Writing and visualization of low-threshold type II Bragg gratings in stressed optical fibers

Type II phase gratings were produced by the use of holographic side writing in high-birefringence optical fibers with UV fluences of 0.06 J/cm(2) over 10 times lower than that previously reported for standard fibers. The grating growth, transmission and reflection spectra, temperature response, short-wavelength light ejection, and high-resolution confocal microscopy images are reported. Diffraction theory is used to interpret the grating microstructure revealed by confocal microscopy. Each period of the grating is shown to consist of a plate of oriented cracks, and arguments relating to the arrangement of the cracks and crack growth are linked to the observed grating-growth dynamics.