Multi-Harmonic Bragg Gratings

摘要

During the last decade, fiber and waveguide Bragg Gratings (BGs) have been studied extensively both theoretically and experimentally and have found widespread use in the. field of optoelectronics. A number of different techniques have been developed for writing high quality BGs in various waveguide geometries. Regardless of their implementation details, modem grating writing techniques can be broadly divided into two main categories, namely holographic and phase-mask based ones. The former rely on an interferometric set-up, while the latter make use of a phase mask, to create a periodic UV-light intensity pattern which is subsequently used to expose and perturb the core of the adjacent waveguide. So far, the vast majority of the standard-grating analyses have only considered simple, single-period (Λ), sinusoidal refractive-index variations These studies have being concentrating primarily on the grating response at the fundamental (λ=λ_B=2n_(eff)Λ) or the Nth-order (λ=λ_B/N) Bragg resonance alone. There have also been a number of studies, pertinent to gratings with non-sinusoidal periodic refractive index perturbations, where, in addition to the fundamental period (A), a number of higher spatial-frequency (i.e., Λ/2, Λ/3, etc) Fourier components have been considered In all these cases, however, the grating response at the Bragg wavelength is primarily due to and follows closely the refractive-index component corresponding to the fundamental grating period (Λ). The presence of higher spatial-frequency components in this case only gives rise to extra reflection peaks at λ=λ_B/2, λ_B/3, etc.