Numerical investigation on the effects of fabrication conditions on fiber Bragg grating spectra using the phase mask technique.

A numerical investigation on how fiber Bragg grating fabrication conditions using the phase mask technique affect the harmonic components of the Bragg wavelength is presented. Both the properties of the phase mask and saturation effects are investigated to determine the underlying cause of the rise of various harmonic reflections other than the Bragg wavelength. Results are compared with published data by various authors.

Variations of the growth of harmonic reflections in fiber Bragg gratings fabricated using phase masks.

The growth of reflectance peaks from optical fiber Bragg gratings has been studied to determine the relative importance of grating features when writing with the phase-mask technique. Measurements of spectra for two different fiber types using two distinct phase masks allowed the contribution from grating features of half the phase-mask periodicity and of the phase-mask periodicity at the Bragg wavelength to be determined. The dominance of the latter periodicity was ascribed to either the small fiber core diameter that limited the extent of the Talbot diffraction pattern, or the enhanced ±2 diffraction orders of a custom-made phase mask used.

Quantitative phase and refractive index analysis of optical fibers using differential interference contrast microscopy.

A systematic and straightforward image processing method to extract quantitative phase and refractive index data from weak phase objects is presented, obtained using differential interference contrast (DIC) microscopy. The method is demonstrated on DIC images of optical fibers where a directional integration routine is applied to the DIC images to extract phase and refractive index information using the data obtained across the whole DIC image. By applying the inverse Abel transform to the resultant phase images, an accurate refractive index profile is obtained.

Quantitative investigation of the refractive-index modulation within the core of a fiber Bragg grating.

A comparison is made between the modeled and experimentally determined microscopic images of a type I Bragg grating produced in the core of an optical fiber using the ultraviolet irradiation of a phase mask. The simulated image of the refractive-index distribution, which assumes a linear relationship between the irradiation intensity and the refractive-index change, is in good agreement with the measured image.

Directional dependence of spectra of fiber Bragg gratings due to excess loss.

The reflectance spectra of chirped fiber Bragg gratings can depend substantially on the direction from which the measurement is taken. The measured difference between forward and backward reflectance spectra measured in a linearly chirped grating was shown to be due to the measured excess loss. Simulation using the popular transfer-matrix model demonstrated that the observed asymmetric behavior could be obtained only when excess loss has an asymmetric spectral shape about the local Bragg wavelengths.