Effect of phase mask alignment on fiber Bragg grating spectra at harmonics of the Bragg wavelength

Abstract

Effects of fabrication conditions on the double-peak structure observed in fiber Bragg gratings at harmonics of the Bragg wavelength were investigated, showing that slight variations in the alignment of the phase mask can affect the grating spectra significantly. A single peak occurs only when the incident beam direction is perfectly normal with respect to the fiber.

Understanding fiber Bragg gratings at harmonics of the Bragg wavelength through spectra and images

“…The sensitivity of the wavelength variation with phase mask tilt angle is much greater than that occurring when the phase mask angle varies (i.e. blazed gratings), with double peaks occurring when the angle is ≥ 0.01° and similar results 19 were obtained at 2λ B /3.…”

“…We have investigated how double-peak properties at twice the Bragg wavelength are related to the writing conditions 19 , via changes to the alignment and position of the fiber with respect to the phase mask (using a 244-nm UV continuous laser source with the scanning beam direct writing method and the 536-nm periodicity phase mask). Rotation of the phase mask resulted in a change in the center wavelength of both peaks, as expected for blazed gratings 2 , but the spacing between the two peaks was virtually unchanged.…”

Fabrication of higher order Bragg gratings in microstructured polymer fibers

“…The existence of these two periodicities in the diffraction field was experimentally confirmed by visual observation of corresponding index modulation imprinted in silica fibers [12][13] and polymer fibers [11] as well as two reflection Bragg peaks at wavelengths λ B and 2λ B in silica fibers [14]. It was also demonstrated for silica fibers that the presence of higher diffraction gives rise to Bragg reflection peaks located at λ B /2 and 2λ B /3 [13,15]. In this paper we demonstrate for the first time that higher order Bragg gratings can be inscribed also in microstructured polymer fibers made of pure PMMA by using the phase mask with 0 th , ±1 st , ±2 nd diffraction orders.…”

Harmonic analysis of fiber Bragg gratings written using apodized phase and amplitude masks

“…1c), but the power spectrum is composed of diffraction orders contributions coming from all sections. Spectral components Λ=ΛPM/p correspond to the Bragg wavelength peak at lB (p=2) and the other peak reflection wavelengths lp can be derived by the following formula [10]:…”