Calculation of the frequency band of a Bragg waveguide

Transmission regions of the silica-core Bragg optical waveguides are analysed. It is shown that a relatively small decrease in the refractive index of the core allows one to narrow down the waveguide transmission region so that to suppress in the spectrum the undesirable emission line propagating in the waveguide, thus ensuring a minimal loss of the fundamental mode at the working wavelength. The example of calculations of a frequency filter based on a Bragg optical fibre is considered, in which the fundamental mode has minimal losses at 0.925 μm but completely suppressed at 1.06 μm. The loss spectrum of a Bragg waveguide and the field distribution of the fundamental mode are presented.