Comparison of FBG wavelengths in the regions of 2/3 of the Bragg wavelength and the Bragg wavelength by piecewise irradiation of a chirped phase mask

Abstract

By using a simple technique of UV laser irradiation at various regions along a chirped phase mask, the responses in the region of 2 / 3 of the Bragg wavelength (i.e. ~1030 nm) and the Bragg wavelength (~1535 nm) are investigated experimentally and compared. The variation of the wavelength of both transmission dips (in the region of the 2 / 3 of the Bragg wavelength and the Bragg wavelength) were proportional to the increase in periodicities of phase mask. The ratios of these wavelengths, for the irradiation of each phase mask section, showed less than 0.7% variation compared with the value of 2 / 3 , confirming that features at ~1030 nm are the 3 rd harmonic of a grating having the phase mask periodicity.