The effects of the zeroth-order diffraction of a phase mask on the creation
of Bragg gratings using the mask technique were theoretically and experime
ntally investigated. Experimental results showed that the zeroth order diff
raction of 1% total power, while in interference with the first-order diffr
action 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 smal
l 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 ca
lculation agrees well with the experimental results.