| 摘要 |
A method of avoiding unwanted phase discontinuities between adjacent sections of a long Bragg grating written section-by-section in an optical fibre (11) uses masks (10) with alignment parts (b' to b, c' to c .... f' to f) additional to their writing parts (a to b, b to c ... f to g). Each alignment part is a replica of a portion of the writing part of the adjacent mask. Light of the same wavelength as used for writing grating sections excites stronger luminescence in regions of waveguide where there has been no irradiation induced raising of the refractive index than in regions where such index raising has occurred. Therefore, for such light directed through the alignment part of the mask and into the already-written previous section of the grating, the intensity of luminescent light propagating to an end of the waveguide varies according to how well or how badly the bright fringes produced by the mask register with the corresponding irradiated portions of the written Bragg grating. Fine adjustment of mask position is made to obtain the intensity corresponding to the desired level of registry before writing with this mask is commenced. <IMAGE> |
