| 摘要 |
A method and apparatus for writing an apodised grating of improved quality into a photosensitive material using an interference pattern of fringe period <custom-character file="US20040033018A1-20040219-P00900.TIF" wi="20" he="20" id="custom-character-00001"/>gr. An unapodised part of the grating is written by exposing the photosensitive material with a succession of exposures separated from each other by an odd number of fringe periods and an apodised part of the grating is written by exposing the photosensitive material with a first set of N exposures, where N is an even number, separated from each other by an odd number of fringe periods, the first set of N exposures having a positive phase offset +phi relative to the unapodised part of the grating and exposing the photosensitive material with a second set of N exposures separated from each other by an odd number of fringe periods, the second set of N exposures having a negative phase offset -phi relative to the unapodised part of the grating. |
