Effects of the zeroth-order diffraction of a phase mask on Bragg gratings

Abstract

The effects of the zeroth-order diffraction of a phase mask on the creation of Bragg gratings using the mask technique were theoretically and experimentally investigated. Experimental results showed that the zeroth-order diffraction of 1% total power, while in interference with the first-order diffraction of 44% each, dramatically affected the structure of the gratings in a polymer optical preform, including their period. Theoretical analysis by taking the zeroth-order diffraction into account predicted that a very small part of the zeroth-order component (0.1%) would have substantial effects on the gratings, which will be no longer uniform along both the directions of the incident laser beam propagation and the groove array. Theoretical calculation agrees well with the experimental results.

Demonstration of inscription and ablation of phase masks for the production of 1st, 2nd, and 3rd order FBG gratings using a femtosecond laser

“…Higher order contributions are ignored as they can be minimized by increasing the spacing between the fiber and the mask. The effect of a significant zeroth order contribution on FBG inscription using a phase mask has been analyzed by Dyer et al 8 and by Xiong et al 9 .…”

High order Bragg gratings for short wavelengths operation

“…The emergent field distribution behind the phase mask is composed of a set of diffracted plane waves [6,8] propagating at angles , satisfying…”

“…In 1993, B. Malo et al observed excimer-pulse-written high order gratings by use of a zeroth-order nulled phase mask [5]. Nevertheless, the presence of the 0th order diffraction beam, which interferes with ± 1st orders and causes the formation of a periodic Talbot interference pattern [6]. It affects the intensity distribution behind the phase mask, changing the FBG properties.…”

Effects of fiber cladding on UV beams and fringe patterns in side-exposure FBG writing

“…Dyer et al 6 investigated the interference field produced by a phase mask under excimer laser irradiation and assessed the near-field fluence and energy density distributions by considering the interference of the plane waves with finite spatial and temporal coherence. In a recent paper by Xiong et al 7 , the effects of the zerothorder diffraction of a phase mask on Bragg gratings are investigated both theoretically and experimentally. Similar to the previous work, the analysis presented in Ref.7 is based on the plane wave model.…”

“…[3][4][5][6][7], the fringe patterns are analyzed without taking the affect of fiber cladding into account. In fact, the cladding of the fiber acts as a cylindrical lens to the incident UV beams during the side-writing process.…”