line-width fiber Bragg gratings

摘要

Special, narrow-linewidth fiber Bragg gratings (FBGs) can serve as wavelength references for both sensor applications and optical telecommunications. With line-widths of a few GHz and contrast exceeding 95%, phase-shifted FBGs offer a good alternative to etalons or gas cells as easy-to-use and cost-effective wavelength references. To enable calibration and to assess the wavelength stability of newly developed FBGs down to parts in 107, quantifying drifts caused e.g. by aging, polarisation dependence, residual sensitivity to temperature or strain, we have developed high resolution measuring methods which are linked to a traceable wavelength. We present results from three complementary methods based on Fourier Transform spectroscopy, tunable laser spectroscopy and a new laser stabilisation technique using polarisation modulation. For the central wavelength of phase-shifted FBGs we achieved an accuracy below 10~(-7).